Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session JP8: Poster Session IV: Education and Outreach; Undergraduate and High School Research; DIII-D Tokamak II; Laser and Plasma Based Accelerators |
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Room: Grand Hall East |
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JP8.00001: EDUCATION AND OUTREACH |
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JP8.00002: Plasma Science and Applications at the Intel Science Fair: A Retrospective Lee Berry For the past five years, the Coalition for Plasma Science (CPS) has presented an award for a plasma project at the Intel International Science and Engineering Fair (ISEF). Eligible projects have ranged from grape-based plasma production in a microwave oven to observation of the effects of viscosity in a fluid model of quark-gluon plasma. Most projects have been aimed at applications, including fusion, thrusters, lighting, materials processing, and GPS improvements. However diagnostics (spectroscopy), technology (magnets), and theory (quark-gluon plasmas) have also been represented. All of the CPS award-winning projects so far have been based on experiments, with two awards going to women students and three to men. Since the award was initiated, both the number and quality of plasma projects has increased. The CPS expects this trend to continue, and looks forward to continuing its work with students who are excited about the possibilities of plasma. You too can share this excitement by judging at the 2010 fair in San Jose on May 11-12. [Preview Abstract] |
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JP8.00003: Science Education Research Using Web-based Video Lisa Tarman, Pamella Ferris, Dan Bruder, Nick Gilligan, James Morgan, John DeLooper The Princeton Plasma Physics Laboratory in collaboration with teachers and students has developed a variety of educational outreach activities to demonstrate basic physical science principles using a variety of instructive and entertaining science demonstrations at elementary, middle and high school levels. A new effort has been initiated to demonstrate this material using web based videos. This can be a resource for the teacher, parent or student. In addition, the video is coupled to web-based lesson plans for the educator. The goal of these videos and lesson plans is to create enthusiasm and stimulate curiosity among students and teachers, showing them that science is interesting, fun, and within their grasp. The first video demonstrates a number of activities one can accomplish using a half-coated fluorescent tube. Additional demonstrations will be added over time. [Preview Abstract] |
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JP8.00004: Plasma Display at the Liberty Science Center Dan Bruder, Nick Gilligan, Lisa Tarman, Pamella Ferris, James Morgan, John DeLooper, Andrew Zwicker The Liberty Science Center (LSC) is the largest (300,000 sq. ft.) education resource in the New Jersey -- New York City region. PPPL in collaboration with the LSC has had a display at the center since 2007 More than 1.5 million visitors have come to the museum since the plasma display has been introduced. The plasma display has had significant use during that time frame. During the summer of 2009 a redesigned plasma exhibit was created by a student teacher-team using the lessons learned from the existing exhibit. The display includes a DC glow discharge tube with a permanent external magnet allowing visitors to manipulate the plasma and see how plasma can be used for fusion research. The goal of the display is to allow an individual to see a plasma and understand the potential benefits of fusion energy. [Preview Abstract] |
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JP8.00005: Calibrating and characterizing X-ray diagnostics using the Lawrence Livermore National Laboratory's Electron Beam Ion Trap: A Physics teacher's perspective Chad Gillis, Peter Beiersdorfer, Greg Brown, Joel Clementson, Alex Dixon, Ronny Elor, Edward Magee, Elmar Trabert Using Lawrence Livermore National Laboratory's Electron Beam Ion Trap (EBIT) as an X-ray source, we characterized a flat-field grating spectrometer and calibrated the X-ray transmission of optical-blocking filters. The flat-field grating spectrometer is being used to diagnose magnetically confined plasma and the optical-blocking filters are part of a variety of X-ray diagnostics used to study a plethora of sources including inertial confinement fusion plasma, high energy density plasma, and astrophysical plasma. I will give an overview of the calibration process and also discuss how I expect to relate this experience to teaching high school physics students. This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and is also supported by California State University. [Preview Abstract] |
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JP8.00006: On the Role of an Authentic Research Experience for K-12 Science Teachers Andrew Zwicker, James Morgan, John DeLooper A variety of programs exist that offer K-12 teachers an opportunity to perform scientific research during the summer. ~Since 2001, the NSF has offered a Research Experience for Teachers, based upon the more common Research Experience for Undergraduates (REU). ~The DOE has had the Teacher Research Associate (TRAC) program since 1989 and currently sponsors the Academies Creating Teacher-Scientists (ACTS). ~In each of these, teachers spend 2-8 weeks performing research and developing classroom activities based upon this experience. ~Many programs assess changes in knowledge or attitude towards science, a few look at teacher retention, and one looked at student achievement after a teacher completed a program. ~Currently, PPPL runs two research programs for teachers, one running for two weeks, one for six weeks. ~One program recruits teachers nationally, while the other concentrates its efforts on a single school district. ~Each program will initially run for three years and we will report on our initial data that looks at attitudes, teaching philosophy, and content knowledge before beginning the research project. ~We will also report on expected outcomes after completion of the program. [Preview Abstract] |
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JP8.00007: UNDERGRADUATE AND HIGH SCHOOL RESEARCH |
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JP8.00008: Calculation of stochastic broadening due to low mn magnetic perturbation in the simple map in action-angle coordinates Courtney Hinton, Alkesh Punjabi, Halima Ali The simple map is the simplest map that has topology of divertor tokamaks [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Let. A \textbf{364}, 140--145 (2007)]. Recently, the action-angle coordinates for simple map are analytically calculated, and simple map is constructed in action-angle coordinates [O. Kerwin, A. Punjabi, and H. Ali, Phys. Plasmas \textbf{15}, 072504 (2008)]. Action-angle coordinates for simple map cannot be inverted to real space coordinates (R,Z). Because there is logarithmic singularity on the ideal separatrix, trajectories cannot cross separatrix [\textit{op cit}]. Simple map in action-angle coordinates is applied to calculate stochastic broadening due to the low mn magnetic perturbation with mode numbers m=1, and n=$\pm $1. The width of stochastic layer near the X-point scales as 0.63 power of the amplitude $\delta $ of low mn perturbation, toroidal flux loss scales as 1.16 power of $\delta $, and poloidal flux loss scales as 1.26 power of $\delta $. Scaling of width deviates from Boozer-Rechester scaling by 26{\%} [A. Boozer, and A. Rechester, \textit{Phys. Fluids }\textbf{21}, 682 (1978)]. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793. [Preview Abstract] |
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JP8.00009: Creation of a magnetic barrier at a noble q close to physical midpoint between two resonant surfaces in the ASDEX UG tokamak Justin Vazquez, Halima Ali, Alkesh Punjabi Ciraolo, Vittot and Chandre method of building invariant manifolds inside chaos in Hamiltonian systems [Ali H. and Punjabi A, Plasma Phys. Control. Fusion, \textbf{49}, 1565--1582 (2007)] is used in the ASDEX UG tokamak. In this method, a second order perturbation is added to the perturbed Hamiltonian [\textit{op cit}]. It creates an invariant torus inside the chaos, and reduces the plasma transport. The perturbation that is added to the equilibrium Hamiltonian is at least an order of magnitude smaller than the perturbation that causes chaos. This additional term has a finite, limited number of Fourier modes. Resonant magnetic perturbations (m,n) = (3,2)+(4,3) are added to the field line Hamiltonian for the ASDEX UG. An area-preserving map for the field line trajectories in the ASDEX UG is used. The common amplitude $\delta $ of these modes that gives complete chaos between the resonant surfaces $\Psi $43 and $\Psi $32 is determined. A magnetic barrier is built at a surface with noble q that is very nearly equals to the q at the physical midpoint between the two resonant surfaces. The maximum amplitude of magnetic perturbation for which this barrier can be sustained is determined. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793. [Preview Abstract] |
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JP8.00010: A symplectic map for trajectories of magnetic field lines in double-null divertor tokamaks Willie Crank, Halima Ali, Alkesh Punjabi The coordinates of the area-preserving map equations for integration of magnetic field line trajectories in tokamaks can be any coordinates for which a transformation to ($\psi $,$\theta $,$\phi )$ coordinates exists [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A \textbf{364}, 140 (2007)]. $\psi $ is toroidal magnetic flux, $\theta $ is poloidal angle, and $\phi $ is toroidal angle. This freedom is exploited to construct a map that represents the magnetic topology of double-null divertor tokamaks. For this purpose, the generating function of the simple map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. \textbf{69}, 3322 (1992)] is slightly modified. The resulting map equations for the double-null divertor tokamaks are: x$_{1}$=x$_{0}$-ky$_{0}$(1-$y_0^2 )$, y$_{1}$=y$_{0}$+kx$_{1}$. k is the map parameter. It represents the generic topological effects of toroidal asymmetries. The O-point is at (0.0). The X-points are at (0,$\pm $1). The equilibrium magnetic surfaces are calculated. These surfaces are symmetric about the x- and y- axes. The widths of stochastic layer near the X-points in the principal plane, and the fractal dimensions of the magnetic footprints on the inboard and outboard side of upper and lower X-points are calculated from the map. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793. [Preview Abstract] |
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JP8.00011: Scaling of the stochastic broadening from low mn, high mn, and peeling-ballooning magnetic perturbations in the DIII-D tokamak Michael Zhao, Alkesh Punjabi, Halima Ali The equilibrium EFIT data for the DIII-D shot 115467 is used to construct the equilibrium generating function for magnetic field line trajectories in the DIII-D tokamak in natural canonical coordinates [A. Punjabi, and H. Ali, Phys. Plasmas \textbf{15}, 122502 (2008)]. A canonical transformation is used to construct an area-preserving map for field line trajectories in the natural canonical coordinates in the DIII-D. Maps in natural canonical coordinates have the advantage that natural canonical coordinates can be inverted to calculate real space coordinates (R,Z,$\phi )$, and there is no problem in crossing the separatrix. This is not possible for magnetic coordinates [O. Kerwin, A. Punjabi, and H. Ali, Phys. Plasmas \textbf{15}, 072504 (2008)]. This map is applied to calculate stochastic broadening from the low mn (m,n)=(1,1)+(1,-1); high mn (m,n)=(4,1)+(3,1); and the peeling-ballooning (m,n)=(40,10)+(30,10) magnetic perturbations. In all three cases, the scaling of the widths of stochastic layer near the X-point in the principal plane of the DIII-D deviates at most by 6{\%} from the $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ power Boozer-Rechester scaling [A. Boozer, and A. Rechester, \textit{Phys. Fluids }\textbf{21}, 682 (1978)]. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793. [Preview Abstract] |
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JP8.00012: Beryllium Drive Disc Characterization for Laboratory Astrophysics Experiments J.R. Ditmar, R.P. Drake, C.C. Kuranz, M.J. Grosskopf Laboratory Astrophysics scales large-scale phenomena, such as core-collapse supernovae shocks, down to the sub-millimeter scale for investigation in a laboratory setting. In some experiments, targets are constructed with a 20$\mu $m thick beryllium disc attached to a polyimide tube. A shockwave is created by irradiating the Be disc with $\sim $ 4kJ of energy from the Omega Laser. The Be material is rolled into a 20$\mu $m sheet and then machined to a 2.5mm diameter. Characterizing the roughness and knowing if there are any major features on the initial surface could affect interpretations of data taken during experiments. Structure in the Beryllium discs could become an important parameter in future high-fidelity computer simulations. Surfaces were characterized with a Scanning Electron Microscope and an Atomic Force Microscope. [Preview Abstract] |
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JP8.00013: 1D Hyades Study of Varying Input Parameters of a Gaussian Distribution N. Gjeci, R.P. Drake, E.M. Rutter, M.J. Grosskopf, C.C. Kuranz, B. Fryxell The Center for Radiative Shock Hydrodynamics (CRASH) at the University of Michigan is a collaborative effort in predictive sciences associated with radiative hydrodynamics. Computer simulations aid in high-energy-density physics experiments performed at the OMEGA laser in Rochester, NY. The high intensity laser driven shocks are modeled using 1D Hyades, a Lagrangian radiation-hydrodynamic code. A data set varying input parameters over a Gaussian distribution is created and, using a Latin Hypercube sampling process, used to build sets of simulations to cover the input parameter space. This will advance the uncertainty quantification process, determining the impact of the variance of the experimental parameters. A Latin Hypercube Sampling distribution provides a multi-dimensional sensitivity analysis of the physical parameters of the experiment, enhancing the predictive capabilities of CRASH code. [Preview Abstract] |
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JP8.00014: Absorption Spectra of BaF$_{2}$ Sm$_{2}$O$_{3}$, Sm, Gd, and Ho Plasmas Michael Martin, Serena Bastiani-Ceccotti Knowledge of the opacities of high Z element plasmas is important in indirect drive ICF and the study of stellar evolution. There are few experimental measurements of this quantity, and its theoretical determination is difficult due to the number of possible bound electron configurations. This study aims to better the theoretical understanding of this parameter by looking at the 3d-4f transitions of BaF$_{2}$, Sm$_{2}$O$_{3}$, Sm, Gd, and Ho plasmas at the LULI2000 facility. The plasmas are produced by radiative heating and are cold, 15 -- 40 eV, and relatively dense, $\sim $ .01gm/cm$^{3}$ A plasma is produced by a .5 ns laser pulse irradiating a gold hohlraum and then probed by an x-ray source created by a gold foil irradiated by a 10 ps laser pulse. The transmission is found with simultaneous source and absorption measurements by an x-ray spectrometer in the 8 - 20 {\AA} range We will compare the results with statistical atomic structure codes. From this experiment we will gain further insight into the spectral broadening of neighboring Z elements due to changing plasma temperature and into mixture thermodynamics. This is a first step towards an experimental study of astrophysical domains. [Preview Abstract] |
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JP8.00015: BECOOL: a magnetohydrodynamic ballooning mode eigenvalue solver based on variable order Legendre polynomial basis functions Guy A. Cooper, Randolph S. Peterson, Ralf Gruber, W. Anthony Cooper, Jonathan P. Graves An incompressible variational ideal ballooning mode equation is discretized with the COOL finite element discretization scheme using basis functions composed of variable order Legendre polynomials.\footnote{G.~A.~Cooper, J.~P.~Graves, W.~A.~Cooper, R.~Gruber and R.~S.~Peterson, J.~Comput.~Phys.~{\bf 228} (2009) 4911-4916.} This reduces the second order ordinary differential equation to a special block pentadiagonal matrix equation that is solved using an inverse vector iteration method. A benchmark test of BECOOL (Ballooning Eigensolver using COOL finite elements) with second order Legendre polynomials recovers precisely the eigenvalues computed by the VVBAL shooting code.\footnote{A.~Cooper, Plasma Phys.~Control.~Fusion {\bf 34} (1992) 1011-1036.} Timing runs reveal the need to determine an optimal lower order case. Eigenvalue convergence runs show that cubic Legendre polynomials construct the optimal ballooning mode equation for intensive computations. [Preview Abstract] |
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JP8.00016: Comparison of Magnetospheric Ion Temperature Maps from In-Situ Measurements with Remote ENA-based Measurements Katharine Tallaksen, Amy Keesee, Earl Scime Ion temperatures in the magnetosphere exhibit significant variations that are strongly correlated with solar wind conditions not only during geomagnetic storms, but also during quiet times. Using data that did not distinguish between storm and quiet times, \textit{Borovsky et al}. showed a strong, linear correlation with the solar wind velocity of ion temperatures at 12 Earth radii downtail and at geosynchronous orbit on the nightside of the Earth [\textit{Borovsky et al.,} 1998]. However, \textit{Borovsky's }empirical relations between solar wind speed and magnetosphere ion temperature are only valid for these two spatial locations. Remote measurements of the energetic neutral atom (ENA) flux emitted by the magnetosphere can provide global magnetospheric ion temperature maps that can be used to understand how the solar wind conditions affect different regions of the magnetosphere. These remote measurements can be compared to in-situ measurements to confirm the accuracy of the ENA-based analysis. We will present ion temperature maps of the Earth's magnetosphere constructed from data from the TWINS, Geotail, Cluster, and THEMIS spacecraft and sorted by solar wind velocity (high speed (greater than 400 km/s) wind and low speed wind). The data used cover the interval from January 2008 through April 2009. This work supported by NASA. [Preview Abstract] |
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JP8.00017: GPU-Accelerated FDTD Full-Wave Codes for Reflectometry Simulations B.C. Rose, S. Kubota, W.A. Peebles Recently, GPGPU (General-Purpose computing on Graphics Processing Units) has been gaining popularity in many engineering and science fields as an inexpensive platform for accelerating compute-intensive codes. Here, we report on the application of GPU-computing to microwave reflectometry simulations for NSTX (National Spherical Torus eXperiment) plasmas. Reflectometry is a widespread diagnostic for studying both coherent and turbulent electron density fluctuations in fusion plasmas. A suite of FDTD (Finite-Difference Time-Domain) full-wave microwave propagation codes has been ported to utilize the massively parallel processing capabilities of the NVIDIA C870 GPU. The C for CUDA (Compute Unified Device Architecture) extension of the C programming language was used. For the 1-D FDTD code, it was found that the parallel version ran roughly 6 times faster than the linear equivalent. A more detailed benchmarking of both 1-D and 2-D codes for the GPU and traditional multicore processors will be presented. [Preview Abstract] |
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JP8.00018: Fluctuations and Turbulence in the Enormous Toroidal Plasma Device at UCLA Robert Niederriter, Chris Cooper, Troy Carter, Pavel Popovich Turbulence and transport across magnetic field lines disrupt plasma confinement, which is particularly troublesome in toroidal geometries potentially useful for fusion energy. We investigate fluctuations of a helium plasma in the Enormous Toroidal Plasma Device (ETPD) at UCLA using 4-tip Langmuir probes to measure potential and ion saturation current. ETPD is a simple magnetized torus with major radius 5 m. The toroidal vacuum chamber has a rectangular cross section that is 3 m tall and 2 m wide. Plasma is generated by a lanthanum hexaboride (LaB6) cathode discharge into a helical magnetic field produced by a $\sim 200$ G toroidal field and a $\sim 6$ G vertical field. Typical plasma density is $n_e \sim 10^{13}$ cm$^{-3}$ and typical electron temperature is $T_e \sim 10-20$ eV. Observed fluctuations are characterized and compared with theories of drift waves and interchange modes. [Preview Abstract] |
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JP8.00019: Attempts to produce nearly steady-state conditions in a fully toroidal electron plasma Eric Frater, Faraz Choudhury, Matthew Stoneking The Lawrence Non-neutral Torus II (major radius = 17.4 cm, minor radius = 1.27 cm, B $\sim$ 550 G) confines non-neutral (electron) plasmas in a purely toroidal magnetic field. By employing techniques used in cylindrical Penning-Malmberg traps, electron plasmas are confined in a 270$^{\circ}$ toroidal arc for times exceeding one second. The observed long confinement times indicate the production of nearly steady-state conditions and permit study of intrinsic toroidal effects on dynamics and transport. We report on attempts to trap electrons in a \textit{full} torus. This is done by filling the trap and confining electrons in a partial torus, retracting the electron source, and then removing the electric potential barriers to allow the plasma to occupy the full torus. The long confinement times achieved in the partial torus make this experiment possible. The plasma is diagnosed by measuring the flow of image charge to and from isolated sectors of the fully segmented conducting shell. Electron plasmas (n $\sim$ 5x10$^{6}$ cm$^{-3}$) are confined and exhibit toroidal versions of diocotron modes. Frequency measurements of the \textit{m}=1 diocotron mode along with numerical models yield the total charge in the plasma. This work is supported by National Science Foundation Grant PHY-0812893. [Preview Abstract] |
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JP8.00020: Redesign of Gas Delivery System and Calibration Setup for Magnetic Probes in the Maryland Centrifugal Experiment Graham Taylor, Carlos A. Romero-Talamas, Richard Ellis, Adil Hassam, Catalin Teodorescu, William Young This work consists of two parts. The first part is the design of a new gas feed system for the Maryland Centrifugal Experiment. The system is designed to maintain high vacuum conditions, prevent back flow, and allow for gas mixtures to be used in the experiment. The second part of this work describes a setup to calibrate magnetic probes at different frequencies. The setup will produce different resonance frequencies by adjusting the capacitance in a LRC circuit. The total capacitance is adjusted by connecting capacitors in series or in parallel with jumper cables. [Preview Abstract] |
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JP8.00021: Optimization of Hot Electron ECE Diagnostics on LDX S.H. Nogami, P.P. Woskov, J. Kesner, D.T. Garnier, M.E. Mauel The Levitated Dipole Experiment (LDX) is evaluating the dipole magnetic field configuration for fusion confinement with a levitated 1.1 MA, 68 cm mean diameter, 560 kg superconducting coil (F-coil) inside a 5 m diameter vacuum vessel. Highly peaked plasmas ($\sim$1/r$^4$) are generated by up to 17 kW electron cyclotron resonance heating at 2.45, 6.4, and 10.5 GHz. The high magnetic field gradient around the outside of the dipole coil where the plasma is confined represents a new regime for modeling ECE diagnostics. Millimeter wave radiometers at 110, 137, and 165 GHZ in use on LDX can view ECE harmonics from the 2nd through the 55th depending on the location of the radiometers with respect to the plasma. A study of the viewable harmonics from each of the available radiometers at various positions and proximities to the plasma is necessary to determine the interpretation of the ECE in terms of the hot electron temperatures and densities and the optimum receiver placement for the best measurements. [Preview Abstract] |
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JP8.00022: Python Graphical User Interface (GUI) for Control of the Levitated Dipole Experiment David Jacome, Darren Garnier, Paul Woskov, Jay Kesner The Levitated Dipole Experiment (LDX) is used to study the confinement properties of plasmas in a magnetic dipole field. In LDX a superconducting coil is levitated for up to 3 hours within a large vacuum chamber to produce the confining dipole field. The plasma experiments take place during this time, with $\sim $ 10 second plasma shots, one shot every $\sim $ 5 min. MDSplus software is used to run the experiment and store the data. The software is currently controlled by command line operations. Since levitation time is limited, it's important to maximize efficiency and accuracy of experimental operations. Here, we present a Graphical User Interface (GUI) to efficiently control the operation of the experiment. The need for a GUI that integrates the MDSplus data cycle, cell access control, and routine experimental parameter controls is necessary. The GUI program provides a simple method for monitoring and setting experiment parameters. Python is used as the primary language to run the commands. A program called XRCed distributed by wxPython works as a visual tool. [Preview Abstract] |
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JP8.00023: Intra-shell diffusion in Yukawa balls Paul La Plante, Torben Ott, Michael Bonitz Diffusion of micrometer sized particles has recently been studied in dusty plasmas. When examined experimentally and theoretically in the 2D and quasi-2D case [1], superdiffusion was observed, i.e. the mean-squared displacement of the particles in the long time case was larger than that predicted by the Einstein relation $\langle \vert r(t) \vert^2 \rangle \sim t$. In the case of superdiffusion, the mean-squared displacement grows as $t^{\alpha}$, where $\alpha > 1$. In this contribution, we study spherically confined small dust clusters where the particles arrange in a series of concentric spherical shells. We present the results of molecular dynamics simulation, both in the case where the coupling parameter $\Gamma = \left(Q^2/4\pi\epsilon_0\right)\times\left(1/a_{ws}k_{B}T\right)$ is held constant and the inverse screening parameter varies and vice versa. We also examine different particle numbers that lead to between one and three shells of the Yukawa ball. In most cases studied, normal diffusion or subdiffusion ($\alpha < 1$) was exhibited by the dust particles on the shells. \\[4pt] [1] T. Ott, M. Bonitz, Z. Donk\'o, and P. Hartmann, PRE 78, 026409 (2008) [Preview Abstract] |
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JP8.00024: Stark Broadening Density Profile Measurements in the ZaP Experiment G.V. Vogman, U. Shumlak The ZaP Flow Z-Pinch experiment uses sheared flow to mitigate MHD instabilities. The high-pressure plasma pinches exhibit Stark broadened emission spectra, which are analyzed to determine plasma density. A 20-chord spectroscopic system has been calibrated to quantify chord-to-chord variation in throughput, optical curvature effects, instrument wavelength displacement, and instrument broadening. By correcting for these effects and accounting for Doppler broadening, a Stark broadening profile can be resolved and used as a measure of plasma density. The local electric field from the plasma Stark broadens the spectral shape of line emission producing a Voigt profile. A Fourier expansion technique is used to approximate the Voigt profile for a C III spectral line, which is emitted from the center of the plasma column, and the H$_{\beta}$ line, which is used to resolve density in the peripheral regions of the plasma. By measuring density at different locations, a radial density profile is generated. This profile is then compared to interferometry measurements and is used to gain a better understanding of Z-pinch equilibrium. [Preview Abstract] |
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JP8.00025: Calibration of the Thomson Scattering System on the ZaP Experiment R.J. Oberto, U. Shumlak, B.A. Nelson, R.P. Golingo, D.J. Den Hartog The ZaP Experiment studies the sheared flow stabilization of a Z-pinch plasma. A Thomson scattering system measures the local electron temperature and density in the pinch using a 10 J ruby laser. The scattered light is collected by a fiber optic bundle, separated by a single-grating spectrometer with ruby and H$_{\alpha }$ filters, and binned by an array of photomultiplier tubes (PMTs). The PMT response is digitized, providing a time-resolved signal. Preliminary measurements using a preliminary calibration indicate temperatures from 50 to 150 eV. To calibrate the system completely, a tungsten lamp has been used to measure the system's spectral response, determine PMT gain, and characterize the filters in the spectrometer. The instrument function of the spectrometer has been characterized using a helium-neon laser. The total system throughput will be determined by comparing predicted and measured Raman scattering signals. The calibration will enable absolute density measurements, improved analysis codes, and system optimization. [Preview Abstract] |
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JP8.00026: Implementation of a Hall Probe Array to Characterize Magnetic Fields in the Madison Dynamo Experiment A.M. Rasmus, C.B. Forest, E.J. Kaplan, R.D. Kendrick, N.Z. Taylor This poster will provide an overview of improvements to the Hall probe array diagnostic on the Madison Dynamo Experiment. Two counter-rotating impellers driven by two 75kW motors are used to create a turbulent flow of liquid sodium in a one meter-diameter sphere.~ One of the goals of the experiment is to observe a dynamo; the spontaneous generation of magnetic fields by converting kinetic energy into magnetic energy.~ Previously, an intermittently self-excited magnetic field and a turbulent electromotive force were observed, but no sustained self-excited field was seen.~ A number of improvements to the experiment are being implemented and are predicted to allow sustained self-excited magnetic fields. In order to characterize the induced magnetic field, a new Hall probe array is being installed. The array consists of 6 radial probes as well as an equatorial array, which will allow for measurements of the magnetic field near the center of the vessel.~ These internal hall elements will be spaced 2 cm apart and measure the magnetic field in all three directions.~ Combined with 74 external probes, these diagnostics will allow us to decompose our magnetic field into spherical harmonics for further data analysis. [Preview Abstract] |
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JP8.00027: Flow Measurements of a Hot, Rotating, Unmagnetized Plasma J. Jara-Almonte, C.B. Forest, R. Kendrick, C. Collins The initial construction of the Plasma Couette Experiment (PCX) has been completed at the University of Wisconsin Madison. PCX aims to demonstrate magnetorotational instability (MRI), a proposed mechanism for angular transport in accretion disks, in a laboratory plasma. A hot and unmagnetized plasma is created using a lanthanum hexaboride cathode inside a high-order axisymmetric multicusp confinement scheme consisting or rings of permanent magnets. Electrodes located between cusp lines drive ExB drift of the plasma at the boundary, and viscous coupling provides bulk plasma rotation. Flow measurements are made using a Mach probe, and plasma parameters are established using a swept Langmuir probe. This poster will present an overview of the PCX, as well as initial data from the probes. [Preview Abstract] |
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JP8.00028: Spectral Analysis Software for the Compact Toroid Injection Experiment Donald Belknap The Compact Toroid Injection Experiment (CTIX) operated by UC Davis functions by producing a spheromak-like plasma which is accelerated via a coaxial railgun. In order to examine features of the plasma such as impurities and temperature, the spectrum of the plasma is measured during a shot. Because of the number of shots that may be taken in a single day, a computer analysis program is an expedient method of analyzing the spectra. A graphic user interface (GUI) was designed to allow the user to easily read the spectral images from an archived data file and interactively perform functions such as CCD camera tilt correction, background subtraction, and wavelength calibration. The code for the GUI, background subtraction, wavelength calibration, and tilt correction algorithms are written in a high-level programming language, Igor, to allow for easy extension by CTIX scientists. The code can be extended to add features that can perform analysis on large numbers of spectra. Results of CTIX shots and calibration spectra will be presented. [Preview Abstract] |
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JP8.00029: Efficient Spherical Numeric Integration in Multiple Dimensions Michelle Jamer Numeric integration in three dimensions through approximation can be computationally intensive. Computers using numeric integration find an approximation of the integral by a finite representation. In order to make an accurate approximation, the computer uses many quadrature points in order to evaluate which causes the three-dimensional analysis to be time intensive. The goal of this research is developing a quadrature rule which would use fewer points and thus reduce the computational expense in both two and three dimensional contexts. The research for the most efficient rule is done by testing various numerical integration rules, such as the midpoint rule and Simpson's rule, in the Python programming language. For this project the focus is on symmetrical domains such as spheres and circles. To test the accuracy of the integration rule on a given function, the convergence between both the exact and computed integrals is measured. The best quadrature rule converges and has minimal error when a modest amount of points are used. After analyzing the errors, one can see which quadrature rule fits the integral the best for radially symmetric two and three-dimensional shapes. [Preview Abstract] |
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JP8.00030: First Plasmas in the Wheaton Impulsive Reconnection eXperiment (WIRX) D. Stapleton, D. Blasing, D. Coster, D. Craig, J. Dahlin WIRX is a new experiment that will be studying the three dimensional and impulsive aspects of reconnection. The experiment is composed of two parallel electrodes, linked by a magnetic arcade that is generated by a coil surrounding the electrodes. First plasmas were obtained in April of 2009. A preliminary exploration of WIRX parameter space is presented. An adjustable high power resistor is installed in series with the plasma, allowing plasma currents from 0.5 to 11 kA. A full range of magnetic field strengths are tested from 80 to 400 Gauss. Fueling from one end of the cathode and along the cathode has been investigated. Both allow breakdown with at least 800V across the electrodes but the second allows a longer arcade along the electrodes. The resistance of the plasma exhibits an upper boundary that falls with increased plasma current. Plasma instability is expected to increase with the ratio of plasma current over coil current. Experimental results show a sharp transition between stability in the plasma and instability. Fast camera images of plasmas will be compared with these experimental results. Work supported by U.S.D.O.E. grant DE-FG02-08ER55002. [Preview Abstract] |
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JP8.00031: Design of a pinhole photodiode camera for the Wheaton Impulsive Reconnection Experiment D. Blasing, D. Coster, D. Craig, J. Dahlin, D. Stapleton Absolute extreme ultraviolet (AXUV) photodiode arrays are utilized in the design of two pinhole photodiode cameras to examine the dynamics of the plasma evolution during a single shot. The cameras will resolve the discharge horizontally and vertically into 20 viewing slices each of width $\sim $ 1 cm. Each camera will monitor the entire plasma shot with 0.2$\mu $s resolution. This compliments the existing fast ICCD cameras which only take two pictures per shot but have spatial resolution $\sim $ 1mm. Fast ICCD time scan pictures taken from multiple shots are displayed. The spectrum and the total power of the light emitted by the plasma has been measured and incorporated into the camera design. The expected photodiode current has been estimated. Work supported by U.S.D.O.E. grant DE-FG02-08ER55002. [Preview Abstract] |
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JP8.00032: Three dimensional magnetic field structure of magnetic reconnection using plasma flux ropes Thiago Olson, Tom Intrator, Rachel Oberto, Xuan Sun In nature, magnetic reconnection releases energy stored in stressed magnetic fields, and thus accelerates particles. This type of magnetic relaxation topologically rearranges magnetic field structure. In nature these processes are intrinsically 3D, whereas most models, theories and experiments are 2D, staying within the classic Sweet-Parker picture. The Reconnection Scaling eXperiment (RSX) at Los Alamos National Laboratory includes magnetic fields and current systems in the plasma that support these natural 3D fields. 2D studies have shed much light on the physics, but 3D aspects are largely unconsidered and unknown. Explanation of this behavior demands the need of a 3D picture or map. We present the B-dot probe design needed to map out the B-field structure in the plasma, and the results of the 3D merging of plasma flux ropes. RSX has already yielded data showing the onset, flux pileup, and stagnation of magnetic reconnection between two interacting plasma flux ropes. B-dot probe, and 3D positioner design and construction will be discussed in depth. This work was supported by the Los Alamos Laboratory Directed R{\&}D program, and the Physics Frontier Center for Magnetic Self Organization in Laboratory and Astrophysical? Plasmas, jointly funded by NSF and DOE. [Preview Abstract] |
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JP8.00033: Neutron Activation Diagnostics for FRCHX at AFRL D.A. Sutherland, G.A. Wurden, T.P. Intrator Neutron diagnostics have been developed for MTF on the field reversed configuration heating experiment (FRCHX) to detect both DD and DT neutrons. We are working with time-integrated activation counting systems for absolute measurements of neutron yields, in the range of 10$^6$-10$^{13}$ neutrons/shot. We are using multiple diagnostics due to different activation thresholds and need for diagnostic redundancy. The first system is indium-activation, with an Ortec germanium detector (GEM-10185) coupled to a multichannel analyzer. Indium is sensitive to and provides a count of DD neutrons. The second diagnostic system is Arsenic-activation that will also detect DD neutrons. The third system is Copper-activation, using a sodium iodide (NaI) coincidence system. Only DT neutrons are detected by this system. A fourth system consists of BTI Bubble detectors that are sensitive to both DD and DT neutrons. Thus, four systems will provide an absolute count of DD or DT neutrons from the FRC plasma implosion in FRCHX at the AFRL in Albuquerque later this year. [Preview Abstract] |
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JP8.00034: Applications of a Nd:YAG Laser for In-Situ Removal of Tritium from Plasma Facing Components in a Fusion Reactor Environment Paul Sedita, Charles Gentile, Christina McGahan Studies from TFTR and JET have indicated that long term retention of tritium in plasma facing components account for a significant fraction of the tritium inventory; thus requiring periodic removal of T interned within these first wall components. This investigation will determine the efficacy of removing tritium in an in-situ fashion from co-deposits layers in PFC's employing a continuous wave 325 w Nd:YAG laser. The laser is configured to rapidly heat first wall surfaces using a rastering motion to effectively scan the exposed surfaces within the target area. The top 100 $\mu $m of the target surface is expected to transiently heat up to $\sim $ 1000 C within several seconds, subsequently releasing the trapped (un-expended) tritium for re-use within the fusion fuel cycle. The presentation will discuss the efficacy of this method using empirical data (destructive and non-destructive measurements) from pre and post surface laser heating. [Preview Abstract] |
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JP8.00035: Evaluation of a Non-Destructive Method for the Removal of Dust, Debris, and Co-deposited Tritium from First Wall Surfaces and Plasma Surface Interfaces (PSI) in a Fusion Reactor Christina McGahan, Charles Gentile Diagnostic mirrors and windows located within the vacuum vessel boundary of fusion reactors will be subjected to dust and debris collection, causing reflectivity and clarity respectively to degrade and thus undermining data accuracy and machine performance. Additionally, co-deposited tritium must be removed in an efficient manner so unexpended tritium can be re-introduced into the fusion fuel cycle. A technique for removing carbon, beryllium, and co-deposited tritium from first wall components using a rastering 325 watt continuous wave neodymium-doped yttrium aluminum garnet (Nd: YAG) laser is under investigation. This technique has shown promise in ablating dust and debris without damaging reflective surfaces in addition to removing co-deposited layers of tritium from various diagnostic and PSI components in a non-destructive fashion. We will discuss the physical effects on surfaces and components pre and post laser interaction(s). [Preview Abstract] |
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JP8.00036: In-Situ Removal of Beryllium and Carbon Deposits from ITER Diagnostic Mirrors and Windows Utilizing Nd:YAG Laser Jennifer Zelenty, Charles Gentile Studies from the Joint European Torus (JET) indicate that plasma deposits such as beryllium and carbon will collect on ITER diagnostic mirrors and windows. The presence of such deposits will cause a decrease in reflectivity and light transmission on these diagnostic related surfaces. This investigation will determine the effectiveness of removing plasma deposits from diagnostic mirrors and windows using a 325W continuous wave (cw) Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) Laser. In this study, laser cleaning will be tested on single crystal molybdenum mirror substrates, the material proposed for ITER first mirrors. The mirrors will be coated with either beryllium or carbon deposits. The Nd:YAG laser, directed by a computer controlled laser scanner, will raster the mirror substrates, ablating the deposits on the surfaces. The reflectivity and polarization properties will be tested before and after to determine the efficacy of this laser cleaning technique. The results will be presented and discussed. [Preview Abstract] |
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JP8.00037: Concept for a Low Pressure Gas Fill in a Direct Drive IFE Target Chamber Saswathi Natta, Maria Aristova, Charles Gentile A concept using a low pressure nobel gas has been advanced for attenuating the interaction of (post detonation) He ions on first wall components. In this configuration approximately 1 torr of Ar gas is introduced into the target chamber for the purpose of interacting with energetic He ions before they impinge on first wall surfaces. As a result, effluent processing systems must be designed to take into account a high Ar gas load. Therefore, a two-stage cryopumping system will be configured in line with an array of turbomolecular drag pumps to remove Ar from the effluent gas stream. After exiting the reaction chamber, effluent will pass through the first cryopump stage, at liquid nitrogen temperature (77 K), which will remove argon as well as any trace contaminants from the gas stream. The remaining effluent, consisting of H and He, will pass through the second cryopumping stage, at liquid He temperature (4.2 K), to remove H isotopes from the gas stream. This poster will discuss specific concepts for efficient plasma exhaust processing. [Preview Abstract] |
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JP8.00038: Development of one- and two-dimensional simulations of a thermal dusty plasma R.A. Jefferson, M. Cianciosa, E. Thomas In a ``dusty'' plasma, charged microparticles (``dust'') is added to a background of ions, electrons, and neutral particles. These dust particles fully interact with the surrounding plasma and self-consistently alters the plasma environment leading to the emergence of new plasma behavior. Numerical tools that complement experimental investigations can provide important new insights into the properties of dusty plasmas. This presentation will focus on the initial results from a newly developed code that models transport and thermal properties of dusty plasmas. The code uses a fourth-order Runge-Kutta algorithm with adaptive time steps to solve the equations of motion for a group of microparticles confined in a trapping potential and subject to a neutral drag force and interaction through a screened Coulomb force. This presentation will discuss the physics basis for the 1-D code and extensions to a 2-D version of the code. [Preview Abstract] |
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JP8.00039: Dust Particle Dynamics in a Varying Gravitational Field Aliya Merali, Andrew Zwicker The properties of silica dust suspended in an argon DC glow discharge plasma are analyzed in varying gravitational field. The plasma was created in a 6'' x 1.5'' glass chamber. 340 V was applied to the top of two stainless steel electrodes, placed 4'' apart. In order to trap the dust during microgravity, a floating stainless steel mesh was suspended from the top electrode. The experiment used a current of 1-2 mA and a pressure of 80 to 155 mTorr while gravity ranged from 0 to 1.8g by flying through a series of 30 parabolas. Two CCD cameras recorded the dust cloud illuminated by a 5 mW laser sheet. One camera allowed observation of the interparticle spacing of the dust cloud and individual particle motion. The second camera recorded a wide field view of the overall cloud motion. In hyper-gravity, the dust cloud was 0.26 cm by 1.4 cm. As the gravitational field approached zero, the cloud moved from the center of the chamber, disassembled and reformed on the chamber wall. As gravity increased, the dust particles returned to the center of the chamber and reorganized in their initial formation. During the decrease in the gravitational field, a dust acoustic wave was spontaneously formed as the density of the cloud increased. To better understand the motion of the particles, the electrostatic field was modeled using a particle in cell code. [Preview Abstract] |
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JP8.00040: Measurement of Plasma Parameters in an Argon DC Glow Discharge Dusty Plasma Arthur Safira, Andrew Zwicker, Taylor Caligaris Dust particles in plasmas can gain a charge due to the free ions and electrons. The particles can then be suspended in space by opposing gravitational and electrical forces. These dusty plasmas appear as impurities in plasma processes and fusion reactors, but are also observed in astrophysics in planetary rings and nebulae. In an argon DC glow discharge plasma, dust cloud formation was studied by varying the dust tray location, the dust tray bias, the electrode bias, and the neutral gas pressure. In this set up, two 4 inch ring electrodes were set concentrically, and two 30 fps CCD cameras were used for data collection. Silica, a fluorescent dust mixture, glass beads, and quantum dots were tested as dust cloud substances. Plasma parameters near these dust clouds were measured using a Languimir probe. Dust clouds were readily produced with a pressure of 85$\pm $ 5mTorr, cathode voltage of 253$\pm $30V, anode voltage of 110$\pm $20V, and the dust tray 4 inches from the anode. Dust tray biases proved useful in cloud positioning with -30CV$<$V$_{dt}<$+80V, but at other voltages clouds would not form due to plasma spots or dust tray proximity. Probe measurements indicated an electron density and temperature of 10$^{14}$m$^{3}$ and 2eV, respectively. In addition, at P$<$60mTorr spontaneous dust acoustical waves were observed and studied with a 500,000 fps 28 frame PSI-4 CCD camera. [Preview Abstract] |
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JP8.00041: Nonlocal transport in the hydrodynamics of laser plasma interactions Brendan C. Lyons, Stefan H\"{u}ller For the modeling of laser plasma interactions in hot plasmas, the assumption of an isothermal plasma can be justified as long as the thermal transport rapidly diffuses the absorbed laser energy. For electron temperatures below around 500eV, local heating may be non-negligible, requiring the solving of the energy equation together with the hydrodynamic equations for continuity and momentum. Furthermore, nonlocal transport effects have to be considered when the electron mean free path is comparable to the size of the laser hot spots which give rise to local heating. In this study, electron heat conduction and laser absorption are included in a Eulerian hydrodynamic scheme. The corrections to the transport and coupling coefficients are also taken into account following models which consider laser-induced anisotropy and nonlocal transport. Refs.: A. Brantov, V. Bychenkov et al. Phys. Plasmas 5, 2742 (1998); Phys. Plasmas 6, 3002 (1999); Phys. Plasmas 7, 1511 (2000), A. Bendib et al., Phys. Plasmas 12(3), 032308 (2005). [Preview Abstract] |
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JP8.00042: Picosecond Neutron Yields from Ultra-Intense Laser-Target Interactions C. Leland Ellison, Julien Fuchs High-flux neutron sources for neutron imaging and materials analysis applications have typically been provided by accelerator-based (Spallation Neutron Source) and reactor-based (High Flux Isotope Reactor) neutron sources. A novel approach is to use ultra-intense ($>$ 10$^{18}$ W/cm$^2$) laser-target interactions to generate picosecond, collimated neutrons. Here we examine the feasibility of a source based on current (LULI) and upcoming laser facility capabilities. A Monte-Carlo code calculates angular and energy distributions of neutrons generated by D-D fusion events occurring within a deuterated target for a given incident beam of D+ ions. The parameters of the deuteron beam are well understood from laser-plasma and laser-target studies relevant to fast-ignition fusion. Expected neutron yields are presented in comparison to conventional neutron sources, previous experimental neutron yields, and within the context of neutron shielding safety requirements. [Preview Abstract] |
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JP8.00043: Use of Mirnov Coil Array in Detection of Magneto-Coriolis Waves Kristine Garot, Erik Spence, Mark Nornberg, Ethan Schartman, Austin Roach, Dylan Coster, Cyprian Czarnocki, Hantao Ji It is the goal of the Princeton Magnetorotational Instability (MRI) experiment to better understand the process by which angular momentum is transported in accretion disks.~ The MRI experiment is a liquid gallium Taylor-Couette experiment with independently spinning disks at the ends and an applied axial magnetic field.~ Under turbulent conditions and a strong enough magnetic field, magneto-Coriolis waves are observed using a 2-D Mirnov coil array and global mode analysis.~ A new array has been constructed and added to the previous array, and the positions of the new coils have been chosen to increase the mode resolution.~ Discussion of the observed waves using both the new and old Mirnov coil arrays, along with spectra of the fit modes will be presented. [Preview Abstract] |
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JP8.00044: Wavenumber and Frequency Spectral Analysis from Free-Surface MHD Experiments B. Bartell, M.D. Nornberg, J.R. Rhoads, H. Ji Characterizing turbulent free-surface magnetohydrodynamic flow in a region with a strong magnetic field is critical to understanding some astrophysical phenomena as well as designing a liquid-metal first wall diverter in a fusion reactor. To isolate the effect of a magnetic field on free-surface MHD, an experiment is performed in which liquid gallium flows down a wide aspect ratio channel perpendicular to a uniform, static, magnetic field of up to 2 kG. We measure disturbances in the flow at two locations by tracking the position of laser beam reflections from the liquid's surface with position sensitive photodiodes as a function of time. The distance between the incident lasers on the surface of the stationary liquid metal is 1.2 cm downstream. Given the two time-series and the distance between the measured locations on the surface, we estimate the local wavenumber and frequency spectra using two-point correlation analysis. Evidence from these spectra indicates that turbulence and wave features parallel to the magnetic field are largely damped as the magnetic field increases, thereby reducing the turbulence from three dimensions to two. [Preview Abstract] |
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JP8.00045: MRI Dispersion for a Helicon Plasma Courtney Kaita, Hantao Ji, Cami Collins The magnetorotational instability (MRI) is a basic MHD instability that occurs when a weak magnetic field is present in a differentially rotating disk. MRI is a likely reason for fast angular momentum transport in astrophysical accretion disks. A cohesive understanding of MRI with a range of plasma parameters pertaining to the wide variety of accretion disk systems has become an increasingly pressing concern. In the helicon plasma MRI experiment, plasma is created by a spiral antenna in an axial magnetic field produced by a solenoid. A radial potential difference is applied between a three-ring electrode system which creates plasma rotation through ExB drift. In this experiment, the ion gyro-orbit is much larger than for electrons. The Hall term due to different ion and electron velocities is added to the MHD model, resulting in additional two-fluid effects in the MRI dispersion relation. The characteristic MRI growth rates for the given experimental parameters are examined. [Preview Abstract] |
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JP8.00046: Experimental Characterization of Azimuthal Velocity with Varying Reynolds Numbers in short Taylor-Couette Flow Cyprian Czarnocki, Peter Humanik, Austin Roach, Mark Nornberg, Erik Spence, Michael Burin, Hantao Ji Simulations of Taylor-Couette flow are difficult to reconcile with experimental measurements since the available Reynolds number of the simulations is normally much smaller than in most experiments. The ability to increase fluid viscosity by adding glycerol to water will allow for experiments to be run with a lower Reynolds number, allowing for the experimental results to be compared with simulations. In this experiment a Laser Doppler Velocimeter (LDV) is used to measure internal flow velocity within a short Taylor-Couette apparatus. The azimuthal velocity profiles are measured over a range of radial and axial positions with varying fluid viscosities. A comparison of both simulation and experimental results of azimuthal velocity profiles is presented. The goal for this experiment is to achieve good agreement between the experimental and simulation results and to help better understand the Ekman circulation and its suppression in the Princeton Magnetorotational Instability (MRI) Experiment. [Preview Abstract] |
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JP8.00047: Experimental Investigation of Flow Inside a Short Taylor-Couette Apparatus With an Air Vortex Peter Humanik, Cyprian Czarnocki, Austin Roach, Erik Spence, Mark Nornberg, Hantao Ji The study of magnetohydrodynamics (MHD) and the instabilities involved with systems is one of great interest in astrophysics. Due to the limitations in tracking the flow of fluid conductors, such as the opacity of galintan, systems involving the movement of water and other easily traceable fluids are of great relevance towards predicting flows. In this experiment, the characteristics of a vortex of air that is formed around a cylinder rotating inside a larger coaxial cylinder which is rotating at a different rate are recorded. Laser Doppler Velocimetry (LDV) provides a profile of the speed of particles in the water near the vortex. Using the data about the water speed near the vortex and the characteristics of the vortex, the flow along the air-water boundary can be predicted. The experiment will be conducted over a range of viscosities which can be achieved from mixing glycerol with the water. The results can be used as a reference for further experiments in MHD involving similar vortices. [Preview Abstract] |
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JP8.00048: Evaporative ion cooling in SSX M. Korein, D. Weinhold, J. Santner, T. Gray, M.R. Brown, V.S. Lukin Reconnection of merged plasmas in SSX results in rapid heating of ions and electrons. The SSX ion Doppler spectrometer shows heating of carbon and helium ions up to $100~eV$ in a new slightly prolate flux conserver ($R=0.2~m, L=0.4~m$). A particle orbit simulation in realistic SSX magnetic fields shows that energetic ions are rapidly lost to the walls leaving behind a cooler ion population. We refer to this phenomenon as evaporative ion cooling. A retarding grid energy analyzer and a Mach probe are being used to study energetic ion flux and high velocity flows. Both probes are $\sim1.5~cm$ in diameter and can be scanned across the radius of the device at the mid-plane. Following reconnection, local flow speeds of greater than $60~km/s$ (Mach number $>2$) have been measured by the Mach probe in the present geometry. Preliminary data indicates bi-directional outflows during merging shots. Energetic ion data will be presented if available. The particle orbit code is being used to simulate $\sim10^6$ particles with random initial conditions in SSX. The simulation traces particle orbits and models the probe structure in order to generate predictions of actual probe signals. [Preview Abstract] |
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JP8.00049: Effect of Current Loop Perturbations on Fast Reconnection in MRX K.R. Labe, S. Dorfman, M. Yamada, H. Ji, E. Oz, J. Yoo, J. Xie The Magnetic Reconnection Experiment (MRX) investigates the mechanism responsible for fast reconnection. Two toroidal flux cores produce the plasma and drive the reconnection; the current flows toroidally [1]. A 20 cm diameter circular current loop was installed at one toroidal position at the center of the current sheet; it could be oriented to produce magnetic field either out-of-plane or along the reconnecting field. A voltage of up to 10 kV was applied to the loop for 100 us; the effect of its large-scale perturbations on the reconnection process was measured at several toroidal locations. Preliminary results show that the reconnection rate, as manifested by the flux evolution, is resilient to current loop perturbations. By contrast, detailed characteristics of the reconnection process (e.g. electromagnetic fluctuations, magnetic field profile) are globally affected by even small current loop perturbations. Effects of varying the plasma density as well as the loop voltage and timing will be reported. [1] M. Yamada, et al., Phys. Plasmas \textbf{4}(5), 1936 (1997). [Preview Abstract] |
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JP8.00050: Reconnection Line Breaking Interpreted in Terms of Electron Trajectories Daniel Lecoanet, Russell Kulsrud, Masaaki Yamada In many physical situations, the width of the reconnection layer as predicted by the classical Sweet-Parker theory is smaller than the ion skin depth. In this case, the electrons and ions decouple, and the plasma must be treated as two fluids resulting in a fast reconnection rate with the layer width set by the ion skin depth. The line breaking mechanism in the two-fluid regime is no longer resistive but is driven by the anisotropic electron pressure tensor. By calculating electron trajectories near the origin, we show numerically that this can be interpreted in terms of an unmagnetized region [1]. We find the electrons in the unmagnetized region are freely accelerated by the induced electric field, producing the reconnection current. We measure the average time electrons are accelerated in the unmagnetized region. For plasma parameters similar to those in the Magnetic Reconnection Experiment [2], we find this acceleration time is shorter than the collision time, implying an effective resistivity larger than the classical Spitzer resistivity. Understanding electron trajectories elucidates the reconnection mechanism and places additional constraints on analytic theories of two-fluid reconnection. \\[0pt] [1] R. Kulsrud et al, Phys. Plasmas 12, 082301 (2005).\\[0pt] [2] M. Yamada et al, Phys. Plasmas 4, 1936 (1997). [Preview Abstract] |
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JP8.00051: Numerical Study of Random Noise-Induced Beam Degradation in High Energy Accelerators Arjun Landes, Ronald Davidson, Hong Qin Random noise caused by small machine errors is an inevitable and potentially significant source of beam degradation in high-energy accelerators. Understanding the detailed effects of such noise on beam quality is critical to evaluating the viability of accelerator design and operation. To this end, we study the dynamics of a single particle under the combined influence of random noise and a quadrupole focusing field. The equation of motion for a beam particle propagating through a sinusoidal quadrupole lattice takes the form of the Mathieu equation. We introduce a small random error into the amplitude of the oscillating term in the Mathieu equation, and solve the resulting dynamical equation numerically using Mathematica, employing stochastic integration techniques, to obtain matched solutions to the perturbed equation of motion. These solutions are then compared with the matched solutions to the standard Mathieu equation to determine the effects of the random noise, e.g., as measured by the increase in mean-square displacement of the particle from the beam axis. Statistical properties of the resulting particle dynamics are measured to assess quantitatively the degree of noise-induced degradation in beam quality. [Preview Abstract] |
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JP8.00052: Investigation of Carbon Wire X-pinch backlighting for Pulsed Power Driven Exploding Wire Experiments Sean McGraw, Simon Bott, Farhat Beg Exploding wire experiments have many important applications, including inertial confinement fusion research and laboratory astrophysical plasmas. Understanding of the dynamics of wire arrays is crucial to these applications. Details of wire ablation remain somewhat unclear, which lead to uncertainties in scaling to higher drive currents. The ablated coronal plasma is typically investigated using x-rays in the 3-5 keV range, however much of this plasma is highly transparent to this radiation, and information about the dynamics of coronal plasma above 10$^{19}$/cc is therefore lacking. A possible candidate for lower energy radiography is the carbon x-pinch, which produces x-rays below 1 keV. Experiments are conducted on GenASIS, a linear transformer driver, to study carbon x-pinches for wire array x-ray backlighting. This pulsed power system drives 250 kA into a short circuit and 200 kA into an x-pinch load. X-pinches formed from 20 $\mu$m titanium and 10 $\mu$m stainless steel wires are compared to the carbon system to provide more insight into the evolution and structure of exploding wires. Information from these comparisons will feed directly into the ongoing discussion of wire ablation at high currents. [Preview Abstract] |
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JP8.00053: An experimental study of ion acoustic waves (IAW) in electronegative plasmas: can IAW measurements calibrate diagnostics for the measure of the negative ion fraction? Camron Proctor, Greg Severn Electronegative plasmas are found in nature, in the lower ionosphere for example, and in plasma processing applications, such as vapor deposition, plasma etching, and particle beam sources. To understand the full potential of electronegative plasmas, a better diagnostic of their properties needs to exist. The negative ion fraction $\alpha = n_{-}/n_e$ determines, in part, the degree of electronegativity of plasmas. The fast mode of Ion acoustic waves (IAWs) are often used as a diagnostic for $\alpha$, and are here studied with the intent to use IAWs to calibrate other diagnostics, such as the laser photodetachment technique, which does not furnish absolute measurements. The various diagnostics of $\alpha$ are reviewed. The electronegative plasmas studied were Oxygen and Argon/Oxygen DC discharges confined with a multidipole arrangement of permanent magnets, producing low temperature, low pressure, $(T_e < 1 eV, \: T_i \ll T_e, \: p_0 < 1 mTorr)$ weakly collisional plasmas. [Preview Abstract] |
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JP8.00054: Particle and thermal transport due to drift resistive ballooning modes T. Goldstein, T. Rafiq, A.H. Kritz, G. Bateman, A.Y. Pankin The ion-temperature-gradient and trapped electron modes are primary candidates for producing the turbulence that drives anomalous transport in the core of magnetically confined plasmas. The situation at the edge is different. Since the edge plasma is influenced strongly by collisions, it is expected that resistive ballooning modes (RBMs) are an important driver of turbulence in the edge region. In this work, a new advanced RBM model [1] is tested as a function of plasma parameters. In this model, the eigenvalues and eigenvectors are used together with a quasi-linear mixing length estimate to determine fluxes and diffusivities. Particle and thermal transport coefficients are investigated in systematic scans over plasma density, density gradient, electron and ion temperature gradients, magnetic $q$, collisions, magnetic shear, finite Larmor radius effects, and pressure gradient. In the low temperature plasma region, it is found that RBM diffusivities increase with increasing density gradient, magnetic $q$, and collisionality.\\[4pt] [1] T. Rafiq, et al, poster at this APS meeting [Preview Abstract] |
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JP8.00055: Normal Modes of Magnetized Finite Two-Dimensional Yukawa Crystals Gabriel-Dominique Marleau, Hanno Kaehlert, Michael Bonitz The normal modes of a finite two-dimensional dusty plasma in an isotropic parabolic confinement, including the simultaneous effects of friction and an external magnetic field, are studied. The ground states are found from molecular dynamics simulations with simulated annealing, and the influence of screening, friction, and magnetic field on the mode frequencies is investigated in detail. The two-particle problem is solved analytically and the limiting cases of weak and strong magnetic fields are discussed.\\[4pt] [1] C.\ Henning, H.\ K\"ahlert, P.\ Ludwig, A.\ Melzer, and M.Bonitz. J.\ Phys.\ A {\bf 42}, 214023 (2009)\newline [2] B.\ Farokhi, M.\ Shahmansouri, and P.\ K.\ Shukla. Phys.Plasmas {\bf 16}, 063703 (2009)\newline [3] L.\ C\^andido, J.-P.\ Rino, N. Studart, and F.\ M.\ Peeters. J.\ Phys.: Condens.\ Matter {\bf 10}, 11627--11644 (1998) [Preview Abstract] |
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JP8.00056: Simulation of Power Supply for Vertical Stabilization of Plasmas at ITER Maximilian Swiatlowski, Charles Neumeyer We present the results of simulations of the power supply of an ITER vertical stabilization magnet system. ITER's elongated tokamak geometry enables increased plasma pressures at the cost of the loss of vertical stability, as the vertical-horizontal asymmetry allows small vertical perturbations to grow to dangerous levels. The ITER design calls for three independent magnetic systems to control this unstable growth; we describe the VS3 system which uses a set of in-vessel coils to actively generate a magnetic response when drift is detected. The primary requirements of the power- supply are to provide $80$ kA for $0.3$ s pulses every $10$ s, while maintaining $20$ kA during $1$ s events every $2$ s and $10$ kA otherwise. An IGCT chopper design with variable pulse-width-modulation frequency is chosen to minimize cost and thermal losses. A full model of the circuit is developed in the time-domain simulation program PSCAD, and the design is demonstrated to be capable of delivering the specified signals. A thermal model is created to determine the optimal number of chopper bridges; a 4-wire plasma model is written to ensure the magnet's stabilization properties. We conclude that an IGCT chopper power supply is an effective system to drive the current of the VS3 in-vessel stabilization magnets at ITER. [Preview Abstract] |
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JP8.00057: Use of machine learning techniques for analysis of plasma data Logan Maingi, Harry Mynick, Neil Pomphrey We consider the application of machine learning techniques to results from gyrokinetic (GK) codes such as Gene [1]. GK codes allow accurate computation of physical quantities such as radial fluxes, potential fluctuations, etc. However, such codes are computationally expensive, so use of techniques (eg, neural networks) to reduce the number of simulations necessary is desirable. Strategies are considered to minimize the requisite number of training examples for such a network without risk of error due to underfitting or overfitting.\\[4pt] [1] F. Jenko, W. Dorland, M. Kotschenreuther, B.N. Rogers, ~Phys. Plasmas $<$7$>$, 1904 (2000). [Preview Abstract] |
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JP8.00058: Parallelization of the GKEM Electromagnetic PIC code using MPI and OpenMP Mark Benjamin, Stephane Ethier, Wei-li Lee GKEM is a legacy gyrokinetic PIC code in slab geometry that calculates anomalous transport in fusion plasmas due to drift wave microturbulence. It is currently being used to develop new algorithms for high-beta electromagnetic PIC simulations. This work focuses on the modernization and performance improvement of GKEM through the use of FORTRAN 90 language features and parallelization. MPI-based particle parallelization was implemented as well as loop-level multi-threading using OpenMP directives. Performance improvements and speedup curves for the different stages of the code are discussed. Project supported by the DOE-PPPL High School Internship Program and DOE contract DE-AC02-09CH11466. [Preview Abstract] |
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JP8.00059: Parallelization of LSODE in PIES Using NVIDIA's CUDA Architecture for GPGPU Paul Thompson, Stephane Ethier The Princeton Iterative Equilibrium Solver (PIES) is a powerful tool for computing three dimensional MHD equilibria, without making assumptions about the form of the magnetic field. Part of its strength comes from its ability to handle equilibria with islands and stochastic regions. However, a high-resolution PIES calculation often takes several hours to complete, spending most of its time in the Livermore Solver for Ordinary Differential Equations (LSODE) to follow field-line trajectories. This work examines the feasibility of speeding up these calculations by taking advantage of the parallel computing resources of programmable Graphic Processor Units (GPUs). To this end, the LSODA variant version of LSODE is converted to NVIDIA's C for CUDA application programming interface and tested against its original Fortran version on an NVIDIA Tesla Cluster. Run times are compared between the serial and parallel versions, with special attention given to different scaling options. The new code is also analyzed for bottlenecks and opportunities for additional speedups, with the ultimate goal of developing a PIES-based MHD solver capable of running between experimental shots. [Preview Abstract] |
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JP8.00060: Providing Complete Distribution Function Analysis with NUBEAM FGen Casey Stark, Douglas McCune, Eliot Feibush The TRANSP libraries provide many robust tools for analyzing tokamak plasmas. The development of this long-standing code has focused on physics modeling and producing efficient plasma calculations. In order to make these powerful libraries accessible to more scientists, parts of the code have been incorporated into web services, which can be run using the ElVis scientific graphics display. We present NUBEAM FGen, a new graphical web service interface focusing on distribution function (DF) simulation and analysis now integrated into ElVis. This interface can acquire TRANSP run data and given simulation parameters (a time of interest, duration, number of particles, etc.), will run a NUBEAM simulation on extracted Plasma State files. This simulation outputs the full distribution function in energy, pitch, x, and theta space. The user can analyze the DF data with an interactive get\_fbm session, allowing them to visualize the DF with various plots (contour, slice, 3D, etc.). Users can also download the output for their own processing. The ease of this new approach to DF analysis will allow a much wider audience to utilize the DF tools provided by TRANSP in their own research. [Preview Abstract] |
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JP8.00061: Application of Piecewise Continuous Waveforms in the Paul Trap Simulator Experiment M.S. Gutierrez, E.P. Gilson, R.C. Davidson, A.N. Kabcenell The Paul Trap Simulator Experiment (PTSX) is a compact linear Paul trap that simulates a long, thin charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system by putting the physicist in the frame-of- reference of the beam. Both systems share the same equations of motion which allows for many AG focusing configurations to be studied in a compact laboratory environment instead of a kilometers-long machine. AG systems contain discrete quadrupole magnets but have been modeled with a continuously varying sinusoidal field of equivalent average transverse focusing strength in PTSX. The average transverse focusing frequency characterizes the strength of the transverse confinement in the smooth focusing model, where fast oscillations are averaged over. Initial experimental results demonstrate the validity of the smooth focusing model by applying periodic-step waveforms and sinusoidal waveforms, of equal average transverse focusing strength, to the electrodes of the Paul trap and comparing the resulting radial density profiles. [Preview Abstract] |
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JP8.00062: Diamond Synthesis in a Hybrid PVD/CVD ECR Thin Film Deposition System William Somers, Andrew Zwicker Diamond thin films are extremely hard, thermally conductive, resistant to chemical corrosion, and excellent insulators making them an ideal coating for semiconductors. In our electron cyclotron resonance (ECR) system, physical vapor deposition (PVD) and chemical vapor deposition (CVD) are used to create diamond thin films in a hybrid physical-chemical vapor deposition (HPCVD) system. In this process, a gas mixture that consists of 1{\%} methane and 99{\%} hydrogen is heated with a 2.45 GHz / 2.5 kW microwave source. Diamond deposition occurs from the physical sputtering of carbon from a negatively biased graphite target (PVD) and chemically from the stripped methane, CH$_{4}$, molecules (CVD). A major advantage of our hybrid plasma processing system is that it can sputter diamond at a much lower temperature than typical CVD. A silicon wafer substrate handling system allows us to control rotational speed, bias, and temperature and allows for increased control of diamond deposition. The quality of the diamond films is measured by Raman spectra and SEM images. Initial results of growth rate, uniformity, and quality will be presented. [Preview Abstract] |
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JP8.00063: Optical Analysis of Plasma Ball Filaments Scott Vasquez, Michael Campanell, Stewart J. Zweben Optical methods were used to study the properties of a commercial plasma ball. Using spectrometry, the gas composition of the plasma ball was analyzed. Spectra of known gases were compared with the plasma ball spectrum, confirming the presence of Neon and Xenon. The spectra indicate that faint amounts of Nitrogen may also be present. Photomultiplier tubes were used to measure the radial velocity of filaments in the plasma ball. Digital oscilloscope traces produced with the photomultiplier tubes show that the filaments propagate radially at an average velocity on the order of 10,000 m/s. Furthermore, these traces suggest that that the radial velocity decreases with increasing distance from the electrode. A hotwired commercial plasma ball, with connections for a pulse generator and Variac has been built, allowing for the study of filament velocity at different operating voltages and frequencies. A custom plasma ball whose parameters, such as gas mixture, pressure, electrode configuration, and applied voltage waveform can be varied, has also been constructed. Analysis of the custom plasma ball will give further insight to how such parameters affect the plasma ball's filament formation and behavior. Initial results will be presented. Ultimately, this custom plasma ball, along with the methods used to measure its properties, will be incorporated into an undergraduate physics lab. [Preview Abstract] |
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JP8.00064: High-Speed Imaging Analysis of Discharge Oscillations in the Cylindrical Hall Thruster Evan Davis, Jeffrey B. Parker, Yevgeny Raitses The cylindrical Hall Thruster is a cross-field plasma discharge device, which employs mirror and cusp shaped magnetic field configurations [1]. Several modes of discharge oscillations in the plasma have been observed by a high-speed camera, including a circumferentially propagating spoke and a longitudinal breathing mode. The occurrence and characteristics of these oscillations are strongly influenced by the operating conditions of the thruster discharge. A data analysis package employing various signal processing techniques was developed to parametrically characterize both the spoke and the breathing mode oscillations under variations of the background gas pressure, the discharge voltage, and the magnetic field. \\[4pt] [1] Y. Raitses and N. J. Fisch, Physics of Plasmas \textbf{8}, 2579 (2001). [Preview Abstract] |
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JP8.00065: Recent Bolometry Upgrades and Results from the HIT-SI and NSTX Experiments M.A. Chilenski, T.R. Jarboe, B.A. Nelson, R. Raman, L. Roquemore, B.M. Jones The bolometry suite on the Helicity-Injected Torus (HIT-SI) has recently been upgraded with two new channels in order to measure the radiated power in the mouth of one of the helicity injectors, as well as an upgraded wide-view bolometer to maximize the solid angle imaged at the midplane. This upgrade will allow a better understanding of the magnitude of the power radiated in the injectors versus the confinement region. In addition to a multi-chord bolometer array, the National Spherical Torus Experiment (NSTX) is also equipped with three wide-view bolometers looking at various regions of the plasma. One bolometer looks into the main confinement region at midplane along a chord parallel to the midplane, one looks down to the lower divertor/injector region and one looks from the bottom up. Work is proceeding to cross-calibrate these bolometers to the multi-chord array. Once this calibration is complete, it will be possible to obtain rapid estimates of the total radiated power, which will be compared to the total input power. [Preview Abstract] |
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JP8.00066: Development and Evaluation of a Motional Stark Effect with Laser Induced Fluorescence Diagnostic for Determining the Magnetic Field Magnitude and Angle in NSTX Adam Steiner, E.L. Foley, F.M. Levinton, A. Barlis The motional Stark effect (MSE) diagnostic has been widely used for determining the magnetic field pitch angle profile in the high magnetic fields of large tokamaks. Incorporating laser induced fluorescence (LIF) and a dedicated diagnostic neutral beam into MSE systems has been shown to extend the range of applicability to lower field systems and to provide simultaneous measurements of magnetic field magnitude. An MSE-LIF system built by Nova Photonics has been characterized and redesigned for installation on NSTX. The design has taken into account spatial considerations of interfacing between the system and NSTX and allowed for the inclusion of neutral beam measurement devices including a Faraday probe and a calorimeter. An electrically insulated magnetic shielding system was developed to prevent interference from the external magnetic field of NSTX. Characterization of the neutral beam has shown good performance and agreement with theoretical values with respect to the neutral-ion ratio and species fraction. [Preview Abstract] |
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JP8.00067: RF power deposition during HHFW heating in NSTX Teresa Brecht, R. Bell, J. Hosea, B. LeBlanc, C.K. Phillips, G. Taylor, E. Valeo, J.R. Wilson, P.M. Ryan, P.J. Bonoli, J. Wright High harmonic fast wave (HHFW) heating and current drive (CD) research on the National Spherical Torus Experiment (NSTX) employs a 12 strap antenna which launches radio frequency (RF) waves into the plasma. Improved core heating efficiency is achieved by moving the onset of wave propagation away from the antenna. Current research focuses on understanding RF power losses at the edge region and power partitioning among the plasma species under various discharge conditions. The full- wave code TORIC was used to simulate discharges of interest using equilibrium fits and temperature and density profiles from NSTX discharges. Ion species concentrations, as well as the launched wavelength strongly effect power deposition. Simulation of the power partitioning in L-mode and H-mode, with and without neutral beam injection (NBI) will be discussed. [Preview Abstract] |
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JP8.00068: Heat Flux Characterization in the NSTX Jonathan Surany, Rajesh Maingi Management of the heat flux profile is critically important in spherical tokamaks because they are high power density systems. More specifically, peak heat fluxes as high as 10 MW/m$^{2}$ have been measured in the National Spherical Torus Experiment (NSTX). Infrared cameras placed to view the upper and lower divertors on the NSTX are used to measure the tile temperature and to calculate the heat flux profiles. In this study, we present the dependence of the heat flux profile on neutral beam injected power, plasma current, magnetic balance and magnetic flux expansion, and triangularity. For example, peak heat flux increases linearly with increases in neutral beam injected power, and varies inversely with magnetic flux expansion. These trends follow their basic theoretical expectations. [Preview Abstract] |
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JP8.00069: 3-D reconstruction of incandescent lithium dust particle trajectories in NSTX Jacob Nichols, Lane Roquemore, Werner Boeglin, William Davis, Dennis Mansfield, Charles Skinner, Hans Schneider, Rahul Patel Dust control is a key safety and stability concern for ``next-step'' fusion devices, so understanding the dynamics of dust in a fusion grade reactor is an important issue. Here, a large ensemble of trajectories from pre-characterized lithium dust is collected with the goal of verifying the various dust transport codes. Precise amounts of 40 $\mu $ lithium dust (varying from 1-150 mg) are injected into the National Spherical Torus Experiment (NSTX) plasma using a powder dropper based on a vibrating piezo crystal. The particles are heated to incandescence by electron bombardment, allowing them to be viewed by two separated visible-range fast cameras operating at $\sim $ 10,000 frames per second. The tracks from both cameras can be combined to form a single, 3-D trajectory. Particles are observed to undergo a variety of accelerations both parallel and perpendicular to the magnetic field, depending on their proximity to the scrape-off layer. The velocity, lifetime, and ionization state of the particles will be discussed. [Preview Abstract] |
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JP8.00070: Magnetic Transport Barriers in the DIII-D Tokamak J. Kessler, F. Volpe, T.E. Evans, H. Ali, A. Punjabi Large overlapping magnetic islands generate chaotic fields. However, a previous work [1] showed that second or third order perturbations of special topology and strength can also generate magnetic diffusion ``barriers" in the middle of stochastic regions. In the present study, we numerically assess their experimental feasibility at DIII-D. For this, realistic I- and C-coils perturbations are superimposed on the equilibrium field and puncture plots are generated with a field-line tracer. A criterion is defined for the automatic recognition of barriers and successfully tested on earlier symplectic maps in magnetic coordinates. The criterion is systematically applied to the new puncture plots in search for dependencies, e.g. upon the edge safety factor $q_{95}$, which might be relevant to edge localized mode (ELM) stability, as well as to assess the robustness of barriers against fluctuations of the plasma parameters and coil currents.\par \vskip8pt \noindent [1] H.~Ali and A.~Punjabi, Plasma Phys.\ Control.\ Fusion {\bf 49}, 1565 (2007). [Preview Abstract] |
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JP8.00071: Evaluation and Implementation of Helium Line Ratio Technique for Measurement of Edge Density and Temperature on DIII-D L. Hurd, N.H. Brooks, E.A. Unterberg, O. Schmitz The electron density and temperature in the scrape-off layer of DIII-D have been determined in pure helium plasmas by the helium line ratio technique [1] employing spectral line monitors and an intensified fast-framing CCD camera. Both diagnostics viewed the plasma tangentially on the midplane of the vessel. Three visible He I transitions, one triplet (3$^3$S$\rightarrow$2$^3$P) and two singlets (3$^1$D$\rightarrow$2$^1$P and 3$^1$S$\rightarrow$2$^1$P), were measured simultaneously --- along a single spatial chord with the line monitors and over a 2D region of the outer midplane with the intensified camera. Column brightnesses through the emission shell recorded with the camera were Abel-inverted to yield local intensities with a spatial resolution of a few millimeters. The electron densities and temperatures deduced by the helium line ratio method are compared with results from the Thomson scattering diagnostic on DIII-D.\par \vskip8pt \noindent [1] O.~Schmitz {\em et al.}, Plasma Phys.\ Control.\ Fusion {\bf 50} (2008) 115004. [Preview Abstract] |
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JP8.00072: Comparison of Moderate to High Ion Cyclotron Absorption on Energetic Ions in NSTX and DIII-D J. Burby, R.I. Pinsker, M. Choi Strong absorption of fast waves (FWs) on injected deuterons at ion cyclotron harmonic numbers in the 4-10 range is observed on both DIII-D and NSTX. The results from fast ion $D_\alpha$ spectroscopic measurements from the two devices differ significantly: deposition on fast ions peaks near the cyclotron harmonic layer closest to the magnetic axis in the conventional-aspect-ratio DIII-D, while results from the low-aspect-ratio NSTX show a broader deposition profile [1]. One root of the difference stems from the absorbing fast ions sampling more harmonic layers in NSTX than in DIII-D. We investigate cyclotron absorption in cases with multiple harmonic layers within a single ion gyroradius and related phenomena numerically and analytically by examining the response of individual charged particles to rf fields in various field configurations.\par \vskip8pt \noindent [1] M. Podesta {\em et al.}, {\em RF Power in Plasmas} (Proc.18th Top.\ Conf., Gent, Belgium, 2009), to be published. [Preview Abstract] |
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JP8.00073: Investigation of Ion Cyclotron Emissions on DIII-D During Neutral Beam Injection and Fast Wave Heating A. Axley, R.I. Pinsker Ion cyclotron emission (ICE) spectra are measured with small rf loop antennas at 4 locations in the DIII-D vessel. Two of the loops are located on the centerpost while the other two are on the outboard wall of DIII-D. Both sets of loops are near the midplane. The signal processing is done in software using data from a 1 Gigasample/s 4-channel digitizer to measure the output of these antennas rather than the traditional technique of using an analog spectrum analyzer. Specifically, an FFT is used to determine the spectra up to 500 MHz of each signal. The analysis is performed on data recorded during neutral beam injection, and during high power fast wave (FW) heating. This technique should be capable of resolving the bursting character of ICE in time, as has been often observed in the neutral beam injection case, as well as extending the observations of parametric decay instabilities during FW injection to include the pump (60 or 90 MHz) and its first several harmonics. [Preview Abstract] |
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JP8.00074: Visualization of Turbulence with OpenGL A. Avril, M.A. Makowski, M. Umansky, R. Kalling, D.P. Schissel Turbulence is an all-pervasive phenomenon in plasmas. The edge turbulence is of particular interest for the containment of plasmas during fusion processes. It is simulated with BOUT, a 4D (3 spatial + time coordinates) edge turbulence simulation code that is typical of modern codes in many ways. While predictive, the 4D outputs of these codes are difficult to visualize. In an effort to better understand the macroscopic trends of edge turbulence in toroidal plasmas, we are developing routines to render the BOUT output, using the OpenGL framework in C$^{++}$. These routines will allow us to follow the evolution of isosurfaces through time, and we anticipate gaining insight into the nonlinear dynamics of turbulence as a result. Additionally, these routines could potentially be used to visualize the output of other modeling codes. [Preview Abstract] |
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JP8.00075: Multi-Parameter Scaling of Divertor Heat Flux Profile Width C.J. Miles, D.N. Hill, C.J. Lasnier, M.A. Makowski, A.M. Garofalo We will explore the dependence of the divertor heat flux profile on plasma current, heating power, midplane edge heat flux, magnetic field strength, and other variables. In divertor tokamaks, a major part of the heating power is lost by thermal transport across the plasma boundary into the scrape-off layer (SOL) where the power is primarily transported along field lines to the divertor. It is important that this high heat flux to the divertor surfaces stays below the technologically feasible perpendicular heat flux of approximately 10 MW/m$^2$. Thus, it is valuable to determine a multi-parameter scaling of heat flux profile width for projections to a fusion reactor. We will attempt to do so by analyzing divertor heat flux data inferred from high-speed infrared camera measurements of the surface temperature over time [Preview Abstract] |
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JP8.00076: Confinement Trends in DIII-D High Performance Plasmas A. Neff, A.M. Garofalo, T.C. Luce A research goal on the DIII-D tokamak is to develop the physics basis for steady-state, high performance plasma operation for ITER and future burning plasma devices. To achieve high fusion power density and steady-state with minimal external power requirements, a fusion reactor requires good energy confinement and high bootstrap (self-generated) fraction of the total plasma current. However, a coarse view of DIII-D and JET databases of high performance discharges suggests a decrease in quality of confinement with increasing noninductive current fraction. To assess this trend, and investigate possible causes, a code is being developed to retrieve and analyze the DIII-D experimental data, and generate a database of high confinement plasma discharges. The code uses specified criteria to evaluate the plasma duration at high confinement, and stores various plasma parameters calculated in this time range. Comparisons of the experimental energy confinement time to various inter-device scaling laws, and the dependence on key plasma parameters will be discussed. [Preview Abstract] |
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JP8.00077: Optimization of Optical Filters for the LIBEAM Diagnostic Sean McGuire, C.C. Petty, D.M. Thomas, B. Hudson In tokamak plasmas with an edge transport barrier, a measurement of the edge current density is necessary to understand plasma stability. A LIBEAM diagnostic system has been deployed on DIII-D that measures Zeeman polarimetry of the 2S-2P lithium resonance line in order to determine the magnetic field and corresponding current density within the edge pedestal region. Emission of the lithium resonance line is split by the local magnetic field producing three closely spaced spectral components; isolation of the $\sigma^-$ spectral component is required for measurement of the local magnetic field. A double Fabry-Perot etalon system is currently used for this purpose but a narrower bandpass is desired. This research will determine whether the installation of an exit pinhole will improve the etalon's finesse. However, transmitted light intensity is near a minimum threshold and the efficiency of the entire optical system must be examined and maximized. Optimization may include the installation of new detectors, lenses and fibers. [Preview Abstract] |
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JP8.00078: Electron Cyclotron Emission Radiometer Cristina Morales There is much interest in studying plasmas that generate hot electrons. The goal of this project is to develop a wide band electron cyclotron radiometer to measure the non-Maxwellian rapid rises in electron temperature. These rapid increases in temperature will then be correlated to instabilities in the plasma. This project explores a type of noncontact temperature measurement. We will attempt to show the feasibility of electron cyclotron emissions to measure the Maryland Centrifugal Experiment's electron plasma temperature. The radiometer has been designed to have 100dB of gain and a sensitivity of 24mV/dB given by its logarithmic amplifier. If successful, this radiometer will be used as a diagnostic tool in later projects such as the proposed experiment studying magnetic reconnection using solar flux loops. [Preview Abstract] |
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JP8.00079: DIII-D TOKAMAK II |
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JP8.00080: Non-axisymmetric Plasma Response to External Magnetic Perturbations M.S. Chu, L.L. Lao, T.E. Evans, M.J. Schaffer, E.J. Strait, Y.Q. Liu, M.J. Lanctot, H. Reimerdes Very low frequency non-axisymmetric magnetic response in tokamaks excited by external magnetic perturbations is studied with the MARS-F code [1] using different assumptions on the plasma dynamics. In the limit of vacuum plasma response, the fields are benchmarked against the SURFMN [2] code and an analytic model. In other plasma models, the response is affected by plasma pressure, resistivity, toroidal flow, and the kinetic effects associated with the particle drifts. Depending on the coil arrangement, the plasma response could be dominated by the resonant or non-resonant components of the external field. The responses can be tested by employing different combinations of currents in appropriately designed external coils as those in DIII-D. The combined magnetic field of the axisymmetric plasma equilibrium and its non-axisymmetic responses corresponds to a perturbed 3D plasma equilibrium.\par \vskip8pt \noindent [1] Y.Q.\ Liu, {\em et al.}, Phys.\ Plasmas {\bf 7} (2000) 3681.\par \noindent [2] M.J.\ Schaffer, {\em et al.}, Nucl.\ Fusion {\bf 48} (2008) 024004. [Preview Abstract] |
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JP8.00081: Measurement and Modeling of the Plasma Response to Externally Applied Non-axisymmetric Magnetic Fields H. Reimerdes, M.J. Lanctot, J.M. Hanson, A.M. Garofalo, M.S. Chu, G.L. Jackson, R.J. La Haye, M.J. Schaffer, E.J. Strait, O. Schmitz, Y.Q. Liu, M. Okabayashi, W.M. Solomon Magnetic measurements in DIII-D H-mode plasmas reveal a beta dependent plasma response to externally applied low n magnetic fields. The plasma response must be significant since it correlates with effects on the plasma such as magnetic braking of rotation. This is confirmed by modeling using the ideal MHD plasma response model in the MARS-F code, which predicts the measured plasma response to external $n=1$ fields for values of beta up to $\sim$75\% of the ideal MHD beta limit calculated without a conducting wall. At higher beta non-ideal effects have to be taken into account. The increasing plasma response is responsible for the decrease of the error field tolerance with beta. The knowledge of the perturbed field inside the plasma is an important step towards a quantitative understanding of the error field tolerance and the underlying braking models. [Preview Abstract] |
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JP8.00082: Measuring Resistive Wall Mode Stability in Real-time J.M. Hanson, M.J. Lanctot, G.A. Navratil, H. Reimerdes, E.J. Strait Measurements of the plasma response to externally applied, low-$n$ magnetic fields can be used to determine the resistive wall mode (RWM) stability of the plasma equilibrium. Such a method, if implemented as a real-time algorithm, can be used to gate error field correction, profile control, and RWM feedback control algorithms, enabling operation close to the no-wall stability limit. In addition, the stability estimate can be used to directly update parameters in an advanced RWM controller as the plasma evolves. We have developed an efficient scheme that uses an external field rotating at a single fixed frequency. Because only one frequency is applied, the plasma response can be calculated from measurements by Fourier-analyzing the measurements at only the applied frequency and subtracting the known vacuum pickup due to the control coils. This single-frequency, Fourier-domain analysis uses a small number of arithmetical operations, which is a requisite for real-time implementation. [Preview Abstract] |
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JP8.00083: Active Feedback Control of the Current-driven Resistive Wall Mode (RWM) in DIII-D Y. In, J.S. Kim, M.S. Chu, A.M. Garofalo, G.L. Jackson, R.J. La Haye, M.J. Schaffer, E.J. Strait, M.J. Lanctot, H. Reimerdes, Y.Q. Liu, L. Marrelli, P. Martin, M. Okabayashi Recent \mbox{DIII-D} experiments show that complete RWM feedback stabilization requires good error field correction (EFC), yet the RWM feedback control could not be replaced by EFC. A systematic investigation of feedback response time confirmed that a bandwidth greater than the RWM growth rate is required for direct RWM stabilization. The optimized feedback gain of RWM feedback stabilization was ultimately determined by the minimal level of plasma fluctuations. The parametric dependencies observed for feedback control of current-driven RWMs are consistent with predictions based on pressure-driven RWM models. Additionally, there was an indication of the influence of a second-least stable RWM which had never been identified in experiments. The experimental details are being used to assess the RWM feedback models for prediction of RWM suppression in ITER. [Preview Abstract] |
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JP8.00084: Physics Issues at the Initial Phase of Robust RWM Feedback M. Okabayashi, Y. In, J.S. Kim, G.L. Jackson, A.M. Garofalo, R.J. La Haye, E.J. Strait, T. Bolzonella, L. Marrelli, P. Martin, M.J. Lanctot, H. Reimerdes The magnetic feedback process has robustly suppressed low beta $q_{95}\sim 4$ current-driven resistive wall mode (RWM) by direct feedback beyond application of effective error field correction only. Without feedback, the current-driven RWM usually evolved into a resistive wall tearing mode even when the RWM amplitude is less than a few Gauss. There remain several issues in RWM feedback process, such as how it functions near the onset of magnetic island growth and the impact of uncorrected error fields. Another issue is the operational compatibility of fast direct feedback with slow error field correction at the initial phase of feedback. These issues will be discussed to clarify the requirements for robust RWM feedback control in ITER. [Preview Abstract] |
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JP8.00085: Development of An Energetic Particle Module and Integration into IMFIT With Initial Applications W. Guo, M.S. Chu, L.L. Lao, Y.Q. Liu, Q. Ren, G. Li, C. Pan, D. Yadykin The performance of future burning tokamak experiments depends critically on the behavior of energetic particles. To facilitate the validation of energetic particle physics in present-day experiments, an energetic particle physics module is being developed and integrated into the IMFIT Integrated Modeling tool. This IMFIT module provides a convenient platform to facilitate interactions among various physics codes starting from the experimental data to the analysis of stability and transport with the inclusion of energetic particles. Key components of the module include the EFIT, NUBEAM, CONT, ONETWO, and MARS-K codes, in which the effects of fast ions have been implanted. Starting from experimental data, the energetic particle distribution function is obtained by using various birth and transport models, and their subsequent effect on the stability and transport of the background plasma studied. Initial applications using DIII-D experimental data will be presented. [Preview Abstract] |
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JP8.00086: Improvements to IMFIT Integrated Modeling Tool and Initial Release A. Collier, L.L. Lao, G. Abla, M.S. Chu, H.E. St. John, R. Prater, W. Guo, G. Li, C. Pan, Q. Ren, J.M. Park, R. Srinivasan, M. Worrall The current status of a modern integrated modeling tool named IMFIT used to support key elements of DIII-D and EAST research is summarized. IMFIT is a Python-based GUI tool utilizing a modular framework with a central manager that coordinates tasks between component modules. Different component managers provide access to specific physics codes for equilibrium, stability, and transport analysis. An IMFIT plasma state file and associated translator are being developed to allow efficient inter- and intra-module communication. The IMFIT state file includes all necessary information for transport, stability, equilibrium, and data processing codes. The translator can generate native state files for codes and includes support for bi-directional translation. IMFIT is designed to be portable and includes the capability to dynamically link to codes and also provide source management tools for developers. The first public version of IMFIT has been released. [Preview Abstract] |
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JP8.00087: Tearing-Mode Excitation by Counter ECCD for Validation of Resistive MHD Models in DIII-D L.L. Lao, R. Prater, R.J. La Haye, M.S. Chu, A.W. Hyatt, T.C. Luce, T.H. Osborne, E.J. Strait, G. Abla, V.S. Chan, A. Collier, A.D. Turnbull, V.A. Izzo, W. Guy, G. Li, C. Pan, Q. Ren, R. Srinivasan, J.M. Park Resistive MHD modes play an important role in tokamak plasma confinement and stability. Although ideal MHD is well established as a reliable predictive tool for takamak stability limit, resistive MHD is less understood. In this DIII-D experiment, 3/2 tearing modes of varying amplitudes are systematically excited and their characteristics documented for validation of their linear stability threshold and saturated island structure against PEST3 and NIMROD predictions. Up to 3 MW of counter ECCD power is injected into H-mode plasmas. 3/2 tearing modes with increasing amplitudes are driven as the amount of injected counter ECCD power is stepped up. Detailed stability analyses using PEST3 and NIMROD are being performed for comparison against experimental observations with accurately reconstructed equilibria that allow for the counter ECCD effects. Results will be presented. [Preview Abstract] |
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JP8.00088: Modeling of Plasma Pressure Effects on ELM Suppression With RMP in DIII-D D.M. Orlov, R.A. Moyer, S. Mordijck, T.E. Evans, T.H. Osborne, P.B. Snyder, E.A. Unterberg, M.E. Fenstermacher Resonant magnetic perturbations (RMPs) are used to control the pedestal pressure gradient in both low and high ($\nu_3^*$) DIII-D plasmas. In this work we have analyzed several discharges with different levels of triangularity, different neutral beam injection power levels, and with, $\beta_N$ ranging from 1.5 to 2.3. The field line integration code TRIP3D was used to model the magnetic perturbation in ELMing and ELM suppressed phases during the RMP pulse. The results of this modeling showed very little effect of $\beta_N$ on the structure of the vacuum magnetic field during ELM suppression using $n=3$ RMPs. Kinetic equilibrium reconstructions showed a decrease in bootstrap current during RMP. Linear peeling-ballooning stability analysis performed with the ELITE code suggested that the ELMs, which persist during RMP, i.e.\ ELMing still is observed, are not Type~I ELMs. Identification of these D$_\alpha$ spikes is an ongoing work. [Preview Abstract] |
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JP8.00089: Pellet ELM Triggering Results and Pacing Prospects for DIII-D L.R. Baylor, T.C. Jernigan, N. Commaux, T.E. Evans, P.B. Parks, M.E. Fenstermacher, R.A. Moyer, J.H. Yu Small deuterium pellets have been injected with high speed and dropped with low speed into DIII-D H-mode plasmas from different locations. ELMs have been triggered by pellets injected from all locations, but not from vertically dropped low speed pellets. Experimental details of the pellet triggering of ELMs show that they are triggered before the injected fueling pellets reach the top of the H-mode pedestal, implying that penetration just inside the separatrix is sufficient to trigger ELMs. Results from 1-mm pellets dropped with a speed of 10 m/s into the edge plasma show a strong toroidal deflection in the scrape off layer with minimal penetration into the plasma and no clear triggering of ELMs. A planned upgrade of the pellet injector and new pellet trajectory for ELM pacing studies will be presented. Implications for controlled ELM triggering on ITER will be discussed. [Preview Abstract] |
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JP8.00090: Large, Shattered Pellets for Disruption Mitigation in DIII-D T.C. Jernigan, L.R. Baylor, S.K. Combs, N. Commaux, S.J. Meitner, E.M. Hollmann, Y.H. Yu, D.A. Humphreys, M.A. Van Zeeland, J.C. Wesley A new pellet injector, the ``shotgun" pellet injector for disruption mitigation studies, has been installed on the DIII-D tokamak. The large pellets ($\sim$15~mm diam.\ x 22~mm long, $2.3\times 10^{23}$ electrons with D$_2$) are shattered on a series of plates and directed toward the plasma magnetic axis. Previous experiments using massive gas injection (MGI) showed that the gas was stopped at the plasma edge and only penetrated diffusively until an MHD event, triggered by the cooling wave, transported some of the ionized gas from the edge to the interior. While the disruption forces and heat load to the first wall were significantly reduced by MGI, the core density achieved was insufficient to achieve suppression of runaway electrons from the avalanche process. Initial experiments with the new injector have demonstrated direct penetration of some of the shattered pieces deep into the plasma. Details of assimilation, mitigation, and density achieved in subsequent experiments will be presented. [Preview Abstract] |
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JP8.00091: 3D Field Effects on Disruption-Generated Runaway Electrons in DIII-D D.A. Humphreys, N.W. Eidietis, T.E. Evans, P.B. Parks, E.J. Strait, J.C. Wesley, N. Commaux, T.C. Jernigan, E.M. Hollmann, A.N. James, J.H. Yu A relatively modest conversion of thermal current-carrying electrons to multi-MeV runaway electrons (RE) during a disruption current quench can lead to damage of ITER in-vessel components. Effective mitigation of this conversion process is therefore essential to ITER operation. Injection of large amounts of impurities holds promise for RE mitigation, but has not yet reached the density levels expected to ensure full suppression. Experiments in TEXTOR and other devices have suggested that resonant magnetic perturbations (RMP) may suppress disruption runaways (e.g.\ [1]). We report on recent experiments in DIII-D applying nonaxisymmetric fields during disruptions with RE current channels, produced in ITER-like lower single null configurations using Ar cryogenic pellet injection. Experimental summaries and analysis of the effects of 3D fields on RE generation and deconfinement are presented.\par \vskip8pt \noindent [1] M.~Lehnen, {\em et al.}, Phys.\ Rev.\ Lett.\ {\bf 100} (2008) 255003. [Preview Abstract] |
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JP8.00092: Modeling and Measurement of Disruption Halo Current Evolution on DIII-D N.W. Eidietis, E.M. Hollmann, D.A. Humphreys, T.C. Jernigan, E.J. Strait, J.C. Wesley Disruption halo current $J\times B$ forces present a significant danger to the physical integrity of vessel components in ITER. Understanding the evolution of halo currents is critical to ensuring safe and reliable tokamak operation. A model for halo current evolution was presented in [1] which reliably recreated DIII-D halo current evolution, but it assumes a halo width and temperature, both of which are significant factors in the halo current evolution. A diffusion model for halo width evolution is presented here, and compared to DIII-D data. To better test this model, an upgraded halo current monitoring system with fine toroidal and poloidal resolution is planned for installation in 2010. In addition, the design of an accelerometer array for measuring disruption force asymmetries is presented.\par \vskip8pt \noindent [1] D.A.\ Humphreys and A.G.\ Kellman, Phys.\ Plasmas {\bf 6}, 2742 (1999). [Preview Abstract] |
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JP8.00093: Fast Disruptions and Halo Currents in the International Disruption Database A.W. Hyatt, N.W. Eidietis, S.M. Flanagan, D.A. Humphreys, J.C. Wesley, M.D. Walker The International Disruption Database (IDDB) is an International Tokamak Physics Activity (ITPA) sponsored undertaking hosted at GA. It contains information from thousands of disrupted discharges on many tokamaks. Disruptions potentially apply very large forces and thermal loads on tokamak components. Delineating the expected extremes of disruption phenomena is essential to designing a tokamak that is robust to these off-normal events. Examples of database quantities include disruption current quench (CQ) time and the degree of toroidal asymmetry in the disruption halo currents. We present analysis of IDDB data using a simple isolated current ring model that puts all tokamaks on an equal footing, and shows that the fastest CQ times normalized by plasma area are about 0.6 ms/m$^2$. Some limitations of the simple model are discussed, and recent expansions of the IDDB data set with halo current data from DIII-D are described. [Preview Abstract] |
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JP8.00094: Development of Off-Normal and Fault Event Detection and Response Techniques for ITER and DEMO M.L. Walker, B.S. Sammuli, D.A. Humphreys, J.R. Ferron, R.D. Johnson, B.G. Penaflor, D.A. Piglowski, E.J. Strait Future devices such as ITER and DEMO will demand a sophisticated collection of actions in response to a set of off-normal and fault events. The number of such response actions is significantly larger than on any presently operating fusion device. The objective of these actions is to allow fusion devices to operate disruption-free, thereby making fusion a more attractive power generating technology. We report on work performed at DIII-D to develop appropriate methods for detection of and response to off-normal and fault events and the software and computational infrastructure needed to support these methods. [Preview Abstract] |
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JP8.00095: Recent Investigations of Runaway Electron (RE) Generation and Transport in DIII-D A.N. James, E.M. Hollmann, J.H. Yu, G.R. Tynan, N. Commaux, T.C. Jernigan, N.W. Eidietis, T.E. Evans, R.J. La Haye, E.J. Strait, J.C. Wesley, C.J. Lasnier, M.E. Austin We generated record RE currents in DIII-D of $>$500~kA by terminating stationary discharges via frozen Ar pellet injection. The largest measured RE currents evolved from discharges with $q_0>0.97$ and $\ell_i >0.92$. A new scintillator array observed 3 phases of RE escape to the wall: a toroidal band of prompt release to the upper and lower divertors just after the thermal quench, ~1 ms later a longer 5-50~ms period where RE drifted upward and escaped via slow diffusion and rapid bursts, and a final rapid strike of remaining RE current on the upper divertor. Visible synchrotron or bremsstrahlung emission appeared on the fast camera during the 2nd phase near machine center and drifted to the upper divertor. The electron cyclotron emission radiometer recorded a $\sim$1~ms spike just before the 1st phase radiation burst, and a broader lower intensity emission during the 2nd phase. [Preview Abstract] |
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JP8.00096: Fast Imaging of Runaway Electron Beams in \mbox{DIII-D} J.H. Yu, A.N. James, E.M. Hollmann, J.A. Boedo, N. Commaux, T.C. Jernigan, T.E. Evans, D.A. Humphreys, E.J. Strait, M.A. Van Zeeland, J.C. Wesley We present fast visible images of runaway electron (RE) beam formation and evolution following plasma shutdown induced by Ar pellet injection. The RE beam forms when a sufficiently strong toroidal electric field is generated in the cold plasma after the thermal collapse, and visible RE emission is first detected 3 to 10~ms after the pellet injection. The RE beam persists for up to 50 ms and moves upwards toward the top of the vessel with drift velocities ranging from $<$5 to 120~m/s. When fast electrons make contact with the vessel, gammas produce scintillations in BGO crystal detectors located around the machine and on the fast camera CMOS chip. The emission from well-developed RE beams is localized to the region of tangency between the camera line of sight and flux surfaces, indicating forward-beamed emission from either bremsstrahlung or synchrotron radiation. The beam location and spatial profile of emission is in good agreement with equilibrium reconstruction of flux surfaces. [Preview Abstract] |
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JP8.00097: Modeling Steady-State DIII-D Plasmas for Tearing Stability Studies F. Turco, T.C. Luce, D.P. Brennan, A.D. Turnbull, J.R. Ferron, C.C. Petty, P.A. Politzer, L.L. LoDestro, L.D. Pearlstein, R.J. Jayakumar, T.A. Casper, C.T. Holcomb, M. Murakami In DIII-D, steady-state high-$\beta$ discharges are limited by a $n=1$ tearing mode, causing a radial redistribution of the current density not recoverable with the available noninductive current drive sources. The use of electron cyclotron (EC) current with a broad deposition can prevent the mode onset. The current density profile from an experimental DIII-D equilibrium has been perturbed numerically, mimicking the injection of EC current. The tearing stability index $\Delta^\prime$ is evaluated by the PEST3 code as a function of the perturbation amplitude, shape and radial position. The results are compared to the evolution of the experimental current density found previously to characterize discharges unstable to the $n=1$ tearing instability, and to a previous analytical study performed in cylindrical geometry for similar conditions. [Preview Abstract] |
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JP8.00098: Optimization of the Internal Magnetic Configuration for High Bootstrap Current Fraction and High Beta for Steady-state J.E. Ferron, T.C. Luce, P.A. Politzer, J.C. DeBoo, T.W. Petrie, C.C. Petty, R.J. La Haye, C.T. Holcomb, A.E. White, F. Turco, E.J. Doyle, T.L. Rhodes, L. Zeng A systematic scan of the safety factor ($q$) profile has been
used to study the optimum for steady-state operation, which
requires the maximum possible beta and bootstrap current fraction
($f_{BS}$) and good alignment between the total current density
and the bootstrap current density ($J_{BS}$). The $n_e$, $T_e$,
and $T_i$ profiles at constant $\beta_N = 2.7$ were measured in a
scan of the minimum $q$ ($1.1 |
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JP8.00099: Predictions of ITER Steady State Scenario Using Scaled Experimental Edge Profiles in DIII-D M. Murakami, J.M. Park, J.E. Kinsey, L.L. Lao, T.C. Luce, T.H. Osborne, G.M. Staebler, H.E. St. John, P.B. Snyder, E.J. Doyle, R.V. Budny, D. McCune The DIII-D ITER demonstration shots replicated leading features of the ITER steady state scenario, including noninductive fraction ($f_{NI}$) above 100\%, $q_{95}\sim 5$, plasma shape, aspect ratio and $I_p/aB$. Integrated modeling with a theory-based (GLF23) model is used to extrapolate these results to the ITER steady state scenarios. The boundary conditions for GLF23 are set at $\rho = 0.8$ while the edge profiles at $0.8 < \rho < 1.0$ are scaled with the experimental local $\beta_N(\rho)$. The predicted values of $f_{NI}$ and fusion gain ($Q$) using the ITER Day-1 heating and current drive capability are close, but still somewhat short (by $\sim$10\%) in achieving the $f_{NI} =\,$100\% and $Q = 5$ goal. Sensitivities of $f_{NI}$, $Q$, edge and core stability, and gyrokinetic stability to plasma current, density, and density peaking, etc.\ will be discussed. Possible heating and current drive upgrades will also be explored. [Preview Abstract] |
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JP8.00100: Scaled Experiment of ITER Operational Scenarios on DIII-D and Extrapolation to ITER J.M. Park, M. Murakami, T.C. Luce, P.A. Politzer, L.L. Lao, P.B. Snyder, H.E. St. John, G.M. Staebler, E.J. Doyle Scaled experiments of ITER operational scenarios on DIII-D are projected to ITER using theory-based (GLF23) modeling. Time-dependent transport simulations coupled to free-boundary equilibrium calculation reproduce successfully the time evolution of ITER similarity discharges, including stored energy and internal inductance, if the experimental edge pedestal profiles are imposed as boundary conditions. To extrapolate these results to ITER, iterative solution of core transport with MHD stability calculation of peeling-ballooning modes is employed assuming a moderate density peaking, which is consistent with DIII-D discharges and gyrokinetic calculations. Simulation of the baseline scenario shows that ITER can achieve its goal of fusion gain $Q=10$ with duration of burn $\sim$400~s. ITER performance for the steady state scenario approaches the $f_{NI} =\,$100\% and $Q=5$ goals but shows a trade-off between $f_{NI}$ and $Q$ with variation in $q_{95}$. Sensitivities to edge pedestal and density peaking will be discussed. [Preview Abstract] |
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JP8.00101: Development of Hybrid Scenario on DIII-D for Burning Plasma Devices C.C. Petty, J.C. DeBoo, T.E. Evans, J.R. Ferron, J.E. Kinsey, R.J. La Haye, T.C. Luce, T.H. Osborne, P.A. Politzer, H. Reimerdes, S.L. Allen, M.E. Fenstermacher, C.T. Holcomb, M. Murakami, E.J. Doyle, R.A. Moyer Experiments on DIII-D have extended the hybrid scenario towards the burning plasma regime by increasing the noninductive current fraction to nearly 100\%, and in separate experiments by incorporating edge localized mode (ELM) suppression. Strong core current drive by neutral beam injection and electron cyclotron heating reduced the loop voltage to 0.01~V in hybrids with normalized beta up to 3.5 and an H$_{98}$ factor of 1.4. This demonstrates the potential for hybrids as a high-beta, steady-state scenario that is not sensitive to alignment of the noninductive current profiles. For the first time, large type-I ELMs have been completely suppressed in hybrids at $q_{95}=3.6$ by applying edge resonant magnetic perturbations using $n=3$ internal coils. The ELM suppression lasted for 0.5-1.0 times the current redistribution time for normalized beta up to 2.5 and a fusion performance factor equivalent to $Q=10$ operation in ITER. [Preview Abstract] |
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JP8.00102: Modeling Tokamak Discharges during Startup in DIII-D and Predictions for ITER R.V. Budny, R. Andre, C.E. Kessel, D. McCune, G.L. Jackson, D.A. Humphreys, T.C. Luce, P.A. Politzer The PTRANSP code is being developed for improving predictions of ITER and future Tokamaks [1]. Important goals are predicting plasma performance as well as safe and efficient startup and termination. PTRANSP is being tested on experiments in DIII-D to explore and optimize plasma startup and termination, and to benchmark of transport. An important aspect is to model the boundary accurately since parameters such as the flux consumption and induction {\it li} can vary sensitively on the boundary shape. PTRANSP is being modified to allow for direct input of the flux in R, Z space (from EFIT) instead of using Fourier moments of the boundary. PTRANSP will write quantities such as the inductance and surface voltage at the separatrix surface as well as the flux boundary usually used in TRANSP. The predictive capabilities are being improved also. These include models for predicting temperatures, densities, and toroidal momentum. Predictions for ITER will be discussed. \\ {[}1{]} R.V. Budny, Nuclear Fusion {\bf 49} (2009) 085008. [Preview Abstract] |
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JP8.00103: Operation of the Complete DIII-D Gyrotron System J. Lohr, M. Cengher, J.L. Doane, Y.A. Gorelov, H.J. Grunloh, C.P. Moeller, D. Ponce, R. Prater The 110~GHz six gyrotron system on the DIII-D tokamak has been completed and is now in routine operation in support of experiments. The gyrotrons can be modulated using preprogrammed waveforms at frequencies greater than 5~kHz or under control of the DIII-D Plasma Control System using feedback on various signals, such as Te from fast ECE and fluctuations from magnetic probes. Full control of the elliptical polarization of the injected rf is provided and the individual rf beams can be steered over 40$^\circ$ both poloidally and toroidally. Reliability of 90\% has been achieved. The system has been used for rf pulses up to 5~s in length, injecting over 3~MW into the plasma limited by transmission line efficiency with maximum injected energy over 12~MJ for a single tokamak pulse. The system has been used in instability suppression and to rock the $T_e$ gradient periodically for transport studies. The ECH power has initiated the discharge for breakdown studies and for solenoidless startup and created and maintained H-modes without particle injection. An upgrade to 8 gyrotrons is planned. [Preview Abstract] |
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JP8.00104: Operational Experience with the Six Gyrotron System on DIII-D Y.A. Gorelov, J. Lohr, M. Cengher, D. Ponce For the 2009 experimental campaign, the DIII-D gyrotron system comprised six 110~GHz gyrotrons in the 1~MW class. This marks the completion of a significant upgrade to the ECH system that included the replacement of three short pulse gyrotrons with three long pulse gyrotrons and the acquisition of an additional 3 long pulse tubes, plus the construction of the high voltage power supplies and control infrastructure. As conditioning of the last gyrotron continues during experiments, the rf power from the six tubes has been set at 4.3~MW giving, at 75\% transmission efficiency, an injected power of 3.2~MW for the 4~s pulses typically being used. Improved diagnostic capability, such as video monitoring and Langmuir probes at the launchers, external current monitors for the gyrotron magnets and fast fault handling using Field Programmable Gate Array logic, has provided enhanced protection for the system. Calorimetric loading measurements and the thermal performance of the entire system will be presented. [Preview Abstract] |
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JP8.00105: Summary of RF power measurements on the ECH System on DIII-D M. Cengher, J. Lohr, J.L. Doane, Y.A. Gorelov, C.P. Moeller, J.C. DeBoo, A.W. Leonard, D. Ponce For the six 110~GHz, 1~MW class gyrotrons of the ECH system on DIII-D at GA, the power injected at the tokamak by the electron cyclotron heating (ECH) system is measured for every pulse using calorimetry. The relationship between generated rf power and component cooling was determined originally by the manufacturer with 1\% total power accountability. Transmission line efficiencies have been measured directly at DIII-D for high power. The injected power calculations resulting from combining the generated power measurements corrected for transmission loss have been verified using synchronous detection of ECE signals of plasma heating using modulated rf injection. Direct measurements of the injected power at the tokamak for pulses up to 5~s in length are being developed. The result from the following techniques will be described: measurements of the response of the DIII-D diagnostic bolometers to rf injection, heating of a leaky waveguide gap monitor, detailed rf power accounting in dummy loads and waveguides, and rf pickoff in a 4 port miter. [Preview Abstract] |
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JP8.00106: Local Gas Puff Effects on Fast Wave Antenna Loading in H-mode A. Nagy, S. DePasquale, E. Fredd, N.L. Greenough, J.C. Hosea, R. Nazikian, J.R. Wilson, F.W. Baity, N. Commaux, R.H. Goulding, G. Hanson, A.R. Horton, M. Murakami, D.A. Rasmussen, P.M. Ryan, F. Chamberlain, C.C. Petty, R.I. Pinsker, M. Porkolab Experiments show substantially enhanced resistive fast wave (FW) antenna loading in H-mode plasmas is obtained with a local gas puff during the application of rf. Results with short magnetic field lines connecting the puff orifice and the antenna face are compared with cases with longer field line connections. Scans of gas puff and FW pulse start timing suggest that filling the antenna box with gas prior to the application of rf may lead to antenna breakdown. Effects of the gas puffing on tokamak plasma include increased density, some reduction in confinement time, and strong effects on the edge localized mode character and frequency. The relationships between these results and those obtained in similar experiments elsewhere are discussed. [Preview Abstract] |
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JP8.00107: Design Concepts for a Long Pulse Upgrade for the DIII-D Fast Wave Antenna Array P.M. Ryan, F.W. Baity, J.B.O. Caughman, R.H. Goulding, D.A. Rasmussen, R.I. Pinsker, J.C. Hosea, N.L. Greenaugh, A. Nagy, J.R. Wilson A goal in the 5-year plan for the fast wave program on DIII-D [1] is to couple a total of 3.6 MW of RF power into a long pulse, H-mode plasma for central electron heating. The present short-pulse 285/300 antenna array would need to be replaced with one capable of at least 1.2 MW, 10 s operation at 60 MHz into an H-mode (low resistive loading) plasma condition. The primary design under consideration uses a poloidally-segmented strap (3 sections) for reduced strap voltage near the plasma/Faraday screen region. Internal capacitance makes the antenna structure self-resonant at 60 MHz, strongly reducing peak E-fields in the vacuum coax and feed throughs. Calculations using the 3D EM code CST Microwave Studio indicate peak voltages can be reduced by a factor of 3 and peak E-fields by a factor of 5, compared to the present antenna for the same power and load. Alternative designs for the internal capacitance to cope with geometry constraints will be presented. \\[4pt] [1] Project Staff, ``Five-Year Plan: 2009--2013,'' General Atomics Report GA-A25889 (2008). [Preview Abstract] |
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JP8.00108: Fast Ion Transport during Sawteeth in the DIII-D Tokamak C.M. Muscatello, W.W. Heidbrink, Ya.I. Kolesnichenko, V.V. Lutsenko, Yu.V. Yakovenko, E.A. Lazarus, M.A. Van Zeeland, J.H. Yu The transport of energetic ions in the presence of sawteeth is an important issue in tokamaks operating with the central safety factor $q<1$. By altering the plasma cross section between bean and oval shapes, the nature of the sawtooth crash shifts from one dominated by the internal kink to one dominated by quasi-interchange. The $q$ profile is measured by a motional Stark effect diagnostic. The FIDA diagnostic measures the spatial profile of fast ions before and after the crash. Two-dimensional imaging of the FIDA light diagnoses the transport of counter-circulating fast ions. The FIDA data show that fast ions up to the injection energy are redistributed in the bean while, in the oval, only lower energy ions experience appreciable transport. The observations are in qualitative agreement with the theoretical expectation that significant transport occurs when characteristic orbit times are longer than the sawtooth reconnection timescale. [Preview Abstract] |
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JP8.00109: Global Geodesic Acoustic Modes Driven by Energetic Particles in the DIII-D Tokamak R. Nazikian, G.Y. Fu, N.N. Gorelenkov, G.J. Kramer, M.E. Austin, H.L. Berk, W.W. Heidbrink, G.R. McKee, M.W. Shafer, E.J. Strait, M.A. Van Zeeland Intense axisymmetric oscillations driven by suprathermal passing ions injected in the direction counter to the toroidal plasma current are observed in the DIII-D tokamak. Strong bursting and frequency chirping coincide with large ($10-15\%$) drops in the neutron emission, suggesting that the mode is very effective in displacing beam ions from the plasma core. BES measurements of density fluctuations indicate an outward propagating mode of large radial extent. The large density to temperature ratio of the mode confirms a dominant compressional contribution to the pressure perturbation, indicative of the Geodesic Acoustic Mode (GAM). [Preview Abstract] |
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JP8.00110: Full-orbit Studies of Alfven Eigenmode Induced Fast-ion Losses in DIII-D G.J. Kramer, R. Nazikian, N.N. Gorelenkov, R.B. White, M.A. Van Zeeland, W.W. Heidbrink In recent experiments at DIII-D, cases of a significant discrepancy between measured and predicted fast-ion pressure profiles have been documented. In the region of enhanced fast-ion diffusion strong Alfv\`enic activity was observed. In this paper we present results of full-orbit simulations of fast-ion transport and investigate to what extend the finite Lamor radius influences fast-ion transport. The simulations are done with the SPIRAL code and include the full magnetic and electrical field fluctuation contributions from the AEs. [Preview Abstract] |
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JP8.00111: Active and Passive Spectroscopic Imaging in the \mbox{DIII-D} Tokamak M.A. Van Zeeland, J.H. Yu, N.H. Brooks, K.H. Burrell, R.J. Groebner, A.W. Hyatt, T.C. Luce, M.R. Wade, N. Pablant, W.W. Heidbrink, W.M. Solomon Wide angle, 2D visible imaging of Doppler-shifted, D$_\alpha$ emission from high energy injected neutrals, charge exchange recombination (CER) emission from beam interaction with Carbon VI ions; and visible Bremsstrahlung (VB) from the core of DIII-D plasmas has been carried out using multiple narrowband interference filters combined with a tangentially viewing, fast-framing camera. Measurements of the D$_{\alpha}$ emission from fast neutrals reveal the vertical beam profile and the variation with density in its radial penetration. Modeling of the D$_\alpha$ emission using lookup tables in the ADAS database yields qualitative agreement. Active measurements of carbon CER brightness are in agreement with those made independently using DIII-D's multichordal, CER spectrometer system, confirming the potential of this technique for obtaining 2D profiles of impurity density. Passive imaging of VB is also carried out and the obtained images are inverted to obtain local emissivity profiles. [Preview Abstract] |
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JP8.00112: A Fast MSE Measurement of MHD Magnetic Fluctuations on DIII-D J.D. King, M.A. Makowski, S.L. Allen, C.T. Holcomb, R. Geer, R. Ellis, E.C. Morse Resolved local magnetic fluctuation measurements, along with other fluctuation diagnostics, could provide a means of accurately measuring magnetic island size and evolution. The ability to make such measurements has significant implications for the detailed analysis of the structure of NTMs and other MHD. A new 16 bit, 500~kS/s data acquisition system has been installed on all channels of the existing MSE diagnostic on DIII-D. In addition to the fundamental 2f$_1$ and 2f$_2$ signals used for existing MSE polarimetry measurements, the spectrum contains peaks that strongly correlate to MHD fluctuations. Of particular interest are sideband spectral peaks at $2\omega_{1,2}\pm\omega_{MHD}$, which provide information needed for recovering the amplitude of local magnetic field fluctuations. In this work, a brief quantitative validation of the underlying theory of magnetic fluctuation measurements is presented, relationships between spectral harmonics are shown, and a first attempt at a temporally and spatially resolved MHD measurement is discussed. [Preview Abstract] |
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JP8.00113: Initial Operation of an Improved Thomson Scattering System at DIII-D B.D. Bray, T.M. Deterly, D.M. Ponce, C. Liu A redesigned Thomson scattering data acquisition system has been installed for the eight chord, forty channel divertor Thomson system at DIII-D. The new electronics contain significantly faster and quieter analog components which improve the signal to noise ratio of the system by a factor of three. An internal integration and sample and hold circuit has been added to the new detector modules which replaces aging the digitizers and couples to a standard digitizer used throughout DIII-D. This new design improves the maintainability of the system and replaces unreliable, obsolete components. A description of the system and profiles from the initial year of operation will be presented with status of the upgrade of the complete Thomson system. [Preview Abstract] |
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JP8.00114: Measurements of the Internal Magnetic Field and n=3 Level Populations of Injected Deuterium Using the B-Stark Motional Stark Effect Diagnostic on DIII-D N.A. Pablant, K.H. Burrell, R.J. Groebner, D.H. Kaplan, C.T. Holcomb, B. Den Hartog, H.P. Summers We describe the latest results from the newly upgraded B-Stark diagnostic system installed on the DIII-D tokamak. This system is a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of the Stark-split $D_\alpha$ emission from injected neutral beams. We present a thorough study of the performance of the diagnostic in measuring the magnitude and direction of the internal magnetic field over a range of plasma conditions. Measurements were made with toroidal fields in the range $1.2-2.1$ T and plasma currents in the range $0.5-2.0$ MA. We also present results from a study of the level populations of the $n=3$ state of the injected deuterium neutrals over a range of plasma densities, $1.7-9.0 \times 10^{13}~{\rm m}^{-3}$, and neutral beam voltages, $50-81$ keV. These results are compared against the calculations from an atomic physics code, part of the ADAS package. [Preview Abstract] |
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JP8.00115: Charge Exchange Recombination Detection of Low-Z Impurities in the Extreme UV using Digital Lock-In Techniques N.H. Brooks, O. Meyer A digital technique has been used to extract that portion of the XUV spectrum which varies synchronously in time with the modulation of the 30-Left neutral beam (NB) viewed by DIII-D's SPRED spectrometer [1]. A scalar product of two temporal vectors is performed for each pixel in the SPRED linear array detector--the first vector is the time history of light intensity at that pixel, the second is a NB-derived correlation function. In the spectra resulting from this pixel-by-pixel manipulation of the temporal data, all light from medium-Z and high-Z metals are strongly suppressed, exposing with great clarity the Rydberg-series lines from the H-like charge states of the low-Z impurities He, B, C and O. Time-averaged relative abundances of the low-Z impurities may be readily deduced. Removal of the beam-correlated component of the detected XUV light will be used as a pre-processing step to improve reliability of emission line time histories calculated from SPRED data. \vskip6pt \noindent [1] R.J. Fonck et al., Applied Optics {\bf 21}, 2115 (1982). [Preview Abstract] |
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JP8.00116: Advanced Ion Temperature and Velocity Fluctuation Diagnostic Design and Preliminary Measurements I.U. UzunKaymak, R.J. Fonck, G.R. McKee, D.J. Schlossberg, M.W. Shafer, G. Winz, Z. Yan A high-efficiency, high-throughput custom spectroscopic system is being designed and implemented at DIII-D to measure localized, long-wavelength ion thermal fluctuations associated with drift wave turbulence. A high-transmission grism (prism-coupled transmission grating) and high-throughput collection optics are employed to observe Doppler-shifted emission from the $n=\,$8-7 transition of C VI centered near $\lambda =\,$529~nm. The diagnostic achieves 0.25~nm resolution for 2.0~nm spectral band using eight discrete spectral channels. A turbulence-relevant time resolution of 1~$\mu$s will be achieved using high-speed photodiodes and low-noise preamplifiers. The system sensitivity should allow for measurements of normalized ion temperature fluctuations on the order of $\tilde{T}_I/T_I \leq 1$\%. These measurements will be combined with 2D BES measurements to determine the local multi-field turbulence dynamics. The predicted signal-to-noise for turbulence measurements, signal analysis techniques, and preliminary data will be presented. [Preview Abstract] |
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JP8.00117: Q-band AM Reflectometer on the DIII-D 285$^{\circ}$-300$^{\circ}$ Fast Wave Antenna G.R. Hanson, N. Commaux, F.W. Baity, A.R. Horton, J.B. Wilgen, A. Nagy, R.I. Pinsker A Q-band AM reflectometer has been re-installed onto the 285$^{\circ}$-300$^{\circ}$ fast wave antenna on DIII-D to measure the local density profile in the scrape-off layer (SOL) at the ICRF antenna. This reflectometer sweeps from 32-54~GHz in 100~microseconds and uses 100~MHz amplitude modulation to allow differential-phase measurements. Initial results during RF operation will be presented, including results during gas puffing at the fast wave antenna to increase antenna loading. [Preview Abstract] |
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JP8.00118: LASER AND PLASMA BASED ACCELERATORS |
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JP8.00119: Laser Wakefield Electron Acceleration and Frequency-Domain Holography Using the 1.1 PW Texas Petawatt Laser System Stephen Reed, Watson Henderson, Xiaoming Wang, Peng Dong, Serguei Kalmykov, Erhard Gaul, Mikael Martinez, Gennady Shvets, Todd Ditmire, Michael Downer Preparation for multi-GeV electron acceleration in an underdense plasma driven by the 1.1 PW, 160 fs Texas petawatt laser system will be presented. Laser wakefield acceleration (LWFA) experiments have demonstrated 1 GeV electron beams with muilt- TW class lasers and scaling laws suggest, that 3 - 10 GeV electrons can be produced with a short pulse PW system without external guiding. The Texas Petawatt laser uses an F/{\#} 40 focusing geometry creating a long interaction and transverse region while still maintaining intensities above 10\^{}19 W/cm2. Such geometry creates an opportunity to ``image'' the large wakefield structures using the single shot visualization technique of frequency-domain holography (FDH) in the longitudinal direction. The presented material will include details of the Texas petawatt laser systems, experimental setup and designs for electron generation and detection, FDH measurements and PIC simulations of laser wakefield acceleration for the given laser parameters, as well as preliminary results from anticipated test runs during the fall of 2009. [Preview Abstract] |
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JP8.00120: Frequency domain holography of laser wakefield accelerators in the nonlinear bubble regime S.A. Yi, S. Kalmykov, P. Dong, S.A. Reed, M. Downer, G. Shvets We present the theoretical basis of frequency domain holography (FDH), a technique for single-shot visualization of laser driven plasma wakes. In FDH, the nonlinear index modulations of the plasma wake are recorded as phase shifts in a co-propagating probe pulse, and interference with a reference allows for the reconstruction of the wake structure. Earlier experimental work [N. H. Matlis {\it et al}., Nature Phys. {\bf 2}, 749 (2006)] has shown that reconstruction of the probe phase is sufficient for imaging weakly nonlinear periodic wakes. In the highly nonlinear regime, the laser ponderomotive force blows out plasma electrons and forms a density ``bubble'' that strongly focuses the probe light. We show that imaging the bubble requires full (amplitude and phase) reconstruction of the probe pulse, and find reconstructions of simulated frequency domain holograms in full agreement with direct PIC modeling of the probe pulse. We also assess the sensitivity of the technique to the spectral bandwidth of the probe and reference pulses. In combination with ray-tracing techniques which help evaluate the localized frequency up- and down-shifts of the probe light (``photon acceleration''), FDH appears to be a unique tool for visualization of plasma wakes. This work is supported by the US DOE grants DE-FG02-04ER41321 and DE-FG02-07ER54945. [Preview Abstract] |
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JP8.00121: Electron self-injection and trapping into an evolving plasma bubble S. Kalmykov, S.A. Yi, V.N. Khudik, G. Shvets In the blowout regime of laser wakefield acceleration (LWFA), radiation pressure creates a co-moving bubble of electron density behind the driving laser pulse. Self-injection of initially quiescent electrons into the bubble and their subsequent acceleration are studied both analytically and by particle-in-cell (PIC) simulations. Semi-analytic model treats the bubble as a spherical cavity of electron density moving with a relativistic velocity over an immobile ion background. The non-evolving bubble must be unrealistically large to self- inject quiescent electrons, whereas its slow expansion significantly relaxes this requirement. PIC modeling shows that a defocusing laser may cause self-injection into the expanding bubble, even when a non-evolving pulse would not. This effect is explained in terms of non-stationary Hamiltonian theory. Temporal expansion of the bubble appears to be the dominant mechanism of electron self-injection in rarefied plasmas ($n_0 \sim 10^{17}$ cm$^{-3}$) relevant to the LWFA with petawatt- class lasers. Combination of bubble expansion and contraction results in monoenergetic electron beams due to the termination of self-injection process and phase space rotation. [Preview Abstract] |
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JP8.00122: Stimulated Raman Scattering (SRS) Driven by 30 fs Laser Pulse in Underdense Plasmas T. Matsuoka, Y. Horovitz, C. McGuffey, P.G. Cummings, V. Chvykov, G. Kalintchenko, P. Rousseau, F. Dollar, S.S. Bulanov, V. Yanovsky, A.G.R. Thomas, A. Maksimchuk, K. Krushelnick Propagation of an ultra-short laser pulse in underdense plasma was studied in the parameter range relevant for laser wakefield accelerators (LWFA) at 100 TW laser power. Filamentation of the transmitted laser pulse observed with the transverse interferpmetry was well correlated with stimulated side Raman scattering (SSRS). Experimentally measured scattered light angle relative to the laser axis is well reproduced by an analytic formula for SSRS in the range of the experimental plasma densities. Spectra orthogonal to the laser pulse showed spatially modulated intensity profile and laser intensity dependent shift for Stokes light. 2D-PIC simulation showed the evolution of the laser pulse due to SSRS. [Preview Abstract] |
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JP8.00123: Acceleration of Cone-Produced Electrons by Double-Line Ti-Sapphire Laser Beating Yoshitaka Mori, Hajime Kuwabara, Kiminori Kondo, Yoneyoshi Kitagawa We proposed a new scheme for simultaneously injecting and accelerating electrons. Acceleration and stochastic heating of electrons are demonstrated in a beat wave scheme using a pre-pulse free short-pulse (150 fs) double-line Ti-Sapphire laser. The laser beat wave produces a resonant relativistic plasma wave of field intensity 11 GV/m in a hydrogen plasma of density ${2.5 \times 10^{18} cm^{-3}}$. To inject electrons, we used a hybrid target composed of a cone-drilled plane and a gas jet, where the cone-produced electrons are accelerated via the resonant plasma wave excited in the gas jet set behind the plane, increasing the slope temperature from 0.05 MeV to 0.15 MeV. A one-dimensional particle-in-cell simulation and a stochastic acceleration model confirm the slope temperature increase. [Preview Abstract] |
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JP8.00124: Longitudinal Profile of an Electron Beam Generated from a Laser Wakefield Accelerator Dmitri Kaganovich, Michael Helle, Daniel Gordon, Edward Van Keuren, Antonio Ting Electron beams produced from a laser wakefield accelerator are predicted to have bunch lengths approximately equal to one quarter of a plasma wavelength. For plasma densities on the order of 10$^{19}$ cm$^{-3}$ this corresponds to lengths of $\sim$ 3$\mu$m. Current techniques have proven unable to resolve such a short pulse at relativistic speeds. Work is underway to develop and test a noninvasive single-shot technique to measure the bunch length of high-energy ultrashort electron beams. The technique relies on the mixing of the relativistic beam's transverse electric field with a probe laser within a nonlinear material. The theory of operation and the devices integration into the beam line will be discussed. [Preview Abstract] |
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JP8.00125: Laser Wakefield Accelerator Injection Control and X-Ray Sources C.G.R. Geddes, E. Cormier-Michel, E.H. Esarey, T. Le Corre, C. Lin, N.H. Matlis, K. Nakamura, G.R. Plateau, C.B. Schroeder, R.A. van Mourik , W.P. Leemans, D.B. Thorn, D.L. Bruhwiler, B. Cowan, K. Paul, J.R. Cary Reduced beam energy spread, fluctuation, and emittance are important to applications of compact, high gradient laser-plasma wakefield accelerators including Thomson gamma sources and high energy colliders. Experiments and simulations will be presented on control of injection to improve beam quality compared to use of self-injection by the wake. Trapping of electrons in the wake can be controlled using the beat between multiple laser pulses to via kick electrons in momentum and phase into the wake accelerating phase. Laser and gas target shaping and control are used to further control the accelerator structure. Simulations demonstrate the tuning of accelerator structure required to accelerate such bunches to high energies while retaining high bunch quality. Electron beam source size and position are measured using betatron X-ray emission produced when electrons oscillate in the focusing field of the wake to improve understanding of beam emittance and stability, while also producing a broadband, synchronized fs source of keV X-rays. Supported by US DOE NA-22 and HEP including DE-AC02-05CH11231, SciDAC, and SBIR. [Preview Abstract] |
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JP8.00126: PIC Simulations of Colliding Pulse Injection for Laser Wakefield Acceleration David Bruhwiler, Ben Cowan, Kevin Paul, John Cary, Cameron Geddes, Estelle Cormier-Michelle, Eric Esarey, Carl Schroeder, Wim Leemans The use of colliding laser pulses to control the injection of plasma electrons into the plasma wake of a laser wakefield accelerator (LWFA) is a promising approach to obtaining GeV scale electron bunches with orders of magnitude smaller emittance and energy spread. Colliding pulse injection (CPI) is being explored experimentally by groups around the world. We will present recent particle-in-cell (PIC) simulations of colliding pulse injection, using the parallel VORPAL framework, for physical parameters relevant to ongoing experiments of the LOASIS Program at Lawrence Berkeley Laboratory. The details of how particle trapping starts and stops, in the presence of counter-propagating laser pulses and nonlinear beam loading, is sensitive to noise and other errors in the PIC simulation. Hence, we will present results of different algorithmic choices, including high-order particle shapes and spatial smoothing. [Preview Abstract] |
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JP8.00127: Plasma wave phase velocity and density tapering in laser-plasma accelerators Carl Schroeder, Eric Esarey, Wim Leemans, Wolf Rittershofer, Florian Gr\"{u}ner, Bradley Shadwick In a laser-plasma-based accelerator, the laser-driven plasma wave phase velocity (determined in part by the intensity transport velocity and evolution of the short-pulse drive laser) sets the dephasing length of the plasma accelerating structure and, hence, the energy gain of an accelerated particle beam. The phase velocity of a plasma wave driven by a relativistically-intense, short-pulse laser propagating in a cold underdense plasma is investigated, as well as the drive laser evolution. A relativistic beam may be phase-locked to the plasma wave using a plasma density taper, increasing the single-stage energy gain. The expression for the density taper in a plasma channel to maintain a relativistic beam at a constant plasma wave phase is presented. The optimal laser pulse duration for maximizing energy gain in a tapered plasma channel is calculated. Novel quasi-periodic plasma tapering schemes are considered. [Preview Abstract] |
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JP8.00128: Nonlinear Laser Energy Depletion in Laser-Plasma Accelerators B.A. Shadwick, C.B. Schroeder, E. Esarey Energy depletion of intense, short-pulse lasers via excitation of plasma waves is investigated numerically and analytically.\footnote{\frenchspacing B.~A. Shadwick, C. B. Schroeder, and E. Esarey, ``Nonlinear laser energy depletion in laser-plasma accelerators,'' Phys. Plasmas {\bf 16}, 056704 (2009).} The evolution of a resonant laser pulse proceeds in two phases. In the first phase, the pulse steepens, compresses, and frequency red-shifts as energy is deposited in the plasma. The second phase of evolution occurs after the pulse reaches a minimum length at which point the pulse rapidly lengthens, losing resonance with the plasma. Expressions for the rate of laser energy loss and rate of laser red-shifting are derived and are found to be in excellent agreement with the direct numerical solution of the laser field evolution coupled to the plasma response. Both processes are shown to have the same characteristic length-scale. Channel- guided Gaussian laser pulses, in two and three dimensions are modeled and are well-described by this theory. [Preview Abstract] |
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JP8.00129: Physics of a 10 GeV laser-plasma accelerator E. Esarey, C.B. Schroeder, C.G.R. Geddes, E. Cormier-Michel, W.P. Leemans, D. Bruhwiler, B. Cowan, B.A. Shadwick The single-stage energy gain in a laser-plasma accelerator is limited by laser diffraction, electron dephasing, and laser depletion. Diffraction can be prevented by using a plasma channel and electron dephasing can be mitigated by increasing the on-axis density as a function of distance, which increases the wake phase velocity. Depletion (loss of laser energy to the wake) ultimately limits the single stage energy gain. Beam loading (modification of the wake by the accelerated electron bunch) limits the bunch charge and affects the energy spread and emittance. Advantages of various wake regimes,such as the quasi-linear or the blow-out regime, will be examined. Simulations of a 10 GeV stage driven by the 40 J BELLA laser will be presented. Also discussed are applications to future light sources and colliders. [Preview Abstract] |
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JP8.00130: Full scale quasi-static modeling of the PWFA-based linear collider concept Chengkun Huang, W.-M. An, C. Clayton, C. Joshi, W. Lu, K. Marsh, W. Mori, T. Katsouleas, I. Blumenfeld, M. Hogan, N. Kirby, T. Raubenheimer, A. Seryi, P. Muggli Plasma Wakefield Acceleration (PWFA) has been proposed as a possible way to reduce the size and cost of the next linear collider. The needs to faithfully simulate the drive beam evolution and the main beam dynamics in the future plasma-based linear collider using Particle-In-Cell codes are extremely challenging. However, the recent progress on the development of quasi-static model and the usage of massive parallel computing resources have enabled simulation studies of the near term PWFA experiments and for the conceptual designs of the next generation facilities in full details with realistic linear collider parameters and including necessary effects such as ion motion. The simulation needs for modelling the plasma-based advanced accelerator at the energy frontier is discussed and a path towards this goal is outlined. Results from full scale simulations that include all particles in real plasma will be reported. [Preview Abstract] |
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JP8.00131: Simulation of positron acceleration in Plasma Wake Field Accelerator (PWFA) Weiming An, Wei Lu, Chengkun Huang, Warren Mori The Plasma Wake Field Accelerator (PWFA) concept is very attractive because the accelerating gradient can be three orders of magnitude higher than that of a traditional RF accelerator. In this poster the acceleration of positron beams in PWFA is investigated both in the linear and weakly nonlinear regimes. The results show that a beam-loading efficiency around $50\%$ can be achieved both in the linear and weakly nonlinear regime when the spot sizes of both the drive beam and trailing beam are $k_p\sigma_r\sim 1$. In the linear regime the total charge of the accelerated positron beam and the average accelerating gradient are both smaller than those in the weakly nonlinear regime. Issues related to energy spread are also discussed. [Preview Abstract] |
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JP8.00132: Acceleration of polarized electron beams in plasma-based accelerators Jorge Vieira, Ricardo Fonseca, Lu\'Is Silva, Chengkun Huang, Warren Mori The acceleration of highly polarized particle beams is critical not only to test and validate current physical models, but it is also critical in the search for new physics in high-energy physics (HEP) experiments. Plasma-based accelerators can play an important role in next generations of accelerators, as they can reduce the size of standard acceleration structures by two-three orders of magnitude. However, for high-energy physics applications, and in addition to beam quality requirements such as the emmittance, luminosity, energy, or energy spread, the evolution of the electron beam polarization is also crucial for the use of future linear plasma based colliders in HEP experiments. In this work, the spin-precession in plasma-based acceleration scenarios is examined using the Thomas-- Bargmann-Michel-Telegdi equations. Analytical expressions which show that lower depolarizations can be achieved by using narrower beams, with lower initial energies, are derived. In addition, it is found that mildly relativistic regimes lead to lower depolarizations in comparison to strongly relativistic regimes. Our findings are confirmed with 3D particle-in-cell simulations using QuickPIC. [Preview Abstract] |
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JP8.00133: Effect of frequency and phase fluctuations in multi laser beam systems on wakefield excitation Vishwa Bandhu Pathak, Joana Martins, Ricardo Fonseca, Luis Silva The next generation of ultra high intensity laser systems for laser driven fusion and plasma accelerator facilities will combine multiple lasers beams to achieve very high intensities. These beams may have small frequency and phase mismatches, due to the separate optics involved. We study the effect of random variation in the frequencies and/or the phases of the multiple laser drivers on wakefield generation in underdense plasmas with averages over statistical ensembles of PIC simulations. In our 2D PIC simulations, we have explored the conditions close to optimal excitation of the wake field, by using up to 10 laser pulses. Taking advantage of the absolute reproducibility of the numerical features of the simulations in Osiris, we take ensemble averages over a large number of runs to explore the effects associated with the enhanced laser bandwidth due to frequency fluctuation, and the effects of phase mismatch. Laser wakefield generation can also be seen as a manifestation of stimulated forward Raman scattering(SFRS) in underdense plasmas. We compare the simulation results with our theoretical model for SFRS by a partially coherent laser pump. [Preview Abstract] |
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JP8.00134: Emittance Preservation in Future Plasma Wakefield Accelerators using Adiabatic Matching Reza Gholizadeh, Tom Katsouleas, Patric Muggli, Chengkun Huang, Warren Mori Plasma Wakefield Accelerator has been proven to be a promising technique to lower the cost of the future high energy colliders by offering orders of magnitude higher gradients than the conventional accelerators. However, it has been shown that ion motion is an important issue to account for in the extreme regime of ultra high intensity and ultra low emittance beams, characteristics of future high energy colliders. In this regime, the transverse electric field of the beam is so high that the plasma ions cannot be considered immobile at the time scale of electron plasma oscillations, thereby leading to a nonlinear focusing force. Therefore, the transverse emittance of a beam matched to the initial linear focusing will not be preserved under these circumstances. However, Vlasov's equation predicts a matched profile even in the nonlinear focusing force case. Furthermore, we extend the idea and introduce a plasma section that can match the entire beam to the mobile-ion regime of plasma by adiabatically reducing the plasma ion mass. We also find the analytic solution for the optimal matching section. Simulation results are presented. [Preview Abstract] |
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JP8.00135: Plasma and Beam Measurements for Multi-bunch PWFA Experiments P. Muggli, B. Allen, V. Yakimenko, J. Park, K. Kusche, M. Babzien We study for the first time the excitation of plasma wakefields by a train of electron bunches. The wakefields amplitude strongly depends on the plasma density and the spacing between the electron bunches. In particular, resonant excitation is expected when the plasma density is such that the plasma wavelength is equal to the drive bunch train spacing. The bunch spacing and plasma density therefore need to be accurately measured. We describe the time resolved measurement of the capillary discharge plasma density using Stark broadening of the hydrogen H$_{\alpha }$ line. The plasma density is adjusted by varying the delay between the bunch train arrival time and the plasma discharge time. We also describe the method used to produce the electron bunch train, as well as the measurement of the train spacing using coherent transition radiation interferometry. The bunch train consists of a variable number of equidistant drive bunches followed by a witness bunch. The spacing between the drive bunches is $\approx $300$\mu $m, and the spacing between the last drive bunch and the witness bunches is $\approx $450$\mu $m These spacings can be varied through the beam parameters. Detailed experimental results will be presented. [Preview Abstract] |
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JP8.00136: Numerical Study of the Current Filamentation Instability of an Accelerator Beam in a Capillary Plasma B. Allen, P. Muggli, V. Yakimenko, J. Park, K. Kusche, M. Babzien, C. Huang Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. In the laboratory it could influence the energy deposition by hot electrons in fast-igniter concept for inertial confinement fusion. It could also play an important role in the generation of magnetic fields and of radiation in the after-glow of gamma ray bursts. Using the particle-in-cell code QuickPIC, we simulate the propagation of the BNL-ATF beam in a cm-long plasma produced by a capillary discharge. The occurrence of the instability is investigated as a function of electron beam parameters (including charge and emittance) and plasma parameters (density and length) by evaluating the beam density and magnetic energy. The results show that with beam and plasma parameters achievable at the BNL-ATF the CFI should be observed after only 2 cm of plasma. We present simulation results, discuss further simulation refinements, suggest criteria and threshold parameters for observing the presence of CFI and outline the experiment we will perform at the BNL-ATF. [Preview Abstract] |
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JP8.00137: Designing Particle-in-Cell Algorithms for Advanced Computer Architectures: Application to GPUs V.K. Decyk, T.V. Singh, P. Abreu, R.A. Fonseca, L.O. Silva New emerging multi-core technologies can achieve high performance, but only in special, restricted cases. For example, modern graphic processors units (GPUs) can achieve TFLOP performance in single precision calculations and have low power usage per FLOP. However, the potential performance of GPUs often comes with a price. They are complex and difficult to program effectively. Therefore, algorithms often need to be redesigned to make effective use of these processors. We will describe two approaches to implementing Particle-in-Cell (PIC) codes on GPUs. One is more general and applicable to other emerging multi-core technologies. We will conclude with lessons learned that can be applied to other problems. Some of these lessons will be familiar to those who have programmed vector processors in the past, others will be new. We have also implemented a real-time visualization feature so that the user can interact on the screen with the simulation, watching the virtual particles movement, enabling real time rotation, translation, and zooming of simulation output (EM field intensity, charge density, current) . This was implemented as part of a fully relativistic PIC code that runs of CUDA enabled devices using the CUDA API. [Preview Abstract] |
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JP8.00138: Preliminary results on GPU Acceleration of the PIC Simulation Code OSIRIS Using CUDA Xianglong Kong, M.C. Huang, C. Ren Modern graphics processing units (GPUs) equipped with NVIDIA's massively multithreaded computing architecture, with their teraflop performance potential and high memory bandwidth, offers an opportunity to greatly improve the performance of Particle-in-cell (PIC) codes. There are a variety of approaches being developed for porting PIC codes to a GPU. In this poster we describe how multi-threaded algorithms were implemented for the key parts (field solver, particle pusher, current deposition, current smoothing) of an existing PIC simulation code (OSIRIS) on a GPU using the programming environment CUDA. Initial speedups with double-precision operations will be described. Write conflicts in the current-to-gird deposition part are identified as the performance bottleneck. We will compare several different methods of resolving the write conflicts. We acknowledge the OSIRIS Consortium. This work was supported by DoE under Grants Nos. DE-FG02-06ER54879 and DE-FC02-04ER54789. [Preview Abstract] |
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JP8.00139: Ion beam generation experiments: near-critical density plasma proton acceleration using the Omega EP laser and ion source surface investigation using the T-cubed laser Louise Willingale, A. Maksimchuk, K. Krushelnick, P.M. Nilson, T.C. Sangster, C. Stoeckl, W. Nazarov, G.M. Petrov, J. Davis, C.D. Murphy, V. Ovchinnikov Experiments performed using the Omega EP laser facility ($1000 \; \rm{J}$ in $10 \; \rm{ps}$) investigating proton acceleration from near-critical density plasma will be presented. The laser propagation is investigated experimentally and with PIC simulation as it is expected to be influential on the proton acceleration. Also presented will be experiments investigating front vs rear surface acceleration of ions using the T-cubed laser at the University of Michigan ($4 \; \rm{J}$ in $400 \; \rm{fs}$). Thin foil targets are coated on the front, rear or both sides with a deuterated plastic layer and the accelerated deuterons are used to diagnose the interaction. PIC simulations are used to model the interactions and the influence of the ion acceleration processes on neutron generation experiments will be discussed. [Preview Abstract] |
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JP8.00140: Ion Acceleration in High Contrast High Intensity Laser Interaction with Thin Film and Membrane Targets Franklin Dollar, Takeshi Matsuoka, Chris McGuffey, Louise Willingale, Stepan Bulanov, Vladamir Chvykov, Galina Kalintchenko, Pascale Rousseau, Victor Yanovsky, Alec Thomas, Anatoly Maksimchuk, Karl Krushelnick We present the experimental results on ions acceleration from thin film and membrane targets using the 300TW 30fs HERCULES Laser Facility. The utilization of an F/1 parabolic mirror allow for on target intensities of up to 1022 W/cm2. Use of dual plasma mirrors as well as crossed-polarized wave generation allows for the ASE pedestal to peak intensity contrast of over 10-13. We perfomed measurements of protons from the back side of foils as well as ions generated from 20-200 nanometers thickness silicon nitride membranes using a Thomson parabola spectrometer coupled to a microchannel plate with readout to a CCD. Detailed 2D-PIC computer modeling of these interactions will also be presented and compared to the experimental data. [Preview Abstract] |
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JP8.00141: Parametric Study of Laser Driven Proton Beams from a Critical Density Gas Jet D. Haberberger, F. Tsung, S. Tochitsky, W. Mori, C. Joshi Laser driven ion acceleration (LDIA) is studied via particle-in-cell simulations in a novel parameter space for laser-plasma interactions of a relativistic laser pulse with a gas jet target at the critical plasma density (n$_{c})$. Previous LDIA studies have been based on the interaction of a 1$\mu $m laser pulse with either a solid foil (n$\sim $100n$_{c})$ or a gas jet (n$\le $0.1n$_{c})$. Here we propose focusing a high power CO$_{2}$ laser pulse at a H$_{2}$ gas jet which is tunable around the critical plasma density for 10$\mu $m radiation (10$^{19}$cm$^{-3})$. A rectangular H$_{2}$ gas jet operated near n$_{c}$ lends itself to efficient coupling of the laser light to forward directed electrons instigating the target normal sheath acceleration mechanism to produce a beam of protons. Results are presented here on a parametric study of the peak plasma density and plasma profile to find optimal conditions for total charge, divergence, and energy of the accelerated proton beam. These simulations support an ongoing LDIA experiment at the Neptune Laboratory at UCLA using a 3ps 1TW CO$_{2}$ laser pulse for the production of collimated proton beams. [Preview Abstract] |
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JP8.00142: Hot Electron Confinement in High Intensity Laser-Matter Interactions Lee Elberson, Yuan Ping, Scott Wilks, Ronnie Shepherd, Andrew Mackinnon, Prav Patel, Wendell Hill High-intensity ($>$10$^{18}$ W/cm$^{2})$ lasers can produce relativistic electrons ($\sim $MeV) when focused onto solid density targets. We present measurements of escaped relativistic electron lifetimes in short pulse laser-irradiated solid experiments. Electron durations measured were significantly longer than the laser pulse length, suggesting the presence of phenomena which confine high energy electrons within the target-plasma volume. Investigating the confinement time of high energy electrons exceeds the limits of any simple plasma expansion models. Utilizing the implicit hybrid particle-in-cell code LSP [D. R. Welch \textit{et al.}, Phys. Plasmas \textbf{13}, 063105 (2006)], experimental conditions were simulated to explore the physics of hot electron confinement in laser-irradiated materials. *This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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JP8.00143: Optimization of radiation acceleration regime and the target structure in laser plasma interaction Galina Dudnikova, Chuan Lui, Dennis Papadopoulos, Roald Sagdeev, Ari Zigler Recent work [1,2] indicates that under proper conditions the interaction of ultra-short, high power lasers with thin foils can generate ion beams in the 100-200 MeV energy range with relatively low velocity dispersion. This technology can have major implications to medical ion proton cancer therapy since it can provide a relatively inexpensive table-top alternative to the current used traditional cyclotrons. This paper presents a simulation trade-off study of laser driven generation of quasi-monochromatic ion beams in the thin-foil Radiation Pressure Acceleration (RPA) regime. The radiation pressure accelerates the electron cloud, which in its turn transfers accelerates the ions due to the induced longitudinal charge separation fields. A series of two and three-dimensional PIC simulations are presented with emphasis on stabilizing the target plasma against Raleigh-Taylor and modulational instabilities. Such instabilities are known as the main obstacles in achieving monochromatic beams. \\[4pt] [1] B. Eliasson, C. Lui, et al. New Jour. Phys., 11, 2009.\\[0pt] [2] F. Pegoraro, S.V. Bulanov. Laser Phys., v19, N 2, 2009. [Preview Abstract] |
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JP8.00144: Experimental measure of proton energy loss in short pulse laser generated, proton heated carbon R. Shepherd, H. Chen, S. Feldman, G. Dyer, S. Chen, J. Fuchs, M. Gauthier, P. Audebert, T. Ditmire, P. Beiersdorfer, M. Purvis, A. Hazi, R. London, M. Murillo, L. Benedict, J. Dunn, J. Glosi, S. Hau-Riege, B. Langdon, R. More, J. Rocca, N. Rohringer, F. Streitz, J. Weisheit, F. Graziani We present a new approach to determining stopping power of charged particles in plasmas. We will use short pulse laser-generated protons to heat solid slab targets. The high intensity, short duration laser pulse will generate a burst of protons that isochorically heat the sample, minimizing temperature and density gradients. A second laser-generated proton beam will be sent through the heated target and the relative energy loss will be measured using a proton spectrometer. The heated target thickness will be changed, providing a measure of \textit{dE/dx}. The target conditions will be determined using Frequency Domain Interferometry for density and emissivity for temperature. The target thickness is varied, providing an avenue to determine the \textit{dE/dx}. Preliminary experimental results will be presented. [Preview Abstract] |
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JP8.00145: How Can One Maximize the Current Density {\&} Total Electron Density of a Short-Pulse, Approximately Unidirectional, 5-10 MeV Monoenergetic Electron Beam? G.R. Bennett, A.B. Sefkow, B.W. Atherton, M. Geissel, D.I. Headley, M.C. Herrmann, M.W. Kimmel, J.L. Porter, P.K. Rambo, M. Schollmeier, M. Schwarz A Sandia National Laboratories (SNL) program has the goal of attaining the highest possible conversion of Z-Petawatt-Testbed (ZPW-T; up to 120-J in a 0.5-ps pulse) 1054-nm laser light, into an approximately unidirectional, 5-10 MeV, electron beam -- with maximum current density {\&} maximum total electron density. If sufficiently successful, the technique will be applied to the larger multikiljoule Z-Petawatt laser, when complete. This paper discusses the early progress/plans to date; including LSP Particle-in-Cell simulations, metrology of ultrathin carbon foils, a Double-Plasma-Mirror system to improve the ZPW-T contrast, a novel linear (LP) to circular polarization (CP) rotator, etc. Results will include: simulation, analytical (a rigorous 1D derivation of the relativistic pondermotive electric field for LP vs. CP light), {\&} experimental progress. [Preview Abstract] |
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JP8.00146: Energy Gain of a Free Electron in a Pulsed Electromagnetic Plane Wave with Constant External Magnetic Fields Justin Angus, Sergei Krasheninnikov We consider free electron interactions with a pulsed plane electromagnetic (EM) wave in the presence of static homogeneous magnetic fields. The main goal of this study is to find the energy gained by the electron after the wave has passed. We use the constants of motion, expressed in terms of the EM vector potential, which can be obtained from the relativistic equation of motion for a charged particle. For a constant magnetic field along the axis of the wave an exact solution is obtained for the energy gain for arbitrarily polarized EM plane wave with a Gaussian amplitude profile. It shows that significant energy gain is possible when the rest mass cyclotron frequency is resonant with the frequency of the wave, but that it decays exponentially when we deter from this resonance. For magnetic fields transverse to the axis of the wave it is shown that the governing equations can be reduced to a two-dimensional Hamiltonian system that when time-averaged in the in the limit where the cyclotron frequency is much less than that of the wave remain in Hamiltonian form. Solutions are sought in this limit for these time-averaged equations using both a Gaussian and step function profile for the wave. For both cases it is found that the maximum energy gain is independent of the size of the transverse magnetic fields and scales with the wave amplitude squared. This work was supported the US DoE under Grant DE-FG02-04ER54739. [Preview Abstract] |
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JP8.00147: DC-like phase space manipulation and particle acceleration using chirped AC fields Paul Schmit, Nathaniel Fisch Waves in plasmas can accelerate particles that are resonant with the wave. A DC electric field also accelerates particles, but without a resonance discrimination, which makes the acceleration mechanism profoundly different. We investigate the effect on a Hamiltonian distribution of an accelerating potential waveform, which could, for example, represent the average ponderomotive effect of two counterpropagating electromagnetic waves. In particular, we examine the apparent DC-like time-asymptotic response of the distribution in regimes where the potential structure is accelerated adiabatically. A highly resonant population within the distribution is always present, and we characterize its nonadiabatic response during wave-particle resonance using an integral method in the noninertial reference frame moving with the wave. Finally, we show that in the limit of infinitely slow acceleration of the wave, these highly resonant particles disappear and the response of the bulk distribution becomes identical to the response of a distribution to a uniform DC field. [Preview Abstract] |
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JP8.00148: White light generation under laser driven avalanche breakdown of air Updesh Verma, Ashok Kumar Sharma A theoretical model of avalanche breakdown of air by a Gaussian laser beam and white light generation is developed. An intense laser beam, below the threshold for tunnel ionization heats the seed electrons to high energy that causes avalanche ionization of the air. However, the plasma density has a maximum on axis and falls off with radial co-ordinates. Such a density profile causes refraction divergence of the beam. However, temporal evolution of plasma density causes self phase modulation of the laser pulse causing frequency broadening of the pulse. The hot plasma thus produced causes strong spectral emission in the visible. [Preview Abstract] |
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JP8.00149: Terahertz generation by an amplitude modulated Gaussian laser beam in a plasma Deepak Tripathi, R. Uma, Vipin Kumar Tripathi A theoretical model of an analytical formalism of magnetic field generation due to an amplitude modulated intense laser beam in a plasma is developed. At plasma resonance, where modulation frequency equals the plasma frequency, significant enhancement in the magnetic field is seen. The magnetic field is found to scale directly with laser intensity and plasma frequency, while scaling inversely with laser spot size. [Preview Abstract] |
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JP8.00150: Resonant Excitation of Millimeter Wave by Beating two Lasers in a Plasma Embedded with a Magnetic Wiggler Vijay Garg Two high power lasers of frequencies w$_{1}$ and w$_{2}$, co-propagating in a semiconductor embedded with a magnetic wiggler, produce electromagnetic radiation at the difference frequency (w$_{1 }$-w$_{2})$. The lasers exert a ponder-motive force on the electrons at the difference frequency, giving them longitudinal oscillatory velocity. This velocity beats with the magnetic wiggler to produce a transverse current, driving a millimeter wave at a frequency w$_{1 }$-w$_{2}$ and wave number k$_{1}$-k$_{2}$+k$_{w}$ where k$_{1}$ and k$_{2}$ are the wave number of the lasers and k$_{w}$ is the wave number of the wiggler. For a suitable value of wiggler wave number the process becomes a resonant one, giving high efficiency of millimeter wave generation. [Preview Abstract] |
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JP8.00151: Asymmetric Self-focusing of a Laser Pulse under Relativistic and Ponderomotive Nonlinearities Amrita Singh, Ashok Kumar Sharma A short pulse laser beam suffers self-pulse distortion due to combined effects of nonlinearity induced self-focusing and dispersion. Nonlinearity arises due to relativistic mass variation and ponderomotive force. As the beam propagates through plasma, beam width parameter $\left( f \right)$decreases, so intensity of the beam increases. Self focusing of the beam takes place. As time passes, decrease in $\left( f \right)$ is smaller and smaller, broadening of pulse takes place. Intensity of the beam decreases with time. Hence due to ponderomotive and relativistic nonlinearities, broadening of the pulse takes place and intensity of the beam decreases due to temporal effect. [Preview Abstract] |
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JP8.00152: Dependence of Electron Beam Emittance on Electron Gun Controls, and the Description of Electron Dynamics Using Phase Space Diagrams Ronald Williams, Arnesto Bowman The designs and test results of devices for measuring the emittance of a low energy electron beam are discussed. The emittance is controlled by varying the electron gun's cathode, grid and anode; with the goal of minimizing the emittance. Scanning wire probes are used initially however non-perturbing optical probes are being developed. The tests are performed using a 5 keV electron beam, however the scaling to higher energy beams will be discussed. Multidimensional phase space diagrams for the emittance measurements will be discussed. Also, similar phase space diagrams for electrons propagating across laser and plasma waves will be discussed. These results are important steps toward developing a diagnostic for plasma waves using a low emittance electron beams. [Preview Abstract] |
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