Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session JP6: Poster Session IV: Education and Outreach; Undergraduate and High School Research; DIII-D I; HBT-EP and Other Tokamaks; Short-Pulse Laser-Matter Interactions and Equations of State for HEDP |
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Room: Marsalis A/B, 2:00pm - 5:00pm |
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JP6.00001: EDUCATION AND OUTREACH |
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JP6.00002: Practical Application of Research in Science Education (PARSE) -- A New Collaboration for K-12 Science Teacher Professional Development Andrew Zwicker, Jose Lopez, James Clayton A new collaboration between PPPL, St. Peter's College, the Liberty Science Center, and the Jersey City Public School District was formed in order to create a unique K-12 teacher professional development program. St. Peter's College, located in Jersey City, NJ, is a liberal arts college in an urban setting. The Liberty Science Center (LSC) is the largest education resource in the New Jersey-New York City region. The Jersey City School District has 28,000 students of which approximately 90{\%} are from populations traditionally under-represented in science. The new program is centered upon topics surrounding energy and the environment. In the first year, beginning in 2009, 15-20 teachers will participate in a pilot course that includes hands-on research at PPPL and St. Peter's, the creation of new curricular materials, and pedagogical techniques. Scientists, master teachers, and education professors will teach the course. In subsequent years, the number of participants will be significantly expanded and the curricular material disseminated to other school districts. In addition, an outside evaluator will measure the educational outcome throughout the project. [Preview Abstract] |
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JP6.00003: Education and Outreach Activities at Consorzio RFX, Padova M.T. Orlando, A. Buffa, R. Cavazzana, G. Spizzo Consorzio RFX performs education and public information (PI) activities along two main lines: education at the PhD level and the Fusion Expo. In Europe there is a strong need for attracting and educating young researchers in fusion science and engineering in order to create scientific and engineering staff for the Fusion Programme. This has led to set up the first European Joint Research Doctorate and Network in Fusion Science and Engineering, in collaboration between European fusion Associates and Universities, which is an example of integration between physics and engineering teaching. In addition to this, Fusion Expo is a powerful PI tool to present fusion to the large public, realized by the European Commission, who has entrusted EFDA and Consorzio RFX in Padova with the improvement and update of the exhibition. The expo is itinerant, modular, based on a gradually improving content insight developing from key messages and large eye-catching images (to attract and motivate curiosity), up to in-depth presentations, designed to satisfy a more daring question approach. All of these activities have succeeded because they act together in creating the necessary positive attitude towards fusion research. [Preview Abstract] |
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JP6.00004: Comparison of second order magnetic barriers at a mediant and noble irrational surfaces in the ASDEX UG tokamak Christina Burton, Halima Ali, Alkesh Punjabi Ciraolo, Vittot and Chandre method of building invariant manifolds inside chaos in Hamiltonian systems is used in the ASDEX UG tokamak. In this method, a second order perturbation is added to the perturbed Hamiltonian. It creates an invariant torus inside the chaos, and reduces the plasma transport . The value and beauty of this method is that 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. Relative strength of magnetic barriers at these mediant and noble surfaces are studied. 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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JP6.00005: Comparison of second order magnetic barriers at a mediant and a noble irrational surfaces in the DIII-D tokamak Kenra Payne, Halima Ali, Alkesh Punjabi Ciraolo, Vittot and Chandre method of building invariant manifolds inside chaos in Hamiltonian systems is used in the ASDEX UG tokamak. In this method, a second order perturbation is added to the perturbed Hamiltonian. It creates an invariant torus inside the chaos, and reduces the plasma transport. The value and beauty of this method is that 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) = (3,1)+(4,1) are added to the field line Hamiltonian for the DIII-D. An area-preserving map for the field line trajectories in the DIII-D is used. The common amplitude $\delta $ of these modes that gives complete chaos between the resonant surfaces $\Psi $41 and $\Psi $31 is determined. Closely located mediant and noble surfaces roughly midway between the resonant surfaces are determined. Relative strength of magnetic barriers at these mediant and noble surfaces are studied. 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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JP6.00006: Calculation of stochastic broadening due to noise and field errors 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 [1]. Recently, the action-angle coordinates for simple map are analytically calculated, and simple map is constructed in action-angle coordinates [2]. Action-angle coordinates for simple map can not be inverted to real space coordinates (R,Z). Because there is logarithmic singularity on the ideal separatrix, trajectories can not cross separatrix [2]. Simple map in action-angle coordinates is applied to calculate stochastic broadening due to magnetic noise and field errors. Mode numbers for noise + field errors from the DIII-D tokamak are used. Mode numbers are (m,n)={\{}(3,1), (4,1), (6,2), (7,2), (8,2), (9,3), (10,3), (11,3), (12,3){\}} [3]. The common amplitude $\delta $ is varied from 0.8X10$^{-5}$ to 2.0X10$^{-5}$. For this noise and field errors, the width of stochastic layer in simple map is calculated. This work is supported by US Department of Energy grants DE-FG02-07ER54937, DE-FG02-01ER54624 and DE-FG02-04ER54793 1. A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Let. A \textbf{364}, 140--145 (2007). 2. O. Kerwin, A. Punjabi, and H. Ali, to appear in Physics of Plasmas. 3. A. Punjabi and H. Ali, P1.012, 35$^{th}$ EPS Conference on Plasma Physics, June 9-13, 2008, Hersonissos, Crete, Greece. [Preview Abstract] |
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JP6.00007: Calculation of stochastic broadening in real space due to noise and field errors in the DIII-D tokamak Lisa Brodsky, Alkesh Punjabi, Halima Ali The equilibrium EFIT data for the DIII-D shot 115467 at 3000 ms is used to construct the equilibrium generating function for magnetic field line trajectories in the DIII-D tokamak in natural canonical coordinates. 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. This map is applied to calculate stochastic broadening due to magnetic noise and field errors in the DIII-D. Mode numbers for noise + field errors are (m,n)={\{}(3,1), (4,1), (6,2), (7,2), (8,2), (9,3), (10,3), (11,3), (12,3){\}}. The common amplitude $\delta $ is varied from 0.8X10$^{-5}$ to 2.0X10$^{-5}$. Preliminary results suggest that the width of stochastic layer from noise and field errors in the DIII-D varies from about 7 to 16 cm near X-point, and about 0.6 to 3{\%} of poloidal flux is lost from inside ideal separatrix. 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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JP6.00008: UNDERGRADUATE AND HIGH SCHOOL RESEARCH |
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JP6.00009: Construction of an All-Optical B-Dot Probe William Przybysz, J. Ellis, A. Hansen, R.A. Hardin, E.E. Scime For decades the standard method of performing spatially resolved magnetic fluctuation measurements in plasma has been through the use of inductive coils, ``B-dot probes.'' However, these probes are plagued by both a limited bandwidth and a susceptibility to capacitive pickup, especially in RF generated plasmas. All-optical methods for measuring equilibrium and fluctuating magnetic fields in plasmas have been developed, but are typically limited to line-integrated measurements. The transient internal probe developed at the University of Washington -- Seattle is an all-optical, spatially resolved, magnetic field diagnostic [\textit{Kim et al}., Rev. Sci. Instrum. \textbf{76}, 53504 (2005)], but is limited to a low measurement cadence and by complex infrastructure needs. Here we present proof-of-principle tests of an all-optical, magnetic fluctuation probe constructed from a large Verdet constant, magnetically active crystal and a simple optical detection scheme. The bandwidth of the system exceeds 1 MHz with a sensitivity of less than 0.1 Gauss. The spatial resolution of this system is 25mm. With a higher Verdet constant sensor, this could easily be reduced to 1mm. [Preview Abstract] |
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JP6.00010: Attempts to launch and detect the $m=2$ diocotron mode in a toroidal electron plasma J. Smoniewski, M.R. Stoneking, Bao Ha The Lawrence Non-neutral Torus II (major radius = 17.4 cm, minor radius = 1.27 cm, B $\sim$ 700 G) traps electron plasmas in a purely toroidal magnetic field with confinement 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. 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 $\sim$ $10^7$ cm$^{-3}$) are confined and exhibit toroidal versions of diocotron modes. The $m=1$ mode has been observed and is very similar to the mode observed in cylindrical traps. Numerical modeling including toroidal effects yields the total charge in the plasma from the frequency of the $m=1$ mode. We will report on the ongoing effort to experimentally observe the $m=2$ mode, and to numerically model the mode in toroidal geometry. Measurement of the $m=2$ mode frequency will determine average charge density, which in combination with the total charge information obtained from the $m=1$ mode frequency will permit measurement of radial transport rates. This work is supported by the National Science Foundation. [Preview Abstract] |
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JP6.00011: Intensity Threshold Circuit for Cavity Ring Down Spectroscopy Diagnostic Justin Ellis, Jerry Carr, Saikat Thakur, Robert Hardin, Earl Scime The WVU Helicon Source group is constructing a Cavity Ring Down Spectroscopy (CRDS) system that will provide a new approach to measuring the ion velocity distribution function (ivdf) of an expanding helicon plasma source. The design is based on published CRDS design criteria [\textit{Crunaire et al., }Appl. Phys. B \textbf{85}, 467 (2006)]. Essentially, an acousto-optic modulator (AOM) splits a 668.43 nm laser beam into a zero and first order deflected beam. This first order beam is injected into the cavity, whose length is adjusted with a piezoelectric transducer to match the cavity resonance to the laser frequency. As the light intensity in the cavity reaches a predefined limit, a threshold circuit will send a signal to the AOM to turn off the first order beam. Measurements of the intensity decay time can then be obtained with a photodetector. The complete design of a threshold/trigger apparatus and corresponding electronics will be presented as well as a custom optical scheme for use on the Compact HElicon Waves and Instabilities Experiment (CHEWIE). [Preview Abstract] |
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JP6.00012: Numerical Simulation of MHD Relaxation during Non-Inductive Startup of Spherical Tokamaks T.M. Bird, C.R. Sovinec, D.J. Battaglia, J.B. O'Bryan Nonlinear resistive MHD computation with zero-beta closure is used to investigate the relaxation of helical current filaments into tokamak-like plasmas for non-inductive startup of spherical tokamaks.~ A localized, volumetric current source has been added to the NIMROD~code (nimrodteam.org) to model miniature washer-gun current sources in the lower divertor region of the Pegasus Toroidal Experiment at the Univ. of Wisconsin.~ When the induced magnetic field is smaller than the vacuum field, a helical filamentary current channel forms on open field lines, comparable to experimental results in similar conditions.~ Relaxation into tokamak-like plasmas has been demonstrated in experiment with induced fields that exceed the vacuum field [N. W. Eidietis, et al., J. Fusion Energy 26, 43 (2007)], and simulation results in these conditions with comparisons to experiment are presented.~ We discuss the relaxation process including the roles of diffusion, JxB forces, and magnetic reconnection in the evolution of the magnetic topology. [Preview Abstract] |
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JP6.00013: Process Model of A Fusion Fuel Recovery System for a Direct Drive IFE Power Reactor Saswathi Natta, Maria Aristova, Charles Gentile A task has been initiated to develop a detailed representative model for the fuel recovery system (FRS) in the prospective direct drive inertial fusion energy (IFE) reactor. As part of the conceptual design phase of the project, a chemical process model is developed in order to observe the interaction of system components. This process model is developed using FEMLAB Multiphysics software with the corresponding chemical engineering module (CEM). Initially, the reactants, system structure, and processes are defined using known chemical species of the target chamber exhaust. Each step within the Fuel recovery system is modeled compartmentally and then merged to form the closed loop fuel recovery system. The output, which includes physical properties and chemical content of the products, is analyzed after each step of the system to determine the most efficient and productive system parameters. This will serve to attenuate possible bottlenecks in the system. This modeling evaluation is instrumental in optimizing and closing the fusion fuel cycle in a direct drive IFE power reactor. The results of the modeling are presented in this paper. [Preview Abstract] |
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JP6.00014: Applications of an Ultra-high-speed Digitizer in ICRF Experiments on DIII-D T. Abrams, R.I. Pinsker, F.W. Baity, J.-S. Yoon Three applications of a high speed 4-channel digitizer capable of acquiring 10$^9$ samples per second in ICRF experiments on DIII-D are discussed. The digitizer is used to study fast transients in antenna loading caused by antenna arcs and ELMs. The measured rise time of the ELM-induced increase in antenna loading is on the order of a few microseconds. We have not observed any kind of precursor to an antenna arc; the antenna impedance changes on a sub-microsecond time scale. The feasibility of using the device as an rf amplitude and phase detector was also studied, as a substitute for custom modules such as are presently used. Analysis of the data will be done in software, post-pulse. Finally, the digitizer was used in place of an analog spectrum analyzer to record signals from RF probes, allowing the study of parametric decay in high power fast wave experiments. Again, all signal processing (Fourier analysis) is performed after the data is acquired. [Preview Abstract] |
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JP6.00015: The Impact of Correlations on MHD Equilibrium Reconstruction A.M. Jacobs, J.M. Finn, L.L. Lao, E.J. Strait Equilibrium reconstruction is vital to tokamak operation and post-discharge analysis. EFIT performs equilibrium reconstruction with a $\chi^2$ minimization scheme that utilizes SVD and weighs terms by the variance of the data. It is shown how this regression can be further generalized by incorporating the covariance matrix of the data, which includes correlations between measurements. Sample covariance matrices are computed and used to calculate correlations in a variety of DIII-D magnetic data. The ultimate goal is a modified version of EFIT that takes advantage of the more generalized regression scheme to explore the possibility that highly correlated data could allow for a reduction in uncertainty [1]. The reconstructions of traditional SVD and the generalized covariance scheme are compared. Preliminary results indicate instances of high correlation in quiescent H-mode shots.\par \vskip6pt \noindent [1] C.S. Jones, et al., Nucl.\ Fusion {\bf 46}, 335 (2006). [Preview Abstract] |
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JP6.00016: Measurement of the Electromagnetic Torque on a Rotating Plasma for DIII-D N. Logan, E.J. Strait, H. Reimerdes We study the torque of static and rotating magnetic perturbations on a rotating plasma by deriving an estimate of the electromagnetic torque from measurements of various components of the magnetic perturbation at the wall [1]. This estimate of the torque is then used to determine whether it can account for the experimentally observed changes in the plasma rotation. Preliminary analysis of the locking of a large tearing mode shows that the measured electromagnetic torques behave according to theoretical predictions of their dependency on the magnitude of magnetic perturbations and rotational frequency [2]. The observed torque varies inversely with frequency and linearly with the square of the magnitude of the perturbation. The ultimate goal is to compare the measured electromagnetic torque against the equation of motion and theoretical predictions for the braking effect of magnetic perturbations on a rotating plasma.\par \vskip6pt \noindent [1] I.H. Hutchinson, Plasma Phys. Control. Fusion {\bf 43}, 145 (2001).\break [2] Nave and Wesson, Nucl. Fusion {\bf 30}, 2575 (1990). [Preview Abstract] |
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JP6.00017: Time-Dependent Modeling of Fast Wave Absorption with Multiple Damping Mechanisms W. Unglaub, R.I. Pinsker, R.W. Harvey Plasma response to fast wave absorption is studied in a time-dependent model in which multiple damping mechanisms are present, including direct electron absorption and ion cyclotron harmonic damping in the core and an unspecified edge loss mechanism. Previous study of the plasma response to a step in FW power in a slab model [1] is extended to take into account more realistic effects such as the density rise with FW injection and confinement degradation with increased heating power. To extend this work to a axisymmetric toroidal equilibrium, we couple the GENRAY ray-tracing code to the ONETWO transport code. In both models, it is found that the final partitioning of power among the various damping mechanisms and the time needed to reach the final state strongly depend on initial conditions. The time to reach steady-state can be many energy confinement times.\par \vskip6pt \noindent [1] R.I. Pinsker, in RF Power in Plasmas (Proc. 17th Top. Conf, 2007), (AIP, NY, 2007) p. 447.\par [Preview Abstract] |
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JP6.00018: Target Injection By Electrostatic Acceleration R.K. Friend, R.W. Petzoldt, E. Valmianski, L. Carlson, J. Stromsoe, J. Hares For a direct drive IFE source, the fuel targets must enter the reaction chamber with precise velocity so that they may be accurately irradiated. In this work, a system of electrostatic rings provides acceleration and also enables steering of the target during acceleration. A charge is first placed on the fuel target. Optical fibers mounted on each accelerator electrode trigger a voltage jump in that ring when the target breaks their path. Every third ring will be connected in parallel and accelerating voltage will be advanced as the target passes each electrode. A laser backlights the target along its injection trajectory creating a Poisson spot in the shadow of the fuel target. This spot is used to track the transverse position of the target. Two of the three phases will have rings that are split to allow transverse direction control. Up to $\pm$5~kV accelerating voltage between electrodes will be utilized to achieve 15-20~m/s in 0.9~m. [Preview Abstract] |
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JP6.00019: Penning Gauge Sensitivity and Spectra for Use in DIII-D T.Y. Sheffield, W.P. West, N.H. Brooks, R.J. Boivin, B. Labombard Cold cathode ionization gauges are useful in DIII-D for measuring the neutral density in the periphery region and preferable to those using a hot filament due to increased reliability. We will report on investigations of the performance of a Penning gauge under conditions expected in DIII-D. In particular, the sensitivity of the gauge in a magnetic field tilted at small angles from the axis, the performance and sensitivity with pressures ranging from 0.01 to 10$\,$mTorr, and spatial plasma mode jumps as pressure and magnetic field strength vary will be discussed. Spectral line intensity emitted by the discharge within the gauge will be presented with the aim of reliably reporting the partial pressures of impurity gases. Electron density, temperature, and fluctuations within the gauge are examined using a Langmuir probe. [Preview Abstract] |
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JP6.00020: Non-unique monopole oscillations of harmonically confined Yukawa systems Samuel Ducatman, Christian Henning, Hanno Kaehlert, Michael Bonitz Recently it was shown that the Breathing Mode (BM), the mode of uniform radial expansion and contraction, which is well known from harmonically confined Coulomb systems [1], does not exist in general for other systems [2]. As a consequence the monopole oscillation (MO), the radial collective excitation, is not unique, but there are several MO with different frequencies. Within this work we show simulation results of those monopole oscillations of 2-dimensional harmonically confined Yukawa systems, which are known from, e.g., dusty plasma crystals [3,4]. We present the corresponding spectrum of the particle motion, including analysis of the frequencies found, and compare with theoretical investigations.\newline [1] D.H.E. Dubin and J.P. Schiffer, Phys. Rev. E 53, 5249 (1996)\newline [2] C. Henning at al., accepted for publication in Phys. Rev. Lett. (2008)\newline [3] A. Melzer et al., Phys. Rev. Lett. 87, 115002 (2001)\newline [4] M. Bonitz et al., Phys. Rev. Lett. 96, 075001 (2006) [Preview Abstract] |
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JP6.00021: Performance and Characterization of X-ray Detection Devices for Laboratory Astrophysics Research Mariano Lowenstern, R. Paul Drake, Nicholas Lanier, Eric Harding, Channing Huntington, J. Eduardo Mucino, Anthony Visco Various detection tools are utilized in laser driven experiments with a focus on Inertial Confinement Fusion and Astrophysics. Amongst them are framing cameras (devices that convert incident x-rays into electrons that are in turn amplified by a microchannel plate (MCP) and detected by a phosphor material) and x-ray films. We have implemented a detached Au transmission photocathode (160 {\AA} thick) on a MCP. We have evaluated it using a 1.5 keV Al K-alpha x-ray source, finding an improvement in the effective quantum efficiency combined with a modest decrease in the overall resolution of the detection system. We will also report results of the characterization of AGFA-D7 film using laser generated x-rays. [Preview Abstract] |
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JP6.00022: Comparison of one- and two-dimensional simulations of laser driven shock experiments using 1D and 2D HYADES J. Eduardo Mucino, R. Paul Drake, Dan Austin, Mike J. Grosskopf Computer simulations play an important role in target design, experimental planning, and diagnostic selection for experiments in high-energy-density physics, such as those performed at the OMEGA laser facility in Rochester, NY, which involve shocks driven by high intensity lasers. These experiments can be modeled using one-dimensional and two-dimensional versions of a Lagrangian radiation-hydrodynamic code, HYADES. The one-dimensional simulations are effective for scaling calculations but cannot account for the lateral flow of mass and/or energy that are present in two dimensions. This study seeks to quantify the extent to which lateral flow of mass and energy affects the evolution of the simulated flow by identifying differences between the one- and two-dimensional pressure, density, and electron temperature profiles. We are assessing these effects both in thin targets that experience post-shock ablative acceleration and thick targets that are not accelerated, for a range of laser intensities. [Preview Abstract] |
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JP6.00023: Advances in Dust Detection and Removal for Tokamaks A. Campos, C.H. Skinner, A.L. Roquemore, J.O.V. Leisure, S. Wagner Dust diagnostics and removal techniques are vital for the safe operation of next step fusion devices such as ITER. An electrostatic dust detector[1] developed in the laboratory is being applied to NSTX. In the tokamak environment, large particles or fibres can fall on the grid potentially causing a permanent short. We report on the development of a gas puff system that uses helium to clear such particles from the detector. Experiments with varying nozzle designs, backing pressures, puff durations, and exit flow orientations have obtained an optimal configuration that effectively removes particles from a 25 cm$^{2}$ area. Dust removal from next step tokamaks will be required to meet regulatory dust limits. A tripolar grid of fine interdigitated traces has been designed that generates an electrostatic travelling wave for conveying dust particles to a ``drain.'' First trials have shown particle motion in optical microscope images. [1] C. H. Skinner et al., J. Nucl. Mater., 376 (2008) 29. [Preview Abstract] |
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JP6.00024: Monte Carlo Modeling of a Carbon-Based ICF Neutron Diagnostic B.E. Cochran, S.H. Fay, C.M. Kuhn, E.E. Smith, S.L. Stephenson, T.C. Sangster, V. Glebov, S.J. Padalino A carbon diagnostic system is being developed and tested at OMEGA to determine the tertiary neutron yield during an inertial confinement fusion (ICF) implosion. Past computational work has exclusively used MCNPX (Monte-Carlo N-Particle Extended), despite its inability to formally model the true time-dependent radioactive decay of $^{11}$C. Tools have been developed to efficiently extrapolate information from Ptrac files in MCNPX. In addition, modeling the system with Geant4 (GEometry ANd Tracking) as a supplement to the results obtained with MCNPX is in progress. Results will be presented. [Preview Abstract] |
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JP6.00025: Alpha Particle Redistribution due to Sawtooth Instability in ITER David Liu, Nikolai Gorelenkov, Roscoe White, Janardhan Manickam The sawtooth crash is known to displace energetic alpha particles out of the core region and into ripple loss orbits, which can decrease heating efficiency, drive Alfvenic instabilities and damage the wall. This study uses the ORBIT guiding center code to examine redistribution in trapped and passing alphas. A time dependent 1/1 helical magnetic perturbation as well as potential gradient equations are added into the code to accurately simulate crash conditions. Several important parameters such as amplitude, crash time, initial surface, energy, orbit width, precession frequency, and ripple were varied to study their effect on the redistribution and loss. Diffusion of passing particles was examined by adding a 2/1 helical mode with a similar sawtooth pattern in order to get significant breaking of flux surfaces and stochasticity in field lines. Different dynamics of trapped and passing alpha redistribution predicted by theory is observed in simulations. [Preview Abstract] |
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JP6.00026: Parametric Characterization of RF Plasma Cathode Jennifer Hendryx, Yevgeny Raitses, Valery Godyak, Nathaniel Fisch A plasma cathode that utilizes electron extraction from a radio frequency (rf) plasma could potentially have a longer lifetime than conventional thermionic and field emissive cathodes [1]. We study the electron extraction for a novel low-frequency rf-cathode [2] in the presence of gas flow. The extracting electrode (anode) is movable and biased with respect to the conducting wall of the rf-cathode. The variable parameters of interest in the rf-cathode operation include extraction voltage, distance between anode and rf-plasma source, and gas flow. The results of varying these parameters will be presented. In addition, we also characterize the initiation of a low pressure rf-discharge using a ferroelectric plasma source [3]. [1] B. Longmier, S. Baalrud and N. Hershkowitz, Rev. Sci. Instrum., 77, 113504 (2006). [2] V. Godyak, Y. Raitses and N. J. Fisch, IEPC-2007-266, 30th Inter. Electric Propulsion Conf., Sept., 2007, Florence, Italy. [3] A. Dunaevsky, Y. Raitses, and N. J. Fisch, J. Appl. Physics 93, 3481 (2003) [Preview Abstract] |
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JP6.00027: Recent and Planned Diagnostic Upgrades for HIT-SI and NSTX M.A. Chilenski, T.R. Jarboe, B.A. Nelson, J.S. Wrobel, R. Raman, L. Roquemore, B.M. Jones, R.G. O'Neil The Helicity-Injected Torus (HIT-SI) is equipped with a variety of diagnostics, including a retractable Langmuir probe, a SPRED (Survey, Poor Resolution, Extended Domain) spectrometer and a bolometer. The Langmuir probe's analysis code has been optimized so that processed data is available shortly after each shot. The SPRED spectrometer has been upgraded with a second channel, and spectral data processing tools have been developed to enable operators to better assess Pulse Discharge Cleaning (PDC) on HIT-SI. Planned bolometry upgrades on HIT-SI include an improved calibration and the addition of two more instruments. The University of Washington bolometer design has also been successfully used on the National Spherical Torus Experiment (NSTX). The design of a new dual-chord bolometer for NSTX will be presented. [Preview Abstract] |
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JP6.00028: Numerical Study of the Pedestal MHD Stability Limit on Upper and Lower Separatrix Triangularies J. von der Linden, A.W. Leonard, R.J. Groebner, T.H. Osborne, P.B. Parks The dependence of the magnetohydrodynamic (MHD) stability limit of the edge plasma on the upper and lower triangularities of a lower single null configuration is examined numerically. Although high triangularity has long been known to increase the pedestal height and improve confinement, the effect of varying upper and lower triangularities separately has never been investigated systematically. To study this dependence, Grad Shafranov equilibrium files are created using the EFIT code and varying triangularities while a constant pressure profile characteristic of experimental measurements is maintained. The edge current is constrained to match the Sauter bootstrap current model using measured edge plasma profiles. These equilibria are used as inputs for the ELITE code to determine the MHD stability limit. Results from this study can be used for optimization of the boundary geometry and control of the edge pedestal pressure. [Preview Abstract] |
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JP6.00029: Study of Magnetorotational Instability in Helicon Plasma Joseph McDonald, Hantao Ji, Alex Gurak Magnetorotational instability (MRI) as a mechanism for the fast outward angular momentum transport that occurs in accretion disks has been studied primarily in experiments utilizing a Couette flow in liquid metals. We intend to achieve MRI in a rotating plasma and observe the effects beyond incompressible MHD that are not allowed in liquid metal experiments. The plasma is created by heating argon gas with helicon RF waves in a weak axial magnetic field which is believed to be a characteristic of accretion disks. A set up of two ring electrodes concentric about a center electrode, each of which can be biased to specific potentials, establishes an electric field that can effectively rotate the plasma, and radial profiles of density and potential can be obtained by a motor-driven Langmuir probe. Detailed setup and results will be reported. [Preview Abstract] |
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JP6.00030: Fluctuation Based Melting Criterion for Classical Few-Particle Systems Dylan Buhr, Patrick Ludwig, Jens B\"oning, Torben Ott, Michael Bonitz A common criterion for defining phase transitions in few-particle systems is the so called ``Lindemann criterion,'' which is based on changes of the ``relative Interparticle Distance Fluctuations'' (IDF). Recent research has revealed that in small systems, the Lindemann criterion will suggest different melting temperatures depending on how the associated IDF value is computed [1]. In previous Monte Carlo simulations we controlled this convergence issue by subdividing the simulation into fixed intervals and calculating the ``Variance of the block averaged IDF'' (VIDF) [2]. The advantages of VIDF as a fluctuation based quantity that constitutes a melting criterion is, (i) the universality of being applicable to various quantities in both classical and quantum systems, and (ii) VIDF is directly related to the physical processes taking place during a phase transition. In this contribution we extend the VIDF analysis to molecular dynamics simulations. [1] D.D. Frantz, J. Chem. Phys. \textbf{115}, 6136 (2001) [2] J. B\"oning et al., Phys. Rev. Lett. \textbf{100}, 113401 (2008) [Preview Abstract] |
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JP6.00031: Wobbler Dynamics for Heavy Ion Fusion Drivers Michael Hay, Ronald Davidson, Hong Qin HIFS-VNL is reviewing beam wobbler methods for NDCX upgrades in addition to future heavy ion fusion and high energy physics applications. The wobbler system will smooth the ion beam and deposit its energy uniformly about an annular region on the target, consequently mitigating the Rayleigh-Taylor instability. The wobbler's two pairs of RF-driven electrode plates form this annular structure by accelerating different axial slices of the incident beam in appropriate transverse directions. A lattice of quadrupole magnets will then reduce the focal size of each slice. The coupled, nonlinear ODE system describing the centroid and envelope dynamics through the wobbler and final focusing magnets has been derived for an elliptic beam of uniform density in axial cross-section. Multidimensional Newton methods identified electrode and lattice configurations yielding sufficient deflection and convergence. In the case of a 1 kA, 50 MeV Ar$^{+}$ incident beam, an Adams-Bashforth-Moulton integrator was used to analyze the dynamics of an infinitesimal slice and estimate design parameters for deflection and transverse compression both with and without self-field effects. Leading-order results have indicated feasible requirements for the wobbler voltages and quadrupole gradients. [Preview Abstract] |
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JP6.00032: Two-Point Computational Modeling Of The National Spherical Torus Experiment Scrape-Off Layer Joseph Barton, Rajesh Maingi A scrape-off layer (SOL) model for the National Spherical Torus Experiment (NSTX) is presented based on Stangeby's [1] two-point model and analytical balance equations. We present solutions in the sheath limited and conduction limited (i.e. high recycling) regimes with increasing complexity by eventually showing solutions with volumetric power loss due to Hydrogen and diverter recycling as well as momentum loss due to frictional collisions, viscous forces, and volume recombination. We observe a density limit at the plasma boundary -- just outside the last closed flux surface -- qualitatively consistent with other reports [2]. We then compare our predictions to heat flux data [3] from the NSTX, with the goal of predicting SOL parameters for future NSTX upgrades and other devices. [1] STANGEBY, P. C. in The Plasma Boundary Of Magnetic Fusion Devices (Institute of Physics, London, 2000). [2] BORRASS, K. et al. Nucl. Fusion 31 (1991) 1035. [3] MAINGI, R. et al. J. Nucl. Mater. 363-365 (2007) 196. [Preview Abstract] |
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JP6.00033: Electron Response to a Charged Particle Beam Propagating through a Warm Background Plasma Brendan C. Lyons, Igor D. Kaganovich The propagation of ion beams through a background plasma has broad applications including astrophysics, particle accelerators, and inertial confinement fusion (ICF). In particular, ion beam drivers offer an attractive alternative to high-intensity lasers for ICF. Previous analytical and numerical studies of beam propagation in cold background plasmas have demonstrated near-complete charge neutralization for long beam pulses and current neutralization for beam pulses wider than the electron skin depth. By solving Maxwell's equations in Fourier space, the self-electric and self-magnetic field of the beam pulse has been determined. Particular attention was paid to the effects of electron temperature of the background plasma on the degree of current and charge neutralization. Visualizations of the electron dynamics in the beam's self-electric and self-magnetic fields have been produced. For large ratios of the beam to background plasma densities, the electron density in the beam decreases more rapidly than the current density near the beam's edge, causing a sharp increase in the electron velocity along the radial direction. Analytical formulae will be tested against particle-in-cell simulation results. [Preview Abstract] |
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JP6.00034: Investigating the Relative Biological Effectiveness of a Hydrogen Plasma Beam on Breast Cancer Cells Kelly Donovan, Susan Thomas, Kate Huggler, Robert O'Donnell, Stephen Padalino Proton therapy has become an accepted form of radiation therapy for tumors in the head, brain, neck, lung and prostate. Compared to other forms of radiation, protons can be applied to a more localized area. Due to the unique energy deposition of the proton beam which produces a flattened Bragg peak in the energy spectrum, it is possible to avoid damaging healthy tissue around the tumor. Past studies have consistently shown survival curves for healthy tissue which indicate effective doses in the range of 2-20 Gy. This study utilized a NEC 5SDH Tandem Pelletron Accelerator in the investigation of the irradiation effects on breast cancer cells. A 3 MeV proton beam passed through a 25 micron thick Kapton window which allowed the cells to remain in atmosphere while being irradiated. Proton energy loss and beam straggling through Kapton and air were determined theoretically using TRIM and confirmed by calibration experiments. A shutter system placed between the window and the cell sample was used to control radiation exposure time. A range of radiation exposure times were tested in an attempt to find the optimal dose. [Preview Abstract] |
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JP6.00035: Velocity Measurements of Free Surface Liquid Metal Flows in a Magnetic Field Scott Pfeffer, Hantao Ji, Mark Nornberg, John Rhoads A potential probe diagnostic was developed and calibrated to map the velocity profile of free-surface liquid metal channel flow and quantify the effect an applied magnetic field played in shaping the velocity profile. The setup for this experiment consists of a wide aspect ratio channel sealed from the air, with argon replacing the air in the channel, placed within an electromagnet capable of producing more than a 2000 Gauss field perpendicular to the flow. An alloy of GaInSn, which is liquid at room temperature, is pumped through the channel by a screw pump at a specified rate. The velocity profile is obtained by measuring the voltage across pairs of probes. Various materials were used to determine which probe material would maximize the signal from the voltage induced by the Hall effect and reduce the voltage due to thermoelectric effects. Extensive calibration was then carried out to ensure an accurate velocity measurement. After amplification and filtering this signal gives us a good measurement of the velocity of the liquid metal over the cross-section of a specific probe. [Preview Abstract] |
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JP6.00036: Construction of a New Beamline at the SUNY Geneseo Pelletron Accelerator for Calibrating a Thomson Parabola Steven Hupcher, Megan Crossman, Charles Freeman, Christian Stoeckl A newly constructed Thomson Parabola will be used to study the energy spectra of protons and other ions at the Multiterawatt (MTW) laser facility at LLE produced from the illumination of a planar target with an ultra-intense laser light ($>$10$^{19}$ W/cm$^{2})$. Charged particles ejected in the forward direction will be spatially separated and recorded on image plates in the parabola. Beams of protons and alpha particles from the tandem pelletron at SUNY Geneseo were used to establish an energy-to-position calibration for the Thomson Parabola, as well as to calibrate the response of the imaging plates to various particle fluxes. A new beamline with a general-purpose scattering chamber was constructed at the SUNY Geneseo 1.7 MV pelletron accelerator laboratory. The beamline is equipped with a general-purpose 28 inch scattering chamber which includes a target manipulator system, faraday cup, and a mounting for a surface barrier detector. [Preview Abstract] |
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JP6.00037: Assembly of the Lithium Tokamak Experiment C.L. Ellison, L. Berzak, R. Kaita, T. Kozub, D. Lundberg, R. Majeski, D. Moser, K. Snieckus, J. Taylor The Lithium Tokamak Experiment (LTX) will explore the effects of liquid lithium as the plasma facing component (PFC) of tokamak walls. Expected modifications include decreased recycling, improved energy confinement times, and flat electron temperature profiles. While the vacuum vessel has been used in the Current Drive Experiment -- Upgrade, the new research emphasis on a full wall (5 m$^{2})$ liquid lithium PFC complicates the design and assembly. For instance, the heated shells (400$^{\circ}$C) for the liquid lithium PFCs require any temperature-sensitive components to be thermally isolated. The potentially reactive nature of the headed lithium restricts the allowable materials within the chamber, e.g., all copper components are plated with nickel or surfaced with stainless steel. The electrical, thermal, and chemical isolation for chamber components thus introduce complexity in the assembly. These will be described in the context of a design that will test the effects of liquid lithium as a first wall. [Preview Abstract] |
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JP6.00038: Measurement of Plasma Flow using High-Speed Imaging M. Klassen, A. Hatzikyriakou, B.A. Grierson, M.E. Mauel When a magnetized plasma is convected by low-frequency fluctuations, the plasma $\mathbf{E}\times\mathbf{B}$ flow can be characterized by a stream function, equal to the electrostatic potential when the flow is expressed in flux coordinates. Under certain circumstances, the equation of particle number continuity, relating cross-field structure and flow to the stream function, can be solved computationally for the potential. We have demonstrated this using a model problem with static boundary conditions. In this poster we report applying this technique to plasma dynamics measured by a high-speed camera or by simultaneous multi-point polar current measurements. The fast camera is mounted to a porthole of Columbia University's Collisionless Terrella Experiment (CTX), which features a dipole plasma believed to be two-dimensional. We seek to image the plasma at a frame rate high enough to distinguish moving structures, determine the stream function, and calculate the magnitude and spatial structure of the plasma potential. We will also investigate the correlation between the fast camera diagnostic and other diagnostics. [Preview Abstract] |
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JP6.00039: Experimental Study of Solar Flares in MRX Nate Williams, Erdem Oz, Masaaki Yamada, Hantao Ji, Seth Dorfman, Brendan McGeehan, James Schroeder Solar flares and coronal mass ejections (CMEs) have a great effect on Earth, causing geomagnetic storms that can damage satellite communication or the orbiting structures themselves. Being unable to take direct measurements, understanding of these phenomena in many ways is limited to calculations and models. This experiment modifies the Magnetic Reconnection Experiment (MRX)[1] to study solar flares in a laboratory setting. Two electrodes placed in separate toroidal positions create a plasma for studying a twisted flux rope model. Magnetic probes map out the magnetic structure, and electrostatic probes measure plasma temperature and density. The arc is monitored by a high speed camera. The equilibrium magnetic field, which maintains the arc shape, and the safety factor can be calculated. Results to be shown can be applied to increase understanding of the mechanism of CME initiation[2]. [1] Yamada et al., 1997. [2] M. Yamada, H. Ji, S. Gerhardt, S. Antiochos, M. Linton, MRX Solar Flare Experiment Proposal, 2007. [Preview Abstract] |
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JP6.00040: Multidipole Confinement of a High-Beta, Flowing Plasma J. Jara-Almonte, C.B. Forest, R. Kendrick, C. Collins The Plasma Couette Experiment has been designed and constructed to~investigate the magnetorotational instability in a plasma. The plasma is produced by a lanthanum hexaboride cathode in a 1 m diameter, cylindrical vacuum chamber. Confinement is provided by a high-order, axisymmetric multicusp magnetic field localized at the chamber walls; the magnets are located inside the vessel and positioned in a ring cusp geometry. Electrodes located between the cusp lines create an electric field which induces plasma rotation in the magnetized region via ExB drift. These flows are expected to viscously couple to the unmagnetized region in the center of the experiment. Energy and particle confinement in both non-confined and magnetically confined geometries are characterized by temperature and density profiles measured with a single tip swept Langmuir probe. Confinement times will be established by comparing stored energy to input power. Magnetostatic simulations and hall probe mappings of the magnet assembly will be compared, and the effectiveness of the axisymmetric multicusp confinement will be discussed. [Preview Abstract] |
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JP6.00041: Gamma X: A Full Capture Mode Detector Array for Carbon Activation Cassarah Brown, Melissa Cummings, Stephen Padalino, Thomas Sangster, Timothy Duffy, Vladimir Glebov A diagnostic was developed to determine the ($\rho $r)$^{2}$ of a DT reaction via the production of tertiary neutrons. High energy neutrons, in the range of 20 to 32 MeV, were incident upon a carbon disk which became activated via the 12C(n,2n) reaction. The activated carbon was then quickly transported to the counting station where it was placed in a NaI detector system where the C11 decay via positron emission could be detected in the form of back-to-back 511 KeV annihilation gamma rays. The 6 paired detectors in the system were aligned orthogonally on Cartesian axes. In comparison to the previous 2 detector system used at Rochester, the new 6 detector system has improved counting statistics substantially by increasing sample size and collection solid angle. To obtain a better understanding of the effects of non-uniformly activated samples, radioactive copper pellets were distributed within the carbon sample matrix in a variety of volumetric distributions. In doing so the effects of non-isotropic activation on the efficiency of the detector system could be determined. [Preview Abstract] |
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JP6.00042: High-Speed RaPToRS Robert Henchen, Benjamin Esham, William Becker, Edward Pogozelski, Stephen Padalino, Thomas Sangster, Vladimir Glebov The High-Speed Rapid Pneumatic Transport of Radioactive Samples (HS-RaPToRS) system, designed to quickly and safely move radioactive materials, was assembled and tested at the Mercury facility of the Naval Research Laboratory (NRL) in Washington D.C. A sample, which is placed inside a four-inch-diameter carrier, is activated before being transported through a PVC tube via airflow. The carrier travels from the reaction chamber to the end station where it pneumatically brakes prior to the gate. A magnetic latch releases the gate when the carrier arrives and comes to rest. The airflow, optical carrier-monitoring devices, and end gate are controlled manually or automatically with LabView software. The installation and testing of the RaPToRS system at NRL was successfully completed with transport times of less than 3 seconds. The speed of the carrier averaged 16 m/s. Prospective facilities for similar systems include the Laboratory for Laser Energetics and the National Ignition Facility. [Preview Abstract] |
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JP6.00043: Reflectivity Measurements of Layering Spheres for Cryogenic ICF Targets Joesph Katz, Kevin O'Connell, Kurtis Fletcher, Edward Pogozelski, Wolf Seka Cryogenically frozen DT targets are used in ICF implosions at the Laboratory for Laser Energetics. To improve the uniformity of the ice layer, a DT target is placed in a spherical cavity called a layering sphere and is illuminated with infrared light, promoting ice sublimation. Areas of greater thickness sublimate faster thereby depositing the material onto thinner sections. The cavity wall consists of a rough gold coating designed to create lambertian scattering which should uniformly illuminate the DT target with laser light. To improve this process, the reflectivity of the spherical cavity wall was measured to determine its uniformity. A DFB laser of wavelength 635 nm was used to illuminate the inner cavity. A fiber optic periscope with a right angle prism was used to measure the surface reflectivity of cylindrical slices. Irregularities in the data correspond primarily to bright spots and port windows. [Preview Abstract] |
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JP6.00044: Investigation of a Plasma Ball using a High Speed Camera James Laird, Stewart Zweben, Yevgeny Raitses, Andrew Zwicker, Igor Kaganovich The physics of how a plasma ball works is not clearly understood. A plasma ball is a commercial ``toy'' in which a center electrode is charged to a high voltage and lightning-like discharges fill the ball with many plasma filaments. The ball uses high voltage applied on the center electrode ($\sim $5 kV) which is covered with glass and capacitively coupled to the plasma filaments. This voltage oscillates at a frequency of $\sim $26 kHz. A Nebula plasma ball from Edmund Scientific was filmed with a Phantom v7.3 camera, which can operate at speeds up to 150,000 frames per second (fps) with a limit of $\ge $2 $\mu $sec exposure per frame. At 100,000 fps the filaments were only visible for $\sim $5 $\mu $sec every $\sim $40 $\mu $sec. When the plasma ball is first switched on, the filaments formed only after $\sim $800 $\mu $sec and initially had a much larger diameter with more chaotic behavior than when the ball reached its final plasma filament state at $\sim $30 msec. Measurements are also being made of the final filament diameter, the speed of the filament propagation, and the effect of thermal gradients on the filament density. An attempt will be made to explain these results from plasma theory and movies of these filaments will be shown. Possible theoretical models include streamer-like formation, thermal condensation instability, and dielectric barrier discharge instability. [Preview Abstract] |
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JP6.00045: Using Pickup Coils to Detect Magnetorotational Instability in Liquid Gallium D. Coster, M.D. Nornberg, E. Schartman, H. Ji, A. Roach The physics of accretion disks in space around bodies like black holes and forming stars is still not fully understood, particularly relating to the mechanisms of fast angular momentum transport. It has become widely accepted that the magnetorotational instability (MRI) is responsible for inciting the turbulent outward flux of angular momentum needed for fast accretion to occur. The goal of the MRI experiment is to provide a better understanding of these mechanisms by realizing MRI at a much smaller scale. It should be able to reproduce the MRI in the lab by passing a magnetic field through liquid gallium that is being quickly rotated and confined between two independently turning cylinders. Previously, non axisymmetric modes have been observed. In order to better resolve these modes, we have constructed a horizontal array of pickup coils to detect fluctuations in the magnetic field. These measurements give us information about the instabilities created in the gallium and will hopefully provide evidence for MRI. Design, calibration, and experimental results will be presented. [Preview Abstract] |
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JP6.00046: Effects of Injection and Confinement Imperfections on Plasma Stability in the Paul Trap Simulator Experiment N. Thomas, M. Chung, R.C. Davidson, M. Dorf, P.C. Efthimion, E.P. Gilson, R. Majeski, E.A. Startsev, H. Wang, A. Arora Analyses of preliminary results are presented from experiments studying the effects of perturbations during plasma injection and confinement on the stability properties of pure ion plasmas trapped in the Paul Trap Simulator Experiment (PTSX). The PTSX is a two-meter-long Paul trap that simulates a long, thin beam of ions travelling through a kilometers-long lattice of quadrupole magnets because the space-varying magnetic fields can be Lorentz transformed into time-varying electric fields. The analogy includes all nonlinear space-charge effects, enabling cost-effective accelerator design prototyping and troubleshooting in a compact laboratory experiment. The effects studied include perturbations to the beam as it enters the lattice and the effects of lattice imperfections on transverse beam confinement, including periodic perturbations, which correspond to imperfections in cyclic particle accelerators. [Preview Abstract] |
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JP6.00047: Analysis of a Helium Brayton Power Cycle for a Direct-Drive Inertial Fusion Energy Power Reactor Scott Wagner, Charles Gentile, Robert Parsells, Craig Priniski Presented is a thermodynamic model analysis and optimization of a helium Brayton power cycle for direct-drive inertial fusion energy (IFE) reactor. Preliminary reactor design goals include production of 2GW of thermal power and an estimated 700MW of electricity using a tertiary indirect helium Brayton cycle. A thermodynamic analysis of the proposed helium Brayton cycle is performed using baseline technology specifications and generalized thermodynamic assumptions. Analytic equations are developed using first and second law analysis. The model constraints are the turbine inlet temperature and pressure set by the reactor temperature of $\sim $700$^{\circ}$C and current turbine specifications of 7MPa, respectively. Optimization of this model is then performed using iterative numerical programming for key variables. Previous analysis shows a 51{\%} cycle efficiency using current technology; best estimates of near-term technology increase the cycle efficiency to 64\%.\footnote{R. Schleicher, A. R. Raffray, C. P. Wong, ``An Assessment of the Brayton Cycle for High Performance Power Plant,'' Fusion Technology, 39 (2), 823-827, March 2001.} Results will be presented. [Preview Abstract] |
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JP6.00048: ABSTRACT WITHDRAWN |
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JP6.00049: Numerical Study of Poloidal Asymmetry of Fast Particle Density in JET NBI Heated Discharges T. Bakowski, A.Y. Pankin, G. Bateman, A.H. Kritz, T. Rafiq, I. Voitsekhovitch The poloidal asymmetry in the distribution of fast NBI deuterium ions, which has been observed in medium and high density JET discharges during trace tritium campaign, is investigated in simulations using the ASTRA integrated modeling code. The NUBEAM Neutral Beam Injection (NBI) Monte-Carlo package is used to follow the evolution of the fast particle distribution function for several JET discharges. Recent improvements to the interface between the ASTRA code and the NUBEAM package are described. The electron and ion NBI power deposition profiles, as well as the profiles for driven current densities, computed using the NUBEAM module in ASTRA, the NUBEAM module in TRANSP, and the NBI Fokker-Planck module in ASTRA, are compared. It is demonstrated that the poloidal asymmetry of the fast particle density disappears in discharges with low line average density. The effect of trapped particles on the fast ion poloidal asymmetry is investigated. [Preview Abstract] |
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JP6.00050: Laue X-ray spectrograph for the 200-TW Trident Laser Nalin Vutisalchavakul, James Cobble, Jonathan Workman With the 200-TW laser at the Trident Laser Facility, experiments on x-ray backlighting were performed. The sub-ps short pulse laser with energy up to 100 J can be shot on targets with different atomic number. The focused laser beam has intensities up to 10$^{21}$ W/cm$^{2}$. The high energy laser interacted with the targets, producing X rays due to K-shell emission. Among other diagnostic devices, a Laue X-ray spectrograph was used to record the x-ray spectrum, which showed emission lines and bremsstrahlung radiation. The Laue spectrograph uses a LiF(200) crystal to disperse the x-ray spectra with a bandpass of 17-70 keV. The spectra were recorded using Fuji image plates. The Laue instrument was designed to include a tungsten shield in the front, a magnetic trap, and a light trap to reduce background noise. Ka lines of Mo, Ag, and Sn were observed. [Preview Abstract] |
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JP6.00051: Effects of Macroparticle Number on Electrostatic and Electromagnetic Space-Charge Models Ian Anderson, Mark Hess, Chong Shik Park When simulating the physics of space-charge dominated beams using a macroparticle representation of the beam, it is essential to accurately compute the beam space-charge fields. Depending on the characteristic length and time scales associated with the space-charge fields for a particular beam system, one may find that electrostatic space-charge calculations may be appropriate, while in other regimes a full electromagnetic space-charge calculation may be necessary. In this paper, we investigate the accuracy of space-charge calculations for both the electrostatic and electromagnetic cases with the assumption of a free space boundary condition. Specifically, we look at the convergence of the electric and magnetic space-charge fields for an accelerating spherical bunch using both Coulomb's Law and Lienard-Wiechert formulations as a function of the macroparticle number and discuss its implications for modern beam space-charge simulations. [Preview Abstract] |
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JP6.00052: Temperature estimation from molecular nitrogen UV spectra in atmospheric pressure plasmas Keenan Pepper, Yongho Kim, Jihun Kim Atmospheric pressure plasmas have many potential applications to fuel processing, surface treatment, and manipulation of chemical reactions. These plasmas are often non-thermal, which means different species are not in equilibrium and have different effective temperatures. This is critical for many applications because it allows high concentrations of reactive species to be produced without using a prohibitive amount of power. In the present work, numerical software was developed to estimate the vibrational and rotational temperatures (T$_{\rm vib}$ and T$_{\rm rot}$) of N$_2$ molecules from their ultraviolet emission spectra. The electron temperature T$_{\rm e}$ can also be estimated by comparing the N$_2$ spectrum to that of the N$_2^+$ molecular ion. This technique is applied to several plasma sources including audio frequency, RF, and microwave devices. The results are presented and their implications for practical applications are discussed. [Preview Abstract] |
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JP6.00053: Design of new dusty plasma apparatus to view 3D particle dynamics of fluorescent dust clouds Kathreen Thome, Alexandra Fontanetta, Andrew Zwicker Particles suspended in dusty plasmas represent both contamination in industrial plasmas and a primary interstellar medium component. Typically, dusty plasma behavior is studied by laser scattering techniques that provide 2D dust cloud images. However, the 3D structure of the dust cloud is essential to understand the waves, group dynamics, and stabilities of the cloud. Techniques used to study this structure include stereoscopic particle image velocimetry and rapid laser scanning. Our UV illumination technique reveals translational and rotational velocities of fluorescent dust particles as a function of UV intensity. The new argon DC glow discharge experiment designed to study the 3D aspects of fluorescent dust consists of a 13.25'' diameter chamber, two 8'' window ports for CCD cameras, one along the plasma and another transverse to it, two additional 8'' window ports transverse to the plasma for laser or UV light illumination of the dust cloud, and a diagnostic probe port. Results from different electrodes--including mesh and ring--observations and imaging will be presented. [Preview Abstract] |
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JP6.00054: Study of effects of external drive on MRX reconnection J. Schroeder, S. Dorfman, M. Yamada, H. Ji, B. McGeehan, E. Oz, N. Williams, W. Daughton, V. Roytershteyn The Magnetic Reconnection Experiment (MRX) studies driven reconnection utilizing two toroidal flux cores [1]. One active topic of research is the relationship between global plasma parameters and local reconnection physics. External drive is determined by the rate at which poloidal magnetic field is pulled back into the flux cores. Findings from the TS-3 experiment [2] and recent 2-D simulations [3] have shown a linear scaling between driving parameters and reconnection rate. This study investigates the relationship of external drive to the out-of-plane electric field and the MHD inflow velocity in MRX. Initial results show a linear scaling between external drive and out-of-place electric field at low fill pressure and reduced dependence at higher fill pressure. Further analysis of the effect of external drive on other relevant plasma parameters and comparisons to 2-D kinetic simulations will be reported. [1] M. Yamada, et al., Phys. Plasmas 4(5),1936 (1997). [2] M. Yamada, et al., Physical Review Letters 65(6),721 (1990). [3] S. Dorfman, et al., Submitted to \textit{Phys. Plasmas.} This work was supported by DOE, NASA, and NSF. [Preview Abstract] |
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JP6.00055: Atmospheric Ball Plasma Interactions C.J. v. Wurden, G.A. Wurden Free-floating atmospheric pressure copper hydroxyl ball plasmas have been studied in air and helium atmospheres, using still and high speed photography (up to 20,000 fps), collimated photodiodes, and spectroscopy. A fine boundary layer between the greenish Cu-OH cloud, and the air, is orange in color. However, when the discharge is initiated into a helium atmosphere, the boundary layer is no longer visible, suggesting that the visible boundary was caused by interactions with oxygen. We have studied scaling of the 10-cm diameter ball plasmas with both the size of the water bucket, and the applied discharge voltage, over the range of 500-5000 volts. When looking at the initial spider-leg breakdown above the water surface, the ratio of H-alpha to H-beta lines suggests a temperature of $\sim $0.3 eV. This is also consistent with the presence of molecular lines of OH, and perhaps CuOH2 in the rising cloud. The cloud is affected by, but can penetrate through an aluminum window screen mesh. [Preview Abstract] |
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JP6.00056: Intensity and Temperature Variance in Sonoluminescence Lyric Elizabeth Gillett Sonoluminescence is the process in which light is produced through ultrasonic pressure waves causing the expansion and subsequent collapse of a gas/vapor bubble, held in an ultrasonic standing wave pattern, in water. This study measured sonoluminescent bubble light intensity output with a photomultiplier tube and a lock-in amplifier, to determine the relationship of the sonoluminescent intensity to variance in water temperature. The results could be indicative of the optimal temperatures at which to conduct sonoluminescence research, and assist in facilitating and advancing sonoluminescence research ventures relating to further study of energy production and nuclear reactions. Though not part of the original experimental design, the initial experimentation suggested a positive correlation between the drive level of the transducer and the light intensity from the sonoluminescent bubble. Further experimentation was conducted in which the transducer drive signal and frequency were continuously optimized as the water temperature rose. After data was graphed and analyzed, it was determined that there was a decrease in sonoluminescent intensity as the water temperature increased. The intensity of the light emitted by the sonoluminescent bubble is understood to be directly related to the density of plasma created in the bubble upon collapse (through Bremsstrahlung.) It is believed that this experimentation resulted in a greater plasma density inside the sonoluminescent bubble, and to that end, this researcher would like to conduct further experimentation. [Preview Abstract] |
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JP6.00057: A Decade of Plasma Camp Doreen Nuzzolese, Andrew Zwicker, Nicholas Guilbert, James Morgan To engage high school physics teachers in plasma physics, The Princeton Plasma Physics Laboratory (PPPL), established The Plasma Science and Fusion Energy Institute, or Plasma Camp, in 1998. Plasma camp is an intensive summer professional development workshop aimed at introducing teachers and their students to physics topics relevant to fusion plasma research and developing ways to integrate plasma physics into existing curricula. Plasma Camp has been evaluated by several different measures. Results have shown that high percentages of alumni have intertwined plasma physics throughout science curriculum across all disciplines and demographics, including demonstrations, lessons, and activities. Evidence has also shown that plasma camp promotes high pedagogical value, as many alumni have gone on to present at conferences, publish articles, conduct research, obtain advanced degrees, and win prestigious awards. [Preview Abstract] |
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JP6.00058: Measurements of the Non-Linear Coupling of Plasma Waves E.K. Snipes, J. McClenaghan, A.J. Noble, A.A. Kabantsev, C.F. Driscoll A separatrix is created in a pure electron plasma column by applying a $\theta$-symmetric wall voltage. This ``squeeze'' voltage traps less energetic electrons in either end and allows more energetic electrons to pass through. These trapped particles enable the novel Trapped Particle Diocotron Mode (TPDM). We excite an ordinary $m=2$ diocotron mode at frequency $f_2$ to amplitude $A_2$ and observe the decay into the $m=1$ TPDM at $f_1 \approx f_2 / 2$. The exponential growth rate, $\Gamma$, of the TPDM is obtained as a function of the amplitude $A_2$ as well as a function of the ``squeeze'' voltage which determines the frequency mismatch $\delta f = f_2 / 2 - f_1$. We calibrate the amplitudes of the modes in terms of the received wall voltages, and obtain a quantitative value of the non-linear coupling coefficient, $V$. These results at $B = 280$~G will be compared to recent results\footnote{A.A. Kabantsev, T.M. O'Neil, Yu.A. Tsidulko, and C.F. Driscoll, Phys.~Rev.~Lett. {\bf 101}, 065002 (2008).} from a separate apparatus at $B > 2000$~G. [Preview Abstract] |
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JP6.00059: DIII-D I |
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JP6.00060: DIII-D Research in Support of ITER E.J. Strait DIII-D research is providing key information for the design and operation of ITER. Recent results have led to improved understanding of several critical issues, including control of edge-localized modes (ELMs), plasma rotation effects, mitigation of disruptions, and plasma-wall interactions. Recent experiments and modeling on ELM suppression with resonant magnetic perturbations have provided key information for the assessment of ELM control coil options in ITER. In addition, DIII-D experiments that simulate the various ITER operating scenarios provide a platform for projections of fusion performance and tests of plasma control. Experiments have investigated the L-H transition threshold and energy confinement dependence on ion mass nummber, at the low values of input torque and plasma rotation that are expected in ITER. We will give an overview of these and other key ITER-related research topics at DIII-D. [Preview Abstract] |
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JP6.00061: Demonstration of ITER Operational Scenarios on DIII-D E.J. Doyle The DIII-D program has recently begun an effort to provide experimental evaluation of the primary ITER operational scenarios, enabling direct cross-comparisons on a single tokamak. This work incorporates leading features of the ITER scenarios and anticipated operating characteristics. The plasma shape, aspect ratio and value of $I/aB$ of the DIII-D discharges match the ITER design, with size reduced by a factor of 3.7. Key aspects of the ITER baseline ELMy H-mode (15~MA in ITER), advanced inductive (13~MA), hybrid (11~MA), and steady-state (9~MA) scenario plasmas have been replicated, providing a unified basis for transport and stability modeling and performance extrapolation. In all scenarios performance equals or closely approaches that required to realize the physics and technology goals of ITER. Baseline plasmas with normalized beta of 1.8-2.0 were studied (limited by tearing modes); for the other scenarios, the normalized beta was in the range 2.7-3.0. Confinement with $H_{98y2} \geq 1$ was seen in all cases. [Preview Abstract] |
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JP6.00062: Comparison of ELMs in Hydrogen and Deuterium Discharges in DIII-D C.J. Lasnier, M.E. Fenstermacher, M. Groth, T.E. Evans, R.J. Groebner, A.W. Leonard, T.H. Osborne, J.G. Watkins, M.W. Jakubowski In this paper we compare the behavior of ELMs in similar hydrogen and deuterium discharges in DIII-D. Discharges were run with deuterium fill gas and deuterium neutral beams, and other discharges with hydrogen fill and hydrogen neutral beams. We compare divertor heat flux profile widths, in-out ratios of divertor heat flux profile width and peak heat flux, ELM frequency, energy loss per ELM, and difference of propagation time of ELM heat pulses to inner and outer divertors, The part of the heat flux carried by ions along field lines at the ion sound speed should be affected by the change in ion mass. We also examine the toroidal symmetry of divertor heat flux during ELMS by comparing thermography at two toroidal locations in hydrogen and deuterium discharges. [Preview Abstract] |
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JP6.00063: Gas Balance in Ohmic Discharges on DIII-D W.P. West, N.H. Brooks, A.W. Leonard, D.G. Whyte, B. Lipschultz, J.G. Watkins, M. Groth, C.J. Lasnier, M.E. Fenstermacher, J.A. Boedo, D.L. Rudakov, E.A. Unterberg Wall retention of deuterium (D) fueling gas in ohmic discharges on DIII-D has been measured by operation in a closed system with no exhaust from the vacuum vessel. Vessel pressures after identical gas injection, with and without plasma operation, are compared. The ion flux to the divertor was measured with fixed Langmuir probes, and SOL plasma density and temperatures were measured with fast-stroke probes. Ten similar discharges with no in-vessel pumping were repeated, followed by three discharges with in-vesssel divetor cryopumps active then regenerated after each discharge. Preliminary analysis indicates the retained D in ohmic discharges is $\sim$90 (20)\% of the injected gas in the un(pumped) discharges, whereas previous gas balance during cryopumped ELMing H-mode discharges indicated no retention. In both the pumped and unpumped ohmic cases, the retained D is $\sim$1\% of the ion fluence to the wall. [Preview Abstract] |
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JP6.00064: Disruption Mitigation with Hyper-Velocity High-Density C60-Fullerene Plasma Jets I.N. Bogatu, S.A. Galkin, J.S. Kim Disruption mitigation in ITER must be a reliable technique with real-time capability. Impurity injection is proposed to convert the plasma energy density ($\sim$1~GJ in 840~m$^3$) into radiation power in $\sim$1~ms and to increase the electron density by two orders of magnitude all over the plasma cross section to suppress the runaway electrons avalanche. But once the impurity atoms are ionized in the thin outer layer of tokamak plasma they can no longer penetrate the confining magnetic field unless they have high velocity. We propose to use hyper-velocity high-density C60-fullerene plasma jets to penetrate into the core tokamak plasma and deliver the necessary mass. We present the following key elements of our concept: a large mass ($\sim$2~g) of molecular gas produced in a pulsed power source, maximized injection velocity into plasma gun by Laval micro-nozzles grid, plasma slug acceleration to hyper-velocity ($\sim$30~km/s), atomic processes during the plasma jet transport, jet penetration into the tokamak hot plasma and confining magnetic field, and a feasibility study of a proof-of-principle experiment on DIII-D. [Preview Abstract] |
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JP6.00065: Simulation of DIII-D Plasma Shutdown by Deuterium Dilution Cooling V.A. Izzo, P.B. Parks, W. Wu To mitigate ITER disruptions and avoid large numbers of runaway electrons, a significant increase in the total (free + bound) electron inventory is likely required. The Rosenbluth criterion --- $E_c\approx 0.12\,n_{e,20}$ --- determines the critical electric field (in V/m) at which exponential runaway avalanching will occur. Here we consider instantaneous dilution cooling of a DIII-D plasma by the injection of 100 times the initial deuterium density to simulate rapid core penetration of a D$_2$ pellet train or liquid jet. The 3D NIMROD MHD simulation is initialized with an equilibrium pressure profile, but a 100$\times$ density increase and a corresponding 100$\times$ temperature reduction. The plasma is assumed to have in situ carbon fraction of 1\% of the pre-dilution density, which produces strong edge radiation at the dilution cooled temperatures. A cooling front propagates inward and ultimately triggers a central 1/1 MHD event. The central current density transiently increases by more than a factor of 2. The 3D simulation is compared with a 1D simulation which incorporates a Kadomtsev mixing model for the 1/1 MHD event. [Preview Abstract] |
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JP6.00066: Impurity Pellet Injector for Disruption Mitigation Studies in DIII-D A.N. James, E.M. Hollmann, J.H. Yu, T.E. Evans, G.L. Jackson, P.B. Parks The DIII-D impurity pellet injector, formerly lithium pellet injector, has been recommissioned primarily for the purpose of disruption mitigation experiments. The first pellet injected into a H-mode plasma was a solid 1~mm cylindrical carbon pellet which completely ablated in the pedestal and did not cause a disruption. More than 90\% of carbon which reached the pedestal was assimilated into the core on a transport time scale of $\sim$10~ms, roughly doubling plasma carbon content. We will report on planned experiments involving injection of low-Z shell pellets made of polystyrene which contain a dispersive payload of tracer material: boron dust in cylinders or 10~atm argon gas in spherical pellets. The goal in both cases being delivery of large quantities of electrons to the core before triggering a thermal quench. Another experiment to be reported involves injecting small carbon pellets during the current quench phase of a disruption to attempt probing the properties of runaway electrons. [Preview Abstract] |
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JP6.00067: Fast Plasma Shutdowns By Massive Hydrogen, Noble and Mixed-Gas Injection in DIII-D J.C. Wesley, M.A. Van Zeeland, T.E. Evans, D.A. Humphreys, A.W. Hyatt, P.B. Parks, E.J. Strait, W. Wu, E.M. Hollmann, J.A. Boedo, V.A. Izzo, A.N. James, R.A. Moyer, D.L. Rudakov, J.H. Yu, T.C. Jernigan, L.R. Baylor, S.K. Combs, M. Groth Experiments conducted with hydrogenic, noble and mixed (H$_2$ + Ar and D$_2$ + Ne) gases injected into H-mode plasmas are described. Gas species, quantity, delivery rate and intrinsic and added impurities (mixtures) all affect the disruption mitigation attributes of the resulting fast plasma shutdowns. With sufficient quantity, effective mitigation is obtained for all species. Optimal results for disruption and runaway avalanche mitigation are with 3$\times 10^{22}$ He delivery in $\sim$2~ms. This yields a favorable combination of moderately-fast current quench, high free-electron densities, $\sim$2$\times 10^{21}\,$m$^{-3}$, gas assimilation fractions $\sim$0.3 and avalanche suppression ratios, $n_e/n_{RB} \sim 0.1$. Favorable scaling of assimilation with increasing quantity is seen for all low-Z gases. The experiments provide validation data for emerging MHD/radiation simulation models and insight about design of injection systems for disruption and avalanche mitigation in ITER. [Preview Abstract] |
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JP6.00068: Dust Production by Impulsive ELM Heating During Plasma Discharges at DIII-D B.D. Bray, W.P. West, D.L. Rudakov Small ($\sim$100~nm radius) dust particles (mean density 4000~m$^{-3}$) are observed in the scrape off layer (SOL) by laser scattering during plasma discharges at DIII-D. The dust detection rate is too low to study dust density evolution in individual discharges, but statistical studies of these particles show significant differences in the dust densities for different plasma configurations. There is a significant increase in dust density during ELMy H-mode discharges relative to other discharges. The dust levels are one half to one third as large during L-mode and ELM-free H-mode discharges. The dust density in ELMy H-mode discharges is sensitive to the pedestal temperature and ELM frequency and can increase as much as a factor of two with pedestal temperature for similar pedestal pressure and injected power. The dust density is also observed to decrease during inter-ELM periods. These measurements suggest the particles are created by impulsive heating from ELMs and the dust density is relatively insensitive to the total heat flux to the wall. [Preview Abstract] |
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JP6.00069: Resonant Character of Edge Plasma Parameters in Stochastic Boundary Experiments at DIII-D and TEXTOR O. Schmitz, B.D. Bray, N.H. Brooks, T.E. Evans, A.W. Leonard, T.H. Osborne, W.P. West, M.E. Fenstermacher, M. Groth, C.J. Lasnier, H. Frerichs, M. Lehnen, B. Unterberg, M.W. Jakubowski, R.A. Moyer, J.G. Watkins Dependence of electron pressure $p_e$ profiles on the edge safety factor during resonant magnetic perturbations (RMPs) is analyzed and compared to heat and particle fluxes. For TEXTOR, a strong reduction of $p_e$ and an increase of target fluxes is measured when the inward penetration of the vacuum stochastic layer is maximized. For DIII-D, target heat and particle fluxes follow the 3-D perturbed separatrix due to a stochastic layer of open, perturbed field lines with a minimum penetration to $\Psi_N=0.95$ in normalized poloidal flux. Experimental measurements show the toroidally spiraling structure of perturbed target plate separatrix lobes depend on $q_{95}$ and that there is a clear $q_{95}$ dependent reduction of $n_e(\Psi_N)$, $T_e(\Psi_N)$ and $p_e(\Psi_N)$ which follows the toroidal phase of the RMP field. The measurements provide evidence for pitch resonant edge stochastisation as a mechanism leading to peeling-ballooning stabilized RMP H-modes at DIII-D. [Preview Abstract] |
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JP6.00070: Spectral Effects on Plasma Performance in ITER Similar DIII-D RMP H-modes T.E. Evans, N.H. Brooks, M.J. Schaffer, E.A. Unterberg, M.E. Fenstermacher, C.J. Lasnier, H. Frerichs, O. Schmitz, B. Unterberg, M.W. Jakubowski, S. Mordijck, R.A. Moyer, J.G. Watkins A significant expansion of the resonant magnetic perturbation (RMP) H-mode operating space has been obtained by combining perturbations from the DIII-D I- and C-coil sets. Using the combined $n=3$ and $n=1$ perturbations of these two coil sets, ELM suppression has been obtained over an extended range of shapes, collisionalities, NBI power and torque levels, toroidal rotation levels, densities and edge safety factor profiles including those relevant to ITER. Combined with new RMP spectral analysis and modeling techniques, this capability has resulted in an improved understanding of RMP physics and provides a stronger basis with which to predict how RMP ELM control will scale to ITER conditions. Experimental data and modeling results will be presented that demonstrate how combined $n=3$ and $n=1$ perturbations of the RMP coils can be used to expand the ELM suppression operating space in ITER similar DIII-D plasmas. [Preview Abstract] |
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JP6.00071: Global Particle Balances and Wall Recycling Changes During the RMP Induced Density Pump-out in DIII-D H-mode Plasmas E.A. Unterberg, N.H. Brooks, T.E. Evans, M.E. Fenstermacher, R. Maingi, R.A. Moyer Resonant magnetic perturbations (RMPs) have been shown to successfully suppress ELMs in DIII-D. A drop in electron density up to 30\% during application of the RMP field usually precedes the suppression and/or mitigation of ELMs at high and low edge electron collisionality ($\nu_e^*$). Consequently, an understanding of the density response to the RMP is a critical issue for achieving ELM suppression in ITER. Coincident with this drop in the line-integrated and pedestal densities, the pedestal $T_e$ increases modestly and $T_i$ increases as much as 50\%-70\% depending on the pre-RMP discharge conditions, which contradicts known stochastic transport theory. Global particle balances show that the pump-out magnitude is directly correlated to the particle wall inventory before the RMP. It is observed that the magnitude of the pump-out trends directly with increasing $\beta_N$ and inversely with pedestal collisionality. Recent experimental results where wall conditions were systematically varied will also be presented. [Preview Abstract] |
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JP6.00072: Target Plate Particle and Power Flux During ELM Suppression Experiments on DIII-D J.G. Watkins, T.E. Evans, C.J. Murphy, M.J. Schaffer, M. Jakubowski, O. Schmitz, C.J. Lasnier Radial profiles of target plate plasma conditions measured with Langmuir probes during ELM suppression using $n=3$ resonant magnetic perturbations [1] have been compared with IRTV heat flux profiles and ```fast'' thermocouples embedded in the divertor tiles. During ELM suppression, $J_{sat}$ and $T_e$ increase and the $J_{sat}$ profile broadens compared to profiles measured between ELMs. An observed three-peak structure appears during ELM suppression and agrees with the spacing and $q_{95}$ dependence predicted by the TRIP3D code. The heat flux calculated from Langmuir probe data (using sheath factor =10 to agree with IRTV) is observed to increase $>$2$\times$ during ELM suppression compared to between ELMs before the RMP is turned on. Global power and particle accounting as well as sheath power transmission at the target plate will be examined.\par \vskip6pt \noindent [1] T.E. Evans, et al., Phys.\ Rev.\ Lett.\ {\bf 92} (2004) 235003. [Preview Abstract] |
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JP6.00073: 3D Simulations of Edge Transport for RMP Experiments at DIII-D H. Frerichs, O. Schmitz, D. Reiter, T.E. Evans, Y. Feng, M.E. Fenstermacher Resonant magnetic perturbations (RMPs) are a candidate for ELM control in ITER. Modeling of the perturbed magnetic field structure during RMPs in the vacuum approach suggests the formation of an open chaotic edge layer, leading to a complex 3D magnetic field. To investigate the resulting impact on plasma and neutral gas transport, the 3D edge transport code EMC3-EIRENE has been extended to poloidal divertor geometry. For this, a new grid topology, i.e., grid cells with non-trivial neighbor relations, has been introduced to the code. This facilitates simulations of regions with poloidally asymmetric radial extensions (such as the edge layer in poloidal diverted tokamaks) and allows, for the first time, 3D simulations of ELM control experiments at DIII-D using a self-consistent treatment of the particle and energy transport. These simulations predict a significant 3D modulation of electron density and temperature by the perturbed magnetic topology. Experimental observations show clear splitting of target particle flux. Modeling results predict this splitting only for small anomalous perpendicular transport coefficients. [Preview Abstract] |
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JP6.00074: Comparisons of ELMing and RMP H-mode Transport Results from a 2D Fluid Code and Theoretical Models S. Mordijck, R.A. Moyer, W.M. Stacey, T.E. Evans Changes in the simulated radial transport from an ELMing to an RMP H-mode are compared. The radial transport coefficients have been calculated with B2-EIRENE (a 2D fluid code coupled to a Monte-Carlo neutral code). The radial particle diffusion increases by a factor 2 between $\Psi_N$ of 0.9 and 1 during the ELM suppressed RMP H-mode compared to the ELMing H-mode. The electron heat conduction does not change and differences in the electron temperature profile can be explained by increased convection. At the same time, the ion heat conduction increase over the entire computational domain of the simulation, outside $\Psi_N = 0.8$ in the RMP H-mode. To better understand the simulated transport changes, differences in the modeled transport coefficients are compared to differences in predictions from theoretical models for the ELMing and RMP H-mode experiments. We introduce quasilinear magnetic diffusion (QMD) coefficients from field-errors (FE) and FE correction coils (FECC) in the ELMing H-mode transport and compare these to the QMD results in RMP H-mode with FE, FECC and edge-localized $n=3$ RMPs from an internal non-axisymmetric coil. [Preview Abstract] |
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JP6.00075: Effect of Resonant Magnetic Perturbations (RMPs) on Local Density Decay During Pellet Injection in DIII-D L. Zeng, T.L. Rhodes, W.A. Peebles, G. Wang, L. Schmitz, E.J. Doyle, L.R. Baylor, T.C. Jernigan, T.E. Evans By using a high temporal (25 microseconds) and spatial ($\sim$0.5~cm) resolution profile reflectometer system, the local density evolution due to deuterium pellet injection has been investigated in \mbox{DIII-D}. It is observed that either no ELMs are triggered, or small ELMs are triggered by fueling pellets during ELM suppressed RMP operation. However, $\sim$150~ms after the pellet injection the plasma returns to ELM-free status. The density evolution shows local density decay time is a decreasing function of radius, with the fastest decay at around normalized $\psi \sim\,$0.92 which is within the magnetic island overlap regime. By contrast, pellet induced local density decay time is almost independent of radius for non-RMP ELMing plasmas, with the decay time 2 times longer than with RMPs. The results suggest RMPs enhance particle transport in plasmas. The dependence of local decay time on the magnitude of RMPs, associated density fluctuations, and $E_r$ behavior are further investigated. [Preview Abstract] |
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JP6.00076: ELM Control Coils for ITER M.J. Schaffer, T.E. Evans, A.M. Garofalo, M.E. Fenstermacher, M. Becoulet, E. Nardon, R.J. Hawryluk, J.E. Menard, J-K Park, S.A. Sabbagh, M. Aldan Fast Type-I ELM heat pulses in ITER are predicted by empirical scaling to severely limit divertor target lifetime. Type-I ELM suppression by weak ($dB/B_o \sim 3\times 10^{-4}$) non-axisymmetric, resonant magnetic perturbations (RMP) was demonstrated definitively on DIII-D. Empirical correlations were developed, but the physical processes are still incompletely understood. The ITER design originally had no place for RMP coils. We proposed, analyzed, and evaluated many conceptual coil sets for their: ability to make suitable resonant field spectra without excessive collateral magnetic braking of plasma rotation; engineering feasibility; and remote maintainability. The presently favored concept can work over the full range of ITER $q$, and the non-resonant torque can be optimized over a wide range. This collaborative work yielded advances on braking and on plasma screening and amplification of resonant and non-resonant non-axisymmetric perturbations. [Preview Abstract] |
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JP6.00077: ELMs Triggered From Deuterium Pellets Injected into DIII-D L.R. Baylor, T.C. Jernigan, N. Commaux, S.K. Combs, T.E. Evans, P.B. Parks, M.E. Fenstermacher, R.A. Moyer, J.H. Yu Fueling pellets have been injected into DIII-D plasmas from 5 different locations and under different plasma H-mode conditions. ELMs have been triggered from pellets injected from all locations and under all the H-mode scenarios. Pellets injected into plasmas with ELMs suppressed by a resonant magnetic perturbation have also been observed to trigger one or more small ELM like events. Experimental details of the pellet triggering of ELMs show that they are triggered before the fueling pellets reach the top of the H-mode pedestal, implying that small shallow penetrating pellets are sufficient to trigger ELMs. To test this idea a pellet dropper has been installed on DIII-D for ELM pacing studies. Initial results from 1mm pellets dropped at 10 m/s into the edge plasma show a strong toroidal deflection. Details of the pellet penetration results from the dropper will be presented and plans to improve the penetration and resulting ELM triggering will be discussed. [Preview Abstract] |
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JP6.00078: Influence of the gradB-drift on the Pellet Particle Deposition in DIII-D and Comparison with Tore Supra N. Commaux, L.R. Baylor, T.C. Jernigan, B. P\'egouri\'e, A. G\'eraud, P.B. Parks Pellet injection is planned to be the main fueling method on ITER. The injection of pellets from the high field side of the plasma is anticipated to benefit from the curvature and gradB-drift effect to deposit the particles close to the center. Experimental data on DIII-D show that this drift effect may be influenced by the $q$ profile. Integer and half-integer $q$ surfaces could damp the drift making them privileged deposition areas in the plasma. This effect is shown by the correlation between the position of the maximum of the deposition profile and the position of integer $q$ surfaces like $q=2$ or $q=3$ for many pellets injected in DIII-D. This can be related to similar results on the French tokamak Tore Supra for low field side injections. The influence of the $q$ profile could be through a parallel current that damps the vertical electric field associated with the drift. The short connection length of the integer $q$ surfaces would increase the efficiency of this effect thus stopping the drift movement in these areas. [Preview Abstract] |
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JP6.00079: Edge MHD Stability of Co-injected QH-mode Discharges in DIII-D T.H. Osborne, K.H. Burrell, M.S. Chu, P.B. Snyder, W.P. West In this paper we compare the ideal MHD stability of the H-mode edge transport barrier region in QH-mode discharges with neutral beam injection oriented toroidally in the same direction as the plasma current (Co-NBI) to previous results with neutral beam injection counter to the plasma current (Counter-NBI). QH-mode had until recently only been obtained in discharges with a large fraction of neutral beam heating in the counter current direction under conditions where low toroidal number peeling modes are the dominate instability (low plasma density and/or strong cross-sectional shaping). The high rotational shear in the edge of Counter-NBI discharges, which is thought to provide the saturation mechanism for the instability [1], was also present in the Co-NBI QH-mode discharges.\par \vskip6pt \noindent [1] P.B. Snyder, et al., 2006 {\em Proc.\ 21st Intl Conf.\ on Plasma Physics and Controlled Nucl.\ Fusion} (Chengdu) (IAEA Vienna) Paper TH/4-1Ra. [Preview Abstract] |
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JP6.00080: Test of a Pedestal Height Model in DIII-D R.J. Groebner, P.B. Snyder, A.W. Leonard, T.H. Osborne A new model of pedestal height has been tested in the DIII-D tokamak. This model, called EPED1, was used to design an experiment and to predict the pedestal height of total pressure as a function of machine control parameters. These parameters included plasma current, toroidal magnetic field, plasma shape and total plasma beta. The model successfully predicted the pressure pedestal height over more than an order of magnitude variation. The EPED1 model is based on the peeling-ballooning MHD theory, which has previously been shown to provide good predictions of the pedestal pressure when the measured pressure pedestal width was used an input to the model. The EPED1 model uses a simple scaling for the pedestal width in normalized poloidal flux, $p_{wid}=0.08 \sqrt{\beta_{pol_{ped}}}$. The factor of 0.08 is taken from a large database of DIII-D pedestal measurements. If this scaling works well for other machines, the EPED1 model could be used to make predictions of pedestal height in new machines, such as ITER. [Preview Abstract] |
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JP6.00081: Pedestal Fueling from Recycling in DIII-D A.W. Leonard, M. Groth, G.D. Porter, M.E. Rensink Fueling of the pedestal in DIII-D is found to be dominated by inboard divertor recycling by assessing a combination of experimental measurements, interpretive modeling and kinetic neutral analysis. The pedestal ionization rate from this analysis can match the inferred outward ion flux across the separatrix only for high density, detached inboard divertor conditions. The 2D profile of surface recycling in the divertor and main chamber between ELMs in H-mode was previously determined in DIII-D [1] from surface mounted Langmuir probes and a plasma configuration where toroidally symmetric recycling was dominant. The measured profile of recycling neutrals is launched by the DEGAS2 code into a 2D background plasma profile reconstructed by the UEDGE fluid model and constrained to match the upstream temperature and density profiles. Divertor plasmas of varying density and temperature are constructed to test sensitivity to uncertainty in the divertor plasma conditions.\par \vskip6pt \noindent [1] A.W.\ Leonard, et al., J.~Nucl.\ Mater.\ {\bf 363-365}, 1066 (2007).\par [Preview Abstract] |
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JP6.00082: Experimental Investigation of ITER Startup and Rampdown Scenarios in the DIII-D Tokamak G.L. Jackson, A.W. Hyatt, J.R. Ferron, T.C. Luce, D.A. Humphreys, T.W. Petrie, T.A. Casper ITER scenario studies have focused on the current flattop phase, but reaching current flattop and successful discharge termination (i.e. a ``soft landing") must also be considered. Experiments in DIII-D have simulated ITER discharges including low inductive electric field ($E_\phi \leq0.3\,$V/m), startup limiting on the low field side (LFS), and $\ell_i$ control mostly for vertical stability control. ITER-like LFS startup has been achieved in two scenarios: constant $q_{95}$ (small bore) and a larger volume diverting earlier in time to reduce heat flux to the outer wall (large bore). With a large bore startup, both hybrid and ITER baseline H-mode discharges have been obtained during the flattop phase. We will present the effects of variations in density, auxiliary power, and current ramp rate on $\ell_i$. Low voltage startup, $V_{loop} \geq2.2\,$V (0.21~V/m) with EC assist will be discussed and initial results simulating the ITER rampdown phase will also be presented. [Preview Abstract] |
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JP6.00083: Control of the Current Profile Evolution During the Ramp-Up Phase at DIII-D Y. Ou, E. Schuster, J.R. Ferron, T.C. Luce, M.L. Walker, D.A. Humphreys, T.A. Casper, W.H. Meyer Setting up a suitable current profile has been demonstrated to be a key condition for advanced scenarios with improved confinement and possible steady-state operation. Experiments at DIII-D focus on creating the desired $q$ profile during the plasma current ramp-up and early flattop phases with the aim of maintaining this profile during the subsequent phases of the discharge. Active feedback control of the $q$ profile evolution at DIII-D has already been demonstrated [1], and an open-loop control scheme has been proposed [2] based on a simplified control-oriented dynamic model [3]. The use of Corsica for both control testing and design is reported, and results of open-loop current profile control experiments are presented.\par \vskip6pt \noindent [1] J.R.\ Ferron, et al., Nucl.\ Fusion {\bf 46} (2006) L13.\hfil\break [2] Y.~Ou, et al., {\em Proc. Am. Control Conf.}, New York (2007).\hfil\break [3] Y.~Ou, et al., Fusion Eng.\ \& Design {\bf 82} (2007) 1153. [Preview Abstract] |
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JP6.00084: Current Profile Evolution Modeling via Subspace Identification Algorithms C. Xu, Y. Ou, E. Schuster, J.R. Ferron, T.C. Luce, M.L. Walker, D.A. Humphreys, T.A. Casper, W.H. Meyer Feedback control in advanced tokamaks requires suitable mathematical models. First-principle modeling is sometimes limited by the lack of theoretical or experimental knowledge of some of the plasma properties. System identification arises as an alternative approach to first-principle modeling, and deals with the problem of generating dynamic models from measured input-output experimental data. We report progress on two identification problems; a bilinear identification (BiLinID) problem for the current ramp-up phase, and a linear identification (LinID) problem for the current flattop phase. Subspace identification, a newly emerging branch in system identification, is used in this work to generate databased models. The subspace identification method provides a state-space representation of the system, enabbling computational simplicity and effectiveness for multivariable systems. [Preview Abstract] |
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JP6.00085: Progress on Model-Based Shape Control for DIII-D Experimental Operations M.L. Walker, D.A. Humphreys, A.W. Hyatt, J.A. Leuer, B.G. Penaflor We report on implementation and experimental use of model-based multivariable shape controllers intended for routine use in DIII-D operation. Manually-tuned shape controllers perform very well for many shapes, but can require substantial experimental time to tune, and can fail to achieve desired operational control performance. Objectives of the model-based control design techniques include reducing or eliminating experimental time for tuning, improving overall quality of control, and preventing loss of plasma discharges due to exceeding coil current limits. Over the past few years, multiple components of the control needed to address these objectives have been developed and tested experimentally. These components are now being integrated and generalized for use in routine operation. Experiments to date show that model-based techniques can produce controllers that significantly improve the quality of steady-state control for certain plasma shapes, although with consequences for other performance characteristics such as disturbance rejection. [Preview Abstract] |
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JP6.00086: Enhancing Physics Operations and Increasing Physics Productivity at DIII-D A.W. Hyatt, D.A. Humphreys, R.D. Johnson, M.L. Walker, J.R. Ferron, J.T. Scoville, M.R. Wade Having begun operation in 1986, DIII-D is a mature tokamak with highly effective physics operations procedures to plan and execute discharges, monitor machine status, and train personnel. A desire to maximize physics productivity per discharge has driven an ongoing process to enhance physics operations. Developments in modeling and simulation software and data-driven improved fault monitoring allow continuing improvement. Productivity enhancements include use of control design and simulation tools to reduce machine time needed to develop new algorithms, ongoing training programs for physics operators, improved physics and control-related trouble reporting, and deployment of new status reporting displays in the DIII-D Control Room. Use of the DIII-D Plasma Control System at other devices such as NSTX, EAST, and KSTAR have provided solutions for use at DIII-D as well. Results of this ongoing process and lessons learned for next generation devices such as ITER will be discussed. [Preview Abstract] |
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JP6.00087: The Stabilizing Effect of Flow Shear on m/n=3/2 Magnetic Island Width in DIII-D R.J. La Haye, R.J. Buttery It is found that flow shear has a stabilizing effect on $m/n=3/2$ neoclassical tearing mode (NTM) islands through a more negative classical tearing stability index $\Delta^\prime$ in the DIII-D [1] tokamak. The heating neutral beams are mixed between co- and counter-directions to vary the torque on the plasma and thus the plasma flow (rotation) and flow shear. This is done ``shot to shot" in the presence of a ``saturated" $m/n=3/2$ NTM while slowly raising the plasma. A heuristic model for the stabilizing effect of flow shear on $\Delta^\prime$ is shown to explain how flow shear acts to reduce NTM island size and obviate the effect of higher beta and concomitant destabilizing helically perturbed bootstrap current.\par \vskip6pt \noindent [1] J.L. Luxon, Nucl.\ Fusion {\bf 42}, 614 (2002). [Preview Abstract] |
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JP6.00088: Energetic Particle Instabilities Simulated in GYRO E.M. Bass, M.S. Chu, R.E. Waltz The Eulerian gyrokinetic code GYRO [1] has been used to study instabilities driven by a sparse, hot species (such as fusion-produced $\alpha$-particles) superimposed on the equilibrium profile in different geometries. The energetic particles are distributed according to a high temperature Maxwellian. Unstable Toroidal Alfv\'en Eigenmodes (TAEs) have been identified in gaps in the Alfv\'en continuum at the degenerate frequency of two toroidally-coupled modes with the same toroidal mode number $n$ and adjacent poloidal mode numbers $m$. Frequency and growth rate have been mapped out as functions of $n$, background plasma pressure gradients (starting from zero), safety factor, magnetic shear, and density gradient of the hot species in flux-tube geometry. Global geometry simulations using measured profiles from DIII-D are compared to TAEs and other Alfv\'en modes observed in that machine [2]. To monitor the gap Alfv\'en modes (and possibly subdominant modes outside the gap) in the presence of background plasma density gradients (and possibly dominant ITG/TEM modes), GYRO will be modified to find frequency and growth rate of sub-dominant modes.\par \vskip6pt \noindent [1]~J.~Candy and R.E.\ Waltz, J.~Comput.\ Phys.\ {\bf 186}, 545 (2003).\hfil\break [2]~M.A.\ Van Zeeland, et al., Nucl.\ Fusion {\bf 46}, S880 (2006).\par [Preview Abstract] |
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JP6.00089: Burst of Fast Ion Loss in DIII-D Quiescent H-mode Plasmas Y.B. Zhu, W.W. Heidbrink, W.P. West, K.H. Burrell High frequency bursts are observed in the fast ion loss collectors during DIII-D counter-injection quiescent H-mode plasmas. The typical frequency lies in hundreds kHz range, which is much higher than the Edge Harmonic Oscillation (EHO). The occurrence of the burst is usually correlated with the presence of the EHO but not always. Comparative studies show that the burst is more sensitive to the perpendicular than tangential injected beams. The amplitude of the bursting can be actively controlled by several factors, such as the plasma outer gap to the vessel midplane, current ramping in internal error field correction coils, and electron cyclotron resonance heating. Co-injection quiescent H-mode does not show any such kind of burst. Neutron flux and fast ion deuterium alpha (FIDA) measurements data will also be presented. [Preview Abstract] |
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JP6.00090: Beam Particle distribution Modification by low amplitude Modes Roscoe White, Nikolai Gorelenkov, William Heidbrink, Michael Van Zeeland Modification of a high energy beam profile by a spectrum of low amplitude modes is investigated. The effects of a time dependent q profile and frequency chirping of the modes are included. It is found that a few modes with amplitudes of delta B/B = 2 x 10$^{-4}$ can have a significant effect on the beam distribution function provided that the spectrum includes modes that produce resonances in the particle distribution and that some modes chirp, ie have time dependent frequencies causing resonances to sweep through the plasma. The importance of the chirping is that as resonances move through the plasma they interact with each other and with particles of different location, energy and pitch. It is known that many modes are present in the experiments, to simulate the experimental results it is necessary to select those modes that through resonance are effective in modifying the distribution. [Preview Abstract] |
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JP6.00091: Simulation of RSAE/EAE and TAE activity in a reversed shear DIII-D case Donald Spong, Michael Van Zeeland The energetic particle gyrofuild model TAEFL has been applied to a DIII-D case where RSAE, TAE and EAE activity was present. This is a useful analysis tool because: (1) it retains the primary non-perturbative affect of fast ions on Alv\'{e}nic mode structures, i.e., the coupling of MHD cosine and sine parities by fast ion diamagnetic flows [which in the phi = 0 plane causes up-down asymmetries], (2) it is applicable to non-circular shaped tokamak equilibria, (3) it focuses on only the most unstable modes, and (4) an efficient implicit stepping algorithm has been developed, allowing rapid scans of linear growth rates and mode structures for cases with significant poloidal coupling. Analysis of the above DIII-D case has identified EAE, RSAE and TAE modes at sub-Alfv\'{e}nic beam velocities (down to $\sim $0.28 times the Alfv\'{e}n velocity). The dominant AE mode is a sensitive function of the q-profile and fast ion parameters. Also, the non-perturbative nature of this model yields mode structures that are consistent with the experimental coherence measurements. [Preview Abstract] |
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JP6.00092: New Fast-Ion D$_{\alpha}$ (FIDA) Capabilities C. Muscatello, W.W. Heidbrink, D. Liu, E. Ruskov, K.H. Burrell, D.A. Taussig, M.A. Van Zeeland FIDA is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha (D$_{\alpha}$) light from energetic ions to infer properties of the fast ions. Validation of the first-generation version of the diagnostic (1G) was obtained independently by several diagnostics and a FIDA simulation code. This code has been generalized to easily treat new installations and is freely available for use elsewhere; neutral particle analyzer signals are also predicted. Unlike the 1G instrument whose measurement extent includes the blue and red-shifted wing, the new instrument (2G) will measure only the blue end resulting from co-circulating ions. The views for the 2G system have a toroidal component which, in conjunction with those of 1G, will extend the coverage of the fast-ion velocity space. In addition to having higher time-resolution, the new instrument also includes another level of background-signal monitoring. Along with tracking temporal changes in the background signal as with the old instrument, 2G FIDA will also have the capability of monitoring the signal from a toroidally displaced reference view. [Preview Abstract] |
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JP6.00093: Beam-Ion Confinement for Different Injection Angles W.W. Heidbrink, C.C. Petty, M.A. Van Zeeland, M. Murakami, J.M. Park, J.H. Yu DIII-D is equipped with neutral beam sources that inject in four different directions; in addition, the plasma can be shifted up or down to compare off-axis with on-axis injection. Fast-ion data for eight different conditions have been obtained: co/counter, near-tangential/near-perpendicular, on-axis/off-axis. Neutron measurements during short beam pulses assess prompt and delayed losses under low-power conditions. As expected, co-injection has fewer prompt losses than counter, tangential than perpendicular, and on-axis than off-axis; the differences are greater at low current than at higher current. Fast-ion D$_\alpha$ (FIDA) measurements diagnose the confinement at higher power. The inferred fast-ion density is higher during co-injection than during counter-injection, although the spatial profile is similar. Comparisons of two-dimensional FIDA images with simulations based upon classical fast-ion behavior show excellent agreement in the on-axis case. The inferred fast-ion diffusion during off-axis injection will be presented. [Preview Abstract] |
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JP6.00094: Validation of Neutral Beam Physics on DIII-D C.C. Petty, J.S. deGrassie, A.W. Hyatt, A.W. Leonard, P.A. Politzer, R. Prater, M.A. Van Zeeland, W.W. Heidbrink, M. Murakami, J.M. Park, W.M. Solomon Experiments on the DIII-D tokamak have utilized the co/counter injection capability and recent diagnostic upgrades to study neutral beam physics in greater detail than previously possible. Particular attention is being paid to validating the neutral beam current drive (NBCD) profile owing to its importance in Advanced Tokamak scenarios. To avoid MHD instabilities and minimize the plasma density, these experiments were done in low-beta L-mode discharges before the onset of sawteeth. Primarily co- and counter-injection were compared to balanced-injection, with the noninductive current profile determined from the poloidal flux evolution measured by motional Stark effect (MSE) polarimetry. In addition, the fast ion pressure profile was determined from the shift in the plasma flux surfaces measured by the MSE diagnostic. The plasma current was varied between 0.6-1.2 MA to study the effect of fast ion transport. These experimental measurements will be compared to TRANSP calculations. [Preview Abstract] |
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JP6.00095: Testing Magnetic Diffusion in the DIII-D Tokamak S. Sears, C.C. Petty, C.B. Forest, B.W. Rice Magnetic diffusion governs the evolution of the current density profile in tokamak discharges. Accurate knowledge of this diffusion is needed to predict and control the current density profile in Advanced Tokamak scenarios. A novel experiment to study magnetic diffusion in the DIII-D tokamak modulated the edge loop voltage at 2-8~Hz and measured the propagation of the poloidal magnetic flux through the plasma using motional Stark effect polarimetry. To interpret the measurements, a simulation code is being developed to numerically solve the perturbed poloidal magnetic flux diffusion equation in real geometries and with real plasma profiles. Complicating factors such as (unintended) oscillations in the plasma boundary or conductivity profile are being included in this analysis. Comparisons between the simulation code and experimental data will be presented. In plasmas free of MHD, this serves as a rigorous test of neoclassical conductivity; while in plasmas with tearing modes, the anomalous consumption of flux will be examined. [Preview Abstract] |
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JP6.00096: Synergy in Two-Frequency Fast Wave Cyclotron Harmonic Absorption in DIII-D R.I. Pinsker, M. Choi, M. Porkolab, W.W. Heidbrink, Y.B. Zhu, F.W. Baity, J.C. Hosea Fast waves (FWs) at 60~MHz and at 90~MHz are coupled to DIII-D discharges for central heating and current drive at net FW power levels up to 3.5~MW. The primary absorption mechanism is intended to be direct electron damping in the plasma core. In 2~T discharges with fast deuteron populations from neutral beam injection, 4th and 6th deuterium cyclotron harmonic absorption on the fast ions competes with direct electron damping. Previous experiments have shown that the 6th harmonic absorption of the 90~MHz FWs is weaker than the 4th harmonic absorption of 60~MHz FWs, in agreement with a model that includes unspecified edge losses. Recent experiments have shown that if the fast deuterons are accelerated by absorption of 60~MHz (4th harmonic) FWs, adding 90~MHz power (6th harmonic) can increase the fusion neutron rate by a larger increment than is obtained with 90~MHz power alone. Details of this synergy between 4th and 6th harmonic absorption are presented. [Preview Abstract] |
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JP6.00097: Ion Finite Drift Orbit Effect in ICRH Modeling Using Quasi-Linear Full Wave and Particle M. Choi, V.S. Chan, L.A. Berry, E.F. Jaeger The simulation package of 2-D linear full wave code (AORSA) and 3-D bounce averaged Fokker-Planck (F-P) code (CQL3D), have been extensively used to interpret present-day ICRF wave heating experiments in tokamaks and to predict future burning plasma experiments such as ITER. Assumed in this approach is zero orbit width and constant wave-particle interaction time. To evaluate the limitations of these assumptions, a 5-D Monte-Carlo Hamiltonian ion guiding center code, ORBIT-RF, has been developed, that includes finite orbit effect and a more accurate treatment of the wave-particle interaction time that are not currently implemented in AORSA and CQL3D. Extensive benchmarking activity is carried out to model the fundamental to high harmonic ICRF wave heating in the Alcator C-Mod and DIII-D tokamaks. Comparisons will be presented and discussed. Specifically, the results indicate that ion finite drift orbit effect becomes more significant for the interpretation of ICRF wave-fast ion interactions at high harmonics in DIII-D tokamak. [Preview Abstract] |
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JP6.00098: HBT-EP AND OTHER TOKAMAKS |
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JP6.00099: HBT-EP External Kink Mode Control Research Program: Recent Progress and Future Plans G.A. Navratil, B. Debono, J.M. Hanson, R. James, J.P. Levesque, M.E. Mauel, D.A. Maurer, T.S. Pedersen, D. Shiraki HBT-EP MHD mode control research is studying advanced Kalman filter control algorithms, ITER relevant internal modular feedback control coil configurations and their impact on kink mode rigidity, and the effects of edge neutral damping as a dissipation mechanism on the kink mode. HBT-EP incorporates a segmented adjustable conducting wall and 40 internal modular feedback control coils driven by a high-speed MIMO digital control system for external kink mode control. Primary research thrusts are to test advanced feedback control algorithms to increase feedback noise immunity, and the study of the physics of kink rotation stabilization by controlled variation of critical parameters such as dissipation and mode rotation. Recent results include measurement of the radial magnetic eigenmode structure and density and temperature perturbations of the external kink, and observation of D$_{\alpha }$ profiles and fluctuations during MHD spectroscopy experiments to quantify edge neutral dissipation. Enhancements of the VALEN modeling code, along with the design and construction of a new passive stabilizing wall and feedback coil system to study control coil modularity and coverage issues and their impact on kink mode rigidity will also be presented. *Supported by U.S. DOE Grant DE-FG02-86ER53222. [Preview Abstract] |
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JP6.00100: ExB Rotation of Magnetohydrodynamic Modes Induced by a Biased Electrode D.A. Maurer, B. Debono, J.M. Hanson, R. James, J.P. Levesque, M.E. Mauel, G.A. Navratil, T.S. Pedersen, D. Shiraki The effect of plasma rotation on the behavior of MHD modes is a topic of importance for both resistive wall and tearing mode stability and their effect on the performance of present and future magnetic fusion devices. On HBT-EP, a biased molybdenum electrode inserted into the edge plasma is used to change the intrinsic ExB rotation of MHD activity of both kink and tearing mode fluctuations. It has been possible to slow MHD mode rotation to near zero rotation frequency using this technique. For large applied bias voltage, MHD is observed to accelerate in the direction opposite to the naturally occurring mode rotation with frequencies up to two or three times the natural rotation rate. Measurements will be presented using a newly installed Triple/Mach probe array, 16 chord D$_{\alpha }$ emission detector, and high density 20 element Hall magnetic field sensor array to characterize the plasma and MHD fluctuations during bias probe induced mode rotation changes. *Supported by U.S. DOE Grant DE-FG02-86ER53222 [Preview Abstract] |
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JP6.00101: Soft X-ray Analysis of HBT-EP Plasmas J.P. Levesque, B. Debono, J.M. Hanson, R. James, M.E. Mauel, D.A. Maurer, G.A. Navratil, T.S. Pedersen, D. Shiraki Measuring soft x-ray emission is a useful and non-invasive diagnostic for studying internal plasma properties and MHD mode structure and dynamics. The HBT-EP tokamak is equipped with two multi-chord soft x-ray systems to study internal profile and fluctuation behavior. A 32-channel soft x-ray tomography system composed of discrete diodes with a thin film filter of Titanium, Zirconium, and Carbon coated directly on to the diode face is used to reconstruct 2-D plasma emissivity profiles at a single toroidal location. Resolution of the system is sufficient to measure the structure and evolution of edge (m,n) = (2,1) tearing modes. In addition, a 16-channel ``fan-array'' assembly based upon a linear diode array and a 400 nanometer Beryllium filter measures emission predominantly from the plasma core. Fan-array measurements of internal sawtooth and (m,n)=(1,1) mode activity will be presented. A planned upgrade to the fan-array for measuring temperature profiles using a multiple set of filters and additional diode arrays will be discussed. [Preview Abstract] |
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JP6.00102: Edge Kink Mode Fluctuation Measurements on HBT-EP D. Shiraki, B. Debono, J.M. Hanson, R. James, J.P. Levesque, M.E. Mauel, D.A. Maurer, G.A. Navratil, T.S. Pedersen The edge plasma region of the Columbia HBT-EP tokamak is well instrumented to study perturbations induced by MHD activity. Internal fluctuation diagnostics with good radial spatial resolution include a 20 element Hall probe array, 16-chord D$_{\alpha }$ emission detector, and a newly designed 4 spatial point combined triple probe/Mach probe array. Also available is an extensive set of external magnetic pickup probes for magnetic mode structure analysis. The design of the Mach probe array allows measurement of the plasma flow in two orthogonal directions. The initial design of the triple/Mach probe array is discussed and plans presented for an improved future design. The amplitude, phase, and frequency of the external kink mode magnetic fluctuation are calculated as a function of time by a Hilbert transform method. The phase relationships between the kink induced temperature and density perturbations and the mode magnetic perturbation have been measured. Triple/Mach probe measurements also allow reconstruction of the local ExB, ion fluid, and the electron diamagnetic flow frames of reference. External magnetics will be used to quantify the kink mode rotation rate and a detailed study of its relation to the ExB, ion, and electron fluid flow frames will be presented. *Supported by U.S. DOE Grant DE-FG02-86ER53222 [Preview Abstract] |
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JP6.00103: Understanding RWM Dynamics using a D$_{a}$ Detector R. James, K. Becker, B. Debono, J. Hanson, J. Levesque, D.A. Maurer, M.E. Mauel, G.A. Navratil, T.S. Pedersen, D. Shiraki The dissipation mechanism responsible for rotational stabilization of the resistive wall kink mode (RWM) continues to be an object of intense research.~On HBT-EP, there is evidence that edge neutral damping is a dissipation mechanism affecting tearing mode behavior [1].~Neutral damping effects on RWMs could also be responsible for dissipation observed during HBT-EP MHD spectroscopy experiments. To quantify these observed effects, we have installed a 20-channel linear photo-detector array to measure D$_{\alpha }$ emission and fluctuations. Qualitative observations of neutral effects on the RWM plus use of the detector and kinetic transport model [2] to measure kink mode radial structure will be reported with a summary of efforts to quantify the contribution of neutral damping on RWM rotational stabilization. [1] E. D. Taylor, \textit{et al}., \textit{Phys. Plasmas} \textbf{9}, 3938 (2002), [2] B. LaBombard, MIT PSFC RR-00-9, (2000). [Preview Abstract] |
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JP6.00104: Real-Time Plasma Rotation Diagnostic for Measuring Small Doppler Shifts on the HBT-EP Tokamak B. DeBono, J.M. Hanson, R. James, D.A. Maurer, M.E. Mauel, G.A. Navratil, T.S. Pedersen, D. Shiraki, J. Levesque, S.F. Paul An optical, fast time-scale toroidal velocity measurement has been developed for use on the HBT-EP tokamak. A unique aspect of this diagnostic's measurement technique is that the Doppler shift is determined from the ratio of the light intensity from two detectors rather than by resolving the emission line with a traditional spectrometer. This is accomplished using an inexpensive, high-throughput measurement of impurity line emission with interference filters as the spectral device. One detector views the plasma through an interference filter whose passband has a negative slope, with a second detector viewing the plasma through a positive-slope filter. The signal ratio varies as the emission line is Doppler shifted across the filter passbands. The measurement technique is not sensitive to changes in plasma emission levels. For interference filters with a linear passband the shifted He-II wavelength can be reduced to a simple function of the signal ratio, the channel's relative responsivity, and the two filters transmission curves. A positively biased probe was inserted into HBTEP's edge plasma and used to induce a toroidally directed E x B$_{p}$ torque on the plasma. Edge plasma toroidal velocity measurements will be reported using a 10{\%} He impurity seed in standard D discharges. [Preview Abstract] |
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JP6.00105: External Kink Mode Feedback: Analysis and Results Jeremy Hanson, Bryan DeBono, Royce James, Jefferey Levesque, Michael Mauel, David Maurer, Gerald Navratil, Thomas Pedersen, Daisuke Shiraki The details of the implementation of the HBT-EP Kalman filtering feedback system will be presented in this poster. Feedback control of external kink modes on HBT-EP is accomplished using arrays of poloidal sensor coils, and small, localized, radial control coils. The control algorithm uses spatial and temporal filtering in series with a Kalman filter that isolates the $n=1$ mode from background noise. The Kalman filter compares measurements of the kink mode with an internal model to make an optimal estimate for the mode's amplitude and phase. Supplementary diagnostics include a poloidal array of Mirnov coils (separate from those used in feedback), radial Hall and triple probe arrays, and a multi-tip Mach probe. Digital, low-latency field programmable gate arrays (FPGAs) are used as controllers. Two singular value decomposition (SVD) based techniques are used to measure the effectiveness of feedback and qualify the behavior of the external kink mode. *Supported by U.\thinspace S. DOE Grant DE-FG02-86ER53222. [Preview Abstract] |
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JP6.00106: The theory of equilibrium reconstruction and Real Time Forecast of tokamak discharges Leonid Zakharov Since 1973 and especially during the last two decades, the equilibrium reconstruction on tokamaks provides the basic data on magnetic configuration for plasma control and interpretation of experimental results. Still some fundamental questions about reconstruction were never answered. Some variations of the current density or pressure in the Grad-Shafranov equation have a little effect on the signals. Even if the resulting fit to the measurements (within their accuracy) seems to be good, without assessment of all possible variances the value of such reconstruction is questionable. Here, a theory and numerical technique is presented which addresses the long standing problem of variances. It allows to calculate the range of ``visible'' (well reconstructed), ``barely visible'' (poorly reconstructed), and ``invisible'' perturbations and to make a quantitative evaluation of diagnostic systems. Also, the optimal algorithm for performing the reconstruction in practice has been formulated. This theory of variances allows to use information of different physical nature and makes possible the Real Time Forecast (RTF) of tokamak discharges, very important, e.g., for ITER, when the transport and equilibrium reconstruction codes work together for predicting the plasma discharge for the following energy confinement time interval. [Preview Abstract] |
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JP6.00107: Stabilization of Tokamak Plasmas by the Addition of Nonaxisymmetric Coils Allan Reiman It has been recognized since the early days of the fusion program that stellarator coils can be used to stabilize current carrying, toroidal, magnetically confined plasmas.[1] More recently, it has been shown that the vertical mode in a tokamak can be stabilized by a relatively simple set of parallelogram-shaped, localized, nonaxisymmetric coils.[2] We show that by superposing sets of these parallelogram-shaped, nonaxisymmetric coils at different locations, it is possible to reproduce the coil current patterns for conventional stellarator coils as well as those for Furth-Hartman coils[3]. This allows us to gain insight into the physics of stabilization produced by various sets of nonaxisymmetric coils by analysis of the effect on stability of localized coils at differing locations. In particular, the relationship between the stabilization effect and the rotational transform generated by the nonaxisymmetric coils is clarified. \newline [1] J. L. Johnson, C. R. Oberman, R. M. Kulsrud, and E. A. Frieman, Phys. Fluids 1, 281 (1958) \newline [2] A. Reiman, Phys. Rev. Lett. 99, 135007, (2007). \newline [3] H.P. Furth and C.W. Hartman, Phys. Fluids 11, 408 (1968). [Preview Abstract] |
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JP6.00108: KSTAR first plasma equilibrium reconstruction and study of global MHD stability control O. Katsuro-Hopkins, S.A. Sabbagh, J.M. Bialek, H.K. Park, K.I. You, S.G. Lee, J.G. Bak, S.W. Yoon, J.H. Kim, J.Y. Kim, A.H. Glasser, L.L. Lao Korea Superconducting Tokamak Advanced Research, KSTAR, equilibria are computed using EFIT and VALEN based on numerical models and recent experimental data from first plasma operation. A 3-D double-walled vacuum vessel model with port penetrations was used to evaluate the vacuum vessel effective resistance and to simulate and compare to the time evolution of experimental magnetic diagnostic measurements during vacuum poloidal field coil testing and plasma start-up scenarios. KSTAR is designed to produce wall-stabilized high beta equilibria. Ideal MHD stability of toroidal mode number of unity using DCON shows a factor of two improvement in the normalized beta limit over the no-wall beta limit (up to 5) at moderate to low plasma internal inductance. Reaching these high normalized beta levels is possible using passive and active control with classical and advanced state-space based control algorithms at the reasonable power levels. [Preview Abstract] |
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JP6.00109: Superbanana plateau regime for neoclassical toroidal plasma viscosity in tokamaks K.C. Shaing, S.A. Sabbagh, M. Chu Neoclassical toroidal plasma viscosity is found to be important in modeling toroidal plasma rotation in tokamaks that have error fields and magnetohydrrodynamic (MHD) activities. The most important regime in fusion grade tokamaks is probably the collisionless regime. In the collisionless regime, where the effective collision frequency for the bananas is less than the \textbf{\textit{E}}$\times $\textbf{\textit{B}} drift frequency, it is assumed in calculating toroidal plasma viscosity that the \textbf{\textit{E}}$\times $\textbf{\textit{B}} drift frequency is larger than the grad $B$ and the curvature drift so that the resonance between these two types of drift cannot occur. Here such an assumption is removed. The new physics introduced is that the resonance between the \textbf{\textit{E}}$\times $\textbf{\textit{B}} drift frequency and the grad $B$ and the curvature drift is now allowed. This leads to the supperbanana plateau regime. The result can be used for the arbitrary value of the radial electric field in the modeling of the plasma rotation when the toroidal symmetry is broken in tokamaks. [Preview Abstract] |
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JP6.00110: Tokamaks and Quasi-Axisymmetric Shaping Allen Boozer, Long-Poe Ku Since the pressure and current profiles are largely self- determined in a fusion plasma, plasma shaping is the primary design freedom. The importance of axisymmetric shaping to the feasibility of fusion in tokamaks is appreciated. Quasi- axisymmetric shaping gives additional degrees of design freedom that are associated with stellarators while retaining the well- confined particle trajectories associated with the axisymmetric tokamak. A factor of four extrapolation is expected to be required in the ratio of driven to bootstrap current between ITER and steady-state DEMO designs that are limited by axisymmetry. Quasi-axiymmetric shaping can not only ensure steady-state maintenance of the magnetic configuration but also address issues of MHD stability, robustness of plasma equilibria, density limit, and turbulent transport modification. Resources have been very limited for carrying out relevant design studies, but cases have been found that indicate the potential for addressing important physics issues that must be addressed between ITER and DEMO. [Preview Abstract] |
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JP6.00111: Local and nonlocal parametric excitation of GAMs by finite beta drift waves Parvez Guzdar, Robert Kleva, Nikhil Chakrabarti, Predhiman Kaw, Volker Naulin, Jens Rasmussen The geodesic acoustic modes (GAMs) can be excited in the edge region of toroidal plasmas by mode coupling to primary modes like the drift waves. We will present mode coupling analysis of the excitation of GAMs by finite beta drift waves. The finite beta effects stabilize the excitation of GAMs. The nonlocal study of the excitation of these modes leads to a complex eigenmode equation which yield bounded solutions on the edge density and temperature pedestals. The solutions show a two scale structure in which the fast scale is dictated by the three-wave frequency resonance condition, while the slow scale is determined by the combination of the edge density and/or temperature scales as well as the ion larmor radius. [Preview Abstract] |
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JP6.00112: SHORT-PULSE LASER-MATTER INTERACTIONS AND EQUATIONS OF STATE FOR HEDP |
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JP6.00113: Electron acceleration in ultra-intense laser ($>$10$^{18}$ Wcm$^{-2})$ interactions with sub-micron structured targets Hideaki Habara, Lei An-le, Keitaro Endo, Toshinori Yabuuchi, Takeshi Matsuoka, Hitoshi Sakagami, Farhat N. Beg, Richard Stephens, Antony Maksimchuk, Karl Krushelnick, Kazuo A. Tanaka The use of sub-micron structure targets is an attractive method for Fast Ignition to enhance energy coupling of the laser into the fast electrons. We have studied electron acceleration using sub-micron structured targets including low-density foam and carbon nano-tube (CNT) in ultra-intense laser plasma interactions. We observe low coupling efficiency of the laser energy into high-energy electrons in present experimental conditions in spite of our previous results showing efficient electron accelerations [1]. Detailed modeling using PIC calculations with various sub-micron structured plasma are presented to understand these results. [1] A.L. Lei et al., Phys. Rev. Lett. 96 (2006) 255006. [Preview Abstract] |
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JP6.00114: Studies of fast electron coupling efficiency using bookend targets V.M. Ovchinnikov, G.E. Kemp, D.W. Schumacher, L. Van Woerkom, R.R. Freeman, K.U. Akli, R.B. Stephens, T. Bartal, F.N. Beg, T. Ma, C.D. Chen, D. Hey, M.H. Key, S. Le Pape, A.J. MacKinnon, A.G. MacPhee, P.K. Patel, W. Theobald Hollow cone targets are widely studied to understand their effects on laser coupling to fast electrons relevant to the FI concept for ICF. ``Bookend'' targets fabricated out of two planar copper foils (100\textit{$\mu $m} x 100\textit{$\mu $m} x 20\textit{$\mu $m}) joined at one edge, making an angle between the two halves similar to an open book, were designed to mock-up the cone geometry in 2D. Experiments were performed on Titan laser at LLNL with the laser delivering approximately 10$^{20}$\textit{W/cm}$^{2}$ to the target ($\sim $150$J$, 0.7\textit{ps}). K$_{\alpha }$ emission measurements from Cu K$_{\alpha }$ imagers (spatially resolved) and a Highly Ordered Pyrolitic Graphite (HOPG) crystal (spectrally resolved) are presented for the Cu bookend targets for various opening angles and laser prepulse levels. The results are compared to recent bookend experiments on the MTW laser at LLE and previously reported studies of hollow cone targets at LLNL.\footnote{L. Van Woerkom et al., Phys. Plasmas 15, 056304~(2008)} [Preview Abstract] |
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JP6.00115: Hot electron energy coupling in ultra-intense laser matter interaction Andreas Kemp, Yasuhiko Sentoku, Max Tabak We investigate the response of plasma gradients during the interaction with ultra-intense energetic laser pulses, using kinetic particle simulations. Energetic laser pulses are capable of compressing preformed plasma gradients over short times, while accelerating low density plasma backwards. As light is absorbed on a steepened interface, hot electron temperature and coupling efficiency drop below the ponderomotive scaling, and we are left with a new absorption mechanism that strongly relies on the electrostatic potential caused by low density preformed plasma. We describe this process, explain electron spectra and identify the parameter regime where strong compression occurs. Finally, we discuss implications for fast ignition and other applications. [Preview Abstract] |
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JP6.00116: Relativistic Electrons from Slab Targets Interacting Strongly with Intense Light in Vacuum from High-Contrast Laser Pulses Tudor Johnston, L. Nikolic, Y. Tyshetskiy, F. Vidal When light of electron-relativistic intensity in several-cycle laser pulses are obliquely incident on slab targets with extremely low pre-pulse energy, copious amounts of high laser harmonic light emerge [1] (See also ongoing work at the ALLS 200 TW Ti-Saph laser at INRS EMT. (Pulses are 24 fs at 10 Hz with 10-10 contrast, even without plasma mirrors).) 2-D PIC (OSIRIS code at INRS) simulations [2] (and earlier work by Naumova et al. [3] have shown that intense beams of electrons are not only injected into the target [2] but that significant relativistic electrons are also emitted more or less along with the emitted light. These frontally-emitted relativistic electrons emerge from the narrow regions of intense current responsible for the harmonics [2] and interact strongly with the incident and emitted light. [1] B. Dromey et al Nature Phys. Lett., 2, 456-459 (2006). [2] T. Johnston et al. Poster YP8 48, Bull. Amer. Phys. Soc 52, 16 November (2007). [3] N. Naumova, et al., Phys. Rev. Lett. 93, 195003 (2004). [Preview Abstract] |
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JP6.00117: Experimental Study on Fast Electrons Transport in Ultra-intense Laser Irradiated Solid Targets by Transition Radiation Zheng Zhijian, Wang Guangcan, Gu Yuqiu The experiment was performed with SILEX laser facility(Ti-saphhire) at LFRC in China. The SILEX parameter: wavelength 0.8$\mu $m, duration 35fs, output power 280TW, contrast 5*105, The focal spot $\phi $10$\mu $m(F/1.7), intensity on target surface 1*10$^{19}$W/cm$^{2}$(F/3). The main diagnostic equipments are the electron spectrometer, OMA spectrometer, optical streak camera. Some experimental results are given: The spectrum of optical emission from rear surface is rather narrow around some particular frequencies(1$\omega$, 2$\omega$, 3$\omega)$, We ascribe and confirm that the spike-like spectral line that is coherent transition radiation; The coherent light is also seen on time-integrated image with ring-patter due to Weibel instability of the fast electron transport; Obtained experimental cure of target thickness vs OTR image intensity is relative to mean free path of fast electron; The measuring optical transition radiation(OTR) duration of 171ps much longer than 1ps duration of fast electron transport target, the possible explanation is that the OTR duration to be determined magnetic diffusion time. [Preview Abstract] |
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JP6.00118: Effect of short-pulse laser prepulse on electron conversion in planar geometry Laurent Divol, Andreas Kemp, Sebastien Lepape Low energy (50 mJ) long (nanoseconds) prepulses are commonly observed on petawatt-class short pulse laser facilities such as Titan (LLNL) just before the main pulse. We will present 2d/3d hydrodynamics simulations performed with the code HYDRA of the impact of a prepulse on the formation of a low density plasma blow-off in front of a planar target and the resulting disturbance of the high density interface where the conversion of the high power impulsion into electrons occurs. 2D PIC simulations of the main pulse interaction, using these hydrodynamics profiles as an initial condition, will be presented. These simulations will be compared with recent experimental measurements obtained at Titan. [Preview Abstract] |
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JP6.00119: Study of fast electron generation and transport in interactions of intense laser pulse with pre-plasma produced by long laser pulse on foil targets T. Yabuuchi, J.A. King, M.S. Wei, B.S. Paradkar, S.N. Chen, T. Ma, F.N. Beg, R.B. Stephens, M. Hatakeyama, N. Nakanii, H. Habara, K. Mima, K.A. Tanaka The influence of pre-plasma on fast electron generation is a critical issue for fast ignition. Multi-layered targets containing a Cu fluorescence layer were irradiated by an intense laser pulse ($ I \leq 2 \times 10^{18} $ W cm$^{-2}$) at the ILE, Japan. Various scale lengths of pre-plasma were generated using a long laser pulse. $K_\alpha$ x-rays spectroscopy and imaging were employed to characterize electron generation and transport. The Cu $K_\alpha$ x-rays were viewed from the front (laser irradiated) side through an Al ablator layer that prevented direct heating of the fluor. The presence of pre-plasma caused an x-ray yield reduction ($\leq 50\%$) and created a ring structure around an x-ray bright spot. Results compared against radiation hydrodynamics and hybrid/PIC modeling will be presented. [Preview Abstract] |
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JP6.00120: Hot electron generation in the ultra-intense laser matter interaction at a steep interface Rohini Mishra, Yasuhiko Sentoku, Andreas Kemp The absorption of ultra-intense laser light in the step-like densities, highly overdense plasma is discussed. To understand absorption physics we performed one-dimensional collisional particle simulation (PICLS1D). These simulations are able to simulate hot electrons generation in the laser plasma interaction, and energy transport thorough the cold resistive plasma. For a high intensity normal incident laser light the absorption is mainly due to $JXB$ absorption. We observed the electrons are trapped in the interaction region by the electrostatic potential, and the $JXB$ force drives the high energy electrons inwards from the trapped region with the frequency $2\omega$. Except these $2\omega$ electron jets there are also large number of leaking electrons with lesser energy and with the frequency $3\omega$, $6\omega$. When we increase the target density, the $JXB$ electron jets start to disappear resulting in to the decrease of total absorption. The physics inhibiting the production of $2\omega$ frequency electrons is discussed. Together with this we have simulated the effects of preplasma, specifically the increased total absorption which leads the production of higher energy electrons. [Preview Abstract] |
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JP6.00121: PIC Modeling of High Intensity Specular Reflectivity Measurements at 28 and 75 degrees L. Nikolic, Y.Y. Tsui, R. Fedosejevs, A. Link, R.R. Freeman, D.W. Schumacher, L.D. Van Woerkom, H. Chen, D.S. Hey, S. Le Pape, A.J. Mackinnon, A.G. MacPhee, P.K. Patel, Y. Ping, M.H. Key, T. Bartal, T. Ma, M.S. Wei, F.N. Beg, C.D. Chen, K.U. Akli, R.B. Stephens The reflectivity and degree of collimation of the reflected light are key parameters in assessing the effectiveness of concentration and redirection of light in cone guiding targets for fast ignition. Experimental measurements have been made of these parameters for planar metallic targets at two angles of incidence of 28 and 75 degrees at the Titan laser facility with 150J, 700fs pulses for intensities of 10$^{19}$ to 10$^{20}$ W/cm$^{2}$. In the current presentation 2D PIC modeling is carried out for these measurements. The results show that the reflectivity increases as the angle of incidence increases from 28 degrees to 75 degrees. Also the reflected light shows increased divergence relative to the input beam due to scattering from a rippled surface. Detailed results from the simulations will be presented. [Preview Abstract] |
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JP6.00122: Short Laser Pulse Absorption in Dense Inhomogeneous Plasmas S.G. Bochkarev, M. Sherlock, V. Yu. Bychenkov, W. Rozmus Short laser pulse absorption in solid density targets has been measured recently over a wide range of laser intensities [1]. We have developed an approximate model of the laser pulse interaction with inhomogeneous solid density targets. First, this model is solved in the 1D geometry of normal incidence for moderate laser intensities and collisional absorption. Scaling of these results with the density gradient and laser intensity have been found and compared with the Vlasov-Fokker-Planck simulations using the new version of the code KALOS [2]. The unique features of KALOS make possible simultaneous investigations of laser energy absorption at the target surface and the transport of heat into the dense target. Next our numerical and theoretical studies have been extended into the collisionless regime of laser absorption and high laser intensities up to 1018 W/cm2. Absorption by relativistic electron generation, the role of plasma waves produced by bunched relativistic electrons and surface target heating have been studied and elucidated by theoretical models. [1] Y. Ping, et al. Phys. Rev. Lett. 100, 085004 (2008). [2] A.R. Bell, et al. Plasma Phys. Control. Fusion 48, R37 (2006). [Preview Abstract] |
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JP6.00123: Relativistic Laser Pulse Propagation in Underdense Plasmas N. Naseri, S.G. Bochkarev, W. Rozmus Propagation of relativistic laser pulses in underdense plasmas remains a subject of active studies because of its relevance to different particle acceleration schemes, inertial confinement fusion by fast ignition and new interaction physics of super intense laser pulses. Finding a stable regime of propagation of these pulses over large distances in long scale length plasmas is critical for many of these applications. In this paper we report on detailed studies of relativistic self-focusing and pulse channeling. First, we examine the relevance and stability of exact stationary solutions in two spatial dimensions (2D) [1] by means of 2D PIC simulations. We have found good agreement between analytical, single channel solutions and PIC simulations results at low densities ne/ncr$<$0.1. Such fully evacuated channels are stable while solutions corresponding to incomplete electron density evacuation are destroyed by Raman and hosing instabilities. At higher densities 0.1 of critical density and above the predicted narrow width, on the order of laser wavelength, of the self-focused channels prevents stable propagation of the laser filaments. We have also found that analytical multi-channel stationary solutions are unstable due to the interaction between filaments. We will also report on the generalization of these results to 3D spatial geometry. [1] Cattani et al. Phys. Rev E, 64, 016412 (2001). [Preview Abstract] |
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JP6.00124: Observation of rapid energy transfer from relativistic, short pulse laser generated electrons to solid material R. Shepherd, H. Chen, Y. Ping, G. Dyer, S. Wilks, H.-K. Chung, K. Fournier, A. Niles, A. Kemp, S. Hansen, K. Widmann, A. Faenov, T. Pikoz, P. Beiersdorfer With the advent of high intensity ultra-short pulse lasers, relativistic electron generation in laser-solid interactions is common in laboratory plasmas. The coupling of these electrons to the surrounding matter plays a critical role in short pulse laser applications such as harmonic generation [1], short pulse x-ray production [2], and fast ignition [3]. We present the experimental observation of the energy transfer and damping rate of relativistic electrons in solid density matter. In general, this data provides a unique window into the time scale for collisional relaxation between relativistic particles and cold classical particles in a dense medium. \\[0pt] [1] Dromet, B., et. Al, ``High hamonic generation in the relativistic limit,'' \textit{Nature}, \textbf{2}, 456-459, (2006). \\[0pt] [2] Salzmann, D., et al, ``Theory of \textit{K-$\alpha $} generation by femtosecond laser-produce hot electrons in thin foils,'' \textit{Phys. Rev. E., }\textbf{65}, 036402-1-5, (2002). \\[0pt] [3] Kodama, R., et al, ``Fast heating of ultrahigh-density plasma as a step towards laser fusion ignition,'' \textit{Nature}, \textbf{412}, 798-801, (2001). [Preview Abstract] |
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JP6.00125: e-PLAS calculation of short pulse heating in wire targets R.J. Mason, F.N. Beg, R. Stephens, L. Van Woerkom, R.R. Freeman The 2-D implicit hybrid simulation code e-PLAS has been used to model energy deposition and hot electron transport in a variety of wire targets (e.g. Cu wires with nail or cone heads) [1]. Implicit $E${\&}$B$-fields [2] permit the use of large cells and time steps while avoiding finite grid heating. Van Leer background plasma fluids allow for ps-long simulations of $\sim $700 $\mu $m wires on a PC with economy. For $\sim $1.7x10$^{20}$ W/cm$^{2}$ pulse intensities we compare results from the use of Cartesian and cylindrical modeling geometry. We probe the effects of cold background electron-ion scatter [3], resistive $E-$fields and hot electron drag on the background heating. Temperature limitation from target ionization is explored. $B-$field trapping of hot electrons generated near critical density is examined as a function of the emission isotropy, energy spectrum, and plasma gradient scale length. Integrated simulations of the absorption and hot electron generation will be discussed. [1] J. Pasley et al., Phys. Plas. \textbf{14,} 120701 (2007). [2] R. J. Mason, J. Comp. Phys.\textbf{ 71,} 429 (1987). [3] R. J. Mason, Phys. Rev. Lett. \textbf{96, } 035001 (2006). [Preview Abstract] |
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JP6.00126: Energy transport in ultra-fast eated solid targets Yasuhiko Sentoku, Tomoyuki Johzaki, Andreas Kemp We discuss hot electron generation in ultra intense laser interaction with initially non-ionized matter. Hot electron energy and the transport inside the target are strongly affected by collisional effects and ionization processes, especially in high-Z material. We have introduced an ionization model into our collisional particle-in-cell code, PICLS, to study hot electron transport in ultra-fast heated matter. Our description of collisional ionization is based on the Thomas-Fermi model, where a local average charge state is calculated from the bulk electron temperature and density. Field ionization is taken into account for ionization of low density plasmas. We have studied laser matter interaction under an irradiation of a laser with $10^{20}$W/cm$^2$. A strong heat inhibition within a micron distance was observed in a gold target because of the large number of lower energy hot electrons produced at the steepened interface by the laser photon pressure. We will discuss the generation of hot electrons and their transport in ultra-fast heated solid targets of various materials. [Preview Abstract] |
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JP6.00127: Three-Dimensional PIC Simulation of Laser-Ion Acceleration from Ultrathin Targets B.J. Albright, L. Yin, K.J. Bowers, B. Bergen, B.M. Hegelich, K.A. Flippo, J.C. Fern\'andez One- and two-dimensional particle-in-cell simulations of the Break-Out Afterburner (BOA) [1] show that new ion acceleration regimes emerge when ultraintense, high- contrast lasers impinge on ultrathin (10s of nm) targets. The BOA has now been demonstrated in three-dimensional (3D) simulations with solid-density targets using VPIC [2]. Comparisons of monoenergetic beams, maximum ion energy, and conversion efficiency have been made with 3D VPIC simulations of ion acceleration from high- contrast circularly polarized lasers [3] with identical intensity, spot size and target composition. Studies have been made of BOA for different intensity and target thickness. [1] Yin et al. LPB 24, 1-8 (2006) ; Yin et al. PoP 14, 056706 (2007). [2] Bowers et al., PoP 15, 055703 (2008). [3] Zhang et al., PoP 14, 123108 (2007); Robinson et al., NJP 10 013021 (2008) [Preview Abstract] |
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JP6.00128: Diagnostics for laser plasma acceleration of ions R.L. Daskalova, C.D. Murphy, E. Chowdhury, J. Morrison, A. Krygier, R.R. Freeman, L. van Woerkom, C. McGuffey, T. Matsuoka, K. Krushelnick, A. Maksimchuk Laser plasma acceleration of ions is a rapidly evolving field, mainly due to the potential applications in oncology by proton therapy, astrophysics and neutron production for radiography. Here we present the details of an experimental investigation of ion acceleration from the rear of a metal foil in which both the prepulse-induced plasma on the front surface as well as the quantity of various ion species accelerated from the rear surface were monitored. A Thompson Parabola Spectrometer (TPS) coupled with CR-39 was employed to record the type and number of the accelerated ions. The relative number of various ions species was found to depend strongly upon the cleaning techniques used in preparation of the target foil. [Preview Abstract] |
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JP6.00129: Proton Radiography of Field Distributions in Ultra-Intense-Laser Plasma Interactions with Pulse of MeV Proton Beams Hirotaka Nakamura, Ryosuke Kodama, Motonobu Tampo, Marco Borghesi, Lorenzo Romagnani, Julien Fuchs, Munib Amin, Ariane Pipahl, Oswald Willi, Takuya Michibata, Kunioki Mima, Hiroshi Azechi Proton radiography has been used to observe transient electric and magnetic fields in laser plasma interactions. We report an experimental investigation of a transient electric field generated around a laser-irradiated-plasma-fiber attached on a tip of a cone-geometry target. The electric field guided and collimated energetic electrons generated by the laser-plasma interactions in the fiber. The front of these fields propagated along the fiber with the energetic electrons at almost the light velocity. Simulation with the Geant4 Monte Carlo code shows the electric field above a few TV/m were excited around the fiber. [Preview Abstract] |
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JP6.00130: Anisotropic energy spectra of fast ions generated by a laser-cluster interaction analyzed by a collisional PIC code Toshihiro Taguchi, Thomas Antonsen, Howard Milchberg Energy spectra of fast ions generated through a laser-cluster interaction are analyzed by our newly developed particle-in-cell (PIC) code, which includes both collisional and ionization processes. A solitaly cluster is irradiated by a strong laser field in a range of 10$^{14}$--10$^{17}$W/cm$^2$. The laser field mainly accelerates electrons in the cluster and their fast components escape very rapidly from the core of the cluster to produce a large static field surrounding the cluster. Ions are accelerated by the large static field and then the cluster expands. Since electrons are preferentially accelerated in the direction parallel to the laser polarization, the static field is anisotropic and ions are also accelerated anisotropically. We have analyzed both an argon cluster and a hydrogen cluster for various laser intensities and study the mechanisms of the anisotropic acceleration detail, especially about the relation to the resonant absorption described in the references [1--2]. [1] T. Taguchi, et al., Phys. Rev. Lett., 92, 20, 2004, 205003. [2] T. M. Antonsen, Jr., et al., Phys. Plasmas 12, 5, (2005), 056703. [Preview Abstract] |
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JP6.00131: The spectral-angular distribution measurements of fast protons from the rear side of a target in experiments on the SOKOL-P facility at laser intensity of 10$^{19}$ W/cm$^{2}$ D.S. Gavrilov, D.A. Vikhlyaev, S.A. Gorokhov, D.A. Dmitrov, A.L. Zapysov, A.G. Kakshin, I.A. Kapustin, E.A. Loboda, V.A. Lykov, A.V. Potapov, V.A. Pronin, G.N. Rykovanov, V.N. Sanzhin, V.N. Saprykin, K.V. Safronov, P.A. Tolstoukhov, A.A. Ugodenko, O.V. Chefonov, A.V. Andriyash The developed in RFNC-VNIITF 10-TW ``SOKOL-P'' laser facility was put into operation in 2002. It delivers the 0.8 ps of pulse duration and up to 8 J of on target energy. The mean intensity of $>$10$^{19}$ W/cm$^{2}$ of high contrast irradiation have been achieved with the help of the off-axis parabola $f $/1.5, providing 6 $\mu $m FWHM focal spot. The ns scale intensity contrast ratio is $>$ 2*10$^{11}$, the energy contrast ratio (to non-ionizing 1 ms ASE pedestal) is 2*10$^{6}$. Due to the high value of contrast ratio ultra thin Al foils down to 0.08 $\mu $m thick are not damaged before the main pulse arrival. Spatial-energy spectrum of fast protons (energies of 1{\ldots}8 MeV) measured by two types of spectrometers; up to 1.5{\%} of conversion efficiency of laser energy to proton energy; and 9 MeV of maximum proton energy have been obtained in laser based acceleration experiments. [Preview Abstract] |
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JP6.00132: High-energy x-ray source development for radiography in High-Energy Density Physics performed on the TRIDENT 200-TW laser J. Workman, J. Cobble, K. Flippo, D.C. Gautier, S. Letzring, D.S. Montgomery, S. Gaillard, N. Vutisalchavakul Experiments were performed on the Trident 200-TW facility to measure K-alpha x-ray emission from high-Z targets using small emission regions to develop phase contrast capabilities. Results from wire targets using Mo, Ag and W are presented and are compared to reduced mass targets. Images are recorded on image plates and a high-energy x-ray CCD camera. Images of static objects show high spatial resolution, high contrast and begin to optimize refractive effects leading to phase contrast imaging. [Preview Abstract] |
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JP6.00133: Effect of laser energy and incidence angle on K-alpha and bremsstrahlung emission from thin foil targets irradiated by a short pulse, high intensity laser Bradley Westover, Andrew MacPhee, Tammy Ma, Farhat Beg, Cliff Chen, Daniel Hey, Brian Maddox, Hye-Sook Park, Bruce Remington We report on experiments performed to characterize a short pulse, high intensity, laser-produced x-ray source for diffraction studies. These experiments were performed using the Titan laser at the Jupiter Laser facility with a 40ps pulse length at intensities varying from 10\^{}16 to 10\^{}18 W/cm\^{}2. The targets were 12 micron thick silver foils. The effects of the laser pulse energy, target angle and spot size on x-ray emission were measured using single photon counting cameras CCD cameras and bremsstrahlung spectrometers arranged upstream, downstream, and orthogonal to the laser. Integrated Tiger Series (ITS), a Monte Carlo code, was used to model the K-shell spectra and bremsstrahlung emission from the target, as well as the response of the bremsstrahlung spectrometers. Absolute k-alpha photon yields and k-alpha to bremsstrahlung ratios as a function of laser pulse energy and the angle between the laser and the target surface were determined; these data are crucial for designing picosecond x-ray diffraction experiments on Omega EP and the NIF. [Preview Abstract] |
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JP6.00134: High contrast lasr-based Mo K-alpha X-ray source at ALLS Cristina Serbanescu, Sylvain Fourmaux, Russel Kincaid, Andrzej Krol, Jean Claude Kieffer We report an efficient Mo $K$-alpha x-ray source produced by tightly focusing high contrast 60 fs, 10 mJ, 100 Hz frequency doubled Ti:Sapphire laser pulses on solid molybdenum targets. The x-ray source gives a sufficient spatial coherence to acquire phase contrast images. X-ray phase contrast allows seeing features not visible in conventional absorption contrast and thus, it is of great interest for biomedical applications, which require high-resolution images. The size of the resultant K-alpha x-ray emission spot, the x-ray spectrum, and the x-ray conversion efficiency are characterized and they will be presented and discussed. Such a high contrast, high repetition rate $K$-alpha x-ray source can be very useful for x-ray imaging. [Preview Abstract] |
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JP6.00135: Measurement of the Electron-Ion Temperature Relaxation Rate in a Dense Plasma J.M. Taccetti, R.P. Shurter, P.M. Goodwin, J.F. Benage Jr. Current theoretical approaches to temperature relaxation, which can be categorized as binary-collision and many-body approaches, disagree. Existing experimental evidence infers a lower relaxation rate compared to the binary-collision approach, but is insufficient to determine which approach is correct. We present the most recent results from an experiment aimed at obtaining the temperature relaxation rate between ions and electrons in a dense, strongly coupled plasma by directly measuring the temperature of each component. The plasma is formed by heating a gas jet with a 10 ps laser pulse. The electrons are preferentially heated by the short pulse laser ($T_{e} \approx$ 100 eV), while the ions, after undergoing very rapid (sub-ps time-scale) disorder-induced heating, should only reach a temperature of 10-15 eV. This results in a strongly coupled ion plasma with an ion-ion coupling parameter $\Gamma_{ii}\approx$ 3-5. We plan to measure the electron and ion temperatures of the resulting plasma independently during and after heating, using collective Thomson scattering for electrons and a high-resolution x-ray spectrometer for the ions (measuring Doppler-broadened absorption lines). [Preview Abstract] |
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JP6.00136: Ion Beam Driven Warm Dense Matter Experiments F.M. Bieniosek, E. Henestroza, M.A. Leitner, S.M. Lidia, B.G. Logan, R.M. More, P.A. Ni, P.A. Seidl, W.L. Waldron, J.J. Barnard We report plans and experimental results in ion beam-driven warm dense matter (WDM) experiments. Initial experiments use a 0.3 MeV K+ beam from the NDCX-I accelerator. The WDM conditions are to be achieved by longitudinal and transverse neutralized drift compression to provide a hot spot on the target with a 1-mm beam spot size, and 2-ns pulse length. As a technique for heating matter to high energy density, intense ion beams can deliver precise and uniform beam energy deposition, in a relatively large sample size, and can heat any solid-phase target material. The range of the beams in solid targets is less than 1 micron, which can be lengthened by using reduced density porous targets. We have developed a WDM target chamber and target diagnostics including a fast multi-channel optical pyrometer, optical streak camera, VISAR, and high-speed gated cameras. Initial experiments will explore measurement of temperature and other target parameters. Experiments are planned in areas such as dense electronegative targets, porous target homogenization and two-phase equation of state. [Preview Abstract] |
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JP6.00137: Equation of State of Warm Dense Matter at DARHT-2 Facility Thomas Kwan, Mark Schmitt, William Daughton, Carl Ekdahl, John Benage, Michael Murillo, Frederick Wysocki Accurate equation-of-state theory on warm dense matter is a big challenge to model and good experimental data is difficult to obtain. One of the difficulties is the creation of a warm dense matter (WDM) suitable for experiments to examine its equation of state. We have examine methods of creating a warm dense matter using three different kinds of energetic particle beams such as short pulse laser, energetic proton beam, and relativistic electron beam. We found that the use of relativistic electrons such as the second axis of the Dual Axis Radiographic Hydro-Test (DARHT) facility at Los Alamos National Laboratory can create WDM ideally suitable for experiments to obtain data on the equation of state of such WDM over an extended parameter space. The electron beam has an energy of 18 MeV and a current of 2 kA. Its pulse length can be varied from 20 ns to 200 ns. We will present results from our calculations on the creation and characterization of WDM using the DARHT electron beam. We will also present our planned experiments specifically for the measurements of equations of state of such a WDM. [Preview Abstract] |
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JP6.00138: Scaling Laws for Plasma Jets-Driven Liner Implosions J. Cassibry, S. Thompson, S. Hsu, D. Witherspoon Plasma jets driven magnetoinertial fusion (PJMIF) is a fusion energy concept which consists of an imploding plasma liner that shock heats and compresses a magnetized target plasma. The liner can be formed by the merging of a cylindrical or spherical distribution of plasma jets, which are launched by a salvo of plasma accelerators. Confinement of the target is inertial, with the thermal conduction suppressed by the magnetic field. Imploding plasma liners can also be an inexpensive path to creating high energy density (HED) plasmas in the laboratory with cm and $\mu $s spatial and temporal scales, respectively. In this poster, we use analytical and smoothed particle hydrodynamic (SPH) modeling to develop scaling relations for peak pressure and confinement time for liner collapse onto a cavity, and for select cases with an adiabatic target. The primary goal is to estimate the initial conditions required for plasma liners in reaching 0.1 to 1~Mbar pressure using imploding shocks. We will use SPH to study selected 1D to 3D cases, with the latter to include the formation of a liner from discrete jets. Scaling relations are developed for peak conditions as a function of the initial jet conditions, specifically the number of jets, thermodynamic properties, and dimensions. We also discuss possible PJMIF scenarios that may be capable of reaching interesting fusion gains (G $\sim $ 5--20). [Preview Abstract] |
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JP6.00139: Analysis of instabilities in merging plasma jets S.A. Galkin, I.N. Bogatu, J.S. Kim, V.I. Sotnikov High velocity (10-100 km/s) high density (10$^{16}$-10$^{18}$ cm$^{-3}$) plasma jets are proposed to form plasma liner to compress magnetized plasma target and to reach MIF conditions [1]. Merging of such plasma jets may cause instabilities, which can affect/destroy the plasma liner formation. 2D/3D numerical simulations of plasma jets merging/colliding were performed with PIC LSP and hybrid DOLPHIN codes. Results of simulations and nature of instabilities will be presented. [1] Y. C. F. Thio, E. Panarella, R. C. Kirkpatrick, C. E. Knapp, F. Wysocki, ``Magnetized Target Fusion in a Spheroidal Geometry with Standoff Drivers,'' Current Trends in International Fusion Research II, ed. E. Panarella, National Research Council Canada, Ottawa, 1999. [Preview Abstract] |
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JP6.00140: Steps to Higher Density on the HyperV Plasma Guns F. Douglas Witherspoon, Andrew Case, Sarah Messer, Richard Bomgardner, Sam Brockington We describe steps underway to substantially increase the density and shorten the length of plasma jets under development at HyperV for fusion and HEDP applications. The basic approach uses symmetrical pulsed injection of high density plasma into a coaxial EM accelerator having a cross-section tailored to prevent formation of the blow-by instability. Efforts to date have been successful at producing jets with high total momentum, but the jet density is only about $5 \times 10^{15}~cm^{-3}$, due primarily to the low currents and energies used to date. Present efforts are focused on upgrading the pfn's for both injection and main EM section. By increasing the injected mass, shortening the injected pulse time, and increasing the main drive current from $<200$ kA to 0.5-1.0 MA, we expect to see jet densities increase to the $10^{16}~cm^{-3} - 10^{17}~cm^{-3}$ range and jet lengths to contract. Upgrades to the TwoPi facility have resulted in an order of magnitude increase in density to $>2 \times 10^{17}~cm^{-3}$ at the implosion center by using top and bottom confining plates and higher energy driving the 64 capillary jets. [Preview Abstract] |
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JP6.00141: Platform development of x-ray absorption-based temperature measurements above 100-eV on the OMEGA laser Paul Keiter, John Benage, Nick Lanier, Heidi Tierney, Jonathan Workman, Andrew Comley, John Morton, Mark Taylor Experiments were performed on the OMEGA laser system at the University of Rochester to develop techniques for measuring radiation temperature in hohlraum-heated foams. The development of this technique in the temperature range of 100-200-eV will be used for platform development of future NIF experiments. We will present time-integrated and time-resolved measurements of x-ray emission from the backlighter materials as well as absorption measurements trough the heated tracer materials. We will also present future directions in the development of this platform. This was performed by the Los Alamos National Laboratory under the auspices of the United States Department of Energy under contract no. DE-AC52-06NA25396. [Preview Abstract] |
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JP6.00142: One-Dimensional, Time-Dependent Neutron Transport Benchmarks Carol Aplin, Douglass Henderson The interaction of fusion neutrons with the burning DT plasma influences the burn dynamics of high gain inertial fusion energy targets that will eventually be used for reactor applications. Neutron interactions are also an important diagnostic tool for nearer term ignition targets. In each case accurate time and spatially dependent reaction rates in the target and the spectrum of neutrons emerging from the target are important quantities to know so that computer simulations can be compared to experimental results. We are developing a code to solve the one-dimensional time-dependent integral form of the neutron transport equation using quasi-analytic methods. This code will be tested against benchmark problems to ascertain its accuracy and will be tested in the BUCKY 1-D radiation hydrodynamics code to test the suitability of integral transport methods for incorporation in IFE simulation codes. Previously, the code has been used to reproduce previous benchmark problems in infinite slab and spherical geometries. Further benchmark problems for finite slab and spherical geometries are under development. [Preview Abstract] |
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