Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session UP8: Poster Session VIII: Tokamak and Related Diagnostics, Complex Dynamics, Sheaths, Strongly Coupled and Dusty, Low Temperature, Fusion Technology, DIII-D II |
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Room: Plaza ABC |
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UP8.00001: MEASUREMENT AND DIAGNOSTICS |
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UP8.00002: Hardware Overview of the Microwave Imaging Reflectometry (MIR) on DIII-D Xing Hu, Christopher Muscatello, Calvin Domier, Neville Luhmann, Xiaoxin Ren, Alexander Spear, Benjamin Tobias, Liubing Yu UC Davis in collaboration with PPPL has developed and installed a 12 by 4 (48) channel MIR system on DIII-D to measure 2-D structure of density fluctuations. In the transmitter path, a four-frequency probing beam is generated by mixing the 65 GHz Gunn oscillator signal with two different 0.5 $\sim$ 9 GHz signals. Carefully designed imaging optics shape the beam to ensure the probing beam wavefront matches the cutoff surfaces. In the receiver path, large aperture imaging optics collect the reflected beam and focus it onto the mini lens antenna array, which provides improved LO coupling and antenna performance over earlier imaging systems. The reflected signal is down-converted for the first time on the array and goes into the innovative electronics for a second down-conversion. Low frequency LOs for the IQ mixer are generated by mixing two reference signals from phase-locked circuits. The double down-converted signal is mixed with the low frequency LOs yielding in-phase and quadrature components of the phase and thus density fluctuation information. [Preview Abstract] |
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UP8.00003: Unfolding of energies of fusion products from the nuclear activation data at JET Jan Mlynar, G. Bonheure, O. Ficker, K. Bauer, S. Popovichev, A. Murari Diagnostics of fusion products, in particular of energetic charged particles, is a challenging task that requires further development. In this respect, activation probes were tested in JET, TEXTOR and ASDEX-U tokamaks as a novel and robust diagnostics, compatible with harsh conditions in future fusion reactors. The activation probe consists of a set of pure, well-characterized materials in which measureable amounts of radioisotopes are produced from nuclear reactions due to energetic particles. The production of each radioisotope can be modelled by an energy dependent yield curve derived from the specific nuclear reaction cross section data. In this contribution, the JET activation probe data will be reviewed with focus on possible spectral reconstruction of the incident fusion particles. A method will be outlined to reliably unfold neutron and proton energies, based on Tikhonov regularisation. First results of the neutron and proton energy spectra unfolded from the activation data will be presented. Although the analyses of the proton data are more complex due to several geometrical factors, the initial results demonstrate the potential of this robust diagnostic method, provided that the ill-conditioned task of unfolding is carefully implemented. [Preview Abstract] |
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UP8.00004: Velocity-space tomography of the fast-ion distribution function Asger Schou Jacobsen, Mirko Salewski, Benedikt Geiger, Manuel Garc\'Ia-Mu\~noz, William Heidbrink, S{\O}ren Bang Korsholm, Frank Leipold, Jens Madsen, Poul Michelsen, Dmitry Moseev, Stefan Kragh Nielsen, Jesper Rasmussen, Morten Stejner, Giovanni Tardini Fast ions play an important role in heating the plasma in a magnetic confinement fusion device. Fast-ion D$_\alpha$(FIDA) spectroscopy diagnoses fast ions in small measurement volumes. Spectra measured by a FIDA diagnostic can be related to the 2D fast-ion velocity distribution function. A single FIDA view probes certain regions in velocity-space, determined by the geometry of the set-up. Exploiting this, the fast-ion distribution function can be inferred using a velocity-space tomography method. This poster contains a tomography calculated from measured spectra from three different FIDA views at ASDEX Upgrade. The quality of the tomography improves with the number of FIDA views simultaneously measuring the same volume. To investigate the potential benefits of including additional views (up to 18), tomographies are inferred from synthetic spectra calculated from a simulated distribution function. The number of experimentally available views can be increased by combining different types of diagnostics in a joint velocity-space tomography. Using this, up to 7 views are available at ASDEX Upgrade from 2014. [Preview Abstract] |
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UP8.00005: Direct extraction of coherent mode properties from imaging measurements in a linear plasma column Adam Light, Saikat Thakur, Christian Brandt, Yancey Sechrest, George Tynan, Tobin Munsat We present imaging measurements of coherent waves in the Controlled Shear Decorrelation Experiment (CSDX). CSDX is a well-characterized linear machine producing dense plasmas relevant to the tokamak edge ($T_e \sim 3$ eV, $n_e \sim 10^{13}$/cc). Visible light from ArII line emission is collected at high frame rates using an intensified digital camera. A cross-spectral phase technique allows direct visualization of dominant phase structures as a function of frequency, as well as identification of azimuthal asymmetries present in the system. Experimental dispersion estimates are constructed from imaging data alone. Drift-like waves are identified by comparison with theoretical dispersion curves, and a tentative match of a low-frequency spectral feature to Kelvin-Helmholtz-driven waves is presented. Imaging measurements are consistent with previous results, and provide non-invasive, single-shot measurements across the entire plasma cross-section. Relationships between imaging and electrostatic measurements are explored, including limitations of both techniques. [Preview Abstract] |
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UP8.00006: 3D particle tracking velocimetry using dynamic discrete tomography for plasma physics applications Dmitry Moseev, Andreas Alpers, Peter Gritzmann, Mirko Salewski 3D particle tracking velocimetry (PTV) is a diagnostic technique which is widely used for studying flows, combustion, and plasmas. Current tomographic particle tracking methods are based on the multiplicative algebraic reconstruction technique and used for reconstructing the distribution of multi-pixel sized particles as greylevel images. Reconstructions obtained by these methods do not necessarily match the experimental data. We propose a new algorithm which can be used for tracking dust particles in tokamaks and stellarators, as well as in low-temperature and complex plasmas. The dynamic discrete tomography algorithm is efficient for data from two projection directions and exact. The non-uniqueness can be detected and tracked individually. The algorithm performance is proportional to N3 on average where N is the number of particles in the reconstruction. There is a room for further improvement of the computational cost scaling. Information from previously reconstructed frames is incorporated in the reconstruction procedure that is formulated as a discrete optimization problem, which has not been applied in PTV previously. [Preview Abstract] |
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UP8.00007: Metamaterial lens of frequency-dependent focus optimized for highest ECE spatial resolution Kenneth Hammond, Scott Massidda, William Capecchi, Francesco Volpe Electron cyclotron emission (ECE) is typically collected from the low-field side of toroidal plasmas by quasi-optical systems optimized for a single frequency. As a result, ECE suffers from losses in transverse resolution in regions with different cyclotron frequencies. For best spatial resolution, it would be desirable for the ECE optics to focus different frequencies to the respective locations in the plasma from which they are emitted. This requires a dramatic increase of focal length with frequency (``reverse chromatic aberration''), not encountered in conventional convergent lenses. Recent simulation work [1,2], however, suggests that metamaterial lenses consisting of arrays of sub-wavelength phase shifters can be engineered to simultaneously focus all frequencies of interest at their respective EC-emitting locations. Here we present the design and initial experimental results for a prototype metamaterial lens for the 8-12 GHz band, and the design of a metamaterial lens for ECE at 80-130 GHz in a DIII-D-like plasma. We also discuss extensions to other millimeter wave diagnostics, as well as to high-power heating.\\[4pt] [1] W.J. Capecchi et al., \textit{Optics Express} \textbf{20}, 8761 (2012);\\[0pt] [2] K.C. Hammond et al., \textit{J. Inf. Milli. THz Waves} \textbf{34}, 437 (2013). [Preview Abstract] |
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UP8.00008: An Alternative Optical Concept for Electron Cyclotron Emission Imaging (ECEI) J. Liu, T. Milbourne, M. Bitter, C. Kung, A. Dominguez, P.C. Efthimion, G.J. Kramer, S. Kubota, H. Park The implementation of the recently developed ECEI systems on tokamak experiments has revolutionized the diagnosis of MHD activities and significantly improved our understanding of instabilities, which lead to disruptions. It is therefore desirable to also have an ECEI system on ITER. However, the large size of the optical components of the presently used ECEI systems, which include up to ten, 1 m high, cylindrical lenses and require access ports of the size of a manhole, preclude the implementation of such an ECEI system on ITER. This paper describes a new optical ECEI concept that employs a single spherical mirror as the only optical component and exploits the astigmatism of such a mirror to produce an image with one-dimensional spatial resolution on the detector. Since it would only require a thin slit as the viewing port to the plasma, it would thereby make the implementation of an ECEI system on ITER feasible. The results obtained from ongoing proof-of-principle experiments with a 140 GHZ microwave system will be presented. [Preview Abstract] |
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UP8.00009: Magnetic and density contributions to Faraday rotation in a synthetic polarimeter Samuel Peana, Linda Sugiyama, William Bergerson A synthetic diagnostic has been developed for the far-infrared polarimeter [1] used in the Alcator C-Mod experiment, based on the the VisIt visualization program. Line integrals of the electron density and magnetic field component in the direction of the viewing chord measure the Faraday rotation of the magnetic field, $\delta\psi_F \simeq c_f (\int \delta n_e\,\mathbf{B}\cdot d\mathbf{l} + \int n_e\,\delta\mathbf{B}\cdot d\mathbf{l})$. Experimentally $\mathbf{B}$ can only be measured at the edge of the plasma, so its contribution to the rotation, relative to $\delta n_e$, is indeterminate. MHD simulation of a C-Mod ohmic impurity snake [2] using M3D shows a 1/1 internal kink-type magnetic perturbation, with $m=1$, 2, 3 components extending to the plasma edge. The synthetic diagnostic sees an overall $n=1$ toroidal oscillation on all three chords, consistent with experiment. The $\delta n_e$ contribution is comparable to $\delta \mathbf{B}$ near the plasma edge (vertical $r=23$ cm), but increases to 20x larger at $r=10$, just outside the snake, while $\delta \mathbf{B}$ remains relative constant. Further comparisons will be presented.\\[4pt] [1] W. Bergerson, et al., Rev.~Sci.~Instr. {\bf 83} 10E316 (2012).\\[0pt] [2] L. Sugiyama, Phys.~Plasmas {\bf 20} 032504 (2013). [Preview Abstract] |
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UP8.00010: In-situ real time measurements of net erosion rates of copper during hydrogen plasma exposure Leigh Kesler, Graham Wright, Ethan Peterson, Dennis Whyte In order to properly understand the dynamics of net erosion/deposition in fusion reactors, such as tokamaks, a diagnostic measuring the real time rates of net erosion/deposition during plasma exposure is necessary. The DIONISOS experiment produces real time measurements of net erosion/deposition by using Rutherford backscattering spectroscopy (RBS) ion beam analysis simultaneously with plasma exposure from a helicon plasma source. This in-situ method improves on ex-situ weight loss measurements by allowing measurement of possible synergistic effects of high ion implantation rates and net erosion rate and by giving a real time response to changes in plasma parameters. Previous work has validated this new technique for measuring copper (Cu) erosion from helium (He) plasma ion bombardment. This technique is now extended to measure copper erosion due to deuterium and hydrogen plasma ion exposure. Targets used were a 1.5 $\mu$m Cu layer on an aluminum substrate. Cu layer thickness is tracked in real time using 1.2 MeV proton RBS. Measured erosion rates will be compared to results from literature and He erosion rates. Supported by US DoE award DE-SC00-02060. [Preview Abstract] |
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UP8.00011: ITER DIAGNOSTICS |
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UP8.00012: Progress on ITER Diagnostic Integration David Johnson, Russ Feder, Jonathan Klabacha, Doug Loesser, Mike Messineo, Brentley Stratton, Rick Wood, Yuhu Zhai, Phillip Andrew, Robin Barnsley, Guenter Bertschinger, Maarten DeBock, Roger Reichle, Victor Udintsev, George Vayakis, Christopher Watts, Michael Walsh On ITER, front-end components must operate reliably in a hostile environment. Many will be housed in massive port plugs, which also shield the machine from radiation. Multiple diagnostics reside in a single plug, presenting new challenges for developers. Front-end components must tolerate thermally--induced stresses, disruption-induced mechanical loads, stray ECH radiation, displacement damage, and degradation due to plasma-induced coatings. The impact of failures is amplified due to the difficulty in performing robotic maintenance on these large structures. Motivated by needs to minimize disruption loads on the plugs, standardize the handling of shield modules, and decouple the parallel efforts of the many parties, the packaging strategy for diagnostics has recently focused on the use of 3 vertical shield modules inserted from the plasma side into each equatorial plug structure. At the front of each is a detachable first wall element with customized apertures. Progress on US equatorial and upper plugs will be used as examples, including the layout of components in the interspace and port cell regions. [Preview Abstract] |
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UP8.00013: ECE Diagnostics for ITER Richard Ellis, Max Austin, Joseph Beno, William Rowan, Perry Phillips, Amanda Hubbard, Hitesh Pandya, Russel Feder ECE on ITER will be used to measure electron temperature profiles and non thermal features of the distribution. The diagnostic has two systems, one radial, and the other viewing at a small oblique angle. Radiation will be conducted to the diagnostic area with large smooth wall waveguide. Emission will be measured with a multichannel Michelson interferometer and two microwave radiometers which cover the fundamental and second harmonic ECE (X and O mode). In-situ calibration employs a hot calibration source which has been designed, constructed, and tested. We report extensive wideband transmission measurements made on the DIII-D Michelson corrugated waveguide system. We have now completed design of the beam splitter box which separates X and O modes for both views. The box inputs are now located flush up against the vacuum windows on the port plug. We have then redesigned the Gaussian beam optics of the system to reduce the size of the calibration sources by 20{\%} to allow a better fit with other diagnostics in the port plug. We will present the details of the entire new design. [Preview Abstract] |
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UP8.00014: Calibration of the Electron Cyclotron Diagnostic for ITER P.E. Phillips, W.L. Rowan, M.E. Austin, K.W. Gentle, H. Huang, J.H. Beno, A. Ouroua, T. Ang, Z.J. Yang Electron temperature measurements will be critical to the non-active and deuterium phase of ITER operation and will take on added importance during the alpha heating phase. The ECE diagnostic for these measurements has front end components that must operate reliably during long pulse operation with high neutron and gamma fluxes in spite of limited opportunities for maintenance. Hence, an in-situ emission source is required to calibrate changes in the front end transmission. The calibration unit is a black body emitter (emissivity \textgreater\ 0.75, 100 GHz \textless\ f \textless\ 1000 GHz) that operates in vacuum at high temperature (700$^{\circ}$ C) without adversely affecting the vacuum or nearby diagnostics. It was developed at UT-Austin. Long-term field testing at EAST and J-TEXT is underway using variations of the ITER design tailored for the machines. Operation in the field at full temperature verified the basic design and suggested improvements in the heater design. [Preview Abstract] |
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UP8.00015: Progress in Development of C$_{60}$ Nanoparticle Plasma Jet for Diagnostic of Runaway Electron Beam-Plasma Interaction and Disruption Mitigation Study for ITER I.N. Bogatu, J.R. Thompson, S.A. Galkin, J.S. Kim We produced a C$_{60}$ nanoparticle plasma jet (NPPJ) with uniquely fast response-to-delivery time ($\sim1 - 2$ ms) and unprecedentedly high momentum ($\sim0.6$ g$\cdot$km/s). The C$_{60}$ NPPJ was obtained by using a solid state TiH$_{2}$/C$_{60}$ pulsed power cartridge producing $\sim$180 mg of C$_{60}$ molecular gas by sublimation and by electromagnetic acceleration of the C$_{60}$ plasma in a coaxial gun ($\sim$35 cm length, 96 kJ energy) with the output of a high-density ($>$10$^{23}$ m$^{-3}$) hyper-velocity ($>$4 km/s) plasma jet. The $\sim75$ mg C$_{60}$/C plasma jet has the potential to rapidly and deeply deliver enough mass to significantly increase electron density (to $n_{e}\sim2.4\times10^{21}$ m$^{-3}$, i.e. $\sim 60$ times larger than typical DIII-D pre-disruption value, $n_{e0}\approx 4\times10^{19}$ m$^{-3}$), and to modify the 'critical electric field' and the runaway electrons (REs) collisional drag during different phases of REs dynamics. The C$_{60}$ NPPJ, as a novel injection technique, allows RE beam-plasma interaction diagnostic by quantitative spectroscopy of C ions visible/UV line intensity. The system is scalable to $\sim1 - 2$ g C$_{60}$/C plasma jet output and technology is adaptable to ITER acceptable materials (BN and Be) for disruption mitigation. [Preview Abstract] |
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UP8.00016: Extended MHD simulations for application to ITER disruption mitigation techniques Simon Woodruff, James Stuber, Sam Schetterer Various disruption scenarios are modeled computationally by use of the CORSICA [1] and NIMROD [2] codes, following the work of Kruger [3] and Strauss [4] with the aim of providing starting-points for investigation of tokamak disruption mitigation techniques [5]. It is found that pressure-driven instabilities previously observed in simulations of DIII-D are verified, and that halo currents from vertical displacements are observed in simulations with implementation of resistive walls for ITER. We discuss implications and plans for simulations of disruption mitigation techniques. We outline validation activities for existing facilities.\\[4pt] [1] J. Crotinger, et al Proc. Sherwood, Austin, TX, USA (1994).\\[0pt] [2] C. Sovinec, et al Phys. Plasma, 10 (5),1727 2003.\\[0pt] [3] S. Kruger et al Phys. Plasmas, 12 (5) pp. 056113-056113-10 (2005).\\[0pt] [4] H. Strauss et al Comp. Phys. Com. 164(1-3) 40-45 (2004).\\[0pt] [5] L. Baylor et al VLT Conference Call (2013). [Preview Abstract] |
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UP8.00017: Component development for the ITER Ion Cyclotron Heating and Current Drive Transmission Line and Matching System R.H. Goulding, M.P. McCarthy, D.A. Rasmussen, D.W. Swain, G.C. Barber, C.N. Barbier, I.H. Cambell, S.L. Gray, R.L. Moon, P.V. Pesavento, R.M. Sanabria, E. Fredd, N. Greenough The transmission line and matching network for the ITER Ion Cyclotron Heating and Current Drive System feeds two equatorial launchers, each with 24 phased current straps combined into groups of three, and each designed to couple up to 20 MW into ELMy H-mode plasmas in the frequency range 40-55 MHz, for pulse lengths up to 3600 s. The network includes $>$ 1 km of 50 Ohm 300 mm diameter transmission line carrying up to 6 MW net power per line at VSWR=1.5. In addition, there are 8 power splitters, 32 hybrid phase shifters incorporating 64 tuning stubs, 32 additional tuning stubs, and 36 vacuum capacitors, which are configured to provide pre-matching in the port cell region adjacent to the antenna, final matching, decoupling of mutual inductances between antenna elements, and passive ELM resilience. The development and design of the various system components will be discussed. High power tests of components have begun, and the latest results will be presented. [Preview Abstract] |
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UP8.00018: Performance Calculations for the ITER Core Imaging X-Ray Spectrometer (CIXS) K.W. Hill, L. Delgado-Aparicio, N. Pablant, D. Johnson, R. Feder, J. Klabacha, B. Stratton, M. Bitter, P. Beiersdorfer, R. Barnsley, G. Bertschinger, M. O'Mullane, S.G. Lee The US is providing a 1D imaging x-ray crystal spectrometer system as a primary diagnostic for measuring profiles of ion temperature (T$_{\mathrm{i}})$ and toroidal flow velocity (v) in the ITER plasma core (r/a $=$ 0-0.85). The diagnostic must provide high spectral resolution (E/$\Delta $E \textgreater\ 5,000), spatial resolution of 10 cm, and time resolution of 10-100 ms, and must operate and survive in an environment having high neutron and gamma-ray fluxes. This work presents spectral simulations and tomographic inversions for obtaining local T$_{\mathrm{i}}$ and v, comparisons of the expected count rate profiles to the requirements, the degradation of performance due to the nuclear radiation background, and measurements of the rejection of nuclear background by detector pulse-height discrimination. [Preview Abstract] |
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UP8.00019: Current status of the ITER MSE diagnostic Howard Yuh, F. Levinton, H. La Fleur, E. Foley, R. Feder, L. Zakharov The U.S. is providing ITER with a Motional Stark Effect (MSE) diagnostic to provide a measurement to guide reconstructions of the plasma q-profile. The diagnostic design has gone through many iterations, driven primarily by the evolution of the ITER port plug design and the steering of the heating beams. The present two port, three view design viewing both heating beams and the DNB has recently passed a conceptual design review at the IO. The traditional line polarization (MSE-LP) technique employed on many devices around the world faces many challenges in ITER, including strong background light and mirror degradation. To mitigate these effects, a multi-wavelength polarimeter and high resolution spectrometer will be used to subtract polarized background, while retroreflecting polarizers will provide mirror calibration concurrent with MSE-LP measurements. However, without a proven plasma-facing mirror cleaning technique, inherent risks to MSE-LP remain. The high field and high beam energy on ITER offers optimal conditions for a spectroscopic measurement of the electric field using line splitting (MSE-LS), a technique which does not depend on mirror polarization properties. The current design is presented with a roadmap of the R\&D needed to address remaining challenges. [Preview Abstract] |
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UP8.00020: Status of the design of the Diagnostic Residual Gas Analyzer System for ITER first plasma T.M. Biewer, C.C. Klepper, B. DeVan, V. Graves, C. Marcus, T. Younkin, P. Andrew, D.W. Johnson Among the ITER procurements awarded to the US ITER Domestic Agency, and subsequently to the ORNL Fusion \& Materials for Nuclear Systems Division, is the design and fabrication of the Diagnostc Residual Gas Analyzer (DRGA) system. The DRGA system reached the Preliminary Design Review (PDR) in Spring 2013, and has transitioned into the Final Design phase. As a result of the PDR, and ITER systems design evolutions, several design changes have been incorporated into the DRGA system. The design effort has focused on the vacuum and mechanical interface of the DRGA gas sampling tube with the ITER vacuum vessel and cyrostat. Moreover, R\&D tasks to demonstrate the 3-sensor instrumentation design (quadrupole mass spectrometer, ion-trap mass spectrometer, and optical Penning gauge) are maturing through the construction and testing of a DRGA prototype at ORNL. Results will be presented at this poster along with the DRGA design overview. [Preview Abstract] |
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UP8.00021: Exploration of ITER Steady-State Scenarios Using FASTRAN/IPS Integrated Transport Modeling M. Murakami, J.M. Park, D.B. Batchelor, S.J. Diem, W.R. Elwasif, A.C. Sontag ITER steady-state (SS) scenarios are examined using an iterative steady-state ($d/dt=0$) solution procedure using FASTRAN solver implemented in Integrated Plasma Simulator framework, self-consistently with heating and current drive (H\&{CD}), MHD equilibrium, and transport models. The objective of the exercise is to understand the range of steady-state solutions using theory-based transport models with the ITER Day-1 H\&{CD} and proposed upgrades (EC launcher modifications). ITER operation performances (fusion gain $Q$ and noninductive fraction $f_{NI}$ and steady burn duration) are compared using different transport models (TGLF, GLF23, CDBM, MMM7.1) based on the edge profiles scaled from recent DIII-D ITER Steady State Demo discharges as well as from the existing pedestal models (EPED). Sensitivities of the operation spaces are studied using different density peaking and plasma current. Reducing $I_p$ increases achievable $f_{NI}$ while peaking density increases $Q$ but limited by MHD stability. Optimization of Day-1 H\&CD mixes is discussed toward the ITER goal ($Q=5$ and $f_{NI}=1$ for 3000~s). [Preview Abstract] |
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UP8.00022: Nonlinear Burn Control and Operating Point Optimization in ITER Mark Boyer, Eugenio Schuster Control of the fusion power through regulation of the plasma density and temperature will be essential for achieving and maintaining desired operating points in fusion reactors and burning plasma experiments like ITER. In this work, a volume averaged model for the evolution of the density of energy, deuterium and tritium fuel ions, alpha-particles, and impurity ions is used to synthesize a multi-input multi-output nonlinear feedback controller for stabilizing and modulating the burn condition. Adaptive control techniques are used to account for uncertainty in model parameters, including particle confinement times and recycling rates. The control approach makes use of the different possible methods for altering the fusion power, including adjusting the temperature through auxiliary heating, modulating the density and isotopic mix through fueling, and altering the impurity density through impurity injection. Furthermore, a model-based optimization scheme is proposed to drive the system as close as possible to desired fusion power and temperature references. Constraints are considered in the optimization scheme to ensure that, for example, density and beta limits are avoided, and that optimal operation is achieved even when actuators reach saturation. [Preview Abstract] |
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UP8.00023: Demonstrated 3600 s Integrator Operation with 5.4 $\mu $V-s Drift Error for ITER Long Pulse Applications Kenneth Miller, Timothy Ziemba, James Prager, Ilia Slobodov Eagle Harbor Technologies has developed a high gain and frequency ultra-stable integrator for small scale concept experiments and long pulse ITER applications. The integrator has a 10 $\mu $s RC time with a frequency response greater than 10 MHz. The device has been operated for the 3600 s with a drift error less than 5.4 $\mu $V-s, which exceeds the ITER specification. Longer period operation has also been demonstrated (72 hours). Additionally, this integrator has an extremely large dynamic range thereby increasing the effective bit depth of a digitizer. These integrators allow for both the fast and slow magnetic/plasma dynamics to be resolved with a single diagnostic. Software has been written for fast, real-time data acquisition and processing using a field programmable gate array (FPGA). [Preview Abstract] |
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UP8.00024: DIII-D TOKAMAK |
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UP8.00025: 3D Magnetic Perturbation Effects on Transport in Tokamaks T.E. Evans, T.L. Rhodes, L. Zeng, G.R. McKee, D.M. Orlov, R.A. Moyer, G.R. Tynan, W. Xiao, R. Nazikian Recent experimental results in DIII-D H-mode plasmas, with a constant level of applied n=3 perturbation fields, have revealed dramatic particle, energy and momentum transport changes simply by altering the relative toroidal phase between the intrinsic n=1 and 2 field-errors and the applied n=3 perturbation field. Here, we present a summary of the experimental observations, including changes in the turbulence and MHD behavior in configurations with either constructive or destructive interference between the intrinsic n=1 and 2 fields and the applied n=3 field. A particularly interesting aspect of these results is that the energy confinement increases by $\sim$35\% when the intrinsic and applied perturbation fields are relatively well aligned to produce a larger total radial field. Similar increases are seen in the particle and momentum confinement. These observations are compared to a hypothesis connecting the structure of the 3D radial magnetic perturbation field to the changes in transport. [Preview Abstract] |
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UP8.00026: DIII-D Magnetic Diagnostics Upgrade for Non-axisymmetric Fields E.J. Strait, J.D. King, C. Paz-Soldan, J.M. Hanson, D. Shiraki, N.C. Logan, R.L. Boivin, D.A. Taussig, M.G. Watkins A recent upgrade has expanded DIII-D's capabilities for measurement of non-axisymmetric fields such as resistive wall modes, locked tearing modes, and the stable plasma response to error fields and applied non-axisymmetric perturbations. The upgrade includes the addition of over 100 new poloidal field and radial field sensors inside the vacuum vessel. Combined with previously installed sensors, these allow simultaneous resolution of toroidal mode numbers $n\le$ 3 on both the low field side and high field side, and provide poloidal resolution as small as 14 cm on the high field side. The large contribution of the axisymmetric field is eliminated by differential measurements of approximately 120 pairs of toroidally separated sensors, using special dual-input integrators. Initial results from the new system will be compared to predictions of 3D equilibrium and stability codes. [Preview Abstract] |
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UP8.00027: 3D Equilibrium Reconstructions in DIII-D L.L. Lao, N.W. Ferraro, E.J. Strait, A.D. Turnbull, J.D. King, H.P. Hirshman, E.A. Lazarus, A.C. Sontag, J. Hanson, G. Trevisan Accurate and efficient 3D equilibrium reconstruction is needed in tokamaks for study of 3D magnetic field effects on experimentally reconstructed equilibrium and for analysis of MHD stability experiments with externally imposed magnetic perturbations. A large number of new magnetic probes have been recently installed in DIII-D to improve 3D equilibrium measurements and to facilitate 3D reconstructions. The V3FIT code has been in use in DIII-D to support 3D reconstruction and the new magnetic diagnostic design. V3FIT is based on the 3D equilibrium code VMEC that assumes nested magnetic surfaces. V3FIT uses a pseudo-Newton least-square algorithm to search for the solution vector. In parallel, the EFIT equilibrium reconstruction code is being extended to allow for 3D effects using a perturbation approach based on an expansion of the MHD equations. EFIT uses the cylindrical coordinate system and can include the magnetic island and stochastic effects. Algorithms are being developed to allow EFIT to reconstruct 3D perturbed equilibria directly making use of plasma response to 3D perturbations from the GATO, MARS-F, or M3D-C1 MHD codes. DIII-D 3D reconstruction examples using EFIT and V3FIT and the new 3D magnetic data will be presented. [Preview Abstract] |
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UP8.00028: Resonant Error Fields and Their Relation to Fully Penetrated Locked Modes in Ohmic Plasmas in DIII-D R.J. La Haye, E.J. Strait, C. Paz-Soldan Relatively small resonant (m/n=2/1) static error fields are shielded in Ohmic plasmas by the natural rotation at the electron diamagnetic drift frequency. However, the drag can lower rotation such that a bifurcation results going from nearly complete shielding to full penetration, i.e., a locked mode island that can induce disruption [1]. Understanding is of importance for the initial plasma operation of ITER without supplementary heating. Error field correction (EFC) is done on DIII-D with either the n=1 C-coil (no handedness) or the n=1 I-coil (more resonant hand). Despite EFC which allows significantly lower plasma density (figure of merit) before penetration occurs, the resulting saturated islands have similar large size; they differ only in phase after typically being pulled in the electron diamagnetic drift direction as they grow to saturation. The data are explained by a change-of-state of the classical tearing index from stable before penetration starts to non-linearly marginal. Comparison to an island evolution model will be presented.\par \vskip6pt \noindent [1] R.J. La Haye et al., ``Model for Effect of Non-Resonant Error Field on Resonant Error Field Locking in Ohmic Plasmas in DIII-D,'' Bull. Am. Phys. Soc. 57, 141, (2012) [Preview Abstract] |
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UP8.00029: Plasma Response Modeling of Changes due to Coupling of Error Fields D.M. Orlov, R.A. Moyer, T.E. Evans, N.M. Ferraro, L. Zeng The applied n=3 external perturbation in DIII-D couples constructively or destructively to the dominantly n=1 and n=2 intrinsic error fields. Recent experiments have shown a very strong dependence of the particle and momentum transport on the relative phase of the I-coil perturbation. In this work, we present the results of the linear two-fluid plasma response modeling (M3D-C1) in terms of the magnetic topology changes associated with alternating relative phase of the perturbation and its effect on the transport in the pedestal region. We show that the intrinsic error fields and sideband modeling in the linear MHD codes significantly change the magnetic topology and produce a wide stochastic region. The effect of the changes in the plasma rotation and the plasma equilibrium on the topology and transport are discussed. The results of the plasma response modeling are compared to the vacuum model and to the experimental measurements. [Preview Abstract] |
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UP8.00030: Diagnosis of 3D Perturbed Equilibrium States of DIII-D B.J. Tobias, J.K. Park, L. Yu, C.M. Muscatello, C.W. Domier, N.C. Luhmann, M.E. Austin, J.D. King, C. Paz-Soldan, A.D. Turnbull Non-axisymmetric 3D equilibria supported by saturated internal magnetic islands have been compared to those induced by external magnetic perturbation and solutions obtained by the IPEC method. Diagnosis of these modes as proxy for the least stable non-axisymmetric configuration provides a simplified path to advancing our understanding of critical aspects of resonant magnetic perturbation suppression of edge localized modes, error field correction, and locked mode disruption avoidance. However, initial comparisons of the measured poloidal mode number to theory have not produced quantitative agreement. Possible sources of discrepancy are explored through improved modeling, new experimental data, and use of the new 3D magnetic and 2D reflectometric diagnostics on DIII-D. [Preview Abstract] |
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UP8.00031: Developing a Roadmap for US Divertor and PMI Research in the ITER Era D.N. Hill, B. Lipschultz, D.G. Whyte, A.M. Garofalo, A.W. Leonard, R. Maingi The role of existing and candidate future facilities for developing driven core, boundary plasma and plasma-facing components (PFCs) solutions for burning plasma experiments will be discussed in light of scientific and technical challenges, testing capabilities, scheduling implications, and cost. Present experiments point to likely integrated core-edge solutions which may enable steady-state high-gain, high power density operation; focused research on existing tokamak facilities could strengthen confidence significantly. In parallel, both existing and new candidate materials suitable for testing under high neutron fluence can be developed and qualified. We will also discuss the potential role of new facilities in closing the knowledge gaps to a Fusion Nuclear Science Facility (FNSF), and what form the final step of integrating core and edge solutions will be (separate, or as part of an FNSF) in terms of size, goals and cost. [Preview Abstract] |
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UP8.00032: Snowflake Divertor Configuration Studies in DIII-D Tokamak V.A. Soukhanovskii, S.L. Allen, B.I. Cohen, M.E. Fenstermacher, D.N. Hill, C.J. Lasnier, M.A. Makowski, A.G. McLean, W.H. Meyer, T.D. Rognlien, D.D. Ryutov, E. Kolemen, R.J. Groebner, A.W. Hyatt, A.W. Leonard, T.H. Osborne, T.W. Petrie, J.A. Boedo, J.G. Watkins Experiments in DIII-D show the snowflake divertor (SFD) configuration is compatible with high performance operation ($H_{98y2}\geq 1$) and results in greatly reduced divertor heat flux between and during edge localized modes (ELMs). The SFD was sustained for many energy confinement times using the standard poloidal field shaping coils in 3-5 MW neutral beam injection-heated discharges. Pedestal and divertor effects resulting from a large region of reduced poloidal magnetic field in the SFD are measured and studied using the 2D multi-fluid code UEDGE. The pedestal pressure appeared to be unchanged, while the energy loss per ELM was reduced by 50\%. Partial detachment of the SFD was observed at higher $n_e$, with an expanded divertor radiation zone and peak ELM heat flux reduced by up to 80\%. [Preview Abstract] |
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UP8.00033: Modeling Divertor Plasma Characteristics for Snowflake Configurations in the DIII-D Tokamak T.D. Rognlien, B.I. Cohen, D.D. Ryutov, M.V. Umansky, S.L. Allen, G.D. Porter, V.A. Soukhanovskii A snowflake divertor is formed when two magnetic X-points are brought in close proximity [1]. Such a configuration is expected to reduce peak divertor heat flux through E.G. magnetic flux expansion, increased volume for line radiation, and longer magnetic connection length. Reduced heat fluxes have been observed on TCV, NSTX, and DIII-D [2]. 2D UEDGE plasma/neutral transport simulations are performed to compare plasma profiles and fluxes near the DIII-D divertor plates for a single-X-point divertor and a snowflake divertor. Radial transport coefficients are fit to yield measured midplane profiles, with divertor profiles computed self-consistently. As observed experimentally [2], a substantial reduction in peak heat flux is found for the snowflake, with flux expansion being a key effect. The impact of plasma convection driven by large local plasma $\beta_p$ near the magnetic null is modeled by $\beta_p$-dependent transport.\par \vskip6pt \noindent [1] D.D.\ Ryutov, Phys.\ Plasmas {\bf 14}, 064502 (2007).\par \noindent [2] S.L.\ Allen, et al., 2012 IAEA Fusion Energy Conf., San Diego, CA,\break ~~post deadline paper.\hfil\par [Preview Abstract] |
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UP8.00034: Carbon Ion Flow Measurements in DIII-D Divertors Using Coherence Imaging Spectroscopy S.L. Allen, W.H. Meyer, G.D. Porter, J. Howard New, single-crystal imaging interferometers along with improved relay optics have been installed in the upper and lower DIII-D divertors. These provide improved images of the Doppler shift and thereby flow of CIII (465 nm) ions. An improved in-situ calibration technique has been implemented, providing zero velocity reference images and measured spectrometer phase vs wavelength. The temperature resolution of the system has been greatly improved, resulting in a stable wavelength calibration. Image intensified cameras have made possible measurements of flow during ELMS and in the non-active divertor. Streamlined data analysis has been used to look for flow trends. In general, we see flow in opposite directions on the inner and outer scrape-off layers in the divertor. [Preview Abstract] |
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UP8.00035: Measurements of Magnetic Topology During 3D Magnetic Perturbations in the X-point Region of DIII-D E.A. Unterberg, M.W. Shafer, A. Wingen, J.H. Harris, D.L. Hillis, T.E. Evans, N.M. Ferraro 2D imaging of soft x-ray (SXR) emission near the X-point region of a diverted, H-mode tokamak show experimental evidence of helical structures inside the separatrix when non-axisymmetric fields are applied. The helical structures are measured to be in the steep-pressure-gradient region, have poloidal mode number $m=11\pm1$, and have a spatial extent of ~5 cm near the X point region. These data characteristics match calculations using the two-fluid, resistive MHD code, M3D-C1, which self-consistently accounts for the on and off resonant plasma response. These calculations are also consistent with displacements in edge Thomson Scattering data. This quantitative evaluation of boundary and internal plasma displacements through comparisons between data and modeling provide valuable insight into the details of how applied 3D magnetic perturbations affect edge stability, in general, and how resonant magnetic perturbations affect ELM stability, in particular. [Preview Abstract] |
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UP8.00036: Scaling of the Heat Flux Width with Plasma Density in DIII-D M.A. Makowski, C.J. Lasnier, J. Nichols, A.W. Leonard, T.H. Osborne, P.B. Snyder The previous study of the relationship between the heat flux width and upstream profiles [1] is extended with the addition of density scans. These scans range from a low-density, attached state to a high-density, detached state on both the inner and outer divertors in both L- and H-mode discharges. Under attached conditions in L-mode both the inner and outer heat flux profiles are well fit by Eich's fitting function [2] and clearly indicate the transition from attached to detached states. Analysis of the density scans will be combined with previous scaling results to extend the heat flux width database. Comparisons to a critical gradient model will also be made to assess its validity under these new conditions.\par \vskip6pt \noindent [1] M.A. Makowski, et al., Phys. Plasmas 19, 056122 (2012).\\[0pt] [2] T. Eich et al., Phys. Rev. Lett. 107, 215001 (2011) [Preview Abstract] |
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UP8.00037: Modeling of the Thermal Footprint at the Strike Point and Fast Thermocouples in Carbon Tiles R.E. Nygren, J.G. Watkins, D.A. Buchenauer, M.A. Makowski, A.W. Leonard Thermal broadening can complicate interpretation of IR images at the strike point because the peaked profile of surface temperature widens as the tile heats due to lateral conduction away from the peak, so the instantaneous values of $\lambda_q$ extracted from IR images increases during the shot. Detailed 3D thermal analyses of divertor tiles complement data from edge probes, fast thermocouples (FTCs) and IR thermography and aids interpretation. But the surface temperature reflects the integrated heat load over time, so changes in power or movement of the plasma complicates this interpretation. The array of 16 embedded FTCs in DIII-D divertor tiles are 8 mm below the surface.The poster focuses on the degree to which the FTCs can help resolve the absolute value of the surface temperature and the extracted profile of surface temperature and related peaked heat load.We include a series of detailed 3D thermal analyses of one DIII-D tile exposed to a (theoretical) peaked heat load characterized by the commonly-used two-parameter fit [1].\par \vskip6pt \noindent [1] T.~Eich, et al., Phys.\ Rev.\ Lett.\ {\bf 107}, 215001 (2011). [Preview Abstract] |
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UP8.00038: Characterizing the Outer Divertor Leg Transition to Full Detachment A.G. McLean, S.L. Allen, M.E. Fenstermacher, C.J. Lasnier, W.H. Meyer, G.D. Porter, V.A. Soukhanovskii, B.D. Bray, T.N. Carlstrom, A.W. Leonard, C. Liu, D. Eldon, M. Groth, P.C. Stangeby, C.K. Tsui Experiments at DIII-D have explored the transition from an attached to fully detached divertor condition in L- and H-mode with an unprecedented level of detail. Improved divertor Thomson scattering capturing $T_e \leq 1\,$eV, coupled with high resolution spectroscopic studies of molecular and neutral emissions, and Stark broadening of the deuterium Paschen series provide essential data for modeling the transition to detachment. 2D $T_e$ and $n_e$ profiles of the outer leg reveal movement of the ionization front away from the plate not replicated in modeling. Measured Paschen and molecular emissions suggest the onset of recombination occurs prior to, and to a greater extent than modeled. These data help guide and expose any missing physics in predictions for detached operation in future devices. [Preview Abstract] |
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UP8.00039: OEDGE Modeling of DIII-D Density Scan Discharges Leading to Detachment J.D. Elder, P.C. Stangeby, C.K. Tsui, A.W. Leonrad, B.D. Bray, N.H. Brooks, J.A. Boedo, D.L. Rudakov, J.G. Watkins, E.A. Unterberg, C.J. Lasnier, A.G. McLean The OEDGE code is used to model the edge plasma for discharges from a density scan experiment on DIII-D. In this experiment the plasma density was increased over a series of L-mode discharges starting with a lower density discharge with both targets attached ($n_e=1.6\times 10^{19}\,$m$^{-3}$) and ending with a higher density discharge with both targets detached ($n_e=4.5\times 10^{19}\,$m$^{-3}$). These discharges used large X-point sweeps to maximize plasma measurements. Scans with the recently installed swing probe at the inner wall provided $n_e$ and $T_e$ measurements of the inner divertor. Target Langmuir probe, Thomson scattering and spectroscopic measurements in the divertor were also made. These discharges are among the best diagnosed discharges ever made on DIII-D. For attached plasmas, OEDGE modeling replicates quite well the relation between divertor measurements and measurements in the main SOL, indicating that for attached divertor conditions the controlling physics appears to have been identified and correctly incorporated in OEDGE. [Preview Abstract] |
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UP8.00040: Identifying the Location of the Separatrix at the OMP in DIII-D Using Power Accounting P.C. Stangeby Two methods are used which employ power accounting to improve the accuracy of identifying R-sep-omp, the location of the separatrix at the outside midplane (omp). The first method uses the measured deposited power profile at the outer target as the primary input, the P-SOL-exhaust method. The other uses the measured power input to the SOL, obtained from the total heating power less the power radiated from inside the separatrix, the P-SOL-input method. The methods were applied to experimental data for 21 H-mode DIII-D discharges. High spatial resolution Thomson scattering measured profiles of between-ELM $n_e$ and $T_e$ were used to calculate the electron parallel conducted heat flux profile which was then matched to the measured P-SOL-exhaust and P-SOL-input by adjusting R-sep-omp relative to that of the Thomson data. The values of R-sep-omp from the 2 methods agree to within $\sim$1 mm of each other and to within $\sim$1 mm of the values given by the ``standard DIII-D method'' [1]. This results in only modest changes to $n_e$ and $T_e$ at R-sep-omp relative to the ``standard'' values, increasing $n_e$ by $\sim$10\% and $T_e$ by $\sim$20\%.\par \vskip6pt \noindent[1] G.D. Porter et al., Phys. Plasmas 5, 1410 (1998). [Preview Abstract] |
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UP8.00041: Experimental Observations of I-Phase at DIII-D D. Eldon, P.H. Diamond, G.R. Tynan, T.L. Rhodes, L. Schmitz, G.R. McKee, R.J. Groebner, P.B. Snyder, T.H. Osborne, M.A. Van Zeeland, T.E. Evans, J.D. King, R.L. Boivin Intermediate or I-phase has received much attention in the context of L-H transitions, but similar behavior is observed in H-L transitions as well. I-phase has been described as a predator prey interaction between Zonal Flows and turbulence [1]. Direct measurements of ZF speed and density fluctuation turbulence are possible with Doppler backscattering and beam emission spectroscopy (BES). Broadband turbulence with frequency of order $\sim$100 kHz has been observed with intensity modulation at $\sim$1 kHz, narrow band. Modulation frequency is an inverse function of pedestal density, which grows during L-H and decays during H-L. Activity at the modulation frequency is observed through many channels: an n=0 magnetic signature on the shelf probes, electron density and temperature fluctuations localized to the pedestal steep gradient region, and filterscope signals. Unlike other radially resolved measurements (BES, ECE), the mode seen by filterscopes is localized to the scrape off layer. BES measures a phase lag between chords separated poloidally (order $\sim$10 km/s flow) but not radially.\par \vskip6pt \noindent [1] K. Miki, et al., Phys. Plasmas 19, 092306 (2012). [Preview Abstract] |
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UP8.00042: Study of Fluctuations with the PCI Diagnostic During the Search for an I-Mode on DIII-D A. Marinoni, J.C. Rost, M. Porkolab, A.E. Hubbard, A.E. White, D.G. Whyte, K.H. Burrell, T.H. Osborne Recent experiments on DIII-D explored the operational space required to achieve the I-mode regime observed on Alcator C-Mod. This regime features an edge energy transport barrier without an accompanying particle barrier, and broadband instabilities known as WCM [1]. Although none of the DIII-D plasmas exhibited all those characteristics, preceding the H-mode transition, the edge electron temperature slowly and intermittently evolved towards a pedestal-like profile 0.4 keV high while maintaining a typical L-mode edge density profile. During this prelude phase, edge density fluctuations measured with the recently upgraded Phase Contrast Interferometer (PCI) are observed to be qualitatively similar to those seen in H-mode: the intensity of fluctuations is reduced, and the frequency spectrum is broadened in the range of 300 kHz and is non-monotonic. The 2D k-f spectra also approach those typical of an H-mode, showing broad fluctuations in k-space and group velocities increasing to 10 km/s. Several branches are observed in 2D spectra, possibly indicating multiple instabilities at play.\par \vskip6pt \noindent [1] D.G. Whyte et al., Nucl. Fusion 50, 105005 (2010). [Preview Abstract] |
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UP8.00043: ECE Imaging of Broadband Turbulence in DIII-D Plasmas S.E. Zemedkun, T. Munsat, B.J. Tobias, C.W. Donier, N.C. Luhmann, Jr Observations of 2D turbulent structures have been performed with the ECEI instrument on DIII-D in plasmas heated by neutral beam injection (NBI) and electron cyclotron heating (ECH), at a fixed heating power (up to 5 MW). Correlation techniques similar to those used in correlation electron cyclotron emission (CECE) systems are employed, with the advantage that the ECEI system detects a full 2D array of plasma locations; vertical separation is provided by an optical system and horizontal separation is provided by frequency discrimination in the detection electronics. Among the results are 2D images of poloidally-propagating drift waves, and correlation properties of fluctuations ($<$200 kHz) in the poloidal direction. Observed dispersion relations for two different heating conditions (ECH and NBI) will be presented. Comparison of results with simulations using GEM code will be discussed. In addition to the physics results, the data demonstrates the viability of the ECEI system in the presence of ECH heating. [Preview Abstract] |
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UP8.00044: Commissioning of the Microwave Imaging Reflectometer (MIR) on DIII-D C.M. Muscatello, C.W. Domier, D. Gamzina, X. Hu, N.C. Luhmann, Jr., X. Ren, P. Riemenschneider, A. Spear, L. Yu, T. Munsat, S.E. Zemedkun, B.J. Tobias A microwave imaging reflectometer (MIR), capable of simultaneously measuring the poloidal and radial structure of density fluctuations, has been developed for DIII-D and installed in May 2013. The MIR diagnostic concept has undergone numerous technological and system-level upgrades since earlier microwave imaging systems, thereby permitting a higher level of robustness and flexibility. Synthetic diagnostic simulations permit determination of the resolvable wavenumbers and density fluctuations levels. Laboratory qualification tests are performed to characterize the system performance compared to the designed parameters. First plasma results are presented in the form of a brief survey of MIR results collected during several select experiments from the 2013 DIII-D experimental campaign. [Preview Abstract] |
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UP8.00045: Recycling Reduction and Density Control with Lithium Injection in DIII-D G.L. Jackson, C.P. Chrobak, R. Maingi, D. Mansfield, A. Roquemore, A.G. McLean Lithium conditioning has been effective in tokamaks for reducing recycling and providing density control, particularly in NSTX and EAST. Since DIII-D has not injected lithium in more than a decade (and then in only very small amounts, 0.4 g total), a unique opportunity exists to extend this experience and examine the physical effects of lithium in a well-conditioned lithium-free machine. A lithium dropper, developed by PPPL, has recently been installed on DIII-D. By injecting 0.09 g of lithium we have observed reductions in recycling, density, and ELM frequency from the first discharge with significant lithium injection. Although modeling of individual 40$\,\mu$m diam. Li granules predicts virtually no penetration beyond the separatrix in auxiliary heated H-mode pulses, Li$^{III}$ emission was detected in the core plasma, albeit with no increase in radiated power. On subsequent discharges without injection no core Li was detected, and only Li$^I$ emission was observed in the SOL and divertor regions. We will present the effects of Li on recycling, ELM frequency, and the edge pedestal, and discuss the long-term observations of lithium on plasma facing components. [Preview Abstract] |
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UP8.00046: Interaction of Turbulence-Driven and Equilibrium Flows in Limit-Cycle L-H and H-L Transitions L. Schmitz, L. Zeng, T.L. Rhodes, E.J. Doyle, W.A. Peebles, G. Wang, G.R. McKee, Z. Yan, G.R. Tynan, J.A. Boedo, P. Diamond, D. Eldon, R.J. Groebner, K.H. Burrell The detailed spatio-temporal evolution of turbulence-driven flow and equilibrium flow have been investigated during limit cycle oscillations (LCO) [1,2] preceding the L-H transition and the H-L back-transition in DIII-D. The phasing between $E\times B$ flow and turbulence envelope indicates radially separated regions of flow drive and flow damping. The ion pressure gradient periodically steepens during transient transport barrier formation in the LCO and initially lags the flow shearing rate $\omega_{E\times B}$, but leads $\omega_{E\times B}$ once equilibrium shear has become dominant before the final transition to H-mode. The first simultaneous measurements of main ion flow evolution across the L-LCO-H-mode transition (via He plasmas) will be discussed, as well as initial evidence of hysteresis in turbulence/flow evolution between forward and back transitions.\par \vskip6pt \noindent [1]~L.~Schmitz, L.~Zeng, et al., Phys.\ Rev.\ Lett.\ {\bf 108}, 155002 (2012).\par \noindent [2]~K.~Miki and P.H.\ Diamond, Phys.\ Plasmas {\bf 19}, 092306 (2012). [Preview Abstract] |
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UP8.00047: Phase Contrast Imaging Measurements of Edge Turbulence Across an H-mode Transition J.C. Rost, A. Marinoni, M. Porkolab, K.H. Burrell The Phase Contrast Imaging (PCI) diagnostic on DIII-D provides a line-integrated measurement of density fluctuations. Analysis of previous PCI data taken during QH mode plasmas has revealed turbulence with short radial wavelengths and high frequencies which is generated by the well in the radial electric field $E_r$. Application of these results allows us to study the rapid evolution in turbulence at an L-H transition. The dominant effect of the L-H transition on turbulence is a 70\% drop in fluctuation amplitude. However high frequency fluctuations are seen to arise on the same time scale as the L-H transition (i.e. a few ms). Interpretation of the 2d spectrum $S(k,f)$ of the PCI data of the line-integrated fluctuation, especially the Doppler shift and the ratio $S(k_{pci})/S(-k_{pci})$, indicates that the high frequency fluctuations are located on the inner edge of the $E_r$ well. There is in addition a region of turbulence the PCI detects which is located outside the minimum of the $E_r$ well. This ongoing work will provide quantitative information on the evolution of the $E_r$ well at high time resolution across the L-H transition, important to understanding the interaction between turbulence and flow shear at the H-mode transition. [Preview Abstract] |
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UP8.00048: Pedestal Structure in DIII-D Steady-State Discharges A.C. Sontag, S.J. Diem, M. Murakami, J.M. Park, J.R. Ferron, T.H. Osborne, C.T. Holcomb A range of DIII-D steady-state discharges have been analyzed to determine the pedestal structure and bootstrap current as a function of several global parameters including $q_{min}$, $q_{95}$ and $\beta_N$. The pedestal structures are compared with EPED predictions. Variations in turbulence, $E\times B$ shearing rate, $j_{BS}$ and MHD stability are examined. DIII-D is developing candidate high-$\beta_N$ steady-state operational scenarios, including high-$q_{min}$ and high-$\ell_i$, through current and pressure profile optimization. Pedestal structure and how it affects the current profile is important for any sustained high performance scenario. High-$q_{min}$ scenarios require a relatively large pedestal height with significant bootstrap current, while high-$\ell_i$ scenarios require a smaller pedestal and reduced bootstrap current. Understanding how the pedestal structure is affected by the other requirements of operating in these scenarios is needed for this optimization. [Preview Abstract] |
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UP8.00049: Use of TGLF Model to Study Pedestal Particle Transport in DIII-D R.J. Groebner, G.M. Staebler, A.W. Leonard, T.H. Osborne, L.W. Owen, D.J. Battagli The TGLF transport model is used to study particle transport in the edge H-mode pedestal in DIII-D and to answer the question: Is the structure of the density pedestal due to fluctuations that drive an inward particle flux that nearly balances an outward diffusive flux? TGLF is used to evaluate a theoretical form for the electron particle flux that contains a term due to a diffusive term driven by the density gradient, an off-diagonal diffusive term driven by the temperature gradient, which typically causes an inward pinch, and a residual flux driven by the curvature drift and Landau damping. The residual flux is expected to be small in the pedestal region compared to the other two terms. Initial simulations with this model have shown a large inward pinch nearly balanced by diffusion in the pedestal. Simulations of density pedestal build-up during ELM-free H-mode will be made to determine if the TGLF predicted particle flux is consistent with experiment and if the model predicts large competing convective and diffusive fluxes. [Preview Abstract] |
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UP8.00050: Optimizing Pedestal Performance with the EPED Model P.B. Snyder, E.A. Belli, R.j. Groebner, T.H. Osborne, J.W. Hughes, H.R. Wilson Fusion energy performance of tokamak plasmas is expected to scale strongly with the pressure at the top of the edge transport barrier (or ``pedestal height"). The EPED model predicts pedestal height by combining calculated peeling-ballooning (PB) and kinetic ballooning mode (KBM) constraints. EPED has been successfully compared to hundreds of cases on 5 tokamaks finding within $\sim$20\% agreement with observed pedestal height. We develop and test methods for optimizing the pedestal height on existing devices as well as ITER, including use of impurities to vary pedestal collisionality, and ``Super H-Mode" operation in strongly shaped plasmas. Ongoing development of the EPED model, including coupling to bootstrap current calculations with the NEO code, and direct electromagnetic gyrokinetic calculations, is also discussed, as is application of the model to ELM suppressed regimes. [Preview Abstract] |
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UP8.00051: Core Perturbations Caused by Edge-Localized Modes (ELMs) in DIII-D Abdullah Zafar, R.A. Moyer, E.M. Hollmann, L. Zeng, M.E. Austin The inward propagation of the perturbations caused by edge-localized modes (ELMs) is studied in DIII-D. ELMs are associated with peeling-ballooning modes in tokamaks, which have eigenfunctions that are localized to the edge and pedestal region, but the core density is seen to respond strongly to each ELM crash. Type-I ELMs are analyzed using various diagnostics (microwave reflectometry, electron cyclotron emission, and soft x-ray). Penetration deep into the core from an ELM crash is observed for type-I ELMs in certain cases. In these cases, the ``hole'' caused by an ELM crash propagates as far as the magnetic axis. The depth of the perturbation is compared to ELM size and the time in-between subsequent ELMs. The time scale that the perturbation is seen to travel in is also analyzed in relation to diffusive or ballistic transport. [Preview Abstract] |
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UP8.00052: Development of an Internal, Localized Magnetic Field Fluctuation Diagnostic on the DIII-D Tokamak T.L. Rhodes, W.A. Peebles, X. Nguyen, C. Wannberg UCLA is developing a new generation internal magnetic field fluctuation diagnostic utilizing cross-polarization scattering [1,2], a process where magnetic fluctuations scatter EM radiation into the perpendicular polarization. The unique scattering geometry offered by Doppler backscattering probe beams are utilized to improve the spatial localization and wavenumber range. When fully developed the system will measure magnetic fluctuations in the core and edge of high-performance tokamak plasmas with cm spatial and microsecond time resolution, and wavenumber range $k\rho_s \sim\,$0.25-9. The diagnostic is being developed on DIII-D but is potentially applicable to spherical tokamaks (NSTX) and future burning plasmas such as ITER. System goals, constraints, and design, including quasi-optical elements are presented. Laboratory measurements of the system performance and comparison to design targets as well as initial plasma tests will be shown.\par \vskip6pt \noindent [1]~T.~Lehner, et al., Europhys.\ Lett.\ {\bf 8}, 759 (1989).\par \noindent [2] Linda Vahala, et al., Phys.\ Fluids B {\bf 4}, 619 (1992). [Preview Abstract] |
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UP8.00053: Evolution of Edge Pedestal Current in Type-1 ELM and ITER Baseline Scenario Discharges on DIII-D D.M. Thomas, T.H. Osborne, R.J. Groebner, H. Stoschus, X. Chen, K.E. Kaplan Based on recent improvements to the DIII-D LIBEAM diagnostic, we have measured the evolution of the edge plasma current density, $j$, in the pedestal region during the Type 1 ELM cycle, as well as during variations in pedestal pressure in ITER baseline scenario as the inter-ELM temperature and density evolve separately. Conditional averaging of our signals along with other diagnostics over multiple Type 1 ELMs improves the sensitivity and time resolution of this technique. New methods of accounting for varying background light during the pedestal rise help to reduce the systematic error in the measurement. Initial analysis shows that the current peak can relax by about a factor of two within a few ms after an ELM, consistent with resistive decay times in the edge. Changes in the current amplitude for high frequency ELM conditions are consistent with damping of the neoclassical current at the higher collisionality typically associated with higher edge densities and lowered edge temperatures. These results are in accord with our emerging picture of ELM physics and pedestal formation. [Preview Abstract] |
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UP8.00054: Ion Orbit Loss Effect on Pedestal Structure W.M. Stacey The effect of ion orbit loss of thermal ions and the compensating return ion current directly on the toroidal and poloidal rotation velocity profiles, and thereby indirectly on the radial electric field, density and temperature profiles in the plasma edge, is investigated for the purpose of understanding the extent to which ion orbit loss determines the edge pedestal structure. Illustrative calculations for DIII-D [1] high-confinement H-mode plasmas are presented and compared with experimental results. Ion orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure on the profiles of poloidal rotation and radial electric field, as well as the ion particle pinch, in the edge plasma. These, in turn, are instrumental in determining pressure, density and temperature profiles. Taking ion orbit loss into account is also found to affect the interpretation of transport parameters from measurements in the edge.\par \vskip6pt \noindent [1] J.L.\ Luxon, Nucl.\ Fusion {\bf 42}, 614 (2001). [Preview Abstract] |
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UP8.00055: Ion Orbit Loss Effect on Structure of Radial Electric Field T.M. Wilks, W.M. Stacey, T.E. Evans The radial electric field is an important factor in the L-H transition, the onset of edge localized modes (ELMs), etc. Therefore the causes and trends of the radial electric field in the edge and scrape off layer regions are of interest. As part of an investigation of mechanisms for controlling the electric field in the edge plasma, the effects of ion orbit loss and the compensating ion return current on the radial electric field in the edge region and scrape off layer are analyzed. Both thermalized plasma ions and fast ion losses are considered in the investigation, and shown to have implications on the toroidal and poloidal rotation velocity profiles, which are closely linked to the radial electric field. Local density and temperature profiles are taken into account in order to model the fraction of ions that pass the separatrix, but orbit back into the edge plasma. The inclusion of fast beam ions along with the orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure of the radial electric field in the edge pedestal. [Preview Abstract] |
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UP8.00056: Examination of the Evolution of Edge Profiles and Ion Transport Between ELMs on DIII-D J.-P. Floyd, W.M. Stacey, S.C. Mellard, R.J. Groebner The measured edge profile evolution between edge-localized modes (ELMs) of DIII-D H-mode discharge 144977 is analyzed with a fine time resolution in order to understand the evolution of diffusive (inferred thermal diffusivities and ion diffusion coefficients) and non-diffusive (particle pinch velocities) transport properties in the edge, using the momentum balance methodology of Ref. [1]. The evolution of the density, temperature, rotation, and radial electric field profiles in the edge pedestal between ELMs provides information of these diffusive and non-diffusive transport processes in the pedestal of H-mode plasmas. This methodology is incorporated into the GTEDGE code developed for DIII-D data interpretation. Using a smaller integration time for the charge-exchange-recombination measurements than past analyses allows a more detailed examination of the time evolution of the ion temperature and rotation velocities.\par \vskip6pt \noindent [1] W.M.\ Stacey and R.J.\ Groebner, Nucl.\ Fusion {\bf 51}, 063024 (2011). [Preview Abstract] |
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UP8.00057: Transport Characteristics of Modulation Resonant Magnetic Perturbations (M-RMP) in DIII-D H-mode Plasmas W.W. Xiao, T.E. Evans, G.R. Tynan, L. Zeng, D.M. Orlov, R.A. Moyer, G.D. Wang, T.L. Rhodes 3D resonant magnetic perturbation (RMP) fields are widely used for the ELM control or mitigation in Tokamaks and stellarators and are being developed as an approach to future burning plasma devices such as ITER. Understanding particle transport is a RMP physics issue. Here, we present a new experimental result of the resonance position of the RMP, which is directly confirmed using induced density perturbation produced by Modulated Resonant Magnetic Perturbations (M-RMP). A comparison study of the resonance locations with fixed q95 and with scanning q95 is presented in this work. Recent experimental results on the particle transport with M-RMP in DIII-D H-mode plasmas, have been investigated as well. These results show that a strong inward particle pinch exists in pedestal region in M-RMP H-mode plasma. [Preview Abstract] |
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UP8.00058: COMPLEXITY AND SELF ORGANIZATION |
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UP8.00059: Single Flux Rope Dynamics in the Reconnection Scaling Experiment Yan Feng, J. Sears, T.P. Intrator, T.E. Weber, H. Swan, K. Gao A magnetic flux tube threaded by current is a flux rope with helically twisted field lines. In the Reconnection Scaling Experiment (RSX) we use a plasma gun to generate a single flux rope with a choice of axial boundary conditions. If this flux rope is driven hard enough, i.e., when $J\cdot B/B^{2}$ is larger than the kink instability threshold, we measure a helically distorted kinked structure. Rather than exploding in an Alfv\'{e}n time, this kink appears to saturate to a steady amplitude, helical, gyrating flux rope, which persists as long as the plasma gun sources the current. To understand it, we have experimentally measured three-dimensional profiles of various quantities of this flux rope. These quantities include magnetic field $B$, plasma density $n$ and potential $\varphi $, ion flow velocity $v_{i}$, so that current density $J$, electron flow velocity $v_{e}$ and electron pressure $P_{e}$ can also be derived. The full set of these quantities allows us to analyze the single flux rope dynamics systematically. Besides gyrating, we also find the flux rope has a spin center, around which the $J \times B-\nabla P_{e} \ne 0$ suggesting that there should be other forces for the radial balancing. We also find that within about 30 cm distance from the plasma gun, there is a reverse current moving around with the flux rope. [Preview Abstract] |
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UP8.00060: Measurement {\&} Imaging for the Reconnection Scaling Experiment H. Swan, J. Sears, Y. Feng, T. Intrator The Reconnection Scaling Experiment (RSX) is a fundamental investigation of the detailed behavior and interactions of plasma flux ropes, both within the framework of MHD and on electron inertial length scales (mm). Effectively determining the dynamics of flux ropes requires precisely located, 3D measurements of a wide array of parameters: density and temperature (pressure), ion velocity, current density (electron fluid flow), and magnetic fields. To achieve this, RSX employs a large suite of diagnostic probes, which are inserted directly into the plasma in various locations and orientations, as well as external cameras and other optical tools. We describe several useful experimental diagnostic developments. These include a homebrew recipe for fabricating Mach probes, with directionality that is easy to implement at construction time, and a straightforward but powerful 3D imaging technique that allows precision location of probes within the experiment, using no more sophisticated hardware than standard webcams. We discuss the challenges of reconstructing plasma dynamics from the myriad data channels involved, and how the new diagnostics help solve these challenges. [Preview Abstract] |
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UP8.00061: Rapid Change of Field Line Connectivity in Stochastic Magnetic Fields Yi-Min Huang, A. Bhattacharjee, Allen H. Boozer Magnetic fields depending on three spatial coordinates generally have the feature that neighboring field lines exponentiate away from each other and become stochastic. Under the condition of large exponentiation, magnetic field line connectivity becomes extremely sensitive to small perturbations. Consequently, small deviations from ideal Ohm's law will violate the ideal magnetohydrodynamic constraint and completely scramble the field line connectivity. This idea of breaking field line connectivity by stochasticity is tested with numerical simulations based on reduced magnetohydrodynamics equations. We employ a simple model starting from a uniform magnetic field in the $z$ direction, and bounded by perfectly conducting planes in $z$. High order hyper-resistivity is employed as the mechanism of breaking field lines. As magnetic field lines is gradually entangled by the spatially smooth applied force, neighboring field line exponentiation becomes large. Field line connectivity is observed to undergo rapid change on Alfven transit time scales, accompanied by sporadic magnetic energy release. [Preview Abstract] |
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UP8.00062: Experimental investigation of plasma relaxation using a compact coaxial magnetized plasma gun in a background plasma Yue Zhang, Alan Lynn, Mark Gilmore, Scott Hsu A compact coaxial plasma gun is employed for experimental studies of plasma relaxation in a low density background plasma. Experiments are being conducted in the linear HelCat device at UNM. These studies will advance the knowledge of basic plasma physics in the areas of magnetic relaxation and space and astrophysical plasmas, including the evolution of active galactic jets/radio lobes within the intergalactic medium. The gun is powered by a 120pF ignitron-switched capacitor bank which is operated in a range of 5 - 10kV and $\sim$100 kA. Multiple diagnostics are employed to investigate plasma relaxation process. Magnetized Argon plasma bubbles with velocities $\sim$1.2Cs and densities $\sim$1020 m$^{-3}$ have been achieved. Different distinct regimes of operation with qualitatively different dynamics are identified by fast CCD camera images, with the parameter determining the operation regime. Additionally, a B-dot probe array is employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify detached plasma bubble configurations. Experimental data and analysis will be presented. [Preview Abstract] |
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UP8.00063: Investigating the Dynamics of Canonical Flux Tubes Jens von der Linden, Evan Carroll, Yu Kamikawa, Eric Lavine, Keon Vereen, Setthivoine You Canonical flux tubes are defined by tracing areas of constant magnetic and fluid vorticity flux. This poster will present the theory for canonical flux tubes and current progress in the construction of an experiment designed to observe their evolution. In the zero flow limit, canonical flux tubes are magnetic flux tubes, but in full form, present the distinct advantage of reconciling two-fluid plasma dynamics with familiar concepts of helicity, twists and linkages. The experiment and the DCON code [1] will be used to investigate a new MHD stability criterion for sausage and kink modes in screw pinches that has been generalized to magnetic flux tubes with skin and core currents. Camera images and a 3D array of $\dot{B}$ probes will measure tube aspect-ratio and ratio of current-to-magnetic flux, respectively, to trace these flux tube parameters in a stability space. The experiment's triple electrode planar gun is designed to generate azimuthal and axial flows. These diagnostics together with a 3D vector tomographic reconstruction of ion Doppler spectroscopy [2] will be used to verify the theory of canonical helicity transport [3].\\[4pt] [1] A. H. Glasser, M. C. Chance Bull. Am. Phys. Soc., 42 (1997)\\[0pt] [2] S. You et al., J. Fusion Energy, 29 (2010)\\[0pt] [3] S. You, Phys. of Plas., 19 (2012) [Preview Abstract] |
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UP8.00064: A Laboratory Astrophysical Jet to Study Canonical Flux Tubes Setthivoine You, Jens von der Linden, Keon Vereen, Evan Carroll, Yu Kamikawa, Eric Sander Lavine A new research program aims to simulate a magnetically driven jet launched by an accretion disk in a laboratory experiment. The experiment replaces an accretion disk that would rotate at impractical speeds in the laboratory with three concentric annular electrodes, independently biased by two sets of pulsed power supplies to generate magnetized plasma shear flows [1]. With three electrodes, the radial electric field can be set up to approximate the rotation profile of an accretion disk. The primary diagnostics include arrays of magnetic probes to measure 3D magnetic fields and arrays of lines-of-sight to measure 3D ion flows from vector tomography of ion Doppler spectral lines [2]. The symmetry of fast gas puff sources [3] is fine-tuned with a fast ion gauge [4] to remove any anchoring effects of discrete gas holes on the azimuthal rotation of the plasma jet. The aim is to understand how magnetically driven astrophysical jets become long and collimated, how they become unstable or turbulent, and investigate the physics from a canonical flux tube point-of-view [5]. A canonical flux tube is a fundamental tube of magnetic flux with helical flows.\\[4pt] [1] E. Carroll [2] K. Vereen [3] Y. Kamikawa [4] E.S. Lavine [5] J. von der Linden, S. You group, this meeting. [Preview Abstract] |
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UP8.00065: Particle diffusion and energization in Arnold-Beltrami-Childress force-free helical magnetic fields B. Dasgupta, F. Holguin, A.K. Ram, D. Mitra It has long been considered that the cosmic magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free in the sense that the Lorentz force vanishes. The Arnold-Beltrami-Childress (ABC) field is an example of a force-free helical magnetic field. The ABC magnetic field lines exhibit a complex and varied structure and can be chaotic. The motion of charged particles in regions of spatially chaotic ABC magnetic field lines displays a variety of dynamical behavior depending on the particle's energy and its initial direction of motion with respect to the local magnetic field vector. Particles started on chaotic magnetic field lines do not necessarily follow chaotic orbits [1]. A class of particles executes periodic motion. For steady-state ABC fields the particles diffuse in space. For time-dependent ABC fields the particles gain energy for extended time periods--the mean kinetic energy has a power-law behavior in time. We present results on the dynamics of particles, and on their spatial diffusion and velocity space energization in ABC fields.\\[4pt] [1] A. K. Ram and B. Dasgupta, {\it Phys. Plasmas} {\bf 17}, 122104 (2010). [Preview Abstract] |
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UP8.00066: PLASMA SHEATH |
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UP8.00067: Improved Measurements of Ion Beam Formation in Expanding Helicon Plasmas Using Upgraded Laser Induced Fluorescence Injection Optics Earl Scime, John McKee, Mark Soderholm, Robert VanDervort A number of studies have demonstrated the spontaneous formation of ion beams in expanding plasmas. Ion beams are identified through measurements of the ion velocity distribution function. The two primary diagnostic techniques for the performing these measurements are laser induced fluorescence (LIF) and retarding field energy analyzers. Each measurement method has its strengths and weaknesses. One particular challenge for LIF is the difficulty in obtaining good signal to noise when the measurement location is far from the point of optical access to the plasma chamber and the light must be conveyed to the experiment through optical fibers. Here we present LIF measurements performed over 3 meters away from a 2.75'' injection port. Laser light is coupled into a polarization preserving, single mode, optical fiber and focused to a beam radius of a few mm after the light emanating from the fiber is collimated with a concave mirror to eliminate chromatic distortion as the laser wavelength is scanned. Significant gains in signal-to-noise were obtained over unoptimized, injection optics; expanding the pressure and RF power range over which LIF measurements could be performed. LIF measurements of the argon ivdf in low and high pressure expanding helicon plasmas will be presented. [Preview Abstract] |
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UP8.00068: The Effect of Magnetic Field on the RF Collisional Sheath Ying Wang, Xianzhu Tang The Chodura sheath has been widely studied for decades. For an oblique magnetic field, there exists in front of the Debye sheath (of thickness several Debye length, in front of the solid surface) a Chodura sheath, also known as the magnetic pre-sheath, of thickness several ion Larmor radius. A 1D particle-in-cell (PIC) code [1] with Monte Carlo collision methods is upgraded for the magnetic field with arbitrary angles. The effect of the magnetic field on RF sheath parameters, such as ion fluxes to the surface and ion/neutral energy and angular distributions, is investigated. A special attention is given to the angles of a few degrees between the magnetic field and the surface. The PIC simulation results are compared with the self-consistent analytical RF sheath model [2] for the magnetic field parallel to the surface.\\[4pt] [1] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, Simultaneous Potential and Circuit Solution for 1d Bounded Plasma Particle Simulation Codes J. Comp. Phys. 104 (1993) 321.\\[0pt] [2] M. A. Lieberman, Model of Magnetically Enhanced, Capacitive RF discharges, IEEE Trans. Plasma Sci., 19 (1991) 189 [Preview Abstract] |
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UP8.00069: High-voltage Sheath Dynamics of Grid Electrodes Changho Yi, Won Namkung, Moo-hyun Cho The Plasma-immersed ion implantation (PIII) is a well-known technology to modify properties of material surfaces. The Pseudo-wave assisted PIII is one kind of PIII, which uses ions in pseudo-wave generated by high-voltage pulses applied to the grid electrodes. Since high-voltage electrodes do not contact film directly, the pseudo-wave PIII takes advantage in preventing arcing problems between electrodes and film. In the pseudo-wave assisted PIII, quantity and energy of implanted ions depend on characteristics of high-voltage sheath around the grid electrodes. Thus, to characterize the implanted ions in the pseudo-wave assisted PIII, we have to understand the dynamics of high-voltage sheath of grid electrodes. In this paper, we present the PIC simulation and experimental results about high-voltage sheath dynamics of grid electrodes. In addition, we present the simple model about high-voltage sheath dynamics of grid electrodes and compare with simulation and experimental results. [Preview Abstract] |
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UP8.00070: Two-Stream Instabilities and Enhanced Friction Forces in the Two Ion Species Plasma Presheath Scott D. Baalrud, Trevor Lafleur, William Fox, Kai Germaschewski A recent theory proposes that ion-ion two-stream instabilities can arise in the presheath of plasmas with two ion species under certain conditions and that these instabilities rapidly enhance the frictional coupling between the ion species [1]. These predictions were later confirmed experimentally [2]. However, recent work has questioned the validity of this theory based on PIC simulations that did not observe instabilities [3]. Using exact numerical solutions of the dispersion relation, we show that the source of this apparent discrepancy is a lower electron temperature in the simulations. Although the previous approximate instability criterion derived in Ref.\ [1] predicts instability at the lower electron temperature, we show here that the results of Ref.\ [3] are in fact consistent with the instability bounds of the exact theory. Furthermore, we find that the exact theory still predicts instability at the measured electron temperature [2]. Finally, we conduct new PIC simulations of the presheath and directly identify ion-ion two-stream instabilities and enhanced friction forces.\\[4pt] [1] Baalrud, Hegna and Callen, PRL 103, 205002 (2009).\newline [2] Yip, Hershkowitz and Severn, PRL 104, 225003 (2010). \newline [3] Gudmundsson and Lieberman, PRL 107, 045002 (2011). [Preview Abstract] |
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UP8.00071: Analysis of Particle Detectors in Plasma Sheaths on Sounding Rockets and in Laboratory Plasmas Lisa Fisher, Kristina Lynch The influence of plasma sheaths on particle measurements is a well-known problem. Improvements in computational speed and memory have made the use of particle-in-cell codes, attainable on a laptop. These codes can calculate complex sheath structures and include most of the relevant physics. We will discuss how the use of one such code, SPIS, has been integrated into our data processing for the MICA sounding rocket. This inclusion of sheath physics has allowed us to describe the current-voltage signature of an ion retarding potential analyzer, called the PIP, to measure the ambient ionospheric temperature, as well as to examine the possibility of ion upflow. These results will be compared with the other instrumentation on MICA, which use traditional thin-sheath approximations. This comparison will emphasize the strengths and weaknesses of these other data analysis methods and call attention to the need to include sheath physics when measuring very low energy populations. Additionally, these instruments have also been tested in the Dartmouth College plasma facility. This provides another set of plasma conditions for testing and extrapolating our method to a future low-orbit mission. [Preview Abstract] |
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UP8.00072: Formation of magnetic presheaths by electron collecting probes in magnetized ExB drifting plasma and current collection Jonathon Heinrich, David Cooke A fundamental and unanswered question in the field of probe theory is ``what is the current limit of electron collecting probes in magnetized ExB drifting plasma?'' The question can be reduced to ``what are the associated electron energization and acceleration processes or how does the plasma couple to the probe?'' Work in the 1990's speculated plasma coupling to positive probes in ExB drifting plasma included the formation of a magnetic presheath, a heated presheath, and whistler wings. We report on the results of three-dimensional electromagnetic particle-in-cell simulations of electron collecting probes in magnetized ExB drifting plasma. Distinct regions developed around the probe: a quasi-trapped electron region encircling the probe and an electron depletion wing that extended along the magnetic field due electron collection by the probe. We present observations of electron heating and energization in the quasi-trapped region, a whistler pulse preceding the electron depletion wing, and electron acceleration by a magnetic presheath associated with the electron depletion wing and the impact of these processes on the probe's current collection. [Preview Abstract] |
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UP8.00073: DUSTY PLASMA |
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UP8.00074: On the dynamics of dust grains with propeller-like features Sergei Krasheninnikov In many cases (e.g. astrophysical plasma, fusion devices) dust grains can have very peculiar shapes, which are far from spherical. Recently it was shown that the dynamics of non-spherical grains in plasma has some rather distinct features. For example, being immersed in a plasma flow, such grains can exhibit ``dithering'' of their trajectory, which can be observed with fast cameras, although spatial resolution of these cameras does not allow resolve the grain themselves. However, available theoretical models describing the dynamics of non-spherical grain in plasma neglect possible propeller-like features of the grain. Here we present the result of theoretical study of the impact of propeller-like shape of the grain on it's dynamics. [Preview Abstract] |
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UP8.00075: Dust-Density Waves Under Microgravity Conditions and Their Influence on the Discharge Tim Bockwoldt, Kristoffer Menzel, Alexander Piel In a capacitively-coupled radio-frequency discharge, micrometer sized particles charge negatively and sediment in the lower sheath. Under microgravity conditions, e.g., on parabolic flights, the dust particles fill the whole plasma except for a central void. In these extended clouds dust-density waves are spontaneously excited and propagate radially outwards. Depending on the discharge parameters and the amount of dust injected into the plasma, the wave field exhibits commensurable or incommensurable frequency clusters with commensurate or incommensurate frequencies. Incommensurable frequencies were found in situations with spatial gradients of the dust plasma frequency [1]. When clusters of commensurable frequencies, e.g., harmonics of a fundamental, are formed, a simultaneous modulation of the plasma glow can be observed [2]. Measurements of the discharge voltage and probe signals show, that the entire discharge is affected. We therefore suggest the model of a self-organized system including the discharge, the dust particles and the electric circuit. In this contribution the findings and the model will be discussed in detail. \\[4pt] [1] Menzel, K.O., Arp, O., Piel A., Vol 104, p. 235002, 2010\\[0pt] [2] Bockwoldt, T., Menzel, K.O., Arp, O., Piel, A.,IEEE Trans. Plasma Sci., Vol 41, 4, 2013 [Preview Abstract] |
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UP8.00076: Examination of the Wake Potential and the Intergrain Force for Particles within a Glass Box Bo Zhang, Jie Kong, Lorin Matthews, Truell Hyde The potential structure created by the ion wakefield has been shown to interact with dust grains immersed within a plasma. This wakefield has been extensively investigated over the subsonic to supersonic regimes using the Cartesian mesh, Oblique boundary, Particles and Thermals In Cell (COPTIC) code for particles in a complex plasma. In this study, two dust particles in a dusty plasma and provided additional confinement by a glass box are examined. The force experienced on both the downstream particle (with and without the upstream particle) and the upstream particle (with and without the downstream particle) is determined simultaneously. By tuning the relative position of each dust particle with respect to their alignment to the plasma flow, the wake potential for each is mapped. It is shown that the structure of the wake potential is strongly affected by both the ion streaming flow and the orientation of the interparticle force. [Preview Abstract] |
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UP8.00077: Synchronization of the dust acoustic wave under microgravity W.D. Suranga Ruhunusiri, J. Goree Synchronization is a nonlinear phenomenon where a self-excited oscillation, like a wave in a plasma, interacts with an external driving, resulting in an adjustment of the oscillation frequency. To prepare for experiments under microgravity conditions using the PK-4 facility on the International Space Station, we perform a laboratory experiment [1] to observe synchronization of the self-excited dust acoustic wave. An rf glow discharge argon plasma is formed by applying a low power radio frequency voltage to a lower electrode. A 3D dust cloud is formed by levitating 4.83 micron microspheres inside a glass box placed on the lower electrode. The dust acoustic wave is self-excited with a natural frequency of 22 Hz due to an ion streaming instability. A cross section of the dust cloud is illuminated by a vertical laser sheet and imaged from the side with a digital camera. To synchronize the wave, we sinusoidally modulate the overall ion density. Differently from previous experiments, we use a driving electrode that is separate from the electrode that sustains the plasma, and we characterize synchronization by varying both driving amplitude and frequency. \\[4pt] [1] Ruhunusiri \& Goree, Phys. Rev. E, 85, 046401 (2012) [Preview Abstract] |
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UP8.00078: Caltech water-ice dusty plasma: preliminary results Paul Bellan, Kilbyoung Chai A water-ice dusty plasma laboratory experiment has begun operation at Caltech. As in Ref. [1], a 1-5 watt parallel-plate 13.56 MHz rf discharge plasma has LN2-cooled electrodes that cool the neutral background gas to cryogenic temperatures. However, instead of creating water vapor by in-situ deuterium-oxygen bonding [1], here the neutral gas is argon and water vapor is added in a controlled fashion. Ice grains spontaneously form after a few seconds. Photography with a HeNe line filter of a sheet of HeNe laser light sheet illuminating a cross section of dust grains shows a large scale whorl pattern composed of concentric sub-whorls having wave-like spatially varying intensity. Each sub-whorl is composed of very evenly separated fine-scale stream-lines indicating that the ice grains move in self-organized lanes like automobiles on a multi-line highway. HeNe laser extinction together with an estimate of dust density from the intergrain spacing in photographs indicates a 5 micron nominal dust grain radius. HeNe laser diffraction patterns indicate the ice dust grains are large and ellipsoidal at low pressure (200 mT) but small and spheroidal at high pressure (\textgreater 600 mT). \\[4pt] [1] Shimizu et al [JGR 115, D18205 (2010)] [Preview Abstract] |
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UP8.00079: Particles in the wake of other particles Dietmar Block, Wojciech Jacek Miloch The charging of dust grains in the wake of another grains in sonic and supersonic collisionless plasma flows is studied by numerical simulations. The simulations are carried out with DiP3D, a three dimensional particle-in-cell code with both electrons and ions represented as numerical particles. We consider two grains aligned with the flow, as well as dust chains and multiple grain arrangements. It is found that the dust charge depends significantly on the flow speed, distance between the grains, and the grain arrangement. Special attention is paid to typical experimental situations like a particle below a layer of particles and small 3D clusters. [Preview Abstract] |
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UP8.00080: Simple explanation of stationary voids in a weakly magnetized nanodusty plasma Franko Greiner, Benjamin Tadsen, Nils K\"ohler, Jan Carstensen, Alexander Piel Voids are an interesting feature of three dimensional dust clouds in laboratory plasmas. To create large dust clouds under normal gravitational conditions on earth, nanodust can be used. In our experiments the nanodust is produced in a rf driven, capacitively coupled, parallel plate reactor using an argon acetylene mixture at 10 - 30\,Pa. It is well known, that density and potential show single humped profiles in such a configuration. In a simplified single particle picture (SPP) the void boundary establishes at a position, where the sum of ion drag force and electric field force are balanced. In contrast to unmagnetized plasmas, where the size of the void increases with increasing particle size, a weak magnetization ($ B \approx 100$~mT) results in a large, stationary void. The void captures nearly the whole discharge volume and is independent of the dust size. Spatially resolved Langmuir probe measurements, due to technical reasons performed in in the pure argon plasma, show that the floating potential profile and density profile are both double humped. Consistent with experimental observation, the SPP leads to the ``non-confinement'' of all particles with radii smaller than a critical value. [Preview Abstract] |
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UP8.00081: Meteor dust in the ionosphere makes dust plasma Scott Robertson, Heiner Asmus Flights of rocket-borne probes into the ionosphere have returned data from 60-100 km altitude on the occurrence of meteoric dust (Robertson et al., J. Atmos. Sol.-Terr. Phys, 2013 in press). The number density of these particles is of order 20,000/cc which exceeds the typical electron density at 60-70 km but is smaller than the electron density typical at 90-100 km. Model equations and rocket data show that the ionosphere makes a transition from the dust particles being almost entirely negatively charged at high altitude to the dust particles being almost equally positive and negative at lower altitudes. The low-altitude result is a consequence of the electron and ion from an ionization event each attaching to dust particles before other processes can occur. Equilibrium is established in which attachment of an electron or ion to a neutral dust particle is equally as probable as it neutralizing a dust particle of the opposite sign. The low altitude region has many more positive and negative dust particles than electrons or ions, hence a dust plasma rather than a dusty plasma. [Preview Abstract] |
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UP8.00082: Collisional Effects on Nonlinear Ion Drag Force for Small Grains I.H. Hutchinson, C.B. Haakonsen Ion drag force arising from plasma flow past an embedded grain in a plasma is a vital part of dusty plasma dynamics. Ion-neutral collisions are often significant for experimental dusty plasmas. They are here included self-consistently in properly nonlinear comprehensive drag calculations, for the first time. The ion drag on a spherical grain is calculated using particle in cell codes SCEPTIC and COPTIC. Using ion velocity ``drift'' distribution appropriate for flow driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality level. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if nonlinear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided. [Preview Abstract] |
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UP8.00083: Stereoscopic observation of the Brownian motion of a single dust particle Christian Schmidt, Alexander Piel, Michael Himpel, Andr\'e Melzer The Brownian motion of a single melamine-formaldehyde particle of 6.8 micron diameter is observed with 3 fast video cameras that are aligned in the xyz directions. The particle is trapped in the ``anodic plasma'' that forms in front of a small, positively DC-biased (0-300 V) additional electrode of 3 mm diameter embedded in the lower electrode of a parallel plate rf-discharge operated at 13.56 MHz, $p_{argon}$ = 10-20 Pa, $U_{pp}$ = 50-150 V. The random motion of the particle in 3D is analyzed in terms of the velocity distribution f(vx,vy,vz) and spatial distribution w(x,y,z). Systematic errors in deriving correct temperatures are discussed and compared with Langevin MD simulations. The eigenfrequencies of the potential trap are derived from FFT-spectra of the individual velocity components and are found consistent with the spatial distribution w(x,y,z). [Preview Abstract] |
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UP8.00084: Transportation of the dust particles using electrical curtain method in TReD(Transport and removal experiments of Dust) device Soon-Gook Cho, Suk-Ho Hong, Min-Keun Bae, In-Jae Kang, Jin-Woo Kim, Hyung-Jin Kim, Sung-Kiu Joo, Myoung-Jae Lee, Kyu-Sun Chung TReD (Transport and Removal experiment of Dust) device is developed to demonstrate the dust removal and reliable dust removal efficiency in realistic scale for the application to advanced tokamaks like KSTAR and/or ITER. Size of the TReD device is the following dimension: 1200(L) x 500(W) x 440(H) mm$^{3}$. Negatively charged dust particles are to be levitated by the negative sheath potential, and to be transported by the diffusion (from generation position) and by the mobility (due to the electric field by the bottom electrodes). The bottom electrodes are composed of 86 thin rectangular bars which are separated by 1 mm between electrodes. Al$_{2}$O$_{3}$ particles are used with size of 1 $\sim$ 10 $\mu$m, as proxies for B$_{2}$O$_{3}$ dust particles to be generated in ITER. The dust particles are injected by dust dispensers and levitated within sheath potential and transported by three phase electric potential applied to bottom electrodes. Characterization of metal-dust containing Helium plasma is to be made by electrical probes and removal efficiency of the dust is going to be addressed in terms of frequency and magnitude of applied voltage. [Preview Abstract] |
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UP8.00085: How Yukawa balls expand Alexander Piel, Tim Bockwoldt, John Goree Yukawa balls [1] are spherical arangements of highly charged microparticles in a complex (dusty) plasma, which are confined in a potential trap and interact by shielded Coulomb forces. When the confinement is switched off, the particle cloud expands rapidly. The analogous process of Coulomb explosions of a xenon nanocluster that has been completely stripped of electrons by a femtosecond laser pulse, see e.g. [2], is an established technique to produce energetic ions. Coulomb explosions represent a self-similar expansion process. In this contribution we demonstrate that the expansion of a Yukawa system is governed by a different principle. Because of the shielding, the expansion starts as blow-off of the surface layer and continues by the inward propagation of a rarefactive wave, which delays the blow-off of deeper layers. The differences between Coulomb explosions and Yukawa expansions are investigated by Molecular Dynamics simulations and analytical models.\\[4pt] [1] Arp et al, Phys. Rev. Lett. 93, 165004 (2004)\\[0pt] [2] Nishihara et al, Nucl. Instrum. Methods A 464, 98 (2001) [Preview Abstract] |
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UP8.00086: Dust acoustic instability in a strongly coupled dusty plasma M. Rosenberg, G.J. Kalman, P. Hartmann, J. Goree Dusty plasmas are plasmas containing charged micron to sub-micron size dust grains (solid particulates). Because the grains can be multiply charged and are much more massive than the ions, the presence of dust can lead to novel waves such as the dust acoustic wave, which is a compressional wave that can be excited by a flow of ions that is driven by an electric field. Moreover, the large dust charge can result in strong Coulomb coupling between the dust grains, where the electrostatic energy between neighboring grains is larger than their thermal (kinetic) energy. When the coupling between dust grains is strong, but not large enough for crystallization, the dust is in the strongly coupled liquid phase. This poster theoretically investigates the dust acoustic instability, which is driven by sub-thermal ion flow, in a three-dimensional dusty plasma in the strongly coupled liquid phase. It is found that strong coupling enhances the instability. The application is to microgravity experiments with dusty plasma planned for the PK-4 and PlasmaLab instruments, which are in development for the International Space Station. Microgravity conditions enable the preparation of dust clouds under these sub-thermal ion flow conditions by avoiding the need for strong electric fields to levitate the dust grains [Preview Abstract] |
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UP8.00087: Wave dispersion in a strongly coupled 2D superparamagnetic dusty plasma P. Hartmann, Z. Donko, M. Rosenberg, G.J. Kalman Dusty plasmas are plasmas containing fine charged solid particulates, or dust grains. Typically, the dust grains interact via a screened Coulomb (Yukawa) interaction, where the screening of the dust charge is due to the background plasma. Here, we consider a two-dimensional (2D) dusty plasma composed of charged superparamagnetic dust which is immersed in a magnetic field \textbf{B} whose magnitude and direction can be varied. In this case, the dust grains thus interact via both Yukawa and magnetic dipole-dipole interactions. Because the induced magnetic dipole moments of the grains lie along \textbf{B}, the interaction between the grains becomes anisotropic as \textbf{B} is tilted with respect to the layer. This poster considers wave dispersion in the strongly coupled liquid phase of this system. The analysis is confined to magnetic tilt angles such that the interaction remains repulsive in the dust layer and corresponds to a stable equilibrium. The theoretical approach uses a reformulated Quasi-Localized Charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole-dipole interactions and the direction of wave propagation in the layer. [Preview Abstract] |
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UP8.00088: Laboratory study of the expansion of a three-dimensional dusty plasma John K. Meyer, Robert L. Merlino The expansion of a three-dimensional dusty plasma was investigated using fast video imaging and particle tracking techniques. The dust suspension was initially trapped in the electrostatic potential formed by an L-shaped grid in a glow discharge plasma. The discharge was formed in argon at a neutral pressure of 125 mtorr at a discharge current of 5 mA. A 3 mT uniform magnetic field was also present. The dust was spherical glass particles of 1 micron diameter, with an initial density on the order of 10$^{\mathrm{4}}$ cm$^{\mathrm{-3}}$. The electron temperature was 2.5 eV, and the estimated dust charge was $-$2000 e. The initially confined dust cloud had a volume on the order of 1-2 cm$^{\mathrm{3}}$. The expansion of the dust cloud was initiated when the confining potential was removed by suddenly switching the bias on the grid to the floating condition. Measurements of the time history of the particle velocities and dust density within the expanding cloud will be presented. [Preview Abstract] |
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UP8.00089: Developing Real-Time Particle Tracking Velocimetry for Complex Plasmas Brian Lynch, Uwe Konopka, Edward Thomas, Ross Fisher Complex plasmas contain, in addition to the usual electrons, ions, and neutral atoms, macroscopic electrically charged (nanometer to micrometer) sized ``dust'' particles. Based on the ratio of the electrostatic potential to kinetic energy, these microparticles can exhibit gaseous, fluid, and even crystal-like behavior. As a result, complex plasmas are a unique testing ground to study multi-particle systems like crystals, fluids, and their transitions and properties. The behavior of complex plasmas is generally studied using digital imaging systems with laser sheet illumination. Following data acquisition, Particle Tracking Velocimetry (PTV) is one of several post-processing techniques used in the determination of dust grain dynamics. The extracted velocity fields provide a spatially resolved particle phase space distribution (PSD) function that can be used to calculate correlation functions and thermal properties of the system. In this presentation, we outline the development of the ``Complex Plasma Analysis'' (CoPlA) software suite, which is based on spatial and temporal predictor methods to facilitate real-time particle tracking. [Preview Abstract] |
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UP8.00090: Design and Assembly of the Magnetized Dusty Plasma Experiment (MDPX) Ross Fisher, Darrick Artis, Brian Lynch, Keith Wood, Joseph Shaw, Kevin Gilmore, Daniel Robinson, Christian Polka, Uwe Konopka, Edward Thomas, Robert Merlino, Marlene Rosenberg Over the last two years, the Magnetized Dusty Plasma Experiment (MDPX) has been under construction at Auburn University. This new research device, whose assembly will be completed in late Summer, 2013, uses a four-coil, superconducting, high magnetic field system ($|$B$|$ $\ge$ 4 Tesla) to investigate the confinement, charging, transport, and instabilities in a dusty plasma. A new feature of the MDPX device is the ability to operate the magnetic coils independently to allow a variety of magnetic configurations from highly uniform to quadrapole-like. Envisioned as a multi-user facility, the MDPX device features a cylindrical vacuum vessel whose primary experimental region is an octagonal chamber that has a 35.5 cm inner diameter and is 19 cm tall. There is substantial diagnostics and optical access through eight, 10.2 cm x 12.7 cm side ports. The chamber can also be equipped with two 15.2 cm diameter, 76 cm long extensions to allow long plasma column experiments, particularly long wavelength dust wave studies. This presentation will discuss the final design, assembly, and installation of the MDPX device and will describe its supporting laboratory facility. [Preview Abstract] |
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UP8.00091: Magnetized Dusty Plasma Experiment (MDPX): Initial Observations and Measurements Edward Thomas, Ross Fisher, Uwe Konopka, Robert Merlino, Marlene Rosenberg The mission of the Magnetized Dusty Plasma Experiment (MDPX) is to study the fundamental properties of a plasma in which first the electrons, then the ions, and finally the charged dust grains come under the influence of an externally applied magnetic field whose magnitude can be increased to 4 T or greater. The MDPX device, which has been under construction for the last two years, is expected to begin magnetized plasma operations in early Fall, 2013. Initial investigations will focus on high magnetic field operations, stable plasma generation at high magnetic field strengths, and the initial characterization of the dust particle response to the magnetic fields. Additionally, these initial tests will also provide an opportunity to test and validate the operation of the diagnostic systems (e.g., Langmuir probes, fast video cameras, particle image velocimetry, laser induced fluorescence, etc.) at high magnetic field strengths. This presentation will discuss the initial performance of the MDPX device, initial observations of plasma and dusty plasma behavior, and the long-term experimental plan for MDPX. [Preview Abstract] |
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UP8.00092: A Novel Experimental Setup to Investigate Magnetized Dusty Plasmas C.A. Romero-Talamas, P. LaRocque, J. Alvarez, J. Sardin Progress on the design and construction of a novel experimental setup to investigate dusty plasmas at the University of Maryland, Baltimore County (UMBC) is presented. The setup includes separation adjustability of discharge electrodes and their orientation with respect to gravity without breaking vacuum, and a pair of water-cooled coils to produce magnetic fields with strengths of up to several Tesla. The coils' orientation is also designed to be adjustable with respect to gravity. A pulse-forming network to power the coils with flattop times of several seconds is under design. The setup is mounted inside a large glass bell jar to provide wide optical access to the dusty plasmas, and to minimize interference of chamber walls and mounts with imposed electric or magnetic fields. Planned experiments include crystallization and wave propagation under strong magnetic fields. [Preview Abstract] |
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UP8.00093: Evolution of frequency clusters in the self-excited and driven dust acoustic wave Jeremiah Williams The presence of particulate matter in a plasma system gives rise to a wide range of new plasma phenomena. These complex systems, known as dusty plasmas, support a number of new collective modes such as the dust acoustic wave. The dust acoustic wave has been the subject of intense experimental and theoretical study since being predicted in 1990 and identified experimentally in 1994. In this work, the spatio-temporal dynamics of this fundamental wave mode are examined applying the Hilbert transform to high speed video imaging of the naturally-occurring and driven wave modes. This provides insight into the instaneous frequency across the propagating wave as a function of time. While we observe the presence of frequency clusters, a result that is consistent with previous measurements, it is also observed that the frequency clusters evolve significantly over time. [Preview Abstract] |
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UP8.00094: Charging and shielding of a non-spherical object in a plasma Lei Zhao, Gian Luca Delzanno We study the charging and shielding of a non-spherical object immersed in a Maxwellian plasma at rest. We consider prolate ellipsoids, varying parametrically the aspect ratio while keeping the surface area constant. The study is conducted with CPIC [1], a newly developed Particle-In-Cell code in curvilinear geometry that conforms to objects of arbitrary shape. For a plasma with temperature ratio equal to unity and for an object with characteristic size of the order of the Debye length, it is shown that the floating potential has a very weak dependence on the geometry, while the charge on the object increases by a factor of three when the aspect ratio changes from one (a sphere) to hundred (a needle-like ellipsoid). This indicates that the screening length depends on the geometry. Scaling studies of the dependence of the charging time and screening length on the aspect ratio and plasma conditions are presented, including theoretical considerations to support the numerical results. \\[4pt] [1] G.L. Delzanno, et al, ``CPIC: a curvilinear Particle-In-Cell code for plasma-material interaction studies,'' under review. [Preview Abstract] |
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UP8.00095: Conductivity of plasma produced from cluster explosions Michael J. Hay, Nathaniel J. Fisch After ionization but before local thermal equilibrium (LTE), plasma characteristic parameters can deviate strongly from homogeneous Maxwellian estimates. This is especially true for dusty plasmas or plasmas formed from structured materials, such as aerogels and aerosols, which retain inhomogeneities on the scale length of the material structures. Plasma collective effects and bulk plasma characteristics, such as conductivity or transport, might then deviate from the those calculated on a near-LTE basis. We consider as an example plasma conductivity effects in plasma produced from the Coulomb explosion of small clusters. [Preview Abstract] |
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UP8.00096: Dust Devil Dynamics L. Couedel, A. Escarguel, W. Horton, S. Benkadda, C. Arnas A self-consistent hydrodynamic model for the onset of a dust devil vortex is derived and analyzed. The toroidal flows and vertical velocity fields are driven by an instability that arises from the inversion of the mass density stratification from solar heating of the sandy surface soil. The nonlinear dynamics in the vertical/horizontal flows drives the toroidal flow through a parametric decay process. Methods developed for triboelectric charging of dust are used to estimate the charging of the sand particles. Elementary comparisons are made with the data from in dust devil observations and research. The parameters for a proposed Dust Devil laboratory experiment are given.. [Preview Abstract] |
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UP8.00097: STRONGLY COUPLED PLASMA |
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UP8.00098: Kinetic approach to the dynamics of strongly coupled inhomogeneous plasmas Hanno K\"ahlert, Gabor J. Kalman, Michael Bonitz Based on the BBGKY hierarchy and an extended STLS ansatz for the two-particle distribution function, we derive kinetic and fluid equations for strongly coupled inhomogeneous plasmas that take both strong coupling and thermal effects into account~[1]. The kinetic equation is employed to study the collective modes in a uniform plasma. The fluid equations are used to study the temperature dependence of the breathing mode of confined dusty plasmas, where excellent agreement with molecular dynamics simulations is observed. In the limit of weak density inhomogeneities, they can be reduced to the equations of linearized elasticity theory. The bulk and shear moduli emerge directly from the theory as integrals over the pair correlation function, and previous results in the literature are recovered~[2]. The theory should be useful to study the collective modes of confined strongly coupled plasmas, where large density variations make the application of methods that were developed for uniform systems impractical. \\[4pt] [1] H. K\"ahlert, G. J. Kalman, and M. Bonitz, submitted \\[0pt] [2] D. H. E. Dubin and J. P. Schiffer, Phys. Rev. E \textbf{53}, 5249 (1996), R.~Zwanzig and R. D. Mountain, J. Chem. Phys. \textbf{43}, 4464 (1965) [Preview Abstract] |
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UP8.00099: Electron screening slows ion thermalization in strongly coupled plasmas Mary Lyon, Scott Bergeson We create strongly coupled plasmas with $\Gamma = 2$ by photo-ionizing atoms in a laser-cooled gas. By changing the laser wavelength, we can deterministically change the plasma screening parameter, $\kappa$, in the range of $\kappa \leq 1$. As $\kappa$ increases, the screening becomes more pronounced and the ion equilibration rate decreases. When we excite the atoms to states below the continuum, a plasma is spontaneously formed on the ns-time scale. These plasmas have a lower electron temperature compared to plasmas generated by ionizing into the continuum. It is expected that as the electron excitation energy decreases further, the plasma will become highly ordered with Coulomb coupling parameters perhaps as high as $\Gamma = 30$. [Preview Abstract] |
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UP8.00100: First principle simulations of phonons and thermal excitations of ultra-cold non-neutral ion plasmas in Penning traps Dominic Meiser, Brian C. Sawyer, Joesph W. Britton, John J. Bollinger Ultra-cold ions in Penning traps are a powerful platform for research in strongly correlated plasmas, quantum information, quantum metrology, and simulation of complex many-body problems of condensed matter theory. Thermal excitations of the ion crystals play a central role in these experiments. On the one hand, the motion associated with them is a limiting factor for the performance of current experiments. Better cooling of the ions could pave the way to new experiments. On the other hand, phonons are instrumental in some of the quantum simulation experiments because they allow one to engineer specific effective interactions between the spins of different ions. To better understand the phonons and thermal excitations in ultra-cold ion crystals we have carried out first principles molecular dynamics simulations. These simulations include a microscopic model for the laser cooling in addition to the cyclotron motion, trapping potentials, and Coulomb interactions between pairs of ions. We present results from these simulations on the stationary properties of planar ion crystals, phonon spectra and phonon mode structures, temperature of the phonon modes, and the dynamics of rearrangements of ions in the crystal. [Preview Abstract] |
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UP8.00101: Shear Viscosity of the One-Component Plasma across Coupling Regimes Jerome Daligault, Scott Baalrud, Kim Rasmussen The shear viscosity coefficient of the one-component plasma is calculated with unprecendented accuracy using molecular dynamics simulations across the entire fluid regime, i.e. from the weakly-coupled regime to the liquid-solid phase transition. The simulations shed light on the two momentum transport mechanisms at the origin of the shear viscosity, namely the bodily movement of particles (that dominates at small coupling) and the action of interactions at a distance (that dominates at large coupling). Their competition results in a minimum of the (reduced) viscosity between the gas-like and liquid-like regimes. Our recently developed effective potential theory of transport coefficients\footnote{Baalrud, Daligault, Phys. Rev. Lett. 110, 235001 (2013)} is shown to compare well with the molecular dynamics simulations. A practical model is presented that spans the entire fluid regime. [Preview Abstract] |
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UP8.00102: Quantum formulation of plasma physics Ahmad Reza Estakhr I formulate plasma physics according to postulates of quantum mechanics, base on electron number density. List of Plasma Quantity: $n_e=\frac{dN}{dV}$ electron number density. $j=n_e.u$ electron number current density where the $u$ denotes velocity. $H_v=\frac {j^2}{2n_e}+U_v=E_v$ This is Number Hamiltonian density where the $U_v$ denotes Number potential energy density and $E_v$ denotes Number total energy density. $R_m$ Magnetic Reynolds Number. $k_m=\frac {R_m}{L}$ Magnetic reynolds wave number. $\psi_m$ magnetic wave function. $\zeta=n_e.\eta$ dynamic magnetic diffusivity where the $\eta$ denotes magnetic diffusivity. Essential Relations: $j=\zeta .k_m=n_e.u$ and then, $\nabla^2\psi_m+k_m^2\psi_m=0$ where the $\nabla^2$ is laplacian operator. $\frac {-\zeta^2\nabla^2\psi_m}{(1+\gamma)n_e}+U_v\psi_m=E_v\psi_m$ this is my equation of plasma that appears to be an relativistic expression of schrodinger equation, where the $\gamma$ denotes lorentz factor and at low speeds $\gamma+1=2$ and so on...etc. [Preview Abstract] |
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UP8.00103: Simulation and Experimental Study on the Efficiency of Traveling Wave Direct Energy Conversion for Application to Aneutronic Fusion Reactions Alfonso Tarditi, Andrew Chap, George Miley, John Scott A study based on both Particle-in-cell (PIC) simulation and experiments is being developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC, [1]) with the perspective of application to aneutronic fusion reaction products and space propulsion [2]. The PIC model is investigating in detail the key TWDEC physics process by simulating the time-dependent transfer of energy from the ion beam to an electric load connected to ring-type electrodes in cylindrical symmetry. An experimental effort is in progress on a TWDEC test article at NASA, Johnson Space Center with the purpose of studying the conditions for improving the efficiency of the direct energy conversion process. Using a scaled-down ion energy source, the experiment is primarily focused on the effect of the (bunched) beam density on the efficiency and on the optimization of the electrode design. The simulation model is guiding the development of the experimental configuration and will provide details of the beam dynamics for direct comparison with experimental diagnostics. \\[4pt] [1] H. Momota et al., Fus. Tech., 35, 60 (1999)\\[0pt] [2] A. Chap et al., Proc. 49th AIAA Joint Propulsion Conference (JPC), San Jose, CA (2013) [Preview Abstract] |
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UP8.00104: Ion velocity distribution function and electric field measurements in a dual-frequency rf sheath Nathaniel Moore, Walter Gekelman, Patrick Prybil, Yiting Zhang, Mark Kushner Ion dynamics are investigated in a dual-frequency rf sheath above a 300 mm diameter biased silicon wafer in an industrial inductively coupled (440 kHz, 500 W) plasma etch tool. Ion velocity distribution (IVD) function measurements in the argon plasma are taken using laser induced fluorescence (LIF). Planar sheets of laser light enter the chamber both parallel and perpendicular to the surface of the wafer in order to measure both parallel and perpendicular IVDs at thousands of spatial positions. A fast (30 ns exposure) CCD camera measures the resulting fluorescence with a spatial resolution of 0.4 mm. The dual-frequency bias on the wafer is comprised of a 2 MHz low frequency bias and an adjustable 10-20 MHz high frequency bias. The bias voltages may be switched on and off (f$_{rep}$ up to 1 kHz, duty cycle 10-90\%). IVDs are measured with several different bias and timing combinations. For the 2 MHz bias, it was found that the IVD is uniform to within 5\% across the waf er. IVDs as a function of phase of the bias were also measured. The electric field in the sheath was measured volumetrically over the wafer at thousands of positions using an emissive probe. The experimental results are compared with a simulation specifically designed for this particular plasma tool. [Preview Abstract] |
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UP8.00105: Self-organized electrode processes in the carbon arc discharge for nanotube synthesis Jonathan Ng, Yevgeny Raitses The atmospheric pressure carbon arc in helium is an important method for nanotube production [1]. Typical arcs operate in a dc mode between a graphite anode, which is consumed, and a lower melting temperature cathode (e.g. copper [2, 3]). It is accepted that electrons from the cathode are emitted by thermionic field emission [2,4], requiring the cathode to be above the melting temperature of its material. Yet, the cathode usually remains undamaged by the arc, raising the question about how the electron current in the arc is supported. Our experiments with copper, stainless steel and aluminum cathodes have revealed that thermo-field emission is the source of most of the arc current at the cathode, but emission is from the carbon deposit formed on the cathode in the course of the arc operation. Due to its low heat conduction, the cathode does not reach its melting temperature and remains undamaged. The evaporation of the graphite anode and formation of the carbon deposit on the cathode are self-organized to maintain the current conduction in the arc.\\[4pt] [1] Journet et. al. Nature 388:756 (1997)\\[0pt] [2] Keidar and Beilis, J. Appl. Phys 106, 103304 (2009)\\[0pt] [3] Fetterman et al, Carbon 46, 1322 (2008)\\[0pt] [4] Hantzsche, Beitr. Plasmaphys., 22, 325(1981) [Preview Abstract] |
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UP8.00106: Effect of anomalous electron cross-field transport on electron energy distribution function in a DC-RF magnetized plasma discharge Yevgeny Raitses, Vincent M. Donnelly, Igor D. Kaganovich, Valery Godyak The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas [1]. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters [2], this rotating structure conducts the largest fraction of the cross-field current.\\[4pt] [1] Y. Raitses, J. K. Hendryx, and N. J. Fisch, IEPC-2009-024, in the Proceedings of the 31st International Electric Propulsion Conference, September, 2009, Ann Arbor, MI;\\[0pt] [2] C. L. Ellison, Y. Raitses and N. J. Fisch, Phys. Plasmas 19, 013503 (2012). [Preview Abstract] |
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UP8.00107: Preparation of diamond-like carbon films using pulsed glow discharge plasmas at atmospheric pressure K. Tanaka, Y. Kikuchi, Y. Matsuo, A. Otsubo, Y. Nishimura, M. Nagata, M. Yatsuzuka Diamond-like carbon (DLC) films have a lot of possibilities for industrial applications due to high mechanical hardness, low friction, chemical inertness, electrical insulation, optical transparency, and biological compatibility. For preparation of DLC films, the glow discharge plasma at atmospheric pressure was generated by a torch-type plasma device with a high-voltage, high-repetition bipolar pulse. A mixed gas of He as a carrier gas and CH4 as a precursor was supplied to the discharge region. A bias voltage was applied between the torch plasma and the substrate in order to prepare a carbon film. The Raman spectrum of the deposited film showed two peaks around 1380 cm$^{-1}$ (D band) and 1580 cm$^{-1}$ (G band), indicating the amorphous carbon film. The deposition rate of the amorphous carbon film was 0.2 $\mu $m/min that was one order larger than the conventional CVD process using low-pressure plasmas. Effects of the bias voltage on the DLC film properties will be shown in the conference. [Preview Abstract] |
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UP8.00108: Sterilization of soybean powder with plasma treatment in atmospheric humid air R. Iwami, Y. Kikuchi, N. Fukumoto, M. Nagata, A. Nakayama, K. Nakagawa Sterilization of foods has been performed by conventional methods such as heat, steam and chemical solutions. However, these sterilization techniques could cause damages to the food material. It is considered that plasma sterilization at atmospheric pressure is one of the promising alternative methods because of the low temperature process. In our previous study, the inactivation of \textit{Bacillus atrophaeus }spores by a dielectric barrier discharge (DBD) plasma produced in atmospheric humid air was investigated in order to develop low-temperature, low-cost and high-speed plasma sterilization technique. The results showed that the inactivation of \textit{Bacillus atrophaeus }spores was found to be dependent strongly on the humidity. In the present study, the plasma treatment technique in humid air is applied to sterilization of soybean powder. Effects of plasma sterilization were successfully confirmed by a colony counting method. It was found that the sterilization efficiency was increased by using the humid air as the discharge gas. In the conference, an improvement of the plasma treatment system to enhance the sterilization efficiency will be shown. [Preview Abstract] |
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UP8.00109: Removal of volatile organic compounds in the confined space using atmospheric pressure discharge plasmas Y. Matsuoka, Y. Kikuchi, N. Fukumoto, M. Nagata, T. Toyoura, M. Matsui, T. Kishimoto Volatile organic compounds (VOCs) are regulated as hazardous pollutants. Thus, the control of VOCs in the atmosphere is one of the most important environmental problems. Removal of VOCs has been generally carried out by conventional methods such as absorption, adsorption and incineration. There are some researches on development of removal system using atmospheric pressure discharge plasmas. In this study, the plasma process is applied to removal of VOCs in the confined space such as an underwater vehicle because of low operating temperature and compact system. A copper wire is helically wound outside a glass tube, and a tungsten rod is inserted inside the glass tube. A dielectric barrier discharge (DBD) plasma is produced inside the glass tube by a high-voltage bipolar power supply for the removal of VOC. The DBD plasma decomposed hexane with the initial concentration of 30 ppm diluted by nitrogen, air and humid air. As the result, the removal efficiency of hexane diluted by nitrogen, air and humid air was 15{\%}, 45{\%} and 80{\%}, respectively. Thus, it is considered that O and OH radicals are effective for removal of hexane. Optimization of the electrodes and the applied voltage waveforms for the enhancement of removal efficiency and the reduction of second products such as ozone will be investigated. [Preview Abstract] |
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UP8.00110: ABSTRACT WITHDRAWN |
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UP8.00111: Rapid X-Band Microwave Breakdown in Ne/Ar John Scharer, Xun Xiang, Brian Kupczyk, John Booske Observations of rapidly formed (\textless~50-300 ns) distributed plasma discharges using X-band microwaves are presented. A stainless steel cylindrical chamber is used to observe microwave breakdown in Ne/Ar gas mixes from 10 to 760 torr. The magnetron illuminates the plasma breakdown chamber using 25 kW, 9.382 GHz with 0.8 $\mu$s pulse-width power. Microwave diodes are used to measure incident and reflected power, providing information to determine the discharge and attenuation characteristics at different pressures. Reflected power measurements show that over 70{\%} of the incident power is reflected due to plasma formation. Ne/ Ar mixture gas shortens the breakdown time. Optical emission spectra experiments allow one to determine the gas temperature, effective electron temperature and plasma density. Microwave mixers are used to compare the amplitude and phase of the reflected signal in phase and in quadrature (90 degrees) relative to a fixed incident phase reference signal. Together with a 1-D plasma model, the effective plasma density, collision frequency and electron temperature are estimated. An ICCD provides fast time-scale optical images to estimate the plasma size, also revealing the temporal plasma formation and decay processes. [Preview Abstract] |
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UP8.00112: Characterization of an atmospheric pressure air plasma source for polymer surface modification Shujun Yang, Jiansheng Tang An atmospheric pressure air plasma source was generated through dielectric barrier discharge (DBD). It was used to modify polyethyleneterephthalate (PET) surfaces with very high throughput. An equivalent circuit model was used to calculate the peak average electron density. The emission spectrum from the plasma was taken and the main peaks in the spectrum were identified. The ozone density in the down plasma region was estimated by Absorption Spectroscopy. [Preview Abstract] |
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UP8.00113: An IGBT-based High Voltage, Variable Pulse Width Nanosecond Pulser for Plasma Creation Applications Timothy Ziemba, Kenneth Miller, James Prager, John Carscadden Eagle Harbor Technologies (EHT) has developed a modular solid state power supply based on IGBT technology, which can support a wide array of applications. The EHT Integrated Power Module (IPM) incorporates fast gate drive technology, high voltage isolation ($\sim$30 kV), fiber optic control, and optional crowbar diodes into a single unit. The EHT IPM can be configured to produce variable pulsed width (20 to 1000 ns), high voltage (\textgreater~20 kV) high repetition frequency (2 MHz) nanosecond pulser. Nanosecond pulser applications include plasma creation for drag reduction, medical applications, water decontamination, fuel mixing and control of flue gas emissions. [Preview Abstract] |
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UP8.00114: A Modular, IGBT Driven, Ignitron Switched, Optically Controlled Power Supply Evan Carroll, Jens von der Linden, Setthivoine You An experiment to investigate the dynamics of canonical flux tubes at the University of Washington uses two high energy pulsed power supplies to generate and sustain the plasma discharge [1]. A modular 240 $\mu F$, 12 kV DC capacitor based power supply, discharged by ignitron, has been developed specifically for this application. Design considerations include minimizing inductance, rapid switching, fast rise times, and electrically isolated control. An optically coupled front panel and fast IGBT ignitron drive circuit [2], sequenced manually or by software, control the charge and discharge of the power supply. A complete, sequenced charge/discharge has been successfully tested with a dummy load, producing a peak current of 100 kA and a rise time of 25 $\mu s$.\\[4pt] [1] J. von der Linden, E. Carroll, E. Lavine, Y. Kamikawa, K. Vereen, S. You, ``Investigating the Dynamics of Canonical Flux Tubes,'' this meeting.\\[0pt] [2] V. Chaplin, P. Bellan, ``Fast Ignitron Trigger Circuit Using Insulated Gate Bipolar Transistors,'' IEEE Trans. Plasma Sci., vol. 41, (2013) [Preview Abstract] |
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UP8.00115: A Plasma--Based DC-DC Electrical Transformer Richard Nebel, John Finn Previous work has indicated that it may be possible to make DC-DC electrical transformers using plasmas. The mechanism is an MHD electromagnetic relaxation process induced by helical electrodes. This process is now being tested on the Bismark device at Tibbar Technologies. [Preview Abstract] |
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UP8.00116: Diagnostics of a nonlocal plasma of a short glow discharge with active boundaries Vladimir Demidov, Alexander Astafiev, Sergie Gutsev, Anatoly Kudryavtsev, Roman Zamchiy Short glow discharges have attracted interest of researchers. In such discharges, the gap is chosen such a way that the positive column with direct electron heating by electric field could not be formed. However, in contrast to the positive column, the properties of the plasmas of NG and FDS are poorly understood. In this work, experimental study of the short glow discharge in helium at different gas pressures and distances between the electrodes are performed. The short discharge has a positive differential characteristic. As a result the discharge is stable even without ballast resistance, which may be important for applications. Experiments confirm that the plasma of the short glow discharge is characterized by a low electron temperature and weak electric field. Since the dimensions of the NG are determined by energy of fast electrons produced in the cathode sheath, in atomic gases, the electron distribution function is nonlocal, i.e. different groups of electrons behave independently of each other (did not have time ``to mix due to collisions''). As the EDF is nonlocal, it allows measurement of the fast part of the EDF by application of measuring wall electrode. The results of measurements by Langmuir and wall probes are in good agreement. [Preview Abstract] |
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UP8.00117: ABSTRACT WITHDRAWN |
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UP8.00118: On Accuracy of CES Microplasma and VUV Photoionization Spectra Determination Alexander Mustafaev, Boris Dobrolezh, Alexander Tsyganov, Vera Yakovleva Energy spectra of electrons released via ionization of admixture in the bulk gas, not using traditional evacuated energy analyzers, can be determined by Collisional Electron Spectroscopy (CES) [1]. This approach may result in miniature gas sensors for medicine, safety equipment, combustion engine control, etc. Said admixtures are ionized by metastable atoms or by vacuum ultraviolet photons, having definite energy, from micro-plasma sources. Electrons energy provides ionization potential and identification of the species. According to CES, electrons may suffer a number of scatterings inside of the bulk gas, but their diffusion path is confined by appropriate sensor's configuration. Using simple plane geometry of CES sensors, we can get EEDF by Druyvesteyn's expression and 2-nd derivative of current-voltage signal at a high (up to atmospheric) gas pressure. Also 2-nd derivative may be, e.g., obtained by $\omega $ modulation and 2$\omega $ detection technique, we used smoothing-differentiating procedure with spline least-squares approximation of current-voltage curve as a more suitable for execution rate critical applications. Modeling noise influence on accuracy and resolution of the method will be reported.\\[4pt] [1] A.A.Kudryavtsev, A.B.Tsyganov. US Patent 7,309,992 [Preview Abstract] |
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UP8.00119: Utilization of plasmas for graphene synthesis Alexey Shashurin, Michael Keidar Graphene is a one-atom-thick planar sheet of carbon atoms that are densely packed in a honeycomb crystal lattice. Grapheen has tremendous range of potential applications ranging from high-speed transistors to electrochemical energy storage devices and biochemical sensors. Methods of graphene synthesis include mechanical exfoliation, epitaxial growth on SiC, CVD and colloidal suspensions. In this work the utilization of plasmas in synthesis process is considered. Types of carbonaceous structures produced by the anodic arc and regions of their synthesis were studied. Ultimate role of substrate temperature and transformations occurring with various carbonaceous structures generated in plasma discharge were considered. Formation of graphene film on copper substrate was detected at temperatures around the copper melting point. The film was consisted of several layers graphene flakes having typical sizes of about 200 nm. Time required for crystallization of graphene on externally heated substrates was determined. [Preview Abstract] |
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UP8.00120: ABSTRACT WITHDRAWN |
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UP8.00121: Repetitive Operation of the E3P-1 Plasma Thruster Andrew Case, Samuel Brockington, F. Douglas Witherspoon HyperV Technologies has developed a novel electric propulsion system based on high plasma density Minirailgun technology. The design goals were for a Specific Impulse (ISP) of over 2000 seconds and repetitive operation at 5 Hertz for 60 seconds. The thruster was successfully operated at 5 Hertz for 92 seconds, with a specific impulse of 2000-2800 seconds at an input power of 2.3kW, exceeding all design goals. Diagnostics for this series of tests include fast photodiodes for measuring plasma jet velocity, time integrated imaging, and Rogowski coils and Pearsons for electrical diagnostics of the high voltage systems. [Preview Abstract] |
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UP8.00122: Destablilized ion sound oscillations in Hall plasma devices for electric propulsion A. Smolyakov, W. Frias, I. Kaganovich, Y. Raitses It is shown that current closure in the chamber walls destabilizes ion acoustic waves in Hall plasmas with ${\mathbf E} \times {\mathbf B}$ electron drift. Such unstable modes may enhance both near-wall conductivity and turbulent electron transport in Hall thrusters for electric propulsion. It is shown that the instability is sensitive to the wall material: the wall with very high dielectric permittivity (such as metal wall) reduces the mode growth rate by an order of magnitude but does not eliminate the instability completely. [Preview Abstract] |
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UP8.00123: Plasma-formed hyperthermal atomic beams for use in thin film fabrication E.P. Gilson, S.A. Cohen, B. Berlinger, W. Chan Enhancing the surface mobility of adsorbents during thin-film growth processes is important for creating certain high-quality thin films. Under the auspices of a DARPA program to develop methods for supplying momentum to adsorbates during thin-film formation without using bulk heating, a hyperthermal atomic beam (HAB) was generated and directed at silicon surfaces with patterned coatings of pentacene, gold, and other surrogates for adsorbents relevant to various thin-film coatings. The HAB was created when the plasma from a helicon plasma source struck a tungsten neutralizer plate and was reflected as neutrals. Time averaged HAB fluxes 100 times greater than in previous PPPL HAB sources have been generated. The effect of the HAB on the patterned coatings was measured using atomic force microscopy (AFM). Results are presented on the flux and energy of the HAB for various system pressures, magnetic fields, and neutralizer biases. AFM measurements of the surface topology demonstrate that the HAB energy, species, and integrated flux are all important factors in altering surface mobility. [Preview Abstract] |
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UP8.00124: Parameters of atmospheric plasmas produced by electrosurgical devices Michael Keidar, Alexey Shashurin, Jerome Canady Electrosurgical systems are extensively utilized in general surgery, surgical oncology, plastic and reconstructive surgery etc. In this work we study plasma parameters created by electrosurgical system SS-200E/Argon 2 of US Medical Innovations. The maximal length of the discharge plasma column at which the discharge can be sustained was determined as function of discharge power and argon flow rate. Electrical parameters including discharge current and voltage were measured. Recently proposed Rayleigh microwave scattering method for temporally resolved density measurements of small-size atmospheric plasmas was utilized. Simultaneously, evolution of plasma column was observed using intensified charge-coupled device (ICCD) camera. [Preview Abstract] |
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UP8.00125: Time-Resolved High-Spatial-Resolution Measurements of Underwater Laser Ionization and Filamentation T.G. Jones, D. Kaganovich, M.H. Helle, J. Penano, A. Ting, D. Gordon Laser triggering and guiding of underwater electrical discharges are being investigated and developed at NRL for applications including advanced micromachining and low-frequency laser acoustic generation. As part of this development we recently made several high-spatial-resolution, time-resolved measurements of underwater optical filamentation and laser ionization. Using 2-laser pump-probe backlit imaging techniques, we were able to achieve time resolution as short as 35 fs and spatial resolution down to 1 micron. Shadowgraph images show few-micron diameter gas bubbles forming throughout the pump beam path in ps timescales. Microbubble numbers and density increased with pulse energy and time during the pump pulse. We also obtained time-resolved spectra of ns-laser-ionized water, revealing black-body radiation lasting more than 100 ns after the ionizing pulse. Results from ongoing underwater laser ionization, filamentation, and discharge-guiding experiments will be presented. [Preview Abstract] |
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UP8.00126: Filamentary Discharges: on the Physics of Plasma Globes M.J. Burin, G.G. Simmons, L. Saucedo, A. Nagy, S.J. Zweben Filamentary structures have been observed in many types of plasma discharges, in both natural and industrial systems. However, some fundamental aspects of their physics remain unclear. A common example can be found within a commercial plasma globe, in which a neon-based gas mixture clearly displays filamentation when driven with a RF high voltage transformer. Recent work has provided the first characterization of these plasma globe filaments [Campanell et al. 2010]. We are now extending this initial work by quantifying filament properties with respect to voltage waveform, ambient pressure, and gas composition, using a custom apparatus with a programmable high voltage supply. Initial results using high-speed photography include significant asymmetry between positive and negative discharges, with the former being more structured than the latter. We also note significant waveform effects on filament number and morphology (see undergraduate poster at this meeting by G.G. Simmons et al., session 14.2). System memory/hysteresis effects are also explored. Our results are discussed in light of theory and observations regarding discharge structures/striations found in planetary atmospheres (e.g. lightning leaders and sprites) and in dielectric barrier discharges. [Preview Abstract] |
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UP8.00127: A new spectrometer design for the x-ray spectroscopy of laser-produced plasmas with high (sub-ns) time resolution M. Bitter, K.W. Hill, P.C. Efthimion, L. Delgado-Aparicio, N. Pablant, P. Beiersdorfer, H. Chen This paper describes a new type of x-ray crystal spectrometer, which can be used in combination with gated x-ray detectors to obtain spectra from laser-produced plasmas with a high (sub-ns) time resolution. The spectrometer consists of a convex, spherically bent crystal, which images individual spectral lines as perfectly straight lines across multiple, sequentially gated, strip detectors. Since the Bragg-reflected rays are divergent, the distance between detector and crystal is arbitrary and can be chosen to optimize the experimental arrangement with respect to detector parameters. The spectrometer concept was verified in proof-of-principle experiments by imaging the L$\beta $1- and L$\beta $2-lines of tungsten, at 9.6735 and 9.96150 keV, from a micro-focus x-ray tube with a tungsten target onto a two-dimensional pixilated Pilatus detector, using a convex, spherically bent Si-422 crystal with a radius of curvature R of 500 mm. These experimental results will be presented. [Preview Abstract] |
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UP8.00128: Progress on Development of Low Pressure High Density Plasmas on the Helicon Plasma Experiment (HPX) R.W. James, O. Duke-Tinson, S. Nolan, E.J. Page, M. Lopez, J. Karama, R.N. Paolino, C. Schlank, J. Sherman, B.S. Stutzman, P.B. Crilly At the Coast Guard Academy Plasma Lab (CGAPL), a small Helicon Plasma Experiment (HPX) is being developed to utilize the reputed high densities (10$^{13}$ cm$^{-3}$ and higher) at low pressure (.01 T) [1], for eventual high temperature and density diagnostic development in future laboratory investigations. HPX is designed to create repeatedly stable plasmas induced by an RF frequency in the 10 to 70 MHz range. We employ a 400 to 1000 Gauss electromagnet that promotes energy conservation in the plasma via external energy production in the magnetic field facilitated by decreased inertial effects, in order to reach the Helicon Mode. With the initial construction phase complete and repeatable plasmas attained, HPX is constructing triple and mach particle probes, magnetic probes, and a single point 300 W Thompson Scattering system backed by a 32-channel Data Acquisition (DAQ) system capable 12 bits of sampling precision at 2 MS/s for HPX plasma property investigations. Progress on the development of the RF coupling system, Helicon Mode development, magnetic coils, and observations from the optical, particle, and electromagnetic scattering diagnostics will be reported.\\[4pt] [1] K. Toki, et al., Thin Solid Films 506-507 (2005) [Preview Abstract] |
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UP8.00129: Kinetic Particle Simulations of Dielectric Surface Breakdown D.V. Rose, D.R. Welch, C. Thoma, R.E. Clark, T.C. Genoni, W.R. Zimmerman Dielectric surface breakdown and flashover in high-voltage gas and vacuum environments are desirable for some applications (e.g., various gas discharge devices) and undesirable for others (e.g., insulator stacks). Accurate modeling of observed breakdown and flashover effects in these devices is difficult due to the complex surface and subsurface material properties of various dielectrics, stochastic processes, charging history, etc. Here, we explore the use of 3D kinetic particle simulations to model dielectric surface breakdown and streamer formation that in turn can lead to surface flashover in high pressure ($\sim$ 1 atm) gas environments. Relatively simple models for secondary charged particle emission from dielectric surfaces are used in conjunction with detailed gas breakdown models. From single initiation points, test simulations yield tree-like surface breakdown patterns, qualitatively consistent with numerous discharge experiments. The development of more advanced surface interaction models is discussed along with applications to specific dielectric breakdown experiments. [Preview Abstract] |
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UP8.00130: Modeling of a short (without positive column) glow discharge with active boundaries Anatoly Kudryavtsev, Konstantin Barzilovich, Eugene Bogdanov, Vladimir Kolobov As boundaries are very important in formation of nonlocal plasma properties, in this study a short dc discharge with cold cathode and application of different voltages to the conducting discharge wall has been simulated. The discharge model is based on a fluid description of ions and neutral species using drift-diffusion approximation for the particle flux. The description of electrons is based on a ``hybrid'' approach with subdivision for trapped and free (fast) electrons. Slow electron transport coefficients as well as electron induced reaction rates are determined from the solutions of the electron Boltzmann equation. The self-consistent electric field is calculated using the Poisson equation. 2D simulations for helium plasma at 1 Torr pressure confirm that the short glow discharge consists of cathode and anode sheaths of space charges, a cathode plasma negative glow, and a Faraday dark space. The plasma region characterized by low electron temperature and weak reversed electric field. It is demonstrated in the model that applied voltage can trap within the device volume energetic electrons arising from atomic and molecular processes in the plasma. It allows measurement of the fast part of the EDF by application of measuring wall electrode. [Preview Abstract] |
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UP8.00131: A new algorithm for fluid simulation of high density plasma discharges Seon-Geun Oh, Young-Jun Lee, HeeHwan Choe, Jae-Hong Jeon, Jong-Hyun Seo Low temperature, high density plasma sources are widely used for the electronic device fabrications such as semiconductor, flat panel display, and solar cell. The inductively coupled plasma or the capacitively coupled plasma reactors are typical ones in these processes. Fluid simulation is one of the methods for transport modeling of high density discharge, because the profiles of plasma quantities are easily obtained. The short shielding time scale of an electric field perturbation is a major restriction on the simulation time step. In most cases, the simulation time step in the explicit method is less than $10^{-13}$ sec. To overcome this limitation, a new method for steady-state fluid simulation of high density plasma discharge is suggested. Following the physical origin of restriction on simulation time step, a new method is developed using both analytic and numerical methods. A simple application of the new method with previously known one is given to study the validity of the method. [Preview Abstract] |
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UP8.00132: Application of Fusion Gyrotrons to Enhanced Geothermal Systems (EGS) P. Woskov, H. Einstein, K. Oglesby The potential size of geothermal energy resources is second only to fusion energy [1]. Advances are needed in drilling technology and heat reservoir formation to realize this potential. Millimeter-wave (MMW) gyrotrons and related technologies developed for fusion energy research could contribute to enabling EGS. Directed MMW energy can be used to advance rock penetration capabilities, borehole casing, and fracking. MMWs are ideally suited because they can penetrate through small particulate extraction plumes, can be efficiently guided long distances in borehole dimensions, and continuous megawatt sources are commercially available. Laboratory experiments with a 10 kW, 28 GHz CPI gyrotron have shown that granite rock can be fractured and melted with power intensities of about 1 kW/cm$^{2}$ and minute exposure times. Observed melted rock MMW emissivity and estimated thermodynamics suggest that penetrating hot, hard crystalline rock formations may be economic with fusion research developed MMW sources. \\[4pt] [1] H. Armstead and J. Tester, \textit{Heat Mining}, E. {\&} F.N. Spon, (1987). [Preview Abstract] |
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UP8.00133: Development of a repetitive compact torus injector Takumi Onchi, David McColl, Mykola Dreval, Akbar Rohollahi, Chijin Xiao, Akira Hirose, Hideki Zushi A system for Repetitive Compact Torus Injection (RCTI) has been developed at the University of Saskatchewan. CTI is a promising fuelling technology to directly fuel the core region of tokamak reactors. In addition to fuelling, CTI has also the potential for (a) optimization of density profile and thus bootstrap current and (b) momentum injection. For steady-state reactor operation, RCTI is necessary. The approach to RCTI is to charge a storage capacitor bank with a large capacitance and quickly charge the CT capacitor bank through a stack of integrated-gate bipolar transistors (IGBTs). When the CT bank is fully charged, the IGBT stack will be turned off to isolate banks, and CT formation/acceleration sequence will start. After formation of each CT, the fast bank will be replenished and a new CT will be formed and accelerated. Circuits for the formation and the acceleration in University of Saskatchewan CT Injector (USCTI) have been modified. Three CT shots at 10 Hz or eight shots at 1.7 Hz have been achieved. [Preview Abstract] |
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UP8.00134: Experimental Characterization of Thermo-electric Driven Liquid Lithium Flow in Narrow Trenches for Magnetic Confinement Fusion Wenyu Xu, Michael Christenson, Peter Fiflis, Davide Curreli, Daniel Andruczyk, David Ruzic The application of liquid metal, especially liquid lithium has become an important topic for plasma facing component (PFC) design. A liquid PFC can effectively eliminate the erosion and thermal stress problems compared to the solid PFC while transferring heat and prolong the lifetime limit of the PFCs. A liquid lithium surface can also suppress the hydrogen isotopes recycling and getter the impurities in fusion reactors. The Lithium/metal infused trench (LiMIT) concept successfully proved that the thermoelectric effect can be utilized to drive liquid lithium flow within horizontally placed metallic open trenches in transverse magnetic field. A limiter based on this concept was tested in HT-7 and gave out positive results. However a broader application of this concept may require the trench be tilted or even placed vertically, for which strong capillary force caused by narrow trenches may be the solution. A new LiMIT design with very narrow trenches have been manufactured and tested in University of Illinois and related results will be presented. Based on this idea new limiters are designed for EAST and LTX and scheduled experiments on both devices will be discussed. [Preview Abstract] |
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UP8.00135: Spinning gas properties and applications V.I. Geyko, N.J. Fisch In the present work, we study an ideal spinning gas in a cylinder with a smooth surface [1]. First, rotation plays a role of an additional energy storage that causes effective change of heat capacity and, hence, reduced compressibility in axial direction. This effect also yields efficiency increase of some thermal cycles, when spinning gas is used as a working body of the cycle with constrains on maximum and minimum temperatures. Second, the spinning breaks the symmetry under which partial pressures of a mixture of gases simply add proportional to the constituent number densities. Thus, remarkably, in a mixture of spinning gases, an inverse problem can be formulated such that the gas constituents can be determined through external measurements only. This work was supported by the U.S. Defense Threat Reduction Agency, the DOE under Contract No. DE-AC02-09CH11466, and by the NNSA SSAA Program through DOE Research Grant No. DE-FG52-08NA28553. \\[4pt] [1] V.I Geyko and N.J. Fisch, Phys. Rev. Lett. \textbf{110}, 150604 (2013). [Preview Abstract] |
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UP8.00136: The cooling of Xenon in LIFE chamber Marcel Klapisch, Michel Busquet In the Inertial Fusion Energy project LIFE, the chamber will be filled with Xenon gas, in order to protect the walls from debris, radiation, and particles. The frequency of laser shots is estimated to be 5 - 10 Hz. It is crucial that the gas has time to cool down between shots, otherwise the walls would overheat and get damaged. Recently described ``Anomalous'' photo-ionization of the 4d electron shell [1], plays an important role in that process. Time history of Te,Tr, and Ne from a new algorithm implemented in a time dependent version of HULLAC [2] will be presented.\\[4pt] [1] Klapisch, M. and Busquet, M., \textit{High Ener. Dens. Phys.} \textbf{9}, 428-34 (2013).\\[0pt] [2] Klapisch, M., Busquet, M., and Bar-Shalom, A., \textit{AIP Conference Proceedings} \textbf{926}, 206-15 (2007). [Preview Abstract] |
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UP8.00137: Proof-of-Principle Experiment for Compact, Energy Efficient Neutron Source: Enabling Technology for Radioactive Waste Transmutation or Sub-Critical Nuclear Reactors Ady Hershcovitch, Thomas Roser, John Santarius A novel neutron source is proposed for radioactive waste transmutation or sub-critical nuclear reactors; it's based on injecting 125 keV deuterium beam through 1-inch tube filled with magnetized tritium plasma to generate 14 MeV D-T neutrons. T target thickness is chosen to slow the D ions to 75 keV. At the opposite end of the tube D ion energy is recovered. Each ion source and tube forms a module. Larger systems can be formed from multiple units. As a D beam propagates through T plasma, it is slowed down by plasma electrons, which are consequently heated. Electron temperature rises until heating is balanced by energy losses. Equilibrium electron temperature is the crucial parameter, since higher temperature, leads to lower drag on the ion beam; therefore, larger target thickness is needed to slow deuterons to 75 keV; with consequently higher neutron yield. A proof of principle experiment, to determine the equilibrium electron temperature, can be perform by injecting 62.5 keV hydrogen beam into hydrogen plasma target and measure the equilibrium electron temperature with Thomson scattering. To reduce electron equilibration with target ions, electron pre-heating can be done rather efficiently with 2.45 GHz microwaves. [Preview Abstract] |
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UP8.00138: Experiment on D-$^{3}$He Burning Physics L. Merriman, B. Coppi The D-$^{3}$He reaction products are charged particles with $ \left\langle {\sigma_{F} {\textrm{v}}} \right\rangle$ about $3{\alpha _F}{10^{-17}}$ cm$^{3}$/sec and ${\alpha _F} \sim 1$ for temperatures around 40keV. The relevant ideal ignition temperature, ${T_I} \simeq$ 27keV for homogeneous plasmas, is a meaningful objective to achieve. For peak densities $n_D^0 + n_{3_{He}}^0 \simeq 10^{15}$cm$^{-3}$, in the range of those obtained by the Alcator experiments, and the plasma pressure is compatible with the toroidal magnetic fields around 14T this condition could be reached. The machine (CANDOR II) that is envisioned [1] is based on recently proposed high field hybrid magnet technology employing moderate (i.e. MgB$_{2}$) and high temperature superconductors. The major radius is ${R_0} \simeq 1.8$m and the minor radii $a \times b = 0.66 \times 1.15$m$^2$ while the plasma current ${I_p} \simeq 15$ MA. Then $\bar B_{p} =\left(I_{p}/5\right)/\left(a\times b\right)^{1/2}\simeq$3.44T. The main technological solutions developed for the Ignitor program are adapted to the design for the new machine.*Sponsored in part by the U.S. DOE.\\[4pt] [1] B. Coppi, Nucl. Instr. and Meth. in Physics Research A2712-3 Holland (1988). [Preview Abstract] |
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UP8.00139: Fusion-Fission Burner for Transuranic Actinides Chan Choi The 14-MeV DT fusion neutron spectrum from mirror confinement fusion can provide a unique capability to transmute the transuranic isotopes from light water reactors (LWR). The transuranic (TRU) actinides, high-level radioactive wastes, from spent LWR fuel pose serious worldwide problem with long-term decay heat and radiotoxicity. However, ``transmuted'' TRU actinides can not only reduce the inventory of the TRU in the spent fuel repository but also generate additional energy. Typical commercial LWR fuel assemblies for BWR (boiling water reactor) and PWR (pressurized water reactor) measure its assembly lengths with 4.470 m and 4.059 m, respectively, while its corresponding fuel rod lengths are 4.064 m and 3.851 m. Mirror-based fusion reactor has inherently simple geometry for transmutation blanket with steady-state reactor operation. Recent development of gas-dynamic mirror configuration has additional attractive feature with reduced size in central plasma chamber, thus providing a unique capability for incorporating the spent fuel assemblies into transmutation blanket designs. The system parameters for the gas-dynamic mirror-based hybrid burner will be discussed. [Preview Abstract] |
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UP8.00140: 3D Printing Utilized In Target Fabrication Sallee Klein, Michael Deininger, Eliseo Gamboa, Mario Manuel, Joe Satcher, Rachel Young, Carolyn Kuranz, Paul Keiter, R. Paul Drake Targets are used in high-energy-density physics, when, once ablated by lasers, are platforms for experiments that study astrophysical phenomenon, hydrodynamic instabilities and a myriad of other physics. Target fabrication has long suffered from difficulty in the repeatability of features from target to target. At the University of Michigan, micro-machined acrylic structures are often used to mitigate variations in targets for any single campaign. However, there are limitations to what can be conventionally machined. Ever sophisticated target designs are broaching the limitations of our traditional means of creating the acrylic structures that have long been such an integral element to our success in target fabrication. 3D printing has opened up new opportunities to build targets that could never have been machined by conventional means. Here, we present the advantages and limitations of 3D printing when utilized in target fabrication. [Preview Abstract] |
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