Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session BP12: Poster Session I (FRC, Spheromak, Mirror)Poster
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Room: Exhibit Hall A |
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BP12.00001: FRC, SPHEROMAK, MIRROR |
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BP12.00002: Hall effect on a Merging Formation Process of a Field-Reversed Configuration Yasuhiro Kaminou, Xuehan Guo, Michiaki Inomoto, Yasushi Ono, Ritoku Horiuchi Counter-helicity spheromak merging is one of the formation methods of a Field-Reversed Configuration (FRC). In counter-helicity spheromak merging, two spheromaks with opposing toroidal fields merge together, through magnetic reconnection events and relax into a FRC, which has no or little toroidal field. This process contains magnetic reconnection and a relaxation phenomena, and the Hall effect has some essential effects on these process because the X-point in the magnetic reconnection or the O-point of the FRC has no or little magnetic field. However, the Hall effect as both global and local effect on counter-helicity spheromak merging has not been elucidated. In this poster, we conducted 2D/3D Hall-MHD simulations and experiments of counter-helicity spheromak merging. We find that the Hall effect enhances the reconnection rate, and reduces the generation of toroidal sheared-flow. The suppression of the ``slingshot effect'' affects the relaxation process. We will discuss details in the poster. [Preview Abstract] |
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BP12.00003: Preliminary Results on a low-energy RMF-FRC Plasma Translation Experiment for Space Propulsion Carrie Hill, Nolan Uchizono, Michael Holmes The U.S. Air Force Research Laboratory-Edwards has developed a new experimental test cell to study the translation physics of Field-Reversed-Configurations (FRC) formed at low-energy (\textless 15 J/pulse). The test-cell is currently equipped with a conical Rotating Magnetic Field (RMF) source, capable of producing a burst of 10 plasmoids at 5 J/pulse. This source has been characterized at full energy with a xenon propellant at a range of flow rates (5-70 sccm), bias fields up to 500 G, and antenna phasing. Data from a suite of diagnostics has been analyzed to track plasmoid formation and axial motion. These diagnostics include voltage and current probes, axial magnetic field probes, magnetic flux loops, and Langmuir probes. A time-of-flight array measures the plasmoid's exit velocity. Emission spectroscopy using streak-imaging is also implemented. A basic global energy balance from these diagnostics is used to estimate the efficiency of the translation process and determine how it scales with magnetic field, flow rate, and antenna phasing. [Preview Abstract] |
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BP12.00004: Preliminary Results on a Low-Energy RMF-FRC Experiment with Water Nolan Uchizono, Carrie Hill, Michael Holmes The U.S. Air Force Research Laboratory-Edwards has developed a new Field-Reversed Configuration (FRC) test cell for researching low-energy (\textless 15J) FRC formation physics. This test cell is currently outfitted with a cylindrical Rotating Magnetic Field (RMF) FRC plasma source. FRC's are compatible with a variety of propellants -- including complex propellants, like water and CO$_{\mathrm{2}}$. Water was the propellant of choice for this experiment. The input conditions of the test cell were varied to study their effects on FRC formation and plasma content. FRC formation was studied using a suite of diagnostics, including voltage and current probes, and excluded-flux measurements. Plasma species composition was studied using a residual gas analyzer, and optical emission spectroscopy. The propellant decomposition and ionization stage used in this experiment is presented in companion work at this conference. [Preview Abstract] |
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BP12.00005: Conditioning of In-Situ Propellants for RMF-FRC Plasma Thrusters Michael Holmes, Carrie Hill, Nolan Uchizono Current ion thrusters use noble gases to limit chemical attack of thruster components. However, thrusters based on Field Reversed Configuration (FRC) plasmas need not directly contact propellants so that reactive propellants such as ammonia, methane, butane, water, or combination of these are possible. The practical need to convert liquid propellant to a gaseous partially ionized state is what drives our research. A decomposition device was built to transition from liquid to gas to partially ionized plasma. Pressure is maintained high enough so that all chemical components have residence times sufficiently long to complete phase change and to reach chemical equilibrium at high temperature so the gas consists of primarily of H$_{2}$O, H$_{2}$, N$_{2}$, O$_{2}$, CO, and CO$_{2}$. This gas is then fed to an inductive discharge that further breaks down molecules and brings the propellant to the proper ionization configuration for the FRC. We will be measuring chemical state, ionization state, and uniformity as propellant enters the discharge region. A parallel FRC thruster effort is underway. [Preview Abstract] |
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BP12.00006: Rotating Magnetic Field FRC Formation Studies using the Multi-Fluid Plasma Model Eder Sousa, Hai Le The multi-fluid plasma model equations are derived by taking velocity moments of the Boltzmann equation for each of the components in a plasma, and each species mass density, momentum density and total energy are evolved in time. This model is used to study field-reversed configuration (FRC) formation dynamics using a Rotating Magnetic Field (RMF) as an electron current drive. Particular interest is placed on the coupling of the RMF to the plasma and collisional effects between the electron, ion and neutral fluids, and some consideration to ionization effects. The simulations are designed such that they can be compared to experimental results using collisional-radiative (CR) models developed at the Air Force Research Laboratory. Distribution A: Approved for public release; distribution unlimited, AFTC/PA clearance No. 15399 [Preview Abstract] |
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BP12.00007: Experimental investigation of magnetic-field topology via a perturbation method in the PFRC-2 device Jackson Matteucci, Samuel Cohen The fundamental question about FRC experiments is whether an FRC has actually formed; specifically, does there exist a magnetized, high-beta, plasma configuration with both no toroidal field and a simply connected configuration-space separatrix? We have investigated the latter part of this question, the existence of a separatrix, in the RMF\textunderscore o-driven PFRC-2 device. The method involved applying an externally generated periodic RF power perturbation to open-field-line plasma at one (remote) axial end of the device while simultaneously searching for evidence of this perturbation near the presumptive FRC.~Measurements of the floating potential and ion saturation current were taken at the axial center of the device using a cylindrical Langmuir probe (r $=$ 0.025 cm). When applying no RMF\textunderscore o, measurements of the floating potential and the ion saturation current showed evidence of the frequency signature of perturbation throughout the entire radial profile of the device, indicating open field lines throughout the device. However, under certain conditions when operating the RMF\textunderscore o, we found no evidence of the perturbation within a certain radius, but instead see the perturbations only beyond this particular radius, indicating a separatrix inside which the magnetic field lines are closed. [Preview Abstract] |
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BP12.00008: LSP simulations of fast ions slowing down in cool magnetized plasma Eugene S. Evans, Samuel A. Cohen In MFE devices, rapid transport of fusion products, e.g., tritons and alpha particles, from the plasma core into the scrape-off layer (SOL) could perform the dual roles of energy and ash removal. Through these two processes in the SOL, the fast particle slowing-down time will have a major effect on the energy balance of a fusion reactor and its neutron emissions, topics of great importance. In small field-reversed configuration (FRC) devices, the first-orbit trajectories of most fusion products will traverse the SOL, potentially allowing those particles to deposit their energy in the SOL and eventually be exhausted along the open field lines. However, the dynamics of the fast-ion energy loss processes under conditions expected in the FRC SOL, where the Debye length is greater than the electron gyroradius, are not fully understood. What modifications to the classical slowing down rate are necessary? Will instabilities accelerate the energy loss? We use LSP, a 3D PIC code, to examine the effects of SOL plasma parameters (density, temperature and background magnetic field strength) on the slowing down time of fast ions in a cool plasma with parameters similar to those expected in the SOL of small FRC reactors. [Preview Abstract] |
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BP12.00009: Beam ion effects on FRC stability Elena Belova Stability properties of a hybrid FRC, in which field reversal is created both by plasma currents and by a low-density energetic component of large-orbit ions, have been studied by means of a generalized energy principle, and also by using 3D numerical simulations using the HYM code. The beam ion -- thermal plasma interaction term has been derived including the effects of radial betatron resonances, and it has been demonstrated that these resonances are important in very kinetic configurations where assumptions for radial orbit averaging are not valid. The resonant condition has been compared with simulation results, and it has been demonstrated to reliably predict the most unstable modes. The HYM code has been modified to allow different distribution functions for the beam ions including a slowing-down and a delta-function distributions. The effects of the cold beams and slowing-down beam ion distributions on stability are studied numerically, using the generalized energy principle as a guide in the search of the stable FRC-beam regime. [Preview Abstract] |
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BP12.00010: NIMROD simulations of the IPA FRC experiment Richard Milroy The IPA experiment [John Slough, George Votroubek and Chris Pihl, Nucl. Fusion \textbf{51}, 053008 (2011)] created a high temperature plasma by merging and compressing supersonic $\theta $-pinch formed FRCs. The NIMROD code has been used to simulate this process. These calculations include the $\theta $-pinch formation and acceleration of two FRC's using the dynamic formation methodology, and their translation to a central compression chamber where they merge and are magnetically compressed. Transport coefficients have been tuned so simulation results agree well with experimental observation. The inclusion of the Hall term is essential for the FRCs merge quickly, as observed experimentally through the excluded flux profiles. The inclusion of a significant anisotropic viscosity is required for the excluded flux profiles to agree well with the experiment. We plan to extend this validation work using the new ARPA-E funded Venti experiment at Helion Energy in Redmond WA. This will be a very well diagnosed experiment where two FRCs merge (like the IPA experiment) and are then compressed to near-fusion conditions. Preliminary calculations with parameters relevant to this experiment have been made, and some numerical issues identified. [Preview Abstract] |
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BP12.00011: 3D Hybrid Simulations of Interactions of High-Velocity Plasmoids with Obstacles Y.A. Omelchenko, T.E. Weber, R.J. Smith Interactions of fast plasma streams and objects with magnetic obstacles (dipoles, mirrors, etc) lie at the core of many space and laboratory plasma phenomena ranging from magnetoshells and solar wind interactions with planetary magnetospheres to compact fusion plasmas (spheromaks and FRCs) to astrophysics-in-lab experiments. Properly modeling ion kinetic, finite-Larmor radius and Hall effects is essential for describing large-scale plasma dynamics, turbulence and heating in complex magnetic field geometries. Using an asynchronous parallel hybrid code, HYPERS, we conduct 3D hybrid (particle-in-cell ion, fluid electron) simulations of such interactions under realistic conditions that include magnetic flux coils, ion-ion collisions and the Chodura resistivity. HYPERS does not step simulation variables synchronously in time but instead performs time integration by executing asynchronous discrete events: updates of particles and fields carried out as frequently as dictated by local physical time scales. Simulations are compared with data from the MSX experiment which studies the physics of magnetized collisionless shocks through the acceleration and subsequent stagnation of FRC plasmoids against a strong magnetic mirror and flux-conserving boundary. [Preview Abstract] |
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BP12.00012: Overview of the C-2U Advanced Beam-Driven FRC Experimental Program H. Gota, M.W. Binderbauer, T. Tajima, S. Putvinski, M. Tuszewski, D. Barnes, S. Dettrick, E. Garate, S. Korepanov, A. Smirnov, M.C. Thompson, X. Yang, A.A. Ivanov The world's largest compact toroid (CT) device, C-2, has recently been upgraded to C-2U at Tri Alpha Energy to seek for a sustainment of field-reversed configuration (FRC) plasma by neutral-beam (NB) injection [1]. The C-2 experimental program was successfully completed with dramatic improvements in confinement and stability of FRC plasmas, as well as demonstrated plasma pressure increase and plasma heating by NB injection. To enhance the NB injection effect and further improve the FRC performance, the C-2U experimental program has started with following key system upgrades: (i) increased total NB input power to 10$+$ MW (15 keV hydrogen) with tilted injection angle; (ii) enhanced edge-biasing capability for stability control; (iii) upgraded particle inventory control systems. The initial C-2U experiment has already demonstrated much further improvements, revealing advanced beam-driven FRC plasmas. In the best operating regime we have successfully achieved plasma sustainment up to 5$+$ ms; while, in the longer-pulsed regime the plasma lifetime can be extended up to the end of NB pulse-duration (8$+$ ms). The overall C-2U experimental program and the initial experimental results will be presented at the meeting.\\[4pt] [1] M.W. Binderbauer \textit{et al.}, Phys. Plasmas \textbf{22}, 056110 (2015). [Preview Abstract] |
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BP12.00013: Diagnostic Overview of the C-2U Advanced Beam-Driven Field-Reversed Configuration Plasma Experiment Matthew Thompson, Hiroshi Gota, Sergei Putvinski, Michel Tuszewski, Michl Binderbauer The C-2U experiment at Tri Alpha Energy seeks to study the evolution of advanced beam-driven field-reversed configuration (FRC) plasmas sustained by neutral beam (NB) injection for 5$+$ ms. Data on the FRC plasma performance is provided by a comprehensive suite of diagnostics including magnetic sensors, interferometry, Thomson scattering, spectroscopy, bolometry, reflectometry, and NB-related fast-ion/neutral diagnostics. While many of these diagnostic systems were inherited from the preceding experiment C-2 [1,2], C-2U has a variety of new and upgraded diagnostic systems: multi-chord far-infrared polarimetry, multiple fast imaging cameras with selectable atomic line filters, proton detector arrays, and 100 channel bolometer units capable of observing multiple regions of the spectrum simultaneously. In addition, extensive ongoing work focuses on advanced methods of measuring separatrix shape that will both improve accuracy and facilitate active control of the FRC plasma. \\[4pt] [1] M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)\\[0pt] [2] H. Gota et al., Rev. Sci. Instrum. 85, 11D836 (2014) [Preview Abstract] |
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BP12.00014: Neutral beam system for the C-2-Upgrade Field Reversed Configuration Experiment Sergey Korepanov, Artem Smirnov, Ryan Clary, Alexandr Dunaevsky, Ivan Isakov, Richard Magee, Vasily Matvienko, Alan Van Drie, Petr Deichuli, Alexandr Ivanov, Konstantin Pirogov, Aleksey Sorokin, Nickolay Stupishin, Roman Vakhrushev In the C-2 field-reversed configuration (FRC) experiment, tangential neutral beam injection (NBI), coupled with electrically-biased plasma guns at the plasma ends and advanced surface conditioning, led to dramatic reductions in turbulence-driven losses [1]. Under such conditions, highly reproducible, macroscopically stable, hot FRCs with a significant fast-ion population, total plasma temperature of $\sim$ 1 keV and record lifetimes were achieved [2]. To further improve the FRC sustainment and provide a better coupling with beams, the C-2 device has been upgraded with a new NBI system, which can deliver up to a total of 10 MW of hydrogen beam power (15 keV, 8 ms pulse), by far the largest ever used in compact toroid plasma experiments. The NBI system consists of six positive-ion based injectors featuring flexible, modular design. This presentation will provide an overview of the C-2U NBI system, including: 1) NBI test facility, beam characterization, and acceptance tests, 2) integration with the machine and operating experience, 3) improvements in plasma performance with increased beam power.\\[4pt] [1] M. Tuszewski et. al, Phys. Rev. Lett 108, 255008 (2012).\\[0pt] [2] M.W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015). [Preview Abstract] |
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BP12.00015: Comprehensive approach to fast ion measurements in the beam-driven FRC Richard Magee, Artem Smirnov, Marco Onofri, Sean Dettrick, Sergey Korepanov, Kurt Knapp The C-2U experiment [1] combines tangential neutral beam injection, edge biasing, and advanced recycling control to explore the sustainment of field-reversed configuration (FRC) plasmas. To study fast ion confinement in such advanced, beam-driven FRCs, a synergetic technique was developed that relies on the measurements of the DD fusion reaction products and the hybrid code Q2D, which treats the plasma as a fluid and the fast ions kinetically. Data from calibrated neutron and proton detectors are used in a complementary fashion to constrain the simulations: neutron detectors measure the volume integrated fusion rate to constrain the total number of fast ions, while proton detectors with multiple lines of sight through the plasma constrain the axial profile of fast ions. One application of this technique is the diagnosis of fast ion energy transfer and pitch angle scattering. A parametric numerical study was conducted, in which additional \textit{ad hoc} loss and scattering terms of varying strengths were introduced in the code and constrained with measurement. Initial results indicate that the energy transfer is predominantly classical, while, in some cases, non-classical pitch angle scattering can be observed.\\[4pt] [1] M. Binderbauer et al., Physics of Plasmas \textbf{22}, 056110 (2015). [Preview Abstract] |
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BP12.00016: Results from E$\parallel$B Neutral Particle Analyzer and Calibration Ion Beam System on C-2U Ryan Clary, A Roquemore, A Kolmogorov, A Ivanov, S Korepanov, R Magee, S Medley, A Smirnov, M Tiunov C-2U is a a high-confinement, advanced beam driven FRC which aims to sustain the configuration for $>5$\,ms, in excess of typical MHD and fast particle instability times, as well as fast particle slowing down times\footnote{M. W. Binderbauer, et al., \textbf{Physics of Plasmas} 22, 056110 (2015)}. Fast particle dynamics are critical to C-2U performance and several diagnostics have been deployed to characterize the fast particle population, including neutron and proton detectors, an electrostatic neutral particle analyzer, and neutral particle bolometers. To increase our understanding of fast particle behavior and supplement existing diagnostics an E$\parallel$B NPA\footnote{S. S. Medley and A. Roquemore, \textbf{Review of Scientific Instruments} 75, 3625 (2004)} was acquired from PPPL which simultaneously measures H$^0$ and D$^0$ flux between 2 and 22\,keV with high energy resolution. In addition, a small, high purity, ion beam system has been constructed and tested to calibrate absolutely fast particle detectors. Here we report results of measurements from the E$\parallel$B analyzer on C-2U and inferred fast particle behavior, as well as the status of the calibration ion beam system. [Preview Abstract] |
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BP12.00017: Studies of C-2U plasmas using Time-Resolved Multi-Chord Ion-Doppler Diagnostic (MCID) Deepak Gupta, Bihe Deng, Kan Zhai, Thomas Roche, Erik Granstedt, Matthew Thompson, Michel Tuszewski C-2U [1] has achieved steady-state operation of advanced beam-driven FRCs using neutral beam injection and edge biasing. To characterize this novel C-2U regime, MCID regularly measures time-resolved radial profiles of impurity ion emissivity, ion velocity, and ion temperature. Comparing thermal-ion temperatures with the pressure balance total temperatures provides the fast-ion pressure in the advanced beam-driven FRC state. Impurity ion measurement together with radial momentum balance yields radial profiles of electric field and electron current density. Such estimates were explored with Helium-mixed FRC plasmas on C-2 [2], and are now performed by using indigenous Oxygen impurities in the advance beam-driven plasmas in C-2U. Conditions and dependence of possible ion heating via edge biasing are also explored. The detailed MCID setup for radial/axial profile measurements and data for multiple physics phenomena will be presented. \\[4pt] [1] M.W. Binderbauer \textit{et al.}, Phys. Plasmas \textbf{22}, 056110 (2015)\\[0pt] [2] D. Gupta \textit{et al.}, Bull. Am. Phys. Soc. \textbf{58}, GP8.00038 (2013) [Preview Abstract] |
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BP12.00018: Core Electron Temperature and Density Sustainment in the C-2U Advanced Beam-Driven FRC Plasma Kan Zhai, John Kinley, Tania Schindler, Helen Zhang, Matthew Thompson C-2U is an advanced beam-driven FRC plasma experiment sustained by neutral beam (NB) injection for 5$+$ ms. Experimental evidence of FRC core electron temperature and density sustainment has been observed in our recent C-2U campaign. After upgrading the existing C-2 [1] NB system from 4 MW to 10$+$ MW of power via six 15 keV NBs, C-2U has FRC plasma sustainment. Electron temperature and density profiles and their temporal evolution measured with Thomson scattering system show that the core electron temperature and density have lasted more than 5 ms before they start to decrease. Core electron temperature of the sustained C-2U advanced beam-driven FRC plasma is also higher than that of previously obtained C-2 high performance FRC plasmas [1]. Detailed results about the electron temperature and density profiles and their evolution with comparison of previous results will be presented at the meeting. \\[4pt] [1] M. W. Binderbauer \textit{et al}., Phys. Plasmas \textbf{22}, 056110 (2015) [Preview Abstract] |
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BP12.00019: Study of micro-bursts in C-2U[1] B.H. Deng, Michael Beall, Michael Binderbauer, Ryan Clary, Jon Douglass, Hiroshi Gota, Sergey Korepanov, Richard Magee, Sergei Putvinski, Thomas Roche, Matthew Thompson, Michel Tuszewski Sustainment of advanced beam-driven FRCs has recently been achieved in C-2U. In typical discharges periodic small amplitude bursts are observed with down chirping in the diamagnetic frequency range. A recently developed state-of-the-art FIR diagnostic allows to resolve details of these events, which exhibit n$=$2 mode structure and are possibly of the interchange type, which is intrinsic to FRC plasmas. The bursts are also a manifestation of the abundant trapped fast ions in the system. More detailed understanding of these events can help the design of next generation FRC experiments. For this purpose, a possible drive mechanism is proposed and a chirplet model is developed to characterize the dynamic behavior of these bursts. The interaction between bursts and equilibrium profile dynamics will be analyzed from data measured by interferometers, bolometer arrays, and magnetic diagnostics. The effect of externally applied ExB shear will also be studied, as will be possible fast ion losses as seen by fast ion diagnostics. \\[4pt] [1] M. Binderbauer \textit{et al}., Physics of Plasmas, 22, 056110 (2015) [Preview Abstract] |
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BP12.00020: Improved density profile measurements in the C-2U advanced beam-driven FRC plasmas Michael Beall, B.H. Deng, Jon Schroeder, Greg Settles, John Kinley, Hiroshi Gota, Matt Thompson The goal of Tri Alpha Energy's C-2U experiment [1] is to demonstrate FRC sustainment via neutral beam injection. Accurate equilibrium profiles are essential for determining optimum operating regimes and studying physics phenomena. Electron density profiles in C-2 [1] were measured by a CO2/HeNe laser interferometer [2]. All C-2 chords were located below the machine axis causing difficulties due to spatial under-sampling in case of vertical plasma motion. As part of C-2U, additional chords were added above the axis and a complimentary 4-chord far-infrared (FIR) interferometer was developed. The FIR system is based on 2 HCOOH lasers optically pumped by a CO2 laser. This upgrade allowed for higher density resolution and broad spectral bandwidth. Results of improved density profile measurement will be presented, including fast ion effects. Plasma wobble is also characterized via density centroid measurements. \\[4pt] [1] M.W. Binderbauer \textit{et al}., Phys. Plasmas \textbf{22}, 056110 (2015)\\[0pt] [2] B. H. Deng \textit{et al}., Rev. Sci. Instrum. \textbf{83}, 10E339 (2012) [Preview Abstract] |
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BP12.00021: Studies of Jet Outflow from Advanced Beam-Driven FRC Plasma on C-2U Daniel Sheftman, Deepak Gupta, Francesco Giammanco, Fabio Conti, Paolo Marsili Experiments demonstrating sustainment of field-reversed configuration (FRC) plasma via neutral beam injection have been carried out on C-2U [1]. Knowledge and control of the axial outflow of plasma particles and energy through open-magnetic-field lines are of crucial importance to the stability and longevity of the advanced beam-driven FRC plasma. Passive Doppler spectroscopy and microwave interferometry measurements provide an initial view of the behavior of the open-field-line plasmas on the C-2U device. These measurements and estimations of plasma density, flow velocity, excluded-magnetic flux, and ion temperature of the jet outflow plasmas are discussed. In addition, possible contributions from fast-ion losses from the advanced beam-driven FRC plasma to the jet will be explored and presented. \\[4pt] [1] M. W. Binderbauer \textit{et al}., Phys. Plasmas \textbf{22}, 056110 (2015) [Preview Abstract] |
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BP12.00022: Control of Compact-Toroid Characteristics by External Copper Shell T. Matsumoto, J. Sekiguchi, T. Asai, H. Gota, T. Roche, I. Allfrey, M. Cordero, E. Garate, J. Kinley, T. Valentine, W. Waggoner A collaborative research project by Tri Alpha Energy and Nihon University has been conducted for several years, which led to the development of a new compact toroid (CT) injector [1] for efficient FRC particle refueling in the C-2U experiment [2]. The CT is formed by a magnetized coaxial plasma gun (MCPG), consisting of coaxial cylindrical electrodes. In CT formation via MCPG, the magnetic helicity content of the generated CT is one of the critical parameters. A bias coil is inserted into the inner electrode to generate a poloidal flux. The resultant bias magnetic field is spread out of MCPG with time due to its low-frequency bias current. To obtain a more effectively distributed bias magnetic field as well as to improve the voltage breakdown between electrodes, the MCPG incorporates a novel $\sim$ 1 mm thick copper shell mounted outside of the outer electrode. This allows for reliable and controlled operation and more robust CT generation. A detailed discussion of the copper shell and experimental test results will be presented.\\[4pt] [1] T. Matsumoto \textit{et al}., Bull. Am. Phys. Soc. \textbf{59}, UP8.00008 (2014) \newline [2] M. Binderbauer \textit{et al}., Phys. Plasmas \textbf{22}, 056110 (2015) [Preview Abstract] |
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BP12.00023: Compact toroid injection into C-2U Thomas Roche, H. Gota, E. Garate, T. Asai, T. Matsumoto, J. Sekiguchi, S. Putvinski, I. Allfrey, M. Beall, M. Cordero, E. Granstedt, J. Kinley, M. Morehouse, D. Sheftman, T. Valentine, W. Waggoner Sustainment of an advanced neutral beam-driven FRC for a period in excess of 5 ms is the primary goal of the C-2U [1] machine at Tri Alpha Energy. In addition, a criteria for long-term global sustainment of any magnetically confined fusion reactor is particle refueling. To this end, a magnetized coaxial plasma-gun has been developed [2]. Compact toroids (CT) are to be injected perpendicular to the axial magnetic field of C-2U. To simulate this environment, an experimental test-stand has been constructed. A transverse magnetic field of $B\approx 1 kG$ is established (comparable to the C-2U axial field) and CTs are fired across it. As a minimal requirement, the CT must have energy density greater than that of the magnetic field it is to penetrate, i.e., $\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$2$}\rho v^{2}\ge B^{2}/2\mu_{0} $. This criteria is easily met and indeed the CTs traverse the test-stand field. A preliminary experiment on C-2U shows the CT also capable of penetrating into FRC plasmas and refueling is observed resulting in a 20 $-$ 30{\%} increase in total particle number per single-pulsed CT injection. Results from test-stand and C-2U experiments will be presented. \\[4pt] [1] M. Binderbauer et al., Physics of Plasmas, 22, 056110 (2015) \newline [2] T. Matsumoto et al., Bull. Am. Phys. Soc. 59, UP8.00008 (2014) [Preview Abstract] |
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BP12.00024: Development of Multi-pulse Compact Toroid Injector System for C-2U I. Allfrey, E. Garate, M. Morehouse, T. Roche, H. Gota, T. Valentine, W. Waggoner, S. Putvinski, M. Cordero, T. Asai, T. Matsumoto, J. Sekiguchi The C-2U [1] experiment aims at sustaining a dynamically formed field reversed configuration (FRC) for 5$+$ ms via injection of 10$+$MW of neutral beams. One of the systems currently used to refuel the C-2U plasma is a single pulse compact toroid injector (CTI) [2]. The CTI is a magnetized co-axial plasma gun, which generates a spheromak-like plasma that is injected into the core of the advanced beam-driven FRC of C-2U. In order to refuel the recent long-lived plasmas in C-2U, a multi-pulse CTI system, whose modular design allows for expandable burst numbers, is being designed. Details of the pulsed power systems used to energize the single pulse and the upgraded multi-pulse CTI will be discussed. Results of injector performance carried out on a dedicated test stand as well as some refueling data on C-2U will also be presented. \\[4pt] [1] M. Binderbauer et al., Physics of Plasmas, 22, 056110 (2015)\\[0pt] [2] T. Matsumoto et al., Bull. Am. Phys. Soc. 59, UP8.00008 (2014) [Preview Abstract] |
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BP12.00025: Fueling Of The C-2U Device By Cryogenic Pellet Injection Erik Trask, Sangeeta Gupta, Marco Onofri, Igo Vinyar The major goal of the C-2U device [1] at Tri Alpha Energy is sustainment of the plasma equilibrium for more than five milliseconds by a combination of neutral beam injection, boundary control, and fueling. Studies of fueling and particle inventory responses have been performed by injection of high speed frozen deuterium pellets. Synchronization of the pellet injector [2] with the shot control system has allowed delivery of a pellet with sub-millisecond accuracy. Pellet injection at different points in the plasma discharge has been done to study ablation parameters and plasma performance. Model simulations of pellet ablation including the effects of fast ions compare well with experimentally estimated ablation rates. \\[4pt] [1] M. Binderbauer et al., \textit{Physics of Plasmas} \textbf{22}, 056110 (2015)\\[0pt] [2] I. Vinyar et al., \textit{Instrumentation and Experimental Techniques} \textbf{57} No. 4, 508-515 (2014) [Preview Abstract] |
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BP12.00026: Dynamic Separatrix Control in C-2U E. Garate, I. Allfrey, S. Putvinski, G. Snitchler, E. Trask, J. Schroeder, J. Romero C-2U's advanced beam driven field reversed configuration (FRC) routinely achieves lifetimes exceeding the magnetic diffusion time of the confinement vessel, which is about 5 ms. In order to supplement the flux conserving properties of the walls, and to allow plasma shaping and separatrix control along the FRC length, we have implemented a set of six independent auxiliary coils on C-2U. The coils are external to the confinement vessel and can be energized at any time during the FRC discharge. Current in the coils can either increase or decrease the magnetic field pressure along the separatrix length, allowing for a variety of different external pressure profiles. Recent experimental results indicate that separatrix control by suitable programming of the auxiliary coil system can lead to increased lifetimes for C-2U FRC's. The auxiliary coil system, experimental results and a discussion of the possible benefits of separatrix control on stability and transport will be discussed. [Preview Abstract] |
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BP12.00027: Fast Filtered Imaging of the C-2U Advanced Beam-Driven Field-Reversed Configuration E.M. Granstedt, P. Petrov, K. Knapp, M. Cordero, V. Patel The goal of the C-2U program\footnote{M.~Binderbauer, et~al. Physics of Plasmas \textbf{22}, 056110 (2015)} is to sustain a Field-Reversed Configuration (FRC) for 5+ ms using neutral beam injection, end-biasing, and various particle fueling techniques. Three high-speed, filtered cameras are used to observe visible light emission from deuterium pellet ablation and compact-toroid injection which are used for auxiliary particle fueling. The instruments are also used to view the dynamics of the macroscopic plasma evolution, identify regions of strong plasma-material interactions, and visualize non-axisymmetric perturbations. To achieve the necessary viewing geometry, imaging lenses are mounted in re-entrant viewports, two of which are mounted on bellows for retraction during gettering and removal if cleaning is necessary. Images are coupled from the imaging lens to the camera via custom lens-based optical periscopes. Each instrument contains a remote-controlled filter wheel which is set between shots to select a particular emission line from neutral D or various charge states of He, C, O, or Ti. Measurements of absolute emissivity and estimates of neutral and impurity density will be presented. [Preview Abstract] |
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BP12.00028: Suppressed Ion-scale Turbulence and Critical Density Gradient in the C-2 Field Reversed Configuration. Lothar Schmitz, D. Fulton, C. Lau, I. Holod, Z. Lin, E. Ruskov, B. Deng, H. Gota, T. Tajima, M. Binderbauer, D. Gupta, J. Douglass In the core of the C-2 advanced beam-driven Field-Reversed Configuration (FRC), ion-scale turbulence is absent, leading to near-classical thermal ion confinement. Only electron-scale modes ($0.5\le k_{\theta } \rho_{s} \le 40$, where $\rho_{s} $ is the ion sound gyro-radius) have been detected via multi-channel Doppler Backscattering. Linear gyrokinetic simulations confirm that ion modes are stable, and show unstable electron interchange modes driven by the electron temperature gradient in the outer FRC core. Core turbulence observations are qualitatively consistent with quenching of long wavelength ion modes via Finite Larmor radius effects, as evidenced by an inverted toroidal wavenumber spectrum. In contrast, ion-scale modes driven unstable primarily by the density gradient are predicted (and observed) in the FRC scrape-off layer (SOL). Density fluctuation levels \textit{\~{n}/n }near the separatrix and in the SOL increase beyond a critical density gradient roughly in agreement with the predicted linear stability threshold. Strong $E\times B$ velocity shear develops $\sim $1 ms after FRC initiation, and is observed to increase the SOL critical density gradient. [Preview Abstract] |
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BP12.00029: Electron Beam-Blip Spectroscopic Diagnostics of the Scrape-off-Layer Parallel Transport in C-2 Dmitry Osin, Matthew Thompson, Eusebio Garate C-2 is a microscopically stable, high-performance field-reversed configuration (FRC), where high plasma temperatures with significant fast ion population and record lifetimes were achieved by a combination of tangential neutral beam injection, electrically biased plasma guns at the ends and wall conditioning [1]. FRC confinement depends on the properties of both the open and closed field lines, therefore, understanding the electron transport in the scrape-of-layer (SOL) is critical. To study parallel heat conduction in SOL, a high-energy pulsed electron beam (e-beam) was injected on-axis into C-2 to produce a heat pulse, which causes a fast rise and slower decay of the electron temperature, $T_e$, in the SOL. The heat-blip was observed by means of He-jet spectroscopy. A small fraction of the total deposited e-beam energy is necessary to explain the measured $T_e$ increase. The electron thermal conductivity along the magnetic field lines can be inferred from the $T_e$ decay. Experiments suggest that a high energy e-beam pulse can serve as a direct diagnostic of heat transport in the SOL.\\[4pt] [1] M.W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015). [Preview Abstract] |
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BP12.00030: Sliding mode control of an FRC plasma axial position Jesus Antonio Romero We study the problem of controlling the position of an axially unstable FRC configuration by acting on discrete voltage levels applied to radial field coil actuators. Due to the discrete, on/off nature of the actuators, the control problem is treated using sliding mode control theory. In sliding mode control, we don't usually design the controllers (usually based on a hystheresis type control logic), but find instead a function of system states (sliding surface) that will act as the error signal with the desired asymptotically stable (sliding) behavior. A simplified rigid plasma model for axial position including perturbations is developed and used to derive a suitable sliding surface for the system. The asymptotic stability of this surface is demonstrated using Liapunov theory, and is shown to be fairly insensitive to plant parameter values. The result is that the proposed control can be used for both axially stable or unstable plasmas without the need to re-tune the parameters used in the sliding surface. This property is important because the equilibrium may have to transit between an axially stable and unstable equilibria on different phases of the FRC discharge. Numerical simulations show the robustness of the control scheme against plant uncertainties and perturbations. [Preview Abstract] |
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BP12.00031: FPIC: A Key Next Step for Stability Studies of Advanced Beam Driven FRCs Sean Dettrick, Dan Barnes, Francesco Ceccherini, Laura Galeotti, Victor Guerrero, Doug Hendrix, Kevin Hubbard, Richard Milroy, Ales Necas The goal of the C-2U experiment [1] is to use neutral beam heating and edge biasing to sustain an advanced beam-driven FRC for many milliseconds, longer than the growth times of known instabilities and the resistive wall time. To guide the experiment further into unexplored parameter regimes, it is desirable to have a stability code suitable for beam-driven FRC plasmas, in which the bulk of ion orbits are not Larmor-like and hence gyrokinetic approximations are inapplicable. Fully kinetic ions are required for stability simulations of beam driven FRCs, as are multiple ion species, end boundary conditions, and a resistive boundary. To meet these challenges a new 3D quasineutral hybrid code, FPIC, is being developed. FPIC has a choice of zero electron mass and finite electron mass Ohm's law solvers. Uniform staggered grids, finite differencing, and cut cell boundaries are used to simplify and optimize the PIC while allowing arbitrary boundary shapes. Finite resistivity of the boundary is implemented by coupling free-space exterior solutions to the cut-cell edges. The code is MPI parallelized and the particle push is GPU accelerated. Code benchmarks will be presented including the stability of the FRC tilt mode. \\[4pt] [1] M.W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015). [Preview Abstract] |
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BP12.00032: Simulations of the C-2/C-2U Field Reversed Configurations with the Q2D code Marco Onofri, Sean Dettrick, Daniel Barnes, Toshiki Tajima C-2U was built to sustain advanced beam-driven FRCs for 5$+$ ms. The Q2D transport code is used to simulate the evolution of C-2U discharges and to study sustainment via fast ion current and pressure, with the latter comparable to the thermal plasma pressure. The code solves the MHD equations together with source terms due to neutral beams, which are calculated by a Monte Carlo method. We compare simulations with experimental results obtained in the HPF14 regime of C-2 [1] (6 neutral beams with energy of 20 keV and total power of 4.2 MW). All simulations start from an initial equilibrium and transport coefficients are chosen to match experimental data. The best agreement is obtained when utilizing an enhanced energy transfer between fast ions and the plasma, which may be an indication of anomalous heating due to beneficial beam-plasma instabilities. Similar simulations of C-2U (neutral beam power increased to 10$+$ MW and angled beam injection) are compared with experimental results, where a steady state has been obtained for 5$+$ ms, correlated with the neutral beam pulse and limited by engineering constraints. \\[4pt] [1] M. Binderbauer et al., Physics of Plasmas 22, 056110 (2015) [Preview Abstract] |
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BP12.00033: Beam-plasma instabilities and their impact on D-D reactivity Ales Necas, R. Magee, T. Tajima, B. Nicks, M. Seggebruch, E. Garate, I. Allfrey, T. Valentine The goal of the C-2U program [1] is to achieve 5$+$ms steady state FRC sustainment via beam injection. In support, we simulate possible beam driven instabilities that are non-destructive, but transfer energy from fast ions to the plasma, causing phase space bunching. Such a mechanism may explain an experimentally observed anomalous neutron signal (10-100$\times$ greater than the predicted thermonuclear component and peaking between 1-2 ms, correlated with a 1 ms beam slowing down time), as other explanations have been eliminated (D in the beams, fast-thermal ion head-on collisions, and miscalculation of Ti). We propose that the hydrogen beam generates an energetic ion population that then drives collective modes in the plasma, giving rise to an instability and increased fusion rate. A two-body correlation function is employed to determine DD reactivity enhancements. The instability changes character from electrostatic (ES; phase velocity is 70{\%} of the beam velocity) in the low beta edge to fully electromagnetic (EM; at magnetosonic speeds) in the core, with an associated reduction in growth rates. A 1D ES analytical dispersion relation will be compared with a 1D3V PIC code [2] (full EM study only performed with PIC code). Results from simulations are consistent with the observed neutron yield. \\[4pt] [1] M. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)\\[0pt] [2] J.W.S. Cook et al., Plasma Phys. Control. Fusion 53, 074019 (2011) [Preview Abstract] |
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BP12.00034: Closed-loop, non-linear feedback control simulations of beam-driven field-reversed configurations (FRCs) N. Rath, M. Onofri, D. Barnes, J. Romero The C-2U device has recently demonstrated sustainment of an advanced, beam-driven FRC over time scales longer than the characteristic times for confinement, fast ion slow-down, and wall current decay. In anticipation of further advances in plasma lifetime, we are developing feedback control techniques for major FRC parameters and resistive instabilities. The LamyRidge code solves the time-dependent extended MHD equations in axisymmetric geometry. In the Q2D code, LamyRidge is combined with a 3-D kinetic code that tracks fast ions and runs in parallel with LamyRidge. Periodically, the background fields in the kinetic code are updated from the MHD simulation and the averaged fast particle distribution is integrated into the fluid equations. Recently, we have added the capability to run Q2D simulations as subordinate processes in Simulink, giving us the ability to run non-linear, closed-loop simulations using control algorithms developed in Simulink. The same Simulink models can be exported to real-time targets (CPU or FPGA) to perform feedback control in experiments. We present closed-loop simulations of beam-driven FRCs under magnetically-actuated feedback control. Results for positionally unstable FRCs are compared with the predictions of a linearized rigid-plasma model. Plasmas predicted to be passively stabilized by the linear model are found to exhibit Alfvenic growth in several cases. Feedback gains predicted to be stabilizing in the linear model are generally found to be insufficient in non-linear simulations, and vice versa. Control of separatrix geometry is demonstrated. [Preview Abstract] |
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BP12.00035: Kinetic equilibria of very high-$\beta $ plasmas Loren Steinhauer Plasma equilibria with many large ion orbits, such as an advanced beam-driven field-reversed configuration, are neither static (Grad-Shafranov) nor describable as a flowing, multi-fluid. A fully-kinetic treatment of the ions is essential for such high-$\beta $ plasmas. A kinetic equilibrium is needed to properly support realistic stability and transport analyses, both of which are strongly affected by large-orbit ions. A hybrid equilibrium model has been developed with a fully-kinetic treatment of both thermal ions and a rapidly-rotating ``beam-ion'' component, such as produced by neutral beam injection, relevant to the C-2U experiments at TAE. It employs analytic Vlasov solutions in that the distribution depends only on the two constants of motion, the Hamiltonian ($H)$ and the canonical angular momentum ($P_{\theta })$. Electrons are treated as a pressure-bearing fluid. Since realistic forms of $f(H$,$P_{\theta })$ are affected by collisions, $f$ is limited to solutions of a simplified Fokker-Planck equation. Importantly, a kinetic end-loss condition applies to unconfined ions, using a particle sink at a rate consistent with Monte-Carlo-like simulations of end loss accounting for a strong end mirror. [Preview Abstract] |
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BP12.00036: Stochasticity and orbit types in advanced beam-driven FRCs Francesco Ceccherini, Laura Galeotti, Dan Barnes, Sean Dettrick, Henk Monkhorst Advanced beam-driven FRCs (Field Reversed Configurations) represent a plasma configuration which is aimed to reach steady state through external sustainment. In an advanced beam-driven FRC the plasma has a very rich selection of orbit types, namely, drift, betatron, figure-8 and type-I. How much each type contributes to the total quantity of orbits strongly depends on both plasma and external field parameters and it may include regular and stochastic orbits with very different ratios. We study the orbit type distribution as well as the fractions of regular and stochastic orbits for a set of realistic advanced beam-driven FRC equilibria in very different plasma regimes. In particular, we investigate the dependences of the orbit type distribution on the equilibrium parameters and we discuss the relevant role of the FRC parameter s in providing a good estimate of the total quantity of stochastic orbits. A first investigation of the possible role of stochastic orbits in thermalizing processes induced by magnetic pumping techniques is presented. [Preview Abstract] |
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BP12.00037: Electrostatic Drift-Wave Instability in Field-Reversed Configuration Calvin Lau, Daniel Fulton, Ihor Holod, Zhihong Lin, Michl Binderbauer, Toshiki Tajima, Lothar Schmitz Recent progress in the C-2 advanced beam-driven field-reversed configuration (FRC) experiment [Binderbauer 2015] at Tri Alpha Energy has led to consistently reproducible plasma lifetimes of 5+ ms, ie. transport regimes. To understand the mechanisms, gyrokinetic particle-in-cell simulations of drift-wave instabilities have been carried out for the FRC [Fulton 2015]. The realistic magnetic geometry is represented in Boozer coordinates in the upgraded gyrokinetic toroidal code (GTC) [Lin 1998]. Radially local simulations find that, in the FRC core, ion scale modes are stable for realistic pressure gradients while the electron scale modes are unstable. On the other hand, in the scrape-off layer (SOL) outside of the separatrix, both ion and electron scale modes are unstable. These findings and linear instability thresholds found in simulation are consistent with the C-2 experimental measurements of density fluctuations [Schmitz 2015]. Collisional effects and instability drive mechanism will be clarified. Nonlocal and nonlinear simulation results will also be reported. [Preview Abstract] |
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BP12.00038: Physics of expander divertors for Field Reversed Configurations Dmitri Ryutov, Peter Yushmanov The SOL and divertor play a significant role in the operation of TAE experimental devices: they provide conditions needed for thermal insulation of plasma electrons from the device ends, allow control of plasma rotation, and contribute to the global magneto-hydrodynamic stability of the plasma. Better understanding of the physics processes associated with divertor expanders is necessary for advancing the plasma parameters to regimes with high electron temperature. The following issues are addressed in the poster: formation and spatial re-distribution of neutral particles formed at the end-plates; effects of neutrals on the heat loss from the main plasma, effects of Charge Exchange on exhaust flow and density distribution in the divertors, and others. Particular attention is paid to the solution of an idealized benchmarking problem of the formation of a potential barrier for electrons in the expanders. Work at LLNL was funded by Tri-Alpha Energy and performed under DoE contract DE-AC52-7NA27344. [Preview Abstract] |
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BP12.00039: Design Point for a Spheromak Compression Experiment Simon Woodruff, Carlos A. Romero-Talamas, John O'Bryan, James Stuber Two principal issues for the spheromak concept remain to be addressed experimentally: formation efficiency and confinement scaling [1]. We are therefore developing a design point for a spheromak experiment that will be heated by adiabatic compression, utilizing the CORSICA and NIMROD codes as well as analytic modeling with target parameters R\textunderscore initial$=$0.3m, R\textunderscore final$=$0.1m, T\textunderscore initial$=$0.2keV, T\textunderscore final$=$1.8keV, n\textunderscore initial$=$1019m-3 and n\textunderscore final$=$ 1021m-3, with radial convergence of C$=$3. This low convergence differentiates the concept from MTF with C$=$10 or more, since the plasma will be held in equilibrium throughout compression. We present results from CORSICA showing the placement of coils and passive structure to ensure stability during compression, and design of the capacitor bank needed to both form the target plasma and compress it. We specify target parameters for the compression in terms of plasma beta, formation efficiency and energy confinement.\\[4pt] [1] Woodruff, Miller Cost sensitivity analysis for a 100 MWe modular power plant and fusion neutron source J. Fus. Eng. Design (2014) [Preview Abstract] |
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BP12.00040: Numerical investigation and optimization of multi-pulse CHI spheromak performance J.B. O'Bryan, C.A. Romero-Talamas, S. Woodruff Nonlinear extended-MHD computation with the NIMROD code is used to explore spheromak formation and sustainment with multi-pulse coaxial helicity injection (CHI). The goal of this research is to optimize spheromak performance in order to find candidate modes of operation for future experimental studies. We are modeling multiple specific shots from the Sustained Spheromak Physics eXperiment (SSPX) to both diagnose the parameters that affect efficiency---in particular, how the injector current and bias flux affect plasma confinement and magnetic helicity content relative to injected power---and to validate the numerical model. Preliminary results show quantitative agreement between several synthetic and experimental diagnostic measurements. The results also find---in addition to changing the magnetic topology and being the mechanism for poloidal flux amplification [E.B. Hooper et al. PPCF 2012]---the non-axisymmetric column mode decreases the decay rate of magnetic helicity relative to the injected current. Operational regimes will eventually be extended beyond those achieved in SSPX. We are also exploring the effect of the flux conserver and injector geometries on spheromak performance. [Preview Abstract] |
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BP12.00041: Development of Synthetic Diagnostics for use in Validation Danielle Lemmon, Simon Woodruff, Carlos A. Romero-Talamas, John O'Bryan Synthetic diagnostics are reproductions of experimental measurements obtained from simulation data, taking the same spatial averages (point, line, plane or volume) as in the experiment. This reduction of data facilitates meaningful direct quantitative comparisons which then allows for validation of simulation results [1]. We demonstrate the development with data sets produced by highly spatially and temporally resolved NIMROD simulations with reference to the spheromak concept under development at UMBC. We present here results from a set of synthetic diagnostics that are scripted in Octave. Quantities such as magnetic field, temperature, and density are visually represented by color-coded graphs and movies to demonstrate how these quantities change over time. We discuss errors that enter into the computation of the quantities.\\[4pt] [1] Oberkampf and Roy Verification and Validation in Scientific Computing CUP (2010). [Preview Abstract] |
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BP12.00042: 3D MHD Simulations of Spheromak Compression James E. Stuber, Simon Woodruff, John O'Bryan, Carlos A. Romero-Talamas The adiabatic compression of compact tori could lead to a compact and hence low cost fusion energy system. The critical scientific issues in spheromak compression relate both to confinement properties and to the stability of the configuration undergoing compression. We present results from the NIMROD code modified with the addition of magnetic field coils that allow us to examine the role of rotation on the stability and confinement of the spheromak (extending prior work for the FRC [1]). We present results from a scan in initial rotation, from 0 to 100km/s. We show that strong rotational shear (10km/s over 1cm) occurs. We compare the simulation results with analytic scaling relations for adiabatic compression.\\[4pt] [1] Woodruff et al Adiabatic Compression of a Doublet Field Reversed Configuration (FRC) J. Fusion Energy 27(1-2):128 (2007) [Preview Abstract] |
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BP12.00043: On the development of a compact toroid injector at the University of Illinois at Urbana-Champaign Michael Christenson, Soonwook Jung, Steven Stemmley, Xia Sang, Kishor Kalathiparambil, David Ruzic The ThermoElectric-driven Liquid-metal plasma-facing Structures (TELS) device is a gas-puff driven, theta pinched, transient plasma source used to simulate extreme events incident on materials in the edge and divertor regions of a tokamak plasma. Previous work has shown that in its current form, TELS can bombard a target with a peak energy of 0.08 MJ m$^{-2}$ over a 0.15 ms pulse, leading to a total heat flux of 0.5 GW m$^{-2}$. While these values are sufficient to mimic Type 1 ELMs in smaller devices, the plasma energy of TELS must be improved by a factor of greater than two to adequately simulate larger-scale Type 1 ELMs. It is for this reason that modifications to the existing TELS device have been proposed in the form of developing a compact toroid (CT) injector since the new self-contained structure allows for higher densities and energies delivered onto a target. The new setup will use a bias field, generating a peak magnetic field greater than 0.1 T and a peak magnetic flux greater than 2 mWb, surrounding the existing plasma gun arrangement to create the CT and the existing theta pinch to compress and translate the plasmoid. Preliminary results and analyses are presented and discussed in relationship to interactions with both solid and liquid metal targets. [Preview Abstract] |
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BP12.00044: Spectroscopic Measurements of Non-Hydrogenic Compact Toroids on CTIX D.Q. Hwang, D. Buchenauer, R.D. Horton, R.W. Evans, R. Klauser, J.A. Whaley, B.E. Mills The CTIX device is currently being used to investigate the production of compact-toroid plasmas consisting primarily of high-Z ions, using ionization and accretion of high-Z neutrals in the acceleration region. The axial density profile of the high-Z ions will be determined by transverse spectroscopic measurements, which are able to identify particular ion species. Ion velocity can then be deduced from axial time of flight. In addition, high-resolution spectroscopy will be used to directly measure high-Z ion velocity via Doppler shifts. These results are important in determining the degree of slip of high-Z ion velocity relative to CT magnetic field. Scaling of this slippage can be measured as a function of ion species, magnetic field strength, and gas injection location, and compared with a test-particle simulation. The results are relevant to determining the ability of the CT to penetrate a magnetic field, either for the purposes of shock formation study, or for applications to runaway electron suppression in large tokamak experiments. Beneficial effects, in terms of discharge reproducibility and surface durability, for a new tungsten-coated inner electrode will also be presented, along with a design for improved diagnostic access through the outer electrode. [Preview Abstract] |
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BP12.00045: Overview of the HIT-SI3 Experiment and Ion Doppler Spectroscopy Results from HIT-SI A.C. Hossack, K.D. Morgan, C.J. Hansen, C.J. Everson, D.A. Sutherland, A.W. Summers, R.N. Chandra, N.H. Nguyen, B.A. Nelson, T.R. Jarboe, D.B. Elliott, B.S. Victor HIT-SI3 is a one-meter diameter spheromak current drive experiment. The plasma is formed and sustained by three inductive helicity injectors. The loop voltage and magnetic flux in each injector are oscillated in phase. The three injectors can be phased 120 or 60 degrees apart giving constant helicity injection. Operating frequencies include 14.5 kHz, 47.5 kHz, and higher. Toroidal current 3 times greater than the quadrature sum of injector currents has been achieved. Results are presented from a new, internal magnetic probe which spans the entire major radius of the flux conserver. Initial results will also be presented from the multi-point Thomson scattering diagnostic, ion Doppler spectrometer (IDS), and laser-induced fluorescence neutral density diagnostic. IDS results from the previous experiment, HIT-SI, are also presented. The spheromak plasma exhibits coherent motion driven by the injector currents and higher injector driving frequencies yielded higher betas than low frequency. Measurements are also compared with NIMROD and PSI-TET simulations and show qualitative agreement with temperature and velocity profiles. Work supported by USDoE. [Preview Abstract] |
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BP12.00046: Thomson Scattering Measurements on HIT-SI3 C.J. Everson, K.D. Morgan, T.R. Jarboe A multi-point Thomson Scattering diagnostic has been implemented on HIT-SI3 (Helicity Injected Torus - Steady Inductive 3) to measure electron temperature. The HIT-SI3 experiment is a modification of the original HIT-SI apparatus that uses three injectors instead of two. This modification alters the configuration of magnetic fields and thus the plasma behavior in the device. The scientific aim of HIT-SI3 is to develop a deeper understanding of how injector behavior and interactions influence current drive and plasma performance in the spheromak. The Thomson Scattering system includes a 20 J (1 GW pulse) Ruby laser that provides the incident beam, and collection optics that are installed such that measurements can be taken at four spatial locations in HIT-SI3 plasmas. For each measurement point, a 3-channel polychromator is used to detect the relative level of scattering. These measurements allow for the presence of temperature gradients in the spheromak to be investigated. Preliminary HIT-SI3 temperature data are presented and can be compared to predictions from computational models. [Preview Abstract] |
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BP12.00047: NIMROD Modeling of HIT-SI and HIT-SI3 Kyle Morgan, Tom Jarboe Previous two-fluid simulations of the HIT-SI experiment using the NIMROD code at low injector frequencies have served as a launching point for modeling of both pressure effects related to Steady Inductive Helicity Injection (SIHI) and the new HIT-SI3 injector configuration. Results from the end of HIT-SI operations have encouraged the inclusion of pressure effects in NIMROD modeling. Previous simulations assumed uniform temperature and density profiles, producing good agreement with low injector frequency operations but poor agreement at high injector frequencies ($f_{inj} > \sim 40$ kHz). Experimental observations at these higher frequencies give evidence of pressure driven activity, as well as a high volume averaged $\beta$. A new series of simulations which allow for the evolution of density and temperature to examine the influence of pressure gradients have been conducted and are compared with both experimental and zero-beta modelled results. The agreement with experimental results is improved from this addition to the model. In addition, this model is applied to examine differences observed with the 3-injector configuration (HIT-SI3) in magnetic profile. Work supported by US DOE. [Preview Abstract] |
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BP12.00048: Two-photon absorption laser induced fluorescence (TALIF) neutral density measurements and two-fluid (plasma-neutral) 3D Extended-MHD simulations with PSI-TET on the HIT-SI3 experiment D.A. Sutherland, T.R. Jarboe, C.J. Hansen, D.B. Elliott Two-photon absorption laser induced fluorescence (TALIF) measurements were made on the HIT-SI3 experiment at the University of Washington through a collaboration with West Virginia University. Monatomic deuterium neutral densities of below 1 x 10$^{\mathrm{17}}$ m$^{\mathrm{-3}}$ were measured in $I_{p} =$10 -- 13 kA deuterium spheromak configurations that had electron number densities on the order of $n_{e} =$ 1 x 10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$. These measurements suggest an ionization fraction of 99{\%} or more in HIT-SI3 spheromak plasmas. Spatial and temporal information concerning the monatomic deuterium neutral density in HIT-SI3 will be presented. These data are being used to validate a self-consistent, multi-fluid (plasma-neutral) model that is currently being implemented in the PSI-TET 3D Extended-MHD code. Preliminary results from validation efforts will be presented, along with other plans for validation and proposed uses of this multi-fluid model on mainstream fusion devices. [Preview Abstract] |
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BP12.00049: A mechanism for the dynamo terms to sustain closed-flux current, including helicity balance, by driving current which crosses the magnetic field Thomas Jarboe, Brian Nelson, Derek Sutherland Recent experiments on HIT-SI demonstrate sustainment with ideal MHD stability, a major breakthrough in spheromak sustainment. The lack of large reconnection events demands a reassessment of the need for reconnection for sustainment. An analysis of imposed dynamo current drive (IDCD) [T.R. Jarboe \textit{et al., }Phys. Plasmas 22, 072503 (2015)] reveals: a) current drive on closed flux surfaces seems possible without relaxation, reconnection, or other flux-surface-breaking large events; b) the scale size of the key physics may be smaller than is often computationally resolved; c) helicity can be sustained across closed flux; d) and IDCD current drive is parallel to the current which crosses the magnetic field to produce the current driving force. In addition to agreeing with spheromak data, IDCD agrees with selected tokamak data. [Preview Abstract] |
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BP12.00050: The Development of SiC MOSFET-based Switching Power Amplifiers for Fusion Science James Prager, Timothy Ziemba, kenneth Miller, Julian Picard Eagle Harbor Technologies (EHT), Inc. is developing a switching power amplifier (SPA) based on silicon carbide (SiC) metal--oxide--semiconductor field-effect transistor (MOSFET). SiC MOSFETs offer many advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities. When comparing SiC and traditional silicon-based MOSFETs, SiC MOSFETs provide higher current carrying capability allowing for smaller package weights and sizes and lower operating temperature. EHT has conducted single device testing that directly compares the capabilities of SiC MOSFETs and IGBTs to demonstrate the utility of SiC MOSFETs for fusion science applications. These devices have been built into a SPA that can drive resistive loads and resonant tank loads at 800 V, 4.25 kA at pulse repetition frequencies up to 1 MHz. During the Phase II program, EHT will finalize the design of the SPA. In Year 2, EHT will replace the SPAs used in the HIT-SI lab at the University of Washington to allow for operation over 100 kHz. SPA prototype results will be presented. [Preview Abstract] |
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BP12.00051: Spherical Penning trap as a small fusion source Dan Barnes, Dan Knapp We are studying by theory, simulation, and experiments whether a useful fusion output can be produced in a small spherical Penning trap. Following previous work [PRL 78, 58 (1996)], we have observed a focus of electrons at the spherical center when the applied voltage is adjusted to a magnetic field dependent value. This virtual cathode can confine ions, leading to fusion reactions with a fractional energy gain. A throughput of electrons by injection and collection near the cylindrical center cathodes leads to a steady state with strong spherical convergence. Very low power is required because electrons are sourced and collected at very low energy. Theory arguments show that major instabilities (such as two-stream) are avoided provided that not too much of the space charge is neutralized by trapped ions. Low frequency ion/electron instabilities are also absent. A small experiment is described. A 0.7 cm radius trap with hyperbolic electrodes is placed inside a permanent magnet system which is engineered to produce a uniform magnetic field. Field strength can be varied from several hundred Gauss to nearly 2 kG by adding additional permanent magnets. Axial holes in the two end cap cathodes allow injection of electrons which are produced by a hairpin tungsten filament. The entire assembly is placed inside a room temperature vacuum chamber which is capable of a base pressure below 10-7 Torr. Present diagnostics are limited to external electrical measurments. We report on initial experiments on electron focus and recent operation with a low pressure deuterium static fill. [Preview Abstract] |
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BP12.00052: Development of Table-Top mirror trap for flute stabilization research Omri Seemann, Ilan Be'ery Mirror traps might be viable candidates for fusion machines. These machines are technically and physically simple but suffer from the Rayleigh-Taylor-like flute instability. A new table top mirror machine was built in order to research ways to mitigate this instability. One possible solution for this problem which was researched in the past is using oscillatory fields. A description of the system and diagnostics, preliminary results and a review of the main mechanisms with which stabilization might occur are presented. [Preview Abstract] |
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BP12.00053: Recent Results from KMAX tandem mirror experiment Xuan Sun, M. Luo, Q. Zhang, M. Lin, P. Shi KMAX, Keda Mirror with AXisymmeticity, is a tandem mirror machine with a length of $\sim$ 10 meters and diameters of 1.2 meters in the central cell and 0.3 meters in the mirror throat. As a versatile plasma experimental platform, KMAX is currently conducting experiments on the Alfven wave launching, electrode biasing, radio frequency heating and etc. The latest results will be presented. In the experiment of Alfven wave launching, we observed the shear Alfven waves decay into the forward and backward propagating compressional waves. And in the bias experiment we successfully extracted plasma current up to 0.5kA with biasing voltage of $\sim$ 1kV. During biasing, the plasma density and temperature have siginificantly increasing. Preliminary results on the radio frequency heating will also be presented. [Preview Abstract] |
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BP12.00054: PLASMA SOURCES \& DIAGNOSTICS |
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BP12.00055: Electron Heating in Microwave-Assisted Helicon Plasmas John McKee, Umair Siddiqui, Zach Short, Miguel Henriquez, Julianne McIlvain, Earl Scime The use of two (or more) rf powers at different frequencies is a technique used in the processing community to influence ion energy characteristics separately from plasma generation. A similar approach is taken here with the focus instead being on the electron population in both argon and helium. The plasma is generated by a helicon source at a frequency f$_{\mathrm{0}} \quad =$ 13.56 MHz. Microwaves of frequency f$_{\mathrm{1}} \quad =$ 2.45 GHz are then injected into the chamber. Where the magnetic field strength is B $=$ 875 G, the electrons will experience heating due to cyclotron resonance with the microwaves. The effects of this secondary-source heating on electron density, temperature, energy distribution function, and population enhancement are examined and compared to helicon-only single source plasmas, as well as emission spectra showing the impact on ion excited state populations. Two different methods of microwave injection/coupling are used---R-wave coupling via injection anti-parallel to the background B field and X-wave coupling via injection perpendicular to the background B field. [Preview Abstract] |
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BP12.00056: Spatially Resolved Measurements of a Double Layer in an Argon Helicon Plasma Evan Aguirre, Umair Siddiqui, John McKee, Earl Scime We report 2-dimensional, spatially resolved observations of a double layer in an expanding helicon plasma. These new measurements investigate the origins of previously observed multiple ion beam populations in the downstream plasma. We use Laser Induced Fluorescence (LIF) to measure the ion velocity distribution functions (IVDFs) of argon ions and neutrals both parallel and perpendicular to the background magnetic field and an rf-compensated Langmuir probe to determine the local plasma potential. These are the first multi-dimensional LIF measurements of ion acceleration in a current-free double layer and were obtained with a recently installed, internal scanning probe system in the HELIX-LEIA experimental facility. [Preview Abstract] |
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BP12.00057: Excitation, propagation and damping of helicon waves in a high density, low temperature plasma J.F. Caneses, B.D. Blackwell The MAGnetized Plasma Interaction Experiment (MAGPIE) is a helicon linear plasma device built to study fusion relevant plasma-surface interactions. In this work, we investigate helicon wave propagation in high density (10$^{18}$-10$^{19}$ m$^{-3})$ low temperature (2-4 eV) magnetized (50-200 G) hydrogen plasma produced by a half-helical antenna operated at 7 MHz and 20 kW. Using the cold dielectric tensor with collisional terms (electron-neutral and Coulomb), helicon wave damping is calculated along the length of MAGPIE using a WKB approximation. Comparison with experiment indicates that wave damping, under these conditions, is entirely collisional. Numerical results from a fully electromagnetic wave code and 2D wavefield measurements indicate that helicon waves are excited at the plasma edge by the antenna's transverse current straps while the helical straps play a secondary role. These waves propagate towards the center of the discharge along the whistler wave ray direction (19 degrees to the background magnetic field), interfere on-axis and form the axial interference pattern commonly observed in helicon devices. [Preview Abstract] |
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BP12.00058: The MARIA Helicon Plasma Experiment at UW Madison: Upgrade, Initial Scientific Goals Mission and First Results Victoria Winters, Jonathan Green, Noah Hershkowitz, Oliver Schmitz, Greg Severn The versatile helicon plasma device, MARIA (Magnetized AnisotRopic Ion-distribution Apparatus), was upgraded with stronger magnetic field B $\le $ 1200G. The main focus is to understand the neutral particle dynamics and ionization mechanism with helicon waves to establish a high-density plasma (10\textasciicircum 20/m\textasciicircum 3) at substantial electron (Te$\approx $5-15eV) and ion (Ti$\approx $1-3eV) temperature. To achieve this, installation of higher RF Power $\le $ 15kW is planned as well as design of an ion cyclotron-heating antenna. To quantify the plasma characteristics, diagnostics including a Triple Langmuir Probe, Emissive Probe, and Laser Induced Fluorescence were established. We show first results from characterization of the device. The coupling of the helicon mode in the electron temperature and density parameter space in Argon was mapped out with regard to neutral pressure, B-field and RF power. In addition, validity of the Bohm Criterion and of the Chodura model starting in the weakly collisional regime is tested. A key goal in all efforts is to develop methods of quantitative spectroscopy based on cutting-edge models and active laser spectroscopy. [Preview Abstract] |
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BP12.00059: Ion acceleration and non-Maxwellian electron distributions in a low collisionality, high power helicon plasma source Yan Li, Yung-Ta Sung, John Scharer Ion acceleration through plasma double layer and non-Maxwellian two temperature electron distributions have been observed in Madison Helicon Experiment (MadHeX) operated in high RF power (\textgreater 1000 W) and low Ar pressure (0.17 mtorr) inductive mode. By applying Optical Emission Spectroscopy (OES)[1] cross-checked with an RF-compensated Langmuir probe (at 13.56 MHz and its second and third harmonics), the fast (\textgreater 80 eV), untrapped electrons downstream of the double layer have a higher temperature of 13 eV than the trapped bulk electrons upstream with a temperature of 4 eV[2]. The reduction of plasma potential and density observed in the double layer region require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. The hot tail electrons of the non-Maxwellian electron distribution affect the formation and the potential drop of the double layer region. The mechanism behind this has been explored via several non-invasive plasma diagnostics tools. The OES measured electron temperatures and densities are also cross-checked with Atomic Data and Analysis Structure (ADAS) and a millimeter wave interferometer respectively. The IEDF is measured by a four-grid RPA and also cross-checked with argon 668 nm Laser Induced Fluorescence (LIF). An emissive probe has been used to measure the plasma potential. [1] J. B. Boffard, R. O. Jung, C. C. Lin, A. E. Wendt, Plasma Sources Sci. Technol. 19, 065001 (2010) [2] Y.-T. Sung, Y. Li, J. E. Scharer, Phys. Plasmas 22, 034503 (2015) [Preview Abstract] |
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BP12.00060: Localized electron heating and downstream density rise in expanding helicon plasma Soumen Ghosh, Kshitish Barada, Prabal Chattopadhyay, Joydeep Ghosh, Dhiraj Bora Localized electron heating and downstream density rise have been observed in presence of diverging magnetic fields in a linear expanding helicon plasma system. Axial wave field measurement shows the presence of damped helicon waves with standing wave character folded into it even at low densities (10$^{16}$ m$^{-3})$. Helicon wavelength is just about twice the antenna length and the phase velocity ($v_{\mathrm{p}})$ is almost equal to the speed required for electron impact ionization. Observations advocate the Landau damping heating by the helicon waves, particularly in our low density plasma. Electron heating, confined away from the antenna centre, strongly indicates a source of local power absorption, occurring due to damped helicon waves [1]. Further downstream from the location of electron heating, a density peak is observed. Location of both electron heating and density peaking can be varied by changing the axial magnetic field topology. A comprehensive discussion regarding the cause behind both the localized electron heating and downstream density rise will be discussed in this presentation. \\[4pt] [1] Soumen Ghosh, K. K. Barada, P. K. Chattopadhyay, J. Ghosh, and D. Bora. Plasma Sources Sci. Technol. 24, 034011, (2015). [Preview Abstract] |
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BP12.00061: High-Beta Plasma Characteristics Using Helicon Sources Shunjiro Shinohara, Daisuke Kuwahara, Kazuki Yano, Amnon Fruchtman Helicon sources have been extensively investigated because of their efficient high-density (up tp $\sim$ 10$^{13}$ cm$^{-3}$) plasmas production in a wide range of operational parameters. Using this source with a large diameter of 74 cm [1], high-beta ($\sim$ 1) plasma characteristics have been investigated. The magnetic field less than \textless 120 G was measured with and without plasma, so that the reduction rate of the magnetic field, i.e., the diamagnetic effect due to the plasma, was evaluated. For a large magnetic field and/or a low fill pressure, the reduction of the magnetic field pressure was found to be nearly equal to the plasma pressure, confirming balance between magnetic and plasma pressures. For a low magnetic field and/or a high fill pressure, however, the magnetic field was hardly changed. We suggest that the neutral pressure associated with a neutral depletion plays a role in weakening of the diamagnetic field. Detailed results with a theoretical analysis will be presented.\\[4pt] [1] S. Shinohara and T. Tanikawa, Rev. Sci. Instrum. \textbf{75} (2004) 1941. [Preview Abstract] |
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BP12.00062: Self-consistent discharge growing model of helicon plasma Shogo Isayama, Tohru Hada, Shunjiro Shinohara, Takao Tanikawa Helicon plasma is a high-density and low-temperature plasma generated by the electromagnetic (Helicon) wave excited in the plasma. It is thought to be useful for various applications including electric thrusters. Physics of helicon plasma production involves such fundamental processes as the wave propagation (dispersion relation), collisional and non-collisional wave damping, plasma heating, ionization/recombination of neutral particles, and modification of the dispersion relation by newly ionized plasma. There remain a number of unsolved physical issues such as, how the Helicon and the TG modes influence the plasma density, electron temperature and their spatial profiles. While the Helicon mode is absorbed in the bulk plasma, the TG mode is mostly absorbed near the edge of the plasma. The local power deposition in the helicon plasma is mostly balanced by collisional loss. This local power balance can give rise to the inhomogeneous electron temperature profile that leads to time evolution of density profile and dispersion relation. In our study, we construct a self-consistent model of the discharge evolution that includes the wave excitation, electron heat transfer, and diffusion of charged particles. [Preview Abstract] |
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BP12.00063: General Color Rendering Index of Wall-stabilized Arc of Water-cooled Vortex Type Takaya Nakamura, Kentaro Yanagi, Shinji Yamamoto, Toru Iwao The arc lighting to obtain the environment to evacuate, save the life, keep the safety and be comfortable are focus on. The lack of radiation intensity and color rendering is problem because of inappropriate energy balance. Some researchers have researched the high-intensity discharge (HID) lamp which is one of the arc lamp with metal vapor, and the line spectrum emitted from the metal vapor is used for improvement of color rendering spectrum. The broad spectrum emitted from continuous spectrum is needed for improvement of color rendering spectrum. It is necessary to perform the calculation using the wall-stabilized arc to equalize the contribution to the temperature distribution which the convection gives it to bell-shaped form in the gas flow-stabilized arc for the axial distance. This research elucidates the development of the argon wall-stabilized arc in order to control the spectrum for improvement of color rendering spectrum with controlling the current and radius. The color rendering is measured by the general color rendering index. As a result, the general color rendering index increases with increasing the current and radius of the wall-stabilized arc in the case of simulation. However, it doesn't change so much in the case of experiment. Therefore, the radius, i.e. the arc temperature distribution, is more important factor. [Preview Abstract] |
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BP12.00064: Radiation Power Affected by Current and Wall Radius in Water Cooled Vortex Wall-stabilized Arc Toru Iwao, Takaya Nakamura, Kentaro Yanagi, Shinji Yamamoto The arc lighting to obtain the environment to evacuate, save the life, keep the safety and be comfortable are focus on. The lack of radiation intensity and color rendering is problem because of inappropriate energy balance. Some researchers have researched the arc lamp mixed with metal vapor for improvement of color rendering spectrum. The metal vapor can emit the high intense radiation. In addition, the radiation is derived from the high temperature medium. Because the arc temperature can be controlled by current and arc radius, the radiation can be controlled by the current and arc radius. This research elucidates the radiation power affected by the current and wall radius in wall-stabilized arc of water-cooled vortex type. As a result, the radiation power increases with increasing the square of current / square of wall radius because of the temperature distribution which is derived from the current density at the simulation. [Preview Abstract] |
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BP12.00065: Contribution of moving speed of vacuum arc cathode spot to the heat conduction process Chihiro Nagasawa, Shinji Yamamoto, Toru Iwao Thermal spraying has been widely used because it can give various functions by coating materials on the surface. It is necessary to remove an oxide layer and form a roughness. However, the blast has problems that occurs crushing and wear of the particles, and residual grid becomes a starting point of rust and peeling. The pretreatment with vacuum arc cathode spot is focused by this problem. Cathode spot with high energy density evaporates the oxide layer and melts the bulk for roughness. However, this process is believed that surface state is changed by the power density and sojourn time because the roughness depends on the location. It remains to be elucidated the formation factor of roughness and removal process. Therefore, the models of heat conduction process and vapor mixed affected by moving speed were proposed. To elucidate the formation factor of roughness and removal process, the contribution of moving speed to the heat conduction process is analyzed. As a result, the molten depth, width, and volume depend on the moving speed. [Preview Abstract] |
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BP12.00066: Long-lived laboratory plasmas sustained by a free-space microwave beam Remington Reid The Air Force Research Laboratory is developing a laboratory experiment to study the free-space interaction of microwave beams with low temperature, low density plasmas. A 10 kW, 4.5 GHz beam is passed through a vacuum chamber outfitted with pressure windows that are transparent to 4.5 Ghz radiation. The pressure windows are approximately 1m in diameter, allowing for minimal interaction between the beam and the chamber. The entire experiment is housed inside an anechoic chamber to minimize reflections. Plasmas generated by the beam have been observed to be stable for more than 10s. A series of optical and microwave diagnostics are being developed to measure the plasma properties, and to quantify the interaction of the plasma and the background neutral gas. [Preview Abstract] |
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BP12.00067: keV-energy x-rays from a low-pressure, low-power, low-field, capacitively coupled 27-MHz hydrogen plasma source Peter Jandovitz, Charles Swanson, Jackson Matteucci, S.A. Cohen We report on the unexpected observation of 0.9--5 keV x-rays coming from a cool (bulk $T_e \sim$ 4 eV), tenuous ($n_e \sim 10^{10}$ cm$^{-3}$) 5-cm-diameter hydrogen plasma column generated in a tandem high-mirror-ratio mirror machine by an external, capacitively-coupled RF (27 MHz) antenna operating at low power, 20--500 W. The x-rays, measured with an Amptek XR-100CR detector, are evidence of energetic electrons that have not been seen previously in experiment or theory in similar plasmas. In the neutral H$_2$ gas pressure range of 0.4 to 1.5 mT, the x-ray emissivity increased with decreasing pressure. No x-rays were observed when operating with argon (or 30/70 argon/hydrogen mixtures) at similar powers and pressures in either capacitively-coupled or helicon modes. X-ray count rate smoothly increased as mirror ratio increased and reached a broad maximum near 80 G, central field. Time-dependent emissivity with pulsed RF power and spatial profiles over a limited axial range have been measured. Possible heating mechanisms, including Fermi acceleration, cyclotron resonance, double layers, and sheaths, are being considered. [Preview Abstract] |
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BP12.00068: Development and characterization of a high-reliability, extended-lifetime H$^-$ ion source Gabriel Becerra, Preston Barrows, Joseph Sherman Phoenix Nuclear Labs (PNL) has designed and constructed a long-lifetime, negative hydrogen (H$^-$) ion source, in partnership with Fermilab for an ion beam injector servicing future Intensity Frontier particle accelerators. The specifications for the low-energy beam transport (LEBT) section are 5-10 mA of continuous H$^-$ ion current at 30 keV with $<$0.2 $\pi$-mm-mrad emittance. Existing ion sources at Fermilab rely on plasma-facing electrodes, limiting their lifetime to a few hundred hours, while requiring relatively high gas loads on downstream components. PNL's design features an electron cyclotron resonance (ECR) microwave plasma driver which has been extensively developed in positive ion source systems, having demonstrated 1000+ hours of operation and $>$99\% continuous uptime at PNL. Positive ions and hyperthermal neutrals drift toward a low-work-function surface, where a fraction is converted into H$^-$ hydrogen ions, which are subsequently extracted into a low-energy beam using electrostatic lenses. A magnetic filter preferentially removes high-energy electrons emitted by the source plasma, in order to mitigate H$^-$ ion destruction via electron-impact detachment. The design of the source subsystems and preliminary diagnostic results will be presented. [Preview Abstract] |
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BP12.00069: Two-fluid simulation of field-reversed configuration and application to conical implosion Zhengquan Yang, Cheng Li Field-reversed configurations (FRC) compression is one candidate for conical imploding magnetic target fusion (MTF). In the scenario, the density of initial plasma is much higher (10$^{20\sim 21}$ cc) than that of liner imploding FRC compression. As the characteristic spatial scales are in the order of ion gyroradius, two-fluid effects become important. In two-fluid MHD simulation, we use full sets of Euler equations for both ions and electrons, and a full set of Maxwell's equations for electromagnetic field. The fluid and field are coupled. Simulation starts with a uniform plasma and a set of 3 current coils. Field of current coils is solved by Maxwell's equations. The current in the middle coil is reversed, and results in magnetic reconnection and FRC formation. The simulation is then applied to a conical implosion, with a liquid metal drive. During the compression, the coil fires to form a FRC which is compressed at high ratio within several microseconds. The final pressure and temperature achieved are significantly improved comparing with compressions with no FRC. [Preview Abstract] |
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BP12.00070: Modeling of energy exchange processes in laser-produced argon plasmas Richard June Abrantes, Ann Karagozian, Hai Le The process of laser-induced breakdown for diagnostics contains a multitude of physical phenomena. An understanding of the interaction between the laser and the plasma is crucial for many applications. In the current work, we developed a collisional-radiative (CR) model for laser-produced argon plasmas. The model is constructed from the LANL database,\footnote{Argon Atomic Data Sets. https://www-amdis.iaea.org/LANL/argon/} which includes all the relevant collisional and radiative processes for all the ionic stages of argon. The laser is coupled to the plasma via multiphoton ionization and inverse Bremsstrahlung; these processes are important for electron production and heating. The use of the CR model allows us to identify dominant mechanisms responsible for initial breakdown of the gas and thermal equilibriation processes. The results are compared with experimental data from laser-induced breakdown experiments.\footnote{Sircar et al. \textit{Appl. Phys. B} 63, 623-627 (1996).} [Preview Abstract] |
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BP12.00071: A new laboratory stellarator for basic plasma research and wave studies Thiery Pierre A new laboratory stellarator was built for basic plasma. The device is designed following the early concept of the Spitzer's B1 to B3 stellarators built in the early 50's. The goal is to study anomalous transport and turbulence in this device, and to study wave chaos at low frequency in this complex closed magnetized plasma. In stellarators, it is well known that a special design of the torsion and of the local curvature of the magnetic field lines is necessary to obtain a stable plasma. In the B3 machine, the torsion of the magnetic field line was not continuously varying in plasma. The second point is the necessity to build a magnetic surface. The new magnetized plasma machine is a table-top machine (r $=$ 6 cm) shaped in a ``Figure Eight'' design including the possibility to vary the twisting of the magnetic field lines. In this way, it is possible to start from a toroidal type configuration without rotational transform (unstable) and to change for a magnetized ``Figure 8'' plasma that produces a stable plasma. The plasma is created by thermionic emission of ionizing electrons emitted from a hot tungsten filament or by microwave excitation at a frequency close to the electron cyclotron frequency. When the radial electric field is minimum, the propagation of ion acoustic waves is studied in the direction parallel to the magnetic field. Wave chaos related to the internal feedback present in this topology is investigated. [Preview Abstract] |
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BP12.00072: Experimental Study on Swirl Flow in an ECR Plasma Kenichiro Terasaka, Shinji Yoshimura, Kanshi Furuta, Takuya Yamada, Masayoshi Tanaka Swirl plasma flow plays an important role to clarify astrophysical phenomena, such as astrophysical jets and solar dynamo, and in the development of plasma propulsion systems. We have studied the effect of plasma rotation on flow structure formation in a cylindrical ECR plasma with the HYPER-II device at Kyushu University, Japan. The HYPER-II device consists of two cylindrical chambers with different diameters: one is the plasma production chamber with 0.3 m in diameter and 0.95 m in axial length, and the other is the diffusion chamber with 0.76 m in diameter and 1.3 m in axial length. An electron cyclotron resonance (ECR) plasma is produced by a 2.45 GHz microwave in the magnetic beach configuration. The azimuthal plasma rotation due to ${\mathbf E} \times {\mathbf B}$ drift is generated by a set of cylindrical electrodes, and the swirl plasma flow with various kinetic helicity is produced in a diverging magnetic field. An axially revers flow structure has been found near the center axis, in which the radial density profile exhibits a density build-up in the flow reversal region. The axial flow structure of rotating plasma shows an interesting behavior compared with non-rotating plasmas. [Preview Abstract] |
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BP12.00073: MEASUREMENT AND DIAGNOSTIC TECHNIQUES |
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BP12.00074: Confocal Laser Induced Fluorescence of Argon Plasmas Earl Scime, Mark Soderholm Laser Induced Fluorescence (LIF) provides measurements of flow speed, temperature and when absolutely calibrated, density of ions or neutrals in a plasma. Traditionally, laser induced fluorescence requires two ports on a plasma device. One port is used for laser injection and the other is used for fluorescence emission collection. Traditional LIF is tedious and time consuming to align. These difficulties motivate the development of an optical configuration that requires a single port and remains fully aligned at all times; confocal LIF. Our confocal optical design employs a single two inch diameter lens to both inject the laser light and collect the stimulated emission from an argon plasma. A pair of axicon lenses create an annular beam path for the emission collection and the pump laser light is confined inside the annulus of the collection beam. The measurement location is scanned radially by manually adjusting the final focusing lens position. Here we present optical modeling of and initial results from the axicon based confocal optical system. The confocal measurements are compared to traditional, two-port, LIF measurements over the same radial range. [Preview Abstract] |
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BP12.00075: Temperature after Arc Discharge Affected by Current Decrement Ratio in Wall Stabilized Arc Ken Sato, Daichi Suzuki, Toru Iwao Recently, the stable supply of electric power is indispensable in a power generation, and a transmission and distribution system of electric power. The GCB (Gas Circuit Breaker) has been researched for performance improvement of the arc interruption of abnormal fault current without the fail. The GCB has been researched for the high capacity and downsizing for development of practical use. Because the power network is expanded, the capacity of interruption current increased for reliability. The GCB should interrupt the arc of high current and voltage, shorten the time to interrupt, and become the high capability in order to improve the reliability and practicability. It is important to prevent the insulation of re-ignition and thermal re-ignition of arc after the arc interruption. It is mainly considered that the factor of thermal re-ignition is the arc temperature distribution after current zero. The temperature distribution has been elucidated by the current decrement ratio (di/dt). However, the variation of temperature distribution and decrement process of the temperature by the wall radius is also important in order to design the circuit breaker. In this paper, temperature after Arc Discharge Affected by Current Decrement Ratio in Wall Stabilized Arc was elucidated in order to know the effect on the temperature in the wall radius. As a result, when the wall radius decreases, the temperature at 0 A after 200 $\mu $s is lower. [Preview Abstract] |
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BP12.00076: Contribution For Arc Temperature Affected By Current Increment Ratio At Peak Current In Pulsed Arc Ryota Kano, Hironori Mitubori, Toru Iwao Tungsten Inert Gas (TIG) Welding is one of the high quality welding. However, parameters of the pulsed arc welding are many and complicated. if the welding parameters are not appropriate, the welding pool shape becomes wide and shallow.the convection of driving force contributes to the welding pool shape. However, in the case of changing current waveform as the pulse high frequency TIG welding, the arc temperature does not follow the change of the current. Other result of the calculation, in particular, the arc temperature at the reaching time of peak current is based on these considerations. Thus, the accurate measurement of the temperature at the time is required. Therefore, the objective of this research is the elucidation of contribution for arc temperature affected by current increment ratio at peak current in pulsed arc. It should obtain a detail knowledge of the welding model in pulsed arc. The temperature in the case of increment of the peak current from the base current is measured by using spectroscopy. As a result, when the arc current increases from 100 A to 150 A at 120 ms, the transient response of the temperature didn't occur during increasing current. Thus, during the current rise, it has been verified by measuring. Therefore, the contribution for arc temperature affected by current increment ratio at peak current in pulsed arc was elucidated in order to obtain more knowledge of welding model of pulsed arc. [Preview Abstract] |
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BP12.00077: Laser Induced Fluorescence (LIF) Measurement System for Neutral Argon (Ar I) Dynamics in the HelCat Plasma Device at UNM Ralph Kelly, Mark Gilmore, Alan Lynn, Tiffany Desjardins, Nick Boynton, Luan Nguyen, Andrew Scruggs, Jorge Romero When neutral and ion densities are spatially nonuniform, neutral-ion collisions can exert a torque on a magnetized plasma column via the FxB force, where F is the force exerted on ions by neutrals. This FxB force may have a significant effect on the dynamics of plasma instabilities and flows. In order to investigate the role of neutral dynamics in helicon discharges in the HelCat (\underline {Hel}icon-\underline {Cat}hode) plasma device at U. New Mexico, an Ar I Laser Induced Fluorescence (LIF) system is being developed. Previous passive spectroscopic measurements of Ar I and Ar II lines indicate that the neutral density profile is hollow (higher n$_{n}$ at larger radius). Additionally, we have not been able to reconcile azimuthal flows measured by Mach probes with those expected from ExB and diamagnetic torques. It is hypothesized that neutrals play an important role in the plasma flow. The LIF system is based on a \textgreater 250 mW, tunable solid state laser. The laser will pump the metastable (2P$^{0}_{3/2})$4s$^{2}$ level to the (2P$^{0}_{1/2})$4p$^{2}$ level using 696.543 nm light, and observe fluorescence radiation from decay to the (2P$^{0}_{1/2})$4s$^{2}$ level at 772.42 nm. The system design and initial results will be presented. [Preview Abstract] |
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BP12.00078: A Lagrangian Interpretation of Laser Induced Fluorescence Signals in a Plasma Feng Chu, Fred Skiff, Jorge Berumen, Sean Mattingly, Ryan Hood Laser induced fluorescence (LIF) is a nonintrusive diagnostic technique that has found applications in the study of a wide range of fundamental and applied problems. Thus it is important to make a correct interpretation of LIF signals. We adopt a Lagrangian approach to model LIF signals by introducing a non-linear conditional probability function $P$(x,v,t;x',v',t'). A simulation is performed to compute the LIF signals and the results are presented. We investigate how mean-field waves affect these signals and metastable state birth rates. The ultimate goal is to construct the complete model for LIF signals by combining optical pumping, mean-field wave effect and metastable state birth rate modulation. [Preview Abstract] |
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BP12.00079: New X-Ray Detector for Caltech Plasma Jet Experiment Ryan Marshall, Paul Bellan Magnetic reconnection is a process that occurs in plasmas where magnetic field lines break and re-attach to form a different topology having lower energy. Since the magnetic field is changing very fast in the reconnection region, Faraday's Law states that there is a large electric field that accelerates electrons which can then create x-rays. X-rays have been previously observed in the Caltech plasma jet experiment and in similar experiments. We have assembled a new detector consisting of a scintillator that is more than 10 times the volume of the previous one and a light guide that allows the photomultiplier tube to be 2 meters from the experiment so that electrical noise is reduced. The setup has been tested using a weak natural Thorium source and will soon be mounted on the Caltech jet experiment in front of a kapton vacuum window that allows x-rays to pass. Kapton has good transmission above 5 KeV. [Preview Abstract] |
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BP12.00080: Development of Experimental System for Optical Vortex Laser Absorption Spectroscopy Shoma Asai, Shinji Yoshimura, Mitsutoshi Aramaki, Naoya Ozawa, Kenichiro Terasaka, Masayoshi Tanaka, Tomohiro Morisaki We have been developing a new diagnostics using optical vortex for a linear ECR plasma device named HYPER-I at the National Institute for Fusion Science, Japan. Optical vortex is realized in laboratory as a cylindrically symmetric propagation mode of light beam known as the Laguerre-Gaussian (LG) mode. An atom moving in the LG beam is subjected to an additional azimuthal Doppler shift in contrast to conventionally used Hermite-Gaussian (HG) beams in which the atom experiences the axial Doppler shift alone. Therefore, it is promising that laser spectroscopy using LG beams have a sensitivity for traversing motion across the light path. Although there are several methods to produce optical vortex, we have adopted the holographic method due to its controllability. In the holographic method, the LG beams are obtained as the first-order diffracted light from the hologram displayed on the spatial light modulator. The quality of LG beams has been improved to be applied to optical vortex laser absorption spectroscopy by optimizing the hologram. The details of experimental system will be reported at the meeting. [Preview Abstract] |
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BP12.00081: Initial Results of Optical Vortex Laser Absorption Spectroscopy in the HYPER-I Device Shinji Yoshimura, Shoma Asai, Mitsutoshi Aramaki, Kenichiro Terasaka, Naoya Ozawa, Masayoshi Tanaka, Tomohiro Morisaki Optical vortex beams have a potential to make a new Doppler measurement, because not only parallel but perpendicular movement of atoms against the beam axis causes the Doppler shift of their resonant absorption frequency. As the first step of a proof-of-principle experiment, we have performed the optical vortex laser absorption spectroscopy for metastable argon neutrals in an ECR plasma produced in the HYPER-I device at the National Institute for Fusion Science, Japan. An external cavity diode laser (TOPTICA, DL100) of which center wavelength was 696.735 nm in vacuum was used for the light source. The Hermite-Gaussian (HG) beam was converted into the Laguerre-Gaussian (LG) beam (optical vortex) by a computer-generated hologram displayed on the spatial light modulator (Hamamatsu, LCOS-SLM X10468-07). In order to make fast neutral flow across the LG beam, a high speed solenoid valve system was installed on the HYPER-I device. Initial results including the comparison of absorption spectra for HG and LG beams will be presented. [Preview Abstract] |
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BP12.00082: Measuring Kinetic Plasma Eigenmodes Sean Mattingly, Jorge Berumen, Feng Chu, Ryan Hood, Fred Skiff We present a method for measuring kinetic plasma eigenmodes of a cylindrical axially magnetized ($1 kG$) laboratory plasma ($n \sim 10^9 cm^{-3}$, $T_e \sim 5eV$, $Ti \sim 0.06eV$) by measuring velocity space correlation functions. This method simultaneously observes two separate laser induced fluorescence schemes. Each scheme has its own indepedently tunable laser and its own set of collection optics. With this setup, we are able to measure the time - averaged correlation function as a function of position on the cylindrical axis parallel to the magnetic field $(z)$ and velocity on the deconvolved ion velocity distribution function $(v)$: $C(z, v, z', v', \tau )$ = $\langle f(z, v, t)f(z', v', t - \tau) \rangle_t$. The freedom of two lasers allows us to measure a two dimensional velocity correlation matrix. This matrix is investigated with the Vlasov equation in the collisionless and weakly collisional regime. The former case, which is continuous, is diagonalized with an integral transform defined by P. J. Morrison\footnote{P. J. Morrison \textbf{Phys. Plasmas} 1, 1447 (1994).} while the latter case, which is discrete, is diagonalized through the use of Hermite polynomials.\footnote{Ng \textit{et al.} \textbf{PRL APS} 92, 2004, 065002.} [Preview Abstract] |
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BP12.00083: Plasma magnetic field diagnostic using two-photon Doppler-free LIF Young Dae Yoon, Paul Bellan A detailed description of a new plasma B field diagnostic using Doppler-free two-photon laser-induced fluorescence is presented. The diagnostic is based on a method previously developed in the context of rubidium vapor experiments. Two counter-propagating 393nm diode laser beams are directed into an argon plasma to excite Ar-II ions from $3s^23p^44s\ {}^4P_{1/2} \longrightarrow 3s^23p^44p\ {}^4S_{3/2} \longrightarrow 3s^23p^44d\ {}^4P_{3/2}$. These levels involve two similar (392.86 and 393.25nm) transition wavelengths, so the two counter-propagating beams effectively cancel out the Doppler effect. The excited ions then decay to the $3s^23p^44p\ {}^4P_{1/2}$ level, emitting a 324.98nm line which is to be detected by a photomultiplier tube. The Zeeman splitting --- normally unobservable because of the large Doppler broadening --- of the resultant fluorescence is then to be analyzed, yielding the magnetic field of the particular location. This method is expected to provide a 3-D localized, non-perturbing measurement of magnetic fields. An experimental implementation is currently in progress. [Preview Abstract] |
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BP12.00084: New level-resolved collision data for neutral argon, benchmarked against the ALEXIS and CTH plasma experiments N. Ivan Arnold, Stuart Loch, Connor Ballance, Ed Thomas Performing spectroscopic measurements of emission lines in cool laboratory plasmas is challenging because the plasma is often neutral-dominated and not in thermal equilibrium. The densities and temperatures are such that coronal models do not apply; meaning that generalized collisional-radiative (GCR) methods must be employed to theoretically analyze the spectral emission. We use existing atomic physics codes to calculate excitation, recombination and ionization atomic data for neutral and low charge states of argon. For the excitation data we compare with previously published theoretical cross sections and experimental optical emission cross sections. We highlight expected differences in the ionization balance due to the new dielectronic recombination data. We also compare synthetic spectra generated from our data with observations taken from the Auburn Linear Experiment for Instability Studies (ALEXIS) and the Compact Toroidal Hybrid (CTH) experiments. [Preview Abstract] |
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BP12.00085: Development of Triple Probe Diagnostic for the Auburn Linear Experiment of Instability Studies (ALEXIS) Csilla Czako, Ivan Arnold, Ami DuBois, Mark Cianciosa, Edward Thomas The Auburn Linear Experiment for Instability Studies (ALEXIS) is a cylindrical, magnetized plasma column that is used to study low frequency ion instabilities relevant to the near-Earth space environment. Additionally, ALEXIS is used as a platform to develop probe and spectroscopic diagnostics in support of other plasma experiments, including high magnetic field experiments. This presentation will focus on the development of a new triple probe diagnostic system for ALEXIS. The key advantage of the triple probe is that it gives real time measurements of electron temperature, plasma density, and plasma potential. The triple probe will initially be used to cross-check against the existing single and double-probe diagnostics on ALEXIS. Moreover, due to the time-response of the triple probe - compared to swept-probe measurements - it may be possible to make direct measurements of density and electron temperature fluctuations in the plasma that complement our previous floating potential fluctuation measurements. [Preview Abstract] |
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BP12.00086: MOVED TO TP12.155 |
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BP12.00087: Investigation of Langmuir-probe-characteristic behavior at high bias frequency Sarah Newbury, Samuel Cohen, Jack Matteucci Langmuir probe characteristics recorded for magnetized DC hollow-cathode neon plasmas yield increasing values for electron temperature, plasma potential, and ion saturation current with increasing frequency of the applied probe bias voltage. The extent to which stray capacitance to the probe plays a role was investigated. Langmuir probe characteristics were recorded at frequencies ranging from 10 Hz to 8 kHz while the applied voltage to the probe was sawtooth modulated -- thus the rate of change of the bias voltage is constant. From these characteristics, the plasma temperature and density, as well as estimates for the capacitance in the wires, were calculated. The consistency and accuracy of these calculations were analyzed and found to indicate that the stray capacitance is the major factor contributing to the effects observed at higher bias frequencies.~ Similar experiments were performed with the PFRC-2 Langmuir probe apparatus, and the results of these experiments confirm the significant role of the stray capacitance. Contributions from electron thermalization, ion transit time, Debye length/probe radius, gyroradius, and displacement current at high bias frequencies have also been considered, but were found to be unlikely to produce the observed effects. [Preview Abstract] |
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BP12.00088: Measurement Of Magnetic Fields In Magnetized Plasmas Using Zeeman Broadening Diagnostics Showera Haque, Matthew S. Wallace, Paul Neill, Radu Presura The Zeeman effect has been used to measure the magnetic field in high energy density plasmas. The measurements are difficult in this regime because the line broadening due to the high plasma density and temperature surpasses the Zeeman splitting. Using an idea proposed by Tessarin \textit{et al}. (2011), we have measured the field in magnetized laser plasmas and the magnetized precursor of wire array z-pinches. Time-gated spectra with one-dimensional space-resolution were obtained at the Nevada Terawatt Facility for laser plasmas created by 20 J, 1 ns Leopard laser pulses, and expanding in the azimuthal magnetic field produced by the 0.6 MA Zebra pulsed power generator, and for wire array plasmas driven by the 1 MA configuration of the Zebra generator. We explore the response of the Al III 4s $^{2}$S$_{1/2}$- 4p $^{2}$P$_{1/2,3/2}$ doublet components and the C IV 3s $^{2}$S$_{1/2}$- 3p $^{2}$P$_{1/2,3/2}$ doublet components to the external magnetic field spatially along the plasma. In these measurements the Zeeman splitting was not resolved, but the magnetic field strength was measured from the difference between the widths of the line profiles. [Preview Abstract] |
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BP12.00089: Mass Spectrometry of 3D-printed plastic parts under plasma and radiative heat environments W.F. Rivera, C.A. Romero-Talamas, E.M. Bates, W. Birmingham, J. Takeno, S. Knop We present the design and preliminary results of a mass spectrometry system used to assess vacuum compatibility of 3D-printed parts, developed at the Dusty Plasma Laboratory of the University of Maryland Baltimore County (UMBC). A decrease in outgassing was observed when electroplated parts were inserted in the test chamber vs. non electroplated ones. Outgassing will also be tested under different environments such as plasma and radiative heat. Heat will be generated by a titanium getter pump placed inside a 90 degree elbow, such that titanium does not coat the part. A mirror inside the elbow will be used to throttle the heat arriving at the part. Plasma exposure of 3D printed parts will be achieved by placing the parts in a separate chamber connected to the spectrometer by a vacuum line that is differentially pumped. The signals from the mass spectrometer will be analyzed to see how the vacuum conditions fluctuate under different plasma discharges. [Preview Abstract] |
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BP12.00090: Thomson Scattering and Spectroscopy Diagnostics for Low Frequency Turbulence Produced in Dual-wire Implosions Christopher Plechaty, Andy Hamilton, Daniel Main, Nate Zechar, Vladimir Sotnikov Low frequency plasma turbulence can be driven by the presence of inhomogeneity in density, temperature, magnetic field, or by velocity shear. Low Frequency instabilities can play an important role in many different types of processes, such as magnetic reconnection [1], plasma structuring in the ionosphere's F-layer [2], structuring of laser-produced plasmas in external magnetic field [3], and anomalous diffusion processes [4] in theta-pinch and Z-pinch plasmas. We plan to carry out experiments at the Air Force Research Laboratory using a pulsed power generator to study two-wire implosions and the generation of the Lower-Hybrid Drift Instability [5,6] in the vicinity of the reconnection region. In this work, we develop the Thomson scattering and visible spectroscopy diagnostics that will be ultimately used to characterize the plasma in these types of experiments. [1] Huba, J. D., \textit{Geo. Res. Let.}, \textbf{4}, 125-128 (1977). [2] Huba, J. D., \textit{J. Geo. Res.}, \textbf{86}, 829-832 (1981). [3] Plechaty, C., \textit{Astrophys. Space Sci.}, \textbf{322}, 195-199 (2009). [4] Sotnikov, V. I., \textit{Sov. Phys. JETP}, \textbf{51}, 295 (1980). [5] Mal'kov, M. A., \textit{Sov. J. Plas. Phys.}, \textbf{11}, 626-631 (1985). [6] Krall, N., \textit{Phys. Rev. A,} \textbf{4}, 2094 (1971). [Preview Abstract] |
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BP12.00091: Spectroscopic investigation of species separation in opening switch plasmas S.L. Jackson, D.G. Phipps, A.S. Richardson, R.J. Commisso, D.D. Hinshelwood, D.P. Murphy, J.W. Schumer, B.V. Weber, C.N. Boyer, R. Doron, S. Biswas, Y. Maron Interactions between magnetic fields and current-carrying plasmas that lead to the separation of plasma species in multi-species plasmas are being studied in a plasma opening switch geometry. Several Marshall guns are used to inject single or multi-species plasmas between coaxial conductors connected to the output of the Naval Research Laboratory's Hawk pulsed-power generator. Following injection of the plasma, the generator is used at roughly half power to apply an electrical pulse with a peak current of 450 kA, a peak voltage of 400 kV, and a rise time of 1.2 $\mu $s. The resulting magnetic field interacts with the plasma through a combination of field penetration and magnetohydrodynamic (MHD) pushing that is not well understood but can lead to the separation of plasma species in multi-species plasmas. An ICCD-coupled spectrometer has been used in combination with magnetic probes, a ribbon-beam interferometer, and particle-in-cell (PIC) modeling to diagnose and understand conditions in the plasma from the time it is injected until the end of the conduction phase of the opening switch. [Preview Abstract] |
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BP12.00092: Experimental Characterization of a Laser-Triggered, Gas-Insulated, Spark-Gap Switch J.F. Camacho, D.J. Brown, M.T. Domonkos, E.L. Ruden, A. Schmitt-Sody, A.P. Lucero, J.P. Canright, R.L. Miner We have developed an experimental test bed to characterize the performance of a laser-triggered spark-gap switch as it transitions from photoionization to current conduction. The discharge of current through the switch is triggered by a focused 532-nm wavelength beam from a Q-switched Nd:YAG laser with a pulse duration of about 10 ns. The trigger pulse is delivered along the longitudinal axis of the switch, and the focal spot can be placed anywhere along the axis of the 5-mm, gas-insulated gap between the switch electrodes. The test bed is designed to support a variety of working gases (e.g., Ar, N$_2$, He, H$_2$) over a range of pressures. Electrical and optical diagnostics are used to measure switch performance as a function of parameters such as charge voltage, trigger pulse energy, insulating gas pressure, and gas species. Data from our experiments will be used to determine the minimum conditions necessary to induce the breakdown and conduction of a gas-insulated electrode gap in the presence of laser-induced photoionization. The electromagnetic particle-in-cell code ICEPIC will be used to produce numerical simulations of the laser-initiated arc discharge, and the experimental data will be used to validate the calculations. [Preview Abstract] |
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