Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session VP13: Poster Session: Magnetic Confinement: FRCs (2:00pm - 5:00pm)On Demand
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VP13.00001: X-ray measurements of electron energy distribution function in the PFRC-2 operating at high power, high field, and low frequency C.P.S. Swanson, S.A. Cohen, S.J. Thomas The PFRC-2 experiment is a Field-Reversed Configuration (FRC) magnetic heating and confinement experiment. The FRC is formed and heated by odd-parity Rotating Magnetic Field (RMF\textunderscore o). In order to directly heat ions using RMF\textunderscore o, the PFRC-2 will operate at higher power (200 kW, from 20 kW), higher field (500 G, from 300 G), and lower RMF\textunderscore o frequency (2 MHz, from 8 MHz) than ever before. Three SDD x-ray pulse-height detectors measure the Bremsstrahlung emissions above 150 eV simultaneously from three viewing chords. The electron temperature is observed to decrease as RMF\textunderscore o frequency is lowered, in agreement with a single-particle collisionless Hamiltonian model. The radial emission profile is measured, including a peak at the presumed o-point of the FRC. Results will be presented for frequencies as low as 2 MHz, where electrons are heated by thermalization with the directly-heated ions. [Preview Abstract] |
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VP13.00002: Electron Temperature measurement using Spectroscopic measurements of Balmer's ratio in PFRC-II Pulsed Hydrogen Plasmas using Collisional Radiative Model. Sangeeta P.Vinoth, Eric Palmerduca, Eugene S.Evans, Charles P.S. Swanson, Arthur Dogariu, Samuel Cohen A method to determine the electron temperature in PFRC-II based on Spectroscopic measurements of Balmer's ratio, H-beta to H-gamma, using Collisional Radiative (CR) model was studied. The distribution functions of atoms, molecules and ions over their excited states are studied in the framework of CR model. In this model the densities of various excited states of specific atom or ion are expressed as a function of electron temperature, electron density and ratio of density of Molecular neutrals to atomic neutrals. Depending on the experimentally measured Balmer's ratio and ratio of neutral density, the electron temperature was measured. While the error bars are large, it certainly appears to be the case that the electron temperature is 100 eV or above, with even higher temperatures during the initial startup phase. This was confirmed with X-ray diagnostics as well. [Preview Abstract] |
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VP13.00003: Overview of the C-2W Field-Reversed Configuration Experimental Program H. Gota, A. Smirnov, M. Binderbauer, T. Tajima, S. Putvinski, M. Tuszewski, R. Magee, T. Roche, E. Trask, P. Yushmanov, the TAE Team TAE Technologies, Inc. (TAE) is a privately-funded company pursuing an alternative approach to magnetic confinement fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and~well-confined particles via neutral-beam injection (NBI). TAE's current experimental device, C-2W (also called ``Norman'')~[1], is the world's largest compact-toroid device which has the following key~features: linear and axisymmetric configuration; NBI with high injection power (up to 20 MW) and intra-discharge variable energy (15--40 keV) functionality; flexible edge-biasing systems in divertors; external magnetic field fast control capabilities, such as ramp-up, and active feedback control of the FRC plasma. In C-2W, record breaking, advanced beam-driven FRC plasmas dominated by fast particles are produced, achieving total plasma temperature of \textgreater 3 keV and sustained in steady state up to 30 ms that is only~limited~by energy storage. Dedicated experimental campaigns have been conducted to further optimize and also characterize FRC plasmas. This paper will review the highlights of the C-2W experimental program and newly obtained experimental results. \newline \newline [1] H. Gota \textit{et al}., Nucl. Fusion \textbf{59}, 112009 (2019). [Preview Abstract] |
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VP13.00004: Radiative Measurements on C-2W Timothy DeHaas, Anton Bondarenko, Matt Tobin TAE Technologies' current experimental device, C-2W, is an~advanced, beam-driven, field-reversed configuration (FRC) with advanced divertors, end bias electrodes, and an active plasma control system [1]. The emergence of C-2W's high performance regime has highlighted the need for further expansion of diagnostic systems to understand equilibrium behavior, global stability, and power loss mechanisms. To that end, the experiment has been fitted with an ensemble (over 300 channels) of XUV and soft X-Ray sensing diodes. The ensemble contains a mixture of both collimated and uncollimated views with broad spatial coverage. The collection of measurements yields the total radiated power from the plasma and has already been used to demonstrated the mitigation of impurity radiation to below 200 kW [2]. Recently, additional units have been deployed to provide axial coverage of the machine, yielding an axial emission profile. The system has been~integrated~into the active plasma control system~to produce~estimates of density and axial position control. Similarly, the diagnostic is fitted with differing thin, metallic, optical filters for coarse spectral resolution. Several Be filters have been added with the express purpose of identifying fast electron~production. Initial observation of plasma emission profiles and x-ray production will be presented. [1] H. Gota et al, Nucl. Fusion 59, 112009 (2019). [2] T. DeHaas, A. DuBois, APS-DPP 2019 Poster UP10.00131 [Preview Abstract] |
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VP13.00005: Tomography on C-2W: First Results from Reconfigured 300-Channel Bolometry System Anton Bondarenko, TAE Team In TAE Technologies' current experimental device, C-2W (also called ``Norman'')~[1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15 - 40 keV, total power up to 20 MW), expander divertors, end bias electrodes, and an active plasma control system. Tomography offers a valuable and non-invasive diagnostic of the FRC plasma, as tomographic reconstructions of the emission profile yield important information on plasma shape, density, transient MHD behavior, and power loss due to radiation and particle flux. Recently, a bolometer system on the C-2W device has been reconfigured with the primary goal of providing tomographic reconstructions of the FRC. The overhauled system consists of 300 photodiode channels with unique lines of sight that intersect a toroidal plane of the FRC near the mid-plane. The photodiodes sense a broad range of wavelengths (including XUV and soft x-rays) as well as charged particles. In addition, thin metallic optical filters on roughly one-third of the channels allow for coarse spectral resolution. Reconstructions of the FRC emission profile are performed via several different tomographic methods, and the results are compared to well-known FRC equilibrium models. The proper treatment of solid angle in the tomographic reconstructions is also discussed. [1]~H. Gota et al, Nucl. Fusion~\textbf{59}, 112009 (2019). [Preview Abstract] |
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VP13.00006: MHD Mode Identification by Higher Order Singular Value Decomposition of C-2W Mirnov Probe Data Matthew Tobin, Thomas Roche, Tadafumi Matsumoto, The TAE Team The C-2W device (also known as `Norman') at TAE Technologies has proven successful at generating stable, long-lived field-reversed configuration plasmas (FRCs) with record temperatures [1]. Detection of magnetohydrodynamic (MHD) mode structures in these plasmas is crucial to understanding plasma instability and the conditions that give rise to it. When they do appear, MHD mode structures cause fluctuations in the magnetic field within and around the plasma, which can be detected by magnetic field sensors such as Mirnov probes. The largest Mirnov probe array in C-2W comprises 64 probes and is roughly evenly spaced in two dimensions [2], creating a unique opportunity to apply higher order singular value decomposition (HOSVD) [3] to efficiently analyze the external magnetic field data these probes record to reconstruct MHD mode structures in the FRC. This method is shown to quickly and effectively detect toroidal modes while indicating longitudinal dependence of mode phases, enhancing the coherence and utility of the vast quantity of data this array produces. [1] H. Gota et al., Nucl. Fusion, 59, 112009 (2019) [2] T. Roche et al., Rev. Sci. Inst., 89, 10J107 (2018) [3] L. De Lathauwer et al., SIAM J. Matrix Anal. Appl. 21, 1253-1278 (2000) [Preview Abstract] |
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VP13.00007: Rigid Motion of C-2W FRC Plasma Kan Zhai, Manjit Kaur, Eli Parke, John Kinley, Roger Smith, Michael Beall, Chuanbao Deng, and the TAE Team C-2W is an advanced beam-driven Field Reversed Configuration (FRC) fusion device, in which plasma sustainment with total temperature at 3keV has been demonstrated [1]. The DC output channels of the C-2W Thomson scattering (TS) polychromators, which are designed for system spectral response calibration and to monitor background plasma radiation for measurement uncertainty analysis, can be used to characterize the plasma motion. Due to the nature of an imaging system designed for TS collection optics, the background radiation recorded in the DC channels of the sixteen polychromators are mainly from the sixteen fixed spatial locations where the TS measurement is designed at. The time evolution of the signals from different polychromators form a unique pattern determined by FRC rigid plasma~motion. Detailed analysis and its comparison with other diagnositics such as the FIR interferometer will be presented. [1] H. Gota et al., Nucl. Fusion~\textbf{59}, 112009 (2019) [Preview Abstract] |
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VP13.00008: Fast ion diagnostics (FIDA) on C-2W Lucas Morton, Erik Granstedt, Nathan Bolte, Richard Magee, Deepak Gupta, Gabriel Player, Sean Dettrick In TAE Technologies' current experimental device, C-2W (also called ``Norman'') [1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15 -- 40 keV, total power up to 20 MW), advanced divertors, end bias electrodes, and an active plasma control system. An in-house model of fast ion orbits and transport was used in conjunction with FIDASIM to explore optimized lines-of-sight for detection of fast ion populations and loss channels. We evaluated emission resulting from fast ion charge exchange (CX) interactions with the heating neutral beams, diagnostic neutral beam, cold edge neutrals, and gas puff valves. A midplane view can provide radially-resolved information on the azimuthal component of the fast ion velocity distribution. Passive emission from large-orbit fast ions interacting with neutrals in the scrape-off layer could inform estimated rates of ion CX loss and slowing-down. Gas puffing provides a way to actively probe the fast ion distribution in regions (such as the mirror throat) where there is no NBI. Preliminary comparisons with data from the main-ion CX diagnostic system will be shown. [1] H. Gota et al., Nucl. Fusion \textbf{59}, 112009 (2019). [Preview Abstract] |
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VP13.00009: FRC fast ion distribution: stability and effects on equilibrium Laura Galeotti, Loren Steinhauer, Francesco Ceccherini, Sean Dettrick, TAE Team Experimental FRC equilibria in TAE's C-2W experiment can be studied utilizing TAE's 2D hybrid equilibrium code which combines the thermal plasma multi-fluid description of TAE's equilibrium code [1] with a kinetic treatment of fast ions added with a MonteCarlo code (MC) through NB injection. These hybrid equilibria may be characterized by ``non-standard'' structures such as current density profiles with a radial double hump and peaks at turning points as well as an inverted fast-ion distribution function, i.e., df/dv \textgreater 0. Since an inverted population can affect the stability of the system through the generation of microinstabilites like drift-cyclotron loss-cone (DCLC) and Alfv\`{e}n-ion cyclotron (AIC), we address the effect of non-Maxwellian distribution functions on equilibrium structures, their stability, and the diagnosable signatures of these equilibria. Our investigation is carried out mainly through studies of fast ion orbits and distribution functions. \textit{[1]~L. Galeotti et al. Phys. Plasmas 18 082509 (2011)} [Preview Abstract] |
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VP13.00010: Interferometry technique to measure 2D FRC equilibria on TAE's Norman device Roger Smith, Jesus Romero, Marco Onofri, Sean Dettrick, Sangeeta Gupta, Laura Galeotti The mid-plane multi-chord FIR interferometer system on the C-2W device (Norman) is used in conjunction with the equilibrium (EQ) field coils and trim coil set to move the plasma axially and thereby determine the equilibrium density profiles in both r and z. Lifetimes for plasmas in Norman are now routinely as long as 30 milliseconds. This allows sufficient time to displace the field reversed configuration (FRC) plasma meters on a millisecond time scale using waveform controlled EQ coils and actively driven trim coils with feedback control. The FRC is typically 2 m long and the confinement vessel (CV) is 6 m in length which allows a generous capability to interrogate the plasma over its half-length and sufficient time to restore the equilibrium to its center position. Details of the FRC density distribution and fluctuation behavior in both r and z past the X point are discussed as well as implications of the coupling of NBI power to a displaced FRC. The implications of the measured profiles as inputs and validation to numerical modeling with respect to heating and sustainment of the FRC by NBI will be presented and discussed. [Preview Abstract] |
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VP13.00011: Density Fluctuations Measured by FIR Interferometer System in C2W FRC C. Deng, M. Beall, E. Parke, R. Smith, K. Zhai, and the TAE Team, M Kaur In the TAE Technologies current experimental device, C-2W (also called ``Norman'') [1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams, advanced divertors, end bias electrodes, and an active plasma control system. The density profile measurements and characterization of fluctuations such as low frequency n$=$1 and n$=$2 rotational modes are made using the powerful 14 chords FIR interferometer system. A new investigation into higher frequency density fluctuations measured by far-forward scattering methods will be presented in this effort. These data will be analyzed for a variety of plasma parameters and machine settings such as biasing voltages, looking towards correlations between density fluctuations and plasma confinement variations. [1] H. Gota et al., Nucl. Fusion 59, 112009 (2019). [Preview Abstract] |
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VP13.00012: RF transfer of momentum and angular momentum in FRC plasmas Francesco Ceccherini, Laura Galeotti, Dan Barnes, Sean Dettrick, Kevin Hubbard, Xiaokang Yang, the TAE Team TAE Technologies’ RF code, RF-Pisa, is deployed to study the transfer of momentum and angular momentum from RF waves to plasma species in an FRC configuration. In particular we address the possibility to enhance the efficiency of the wave-plasma coupling through the utilization of advanced plasma schemes which allow to control the wave polarization and to select narrow resonance regions. The frequency range of interest for our investigation is the ICRH regime. Together with single mode analyses we will carry out a 3D reconstruction to study ( i ) the effects due to realistic and finite size antennas and (ii) the role of the straps phase in defining the resonance volumes and efficiency. Finally, the feasibility to utilize RF in FRCs for current drive will be discussed. [Preview Abstract] |
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VP13.00013: Flow profile measurement with a Mach probe in the open-field line region of C-2W Tadafumi Matsumoto, Thomas Roche, Luis Frausto, the TAE Team In TAE Technologies' current experimental device, C-2W (also called ``Norman'')~[1], record-breaking, advanced beam-driven field-reversed configuration (FRC) plasmas are produced and sustained in steady-state utilizing variable energy neutral beams, advanced divertors, end bias electrodes, and an active plasma control system.~The end biasing plays an important role by heating the FRC plasma, stabilizing global MHD modes, and suppressing turbulence with an ExB sheared flow in the open-field line region.~To study this biasing effect, a combo probe (Mach and Triple Langmuir probes) has been installed in the open-field line region of the C-2W confinement vessel to measure the ion flow outside the FRC separatrix.~This probe has the capability to measure~parallel and~perpendicular flows as well as electron temperature and density at the same location. In addition, radial electric field can be estimated by scanning the floating potential in a radial direction. Experimental setup and results will be presented. [1]~H. Gota~\textit{et al}., Nucl. Fusion~\textbf{59}~112009 (2019). [Preview Abstract] |
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VP13.00014: Impurity-ion rotation dynamics in C-2W Marcel Nations, Deepak Gupta, Lothar Schmitz, Hannes Lienweber, the TAE Team The C-2W experimental device (also called ``Norman'') produces and sustains advanced beam-driven~field-reversed configuration (FRC) plasmas in steady state. Edge biasing of annular electrodes in the divertor region is routinely utilized as a boundary control technique to stabilize the FRC in the confinement vessel. The potential difference between open-field lines in the scrape-off layer creates a local radial electric field near the FRC separatrix and, consequently, \textbf{\textit{E}}$\times $\textbf{\textit{B}} shear flow which suppresses the plasma turbulence. Recently deployed charge-exchange recombination spectroscopy (ChERS) diagnostics are used to measure rotation velocities of high charge-state oxygen impurity ions at 343.4 nm as well as deuterium main ions at 656 nm. Radial momentum balance gives \textbf{\textit{E}}$\times $\textbf{\textit{B}} velocities near the separatrix which dominates the rotation dynamics of the oxygen impurities and are in good agreement with measured main-ion rotation and results from an independent Doppler Backscattering diagnostic. Results show a~strong correlation between applied electrode bias voltage and inferred radial electric fields in the confinement vessel of C-2W. [Preview Abstract] |
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VP13.00015: Analysis of C-2W Electrode Arcing Experimental Data James Sweeney, Erik Granstedt, Peter Yushmanov, Manjit Kaur, Daniel Sheftman, Deepak Gupta, The TAE Team The TAE Technologies C-2W experimental device (also called "Norman") produces advanced beam-driven field reversed configuration (FRC) plasmas [1]. Norman includes electrode biasing for heating and improved plasma stability. Extending the operational boundaries of the electrodes enhances plasma performance, but arc discharges can occur on the electrodes under extreme conditions. Arcing can have detrimental consequences, which require the phenomenon to be understood operationally. An analysis tool was developed to detect and categorize electrode arcs through image processing of high-speed camera data. The information about the electrode arcing state is combined with measurements from other diagnostics to enable statistical analysis of arcing. Correlations of plasma and experimental parameters and their relationship to electrode arcing are presented. [1] H. Gota et al., Nucl. Fusion 59, 112009 (2019) [Preview Abstract] |
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VP13.00016: Simulation of Equilibrium, Stability, and Transport in Advanced FRCs S. A. Dettrick, D. C. Barnes, E. V. Belova, F. Ceccherini, L. Galeotti, S. A. Galkin, S. Gupta, K. Hubbard, O. Koshkarov, C. K. Lau, Z. Lin, Y. Mok, A. Necas, B. S. Nicks, M. Onofri, J. Park, S. V. Putvinski, L. S. Steinhauer, T. Tajima, W. Wang, X. Wei, K. Yakymenko, P. N. Yushmanov The Advanced FRC is a Field Reversed Configuration maintained by neutral beam injection and electrode biasing, with scrape-off-layer (SOL) pumping and electron heat confinement provided by expander divertors. This alternate magnetic confinement system has been developed at TAE Technologies, Inc in the C-2, C-2U and C-2W (aka NORMAN) devices. To study this configuration, hybrid fluid/kinetic equilibrium models have been developed which include the effects of fast ion pressure anisotropy. The 3D hybrid PIC codes FPIC and HYM are being used to understand the interplay of beams and biasing in global stability. The 2D hybrid kinetic/MHD/neutral code, Q2D, is being used to study global transport including coupled perpendicular/parallel FRC/SOL transport, neutral gas effects, and field line expansion and electrostatic potential formation in the expander. The 3D electrostatic PIC codes ANC and GTC-X add wave-particle kinetic ion and electron effects to the global transport studies, including shear flows and sheath effects related to biasing. Parallel electron heat transport in the SOL is studied using the KSOL 1d2v continuum code. [Preview Abstract] |
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VP13.00017: “Blended” Kinetic Simulations of Turbulent Transport in C-2W Calvin Lau, Zhihong Lin, Toshiki Tajima, Sean Dettrick, Lothar Schmitz, The TAE Team In TAE Technologies’ current device, C-2W (also called “Norman”), advanced beam-driven FRC plasmas are produced and sustained in steady state. In past C-2U FRC plasmas, Doppler Backscattering (DBS) measurements reveal distinct density fluctuation spectra in the core and scrape-off layer (SOL) regions. Gyrokinetic microturbulence simulations using the cross-separatrix particle-in-cell ANC code show that the distinct fluctuation spectra arise from the interaction of of the two regions: unstable modes grow in the SOL where energy cascades from shorter to longer toroidal wavelengths; the smaller scale fluctuations can spread across the separatrix into the core. Recently, a “blended” particle model, based on the drift-Lorentz mover, valid throughout the FRC, has been implemented in ANC. This allows for the correct representation of particle trajectories across the low magnetic field regions of the FRC. In addition, the blended model is used to include the non-adiabatic electron response, enabling the self-consistent calculation of particle and heat fluxes for ions and electrons. Simulations of C-2U plasma shows a change in linear mechanism but nonlinear fluctuation spectra remain similar as before. Preliminary simulations of C-2W plasma will also be presented. [Preview Abstract] |
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VP13.00018: FRC as a Two-Fluid Flowing Relaxed State Bradley Scott Nicks, Loren Steinhauer, the TAE Team Various theories have been posited to address the preferred (relaxed) states of a plasma as well as the underlying physical principles that select the preferred state. Previous work [1,2] has indicated that under certain conditions, the preferred configuration of a plasma is a field-reversed-configuration (FRC). As finite-beta effects, strong flows, and two-fluid effects are well-known aspects of FRC experiments, here a relaxation model of two flowing fluid species with constrained species helicity and minimized magneto-fluid energy is used to predict a preference for FRC states within certain helicity regimes. While prior work has focused on classifying relaxed states, here the full relaxed magnetic and flow functions are numerically solved on an ellipsoidal geometry. Flow is allowed in both the toroidal and poloidal directions. First, a uniform density is taken, and then a varying density is allowed. Different regimes of species helicity are examined. In all cases, electron inertia is neglected. Finally, the constraint of conserved angular momentum is applied, and the effects on the relaxed state are evaluated. [1] L. C. Steinhauer, H. Yamada, and A. Ishida, Phys. Plasmas 8, 4053 (2001) [2] R. Bhattacharyya, M. S. Janaki, and B. Dasgupta, Phys. Lett. A 291, 291 (2001) [Preview Abstract] |
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