Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session PO07: MFE: MHD and Energetic ParticlesOn Demand
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Chair: Valerie Izzo, Fiat Lux Room: Rooms 315-316 |
Wednesday, November 10, 2021 2:00PM - 2:12PM |
PO07.00001: Simultaneous Control of Multiple n-Number Resistive Wall Modes Alexander F Battey, Jeremy M Hanson, James M Bialek, Gerald A Navratil DIII-D experiments demonstrate simultaneous stability measurements and control of resistive |
Wednesday, November 10, 2021 2:12PM - 2:24PM |
PO07.00002: Results from a Three-Model Frequency Scan of HIT-SI3 in NIMROD James M Penna, Kyle D Morgan, Aaron C Hossack, Christopher J Hansen The Helicity Injected Torus – Steady Inductive 3 (HIT-SI3) was a spheromak experiment that used three AC transformer and solenoid pairs, known as helicity injectors, to form and sustain a spheromak with DC toroidal current in a process known as Steady Inductive Helicity Injection (SIHI). Changing the injector frequency and temporal phasing between injectors changes the toroidal Fourier spectrum of the applied perturbations, which may have substantial effects on the sustained spheromaks. To examine the effects of different injector frequencies without extensive experimental campaigns, the NIMROD xMHD code is used to run simulations with constant, single and two-temperature models at a range of injector frequencies from 5 to 75 kHz, with the injector fields modeled as boundary conditions on tangential electric and normal magnetic fields at the injector locations. In particular, the presence of plasma-generated n=2 at each injector frequency will be examined, along with effects of temperature and density. Results from a new multichord interferometer brought online in 2021 will be compared to applicable shots from the simulations. Trends HIT-SI3 simulations, and the prior HIT-SI device, will be reviewed and compared to determine trends for SIHI-driven spheromak devices. |
Wednesday, November 10, 2021 2:24PM - 2:36PM |
PO07.00003: Learning plasma equilibria from scratch with deep neural network Grad-Shafranov solver Semin Joung, Jaewook Kim, Sehyun Kwak, MINSEOK KIM, H.S. Kim, J.G. Bak, Y.-c. Ghim Reconstructing plasma equilibria has played an important role in tokamak performance. While the reconstruction can be routinely performed by solving Grad-Shafranov (GS) equation, it is mostly reconstructed based on magnetic measurements and still challenging to produce kinetic equilibria in real time due to unavailability of real time kinetic profiles as well as demands on long computation time. We deal with these issues by developing a deep neural network capable of directly solving GS equation based on unsupervised learning. We demonstrate that the proposed network does not require any precalculated database such as EFIT data and is possible to reconstruct kinetic equilibrium in real time. The proposed method can be a promising approach for ITER and beyond to achieve high quality operations and enhance plasma performance. |
Wednesday, November 10, 2021 2:36PM - 2:48PM |
PO07.00004: Prediction of nonlinearly saturated tearing mode islands with an equilibrium code Joaquim Loizu, Yi-Min Huang, Stuart R Hudson, Daniele Bonfiglio, Antoine Baillod, Arunav Kumar, Zhisong Qu We demonstrate that it is possible to use an MHD equilibrium code to directly predict the nonlinear saturation of tearing modes without resolving the dynamics and without explicit dependence on the plasma resistivity. This is achieved by exploiting the stepped-pressure equilibrium code [1], which can describe equilibria with magnetic islands and magnetic field-line chaos, and by identifying the appropriate constraints under which tearing modes evolve [2, 3]. Calculations are carried out in a slab and for a cylindrical tokamak and the predicted values of wsat are shown to reproduce the theoretical scaling at small values of Δ' and the scaling obtained from resistive MHD simulations at large Δ'. |
Wednesday, November 10, 2021 2:48PM - 3:00PM |
PO07.00005: Normal mode spectrum of Multi-region relaxed Magnetohydrodynamics Arunav Kumar, Matthew Hole, Hooman Hezaveh Hesar Maskan, Zhisong Qu, Robert Dewar, Stuart R Hudson, Joaquim Loizu It is well known, the nature of the ideal-MHD equilibria in three-dimensional toroidal plasma is profoundly affected by resonant surfaces, which give rise to a non-analytic dependence of the equilibrium. Thus, using ideal MHD to model a hot, near collisionless 3D plasmas cannot be formally justified. As a result, the study of MHD stability and Alfvén eigen-mode spectra of (m,n) field harmonics are limited, and remains an open problem in 3D equilibrium fields which are typically a blend of nested magnetic surfaces, islands, and chaotic regions. |
Wednesday, November 10, 2021 3:00PM - 3:12PM |
PO07.00006: Modelling sawteeth in tokamak plasma as a sequence of Multi-region Relaxed MHD equilibria Zhisong Qu, Yao Zhou, Robert Dewar, Arunav Kumar, Joshua Doak, Joaquim Loizu, Matthew Hole The Multiregion Relaxed MHD [1] was successful in the construction of equilibria in 3D configurations, bridging the gap between Taylor relaxation, which allows relaxation but only globally, and ideal MHD, which includes no relaxation at all but infinite constraints. In MRxMHD, the plasma is sliced into sub-volumes separated by ideal interfaces, each undergoes relaxation. Stepped Pressure Equilibrium Code (SPEC) [2] was developed to solve MRxMHD equilibria numerically. |
Wednesday, November 10, 2021 3:12PM - 3:24PM |
PO07.00007: Verification and validation of gyrokinetic and kinetic-MHD simulations for the internal kink instability in the DIII-D tokamak Guillaume R Brochard, Jian Bao, Chang Liu, Nikolai Gorelenkov, Ge Dong, Joseph Mc.Clenaghan, Xishuo Wei, Gyungjin Choi, Javier H Nicolau, Pengfei Liu, William W Heidbrink, Zhihong Lin Verification and validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreements for the growth rate and mode structure of the n=1 internal kink mode in ideal MHD simulations by suppressing all kinetic effects. The simulated radial mode structure agrees quantitatively with the electron cyclotron emission measurement after adjusting, within the experimental uncertainty, the q=1 flux-surface location in the equilibrium reconstruction. Equilibrium plasma pressure gradient and compressible magnetic perturbation strongly destabilize the kink, while poloidal variations of the equilibrium current density stabilize the kink. Furthermore, kinetic effects of thermal ions are found to decrease the kink growth rate in kinetic-MHD simulations, but increase the kink growth rate in gyrokinetic simulations, possibly due to the additional drive of the ion temperature gradient and parallel electric field. Kinetic thermal electrons are found to have negligible effects on the internal kink instability. |
Wednesday, November 10, 2021 3:24PM - 3:36PM |
PO07.00008: Collisional broadening of nonlinear resonant wave-particle interactions. Peter J Catto, Elizabeth A Tolman A procedure providing insight into plasma behavior when resonant wave-particle interactions are the dominant mechanism will be presented without recourse to involved numerical or analytical treatments. These phenomena are characterized by transport appearing to be collisionless even though collisions play a central role in narrow boundary layers. The order of magnitude estimates, including nonlinear effects, provide expressions in agreement with the principle results of toroidal Alfvén eigenmode (TAE), toroidal magnetic field ripple, and heating and current drive treatments. The retention of nonlinearities for alpha particles leads to estimates of the diffusivity at saturation for TAE modes, and the ripple threshold at which superbanana plateau evaluations of transport are modified by finite radial drift effects. The estimates also place a bound on the applied rf wave amplitude for quasilinear descriptions to remain valid for heating and current drive. The phenomenological procedure indicates that when narrow collisional boundary layers must be retained, any stochastic field line behavior occurring is unlikely to be more important than any other nonlinear process in magnetic fusion plasmas. |
Wednesday, November 10, 2021 3:36PM - 3:48PM |
PO07.00009: Alfvenic frequency chirping in tokamaks: Theoretical modelling and simulation using the MEGA code Hooman Hezaveh Hesar Maskan, Yasushi Todo, Zhisong Qu, Boris Breizman, Matthew Hole In this work, we firstly develop a theoretical framework to study long range frequency chirping waves associated with unstable Alfven eigenmodes. Using a Lagrangian formalism and an adiabatic approximation, we show how the nonlinear contribution of energetic particles modifies the radial structure of a global Alfven eigenmode (GAE). Also, a new conservation law is introduced for energetic particles in resonance with chirping waves. This conservation law does not depend on the frequency of the perturbation and remains conserved even during the frequency chirping. For the second step, self-consistent simulations are performed using the hybrid model of the MEGA code. Using the new conservation law, we propose a new phase-space analysis method which enables an appropriate study of energetic particles phase space during frequency chirping of Alfvenic perturbations. For chirping waves associated with an n=6 toroidicity-induced Alfven eigenmode (TAE), coherent structures (holes and clumps) are formed and evolved in phase space. We demonstrate that these structures cause convective transport in phase-space leading to radial drifts of the particles. It is also shown that the rate of frequency chirping increases with the damping rate of the TAE. Our observations of the nonlinear behaviour of the TAE and the phase space dynamics of the energetic particles are consistent with our theoretical model and the Berk-Breizman (BB) theory. |
Wednesday, November 10, 2021 3:48PM - 4:00PM |
PO07.00010: Effects of negative triangularity shaping on energetic particle driven Alfvén eigenmodes Yashika Ghai, Donald A Spong, Jacobo Varela Rodriguez, Luis Garcia, Michael A Van Zeeland Simulations using the gyro fluid code FAR3d indicate that the profile and shape changes associated with negative triangularity (NT) can lower the growth rate of energetic particle (EP) driven Alfvén eigenmodes (AEs) in DIII-D compared to positive triangularity plasmas. There has been a renewed interest in NT plasma shaping due to observations of reduced microturbulence and higher normalized beta. An investigation of shaping effects on the EP-driven, linear AE activity in DIII-D is performed using FAR3d that identifies AEs at similar frequencies as observed in the experiments. Because AEs have a global mode structure and are caused by the couplings between adjacent poloidal modes, it is expected that plasma shaping will influence their stability. However, DIII-D experiments did not show significant effects of NT shape on AE-induced fast ion transport. The present work also extends simulations to the nonlinear regime to study the effects of different types of plasma shaping on AE-driven transport. These findings may inform the choice of plasma shapes for future fusion devices that can mitigate or suppress EP-driven AEs. |
Wednesday, November 10, 2021 4:00PM - 4:12PM |
PO07.00011: Saturation phase of the Toroidal Alfven Eigenmodes in the Large Helical Device: MHD burst Jacobo Varela Rodriguez, Donald A Spong, Yasushi Todo, Luis Garcia, Yashika Ghai, Juan Ortiz The aim of the study is reproducing the saturation phase of the Toroidal Alfven Eigenmodes (TAEs) in the Large Helical Device (LHD), particularly the destabilization of MHD bursts. A set of linear and nonlinear simulations are performed using the FAR3d code. The linear simulations indicate the overlapping of 1/2-1/1, 2/3-2/4 and 3/5-3/6 TAEs between the inner-middle plasma region in the frequency range of 45-75 kHz, destabilized by EP with an energy of 45 keV and EP β = 0.022. The nonlinear simulation reproduces the TAE saturation phase and the triggering of the MHD burst observed in the experiment. The nonlinear simulation indicates an energy transfer from the 1/1-1/2 TAE towards the 2/3-2/4 and 3/4-3/5 TAEs, leading to the destabilization of the n=2 and 3 TAEs. MHD burst is triggered by the broad radial overlapping of the unstable TAEs. The 1/1-1/2 TAE eigenfunction extends from the inner to the plasma periphery, thus the AE perturbation extends from the inner to the plasma periphery, leading to a collapse of the EP density profile at the middle-outer plasma region and a partial lost of the EP population by an enhancement of the outward EP transport. The nonliner simulations also show the formation of shear flows during the TAEs saturation phase, enhanced during the MHD burst. |
Wednesday, November 10, 2021 4:12PM - 4:24PM |
PO07.00012: Interaction of Resonant Magnetic Perturbations with Energetic Particle Modes Matthew Hole, Junghee Kim, Jisung Kang, Jun-Gyo Bak, Clive A Michael, Zhisong Qu, Joshua Doak, Hooman Hezaveh Hesar Maskan, Adelle Wright, David Pfefferle Over several campaigns, we have explored drive of Alfvén eigenmode activity in KSTAR. The broad purpose of these experiments has been to develop scenarios to study energetic particle driven modes, as well as enable experimental studies of wave-particle-plasma interaction and particle loss at higher beam power. To date, we have reported the drive of beta-induced Alfven eigenmodes [M. J. Hole et al 2013 Plasma Phys. Control. Fusion 55 045004], and bursty chirping modes observed during early NBI heating M J Hole et al 2019 Plasma Phys. Control. Fusion 61 025016 ]. In this contribution we report on KSTAR discharge campaigns in 2020 and 2021 which involve scans over NBI power, pulse width modulation, and perveance to excite and select the Alfvenic mode of interest, followed by application of 3D Resonant Magnetic Perturbation coils with different phasing and current waveforms. |
Wednesday, November 10, 2021 4:24PM - 4:36PM |
PO07.00013: Numerical Simulation and Experimental study of fast Ion confinement with neutral beam injection on EAST Jinfang Wang, Xiaojuan Liu, Youjun Hu, Yawei Hou, Baolong Hao, Guoqiang Zhong, Juan Huang, Nong Xiang The confinement of fast ions is one of the key problems. For the fast ion loss, a great deal of work has been done[1-2]. This research applies numerical and experimental measurement to investigate the fast ion confinement. By using the multi-step fitting numerical method, we present analytical quantitative expressions of beam heating percentage and beam torque. |
Wednesday, November 10, 2021 4:36PM - 4:48PM |
PO07.00014: Spatial Structure of Fast-ion Driven instabilities inferred from Soft X-ray emission in the MegaAmp Spherical Tokamak Henry Hingyin Wong, Clive A Michael, Nicolas Fil, Gyungjin Choi, Pengfei Liu, Anthony R Field, Michael Fitzgerald, Neal A Crocker, Ken G McClements, Luca Garzotti, Zhihong Lin, Troy A Carter Mode structure is obtained for bursting fast-ion driven MHD instabilities in the Mega Amp Spherical Tokamak (MAST) from inversion of soft X-ray (SXR) emission measurements. SXR emissivity fluctuations associated with the modes are isolated using cross-correlation with Mirnov coil measurements. Comparison of measured frequencies, toroidal mode numbers and structure with theory show that the bursts include fishbones and another type of mode whose time-dependent structure are consistent with expectations for energetic particle modes (EPM). The frequency of the bursting modes is observed to decrease with time, from just below the toroidal Alfvén eigenmode (TAE) frequency to just above the plasma rotation frequency. The structure measurements show that the radial location of peak fluctuation amplitude of individual bursts get closer to the plasma core when the mode frequency approaches the plasma rotation frequency. Although the frequency of some of the observed modes are closer to the TAE frequency than the rotation frequency, the location of these modes disagrees with the results of TAE simulations carried out with the MISHKA ideal MHD linear eigenmode code. This highlights the need for models with physics beyond ideal MHD to accurately describe and predict these modes. The mode structure measurements will be compared with linear simulations using the Gyrokinetic Toroidal Code (GTC) [1]. In future work, the measured and simulated fluctuation peak locations could be used as initial input to energetic particle transport models, such as the kick model. |
Wednesday, November 10, 2021 4:48PM - 5:00PM |
PO07.00015: Initial FIDA results on MAST-U with on and off-axis beam deposition Clive A Michael, Andrew Jackson, Ken G McClements, David Keeling, Neal A Crocker, Henry Hingyin Wong, Charles Vincent, Scott Allan, Bhavin Patel, Stuart Henderson, Nicolas Fil, Juan Rivero-Rodriguez, Marco Cecconello, Sam Gibson, Christopher Wade, Rory Scannell, Sergei Sharapov, Michael Fitzgerald A tangentially-viewing fast ion D-alpha spectrometer has been re-installed on MAST-U in order to diagnose the spatial and velocity distribution of the high-energy portion of the fast ion distribution [1]. Comparison of the signal to calculations based on the TRANSP/FIDASIM codes can be used to assess fast ion transport models. The influence of fast ion and bulk plasma-driven MHD on the FIDA signals can also be investigated with high time resolution (~.3ms). With two on-axis beams operating in MAST, there was strong mode activity and consequential fast ion transport [2]. However, because one of the beams is shifted off-axis in MAST-U, fast ion gradients are reduced in the core, suppressing the drive for core instabilities in the region of low magnetic shear. This is expected to result in improved fast ion transport and enhanced current drive. To assess this, FIDA data will be compared with classical modelling in cases with both on-axis single beam heating as well as combined on/off-axis beams. Consistency with other fast ion diagnostics will be investigated, in particular with a fission chamber, but also including an NPA, FILD and neutron camera. The operational windows for good FIDA signal to background ratio will also be assessed. |
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