Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session PO05: MFE: Diagnostics and DisruptionsLive Streamed
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Chair: Jeffrey Herfindal, ORNL Room: Ballroom 111 B |
Wednesday, October 19, 2022 2:00PM - 2:12PM |
PO05.00001: Quantitative analysis of anomalous electron heating and momentum transfer by lower hybrid drift waves during guide field reconnection Jongsoo Yoo, Hantao Ji, Aaron Goodman, Sayak Bose, Jonathan Ng, Li-jen Chen, Masaaki Yamada, William R Fox, Andrew D Alt The electrostatic lower hybrid drift wave (ES-LHDW) has been observed in the electron diffusion region of the Magnetic Reconnection Experiment (MRX). The ES-LHDW is capable of generating both electric field and density fluctuations, which are measured by an electrostatic probe [1]. We confirm that the observed ES-LHDW is in the quasilinear stage by verifying the linear relationship between the reconnection electric field fluctuations and the density fluctuations [2]. This justifies the use of quasilinear analysis of all anomalous (second order) terms such as anomalous resistivity and anomalous heating based on the measured amplitude. In a typical example with a moderate guide field, the anomalous resistivity can account for about 25 % of the reconnection electric field. Anomalous electron heating is about four times higher than the classical Ohmic heating. These results indicate that the ES-LHDW can affect both electron and reconnection dynamics. We discuss the physics of each anomalous term by looking at the linear relationship between physical quantities. |
Wednesday, October 19, 2022 2:12PM - 2:24PM |
PO05.00002: Efficient way to find maximum a posteriori of nonnegative gaussian process tomography for plasma radiation during SPI induced disruption experiments Jaewook Kim, Jayhyun Kim, Juhyeok Jang, Sehyun Kwak, Young-chul Ghim Shattered pellet injector (SPI) is designed to protect tokamaks from disruptions by dissipating stored plasma energy prompted by the injected pellets. KSTAR is equipped with two SPIs which allow us to study how differently the stored plasma energy is dissipated for different combinations of various pellet types and the relative injection times. For this purpose, reconstructing distribution of radiative power loss in space and time caused by the pellets is important. Total radiative power loss at a poloidal section is obtained by a tomographic reconstruction using the fast bolometer made of poloidal filtered AXUV detector arrays. Using the Gaussian process prior, reconstruction can be performed even with fewer number of lines of sight compared to the number of pixels, but the result shows negative radiation power for an asymmetric radiation distribution by the pellets. More accurate results could be obtained with the nonnegative prior and the Gibbs sampler, but it becomes computationally expensive when we have to deal with more than 1000 frames in each experiment. By introducing a more efficient method of calculating the maximum a posteriori for the truncated multivariate normal distribution, we are able to check the total radiation power results immediately after each experiment. |
Wednesday, October 19, 2022 2:24PM - 2:36PM |
PO05.00003: Accuracies of motional Stark effect measurements under multiple-ion-source neutral beam injection Jinseok Ko, Juyoung Ko The motional Stark effect (MSE) diagnostic in the KSTAR tokamak has been operational along with the neutral beam injection composed of three ion sources. Operating such a beam system imposes constraints on the beam energy deployment as well as on MSE measurements due to the beam emission spectral overlaps. Previous efforts to identify this effect include a simple Stokes vector model and a numerical optimization based on measured intensities of polarized light before and after the beam overlap. Advanced from these previous efforts, a model has been extended to cover a wide range of neutral beam energies and a scenario where the main MSE signal source is switched to a different beam ion source. The model also includes the distortion of band-pass filter transmission functions, beam energy fractional components, and reference pitch angle profiles obtained from the MSE measurements on KSTAR discharges during an entire campaign. The parameter space of two beam ion source energies on the expected systematic pitch angle offset has been generated to provide precise and quantitative guidelines on neutral beam operations where good MSE measurements are necessary. |
Wednesday, October 19, 2022 2:36PM - 2:48PM |
PO05.00004: Coast Guard Academy Plasma Lab (CGAPL) and Air Force Institute of Technology (AFIT) Plasma Diagnostics Measurement Investigations Royce W James, Lorraine A Allen, Richard W Freeman, Christopher Heckman Together CGAPL, NRL, U.S. Naval Academy, ODU and AFIT have CGAPL and AFIT collaborate in plasma diagnostic development for both low and high-temperature plasmas. The small Helicon Plasma Experiment (HPX) at the Coast Guard Academy Plasma Lab (CGAPL), continues to progress toward utilizing the reputed high densities (1013 cm-3 and higher) at low pressure (.01 T) of helicons, for eventual high temperature and density diagnostic development in future laboratory investigations. Our 2.5 J YAG laser Thomson Scattering system utilizes a high-performance volume-phase-holographic (VPH) grating spectrometer, charge-coupled device (CCD) camera, and a General Atomics polychromator optimized for TS measurements of 5 eV < Te < 2000 eV over a 109-degree scattering angle. An Impedance Probe built from technology in the ‘Space PlasmA Diagnostic suitE’ (SPADE) mission is due to launch onboard the SeaLion 3U CubeSat mission with multiple payloads is also in final testing. The AC impedance measurements are collected as raw data using a sweeping frequency through surface-mounted antennas. While the compact multispectral ‘Pixel Sensor’ with a 450 nm - 1000 nm spectral range plus the motion and position sensor data are bundled and transmitted through the CubeSat bus. Preliminary observations from these diagnostics will be reported. |
Wednesday, October 19, 2022 2:48PM - 3:00PM |
PO05.00005: Detection of Edge Plasma Turbulence Using Ultra Speed Camera and Artificial Intelligence Sarah Chouchene, Frédéric Brochard, Mikael Desécures, Nicolas Lemoine, Jordan Cavalier The loss of confinement due to the plasma edge turbulent transport in magnetic fusion devices is still an issue for confining reactor-relevant amount of energy [1]. The work presented in this contribution aims at improving the characterization of the coherent structures (known as filaments or blobs) responsible of this transport. |
Wednesday, October 19, 2022 3:00PM - 3:12PM |
PO05.00006: Bayesian modelling of the visible spectroscopy reference system at ITER Sehyun Kwak, Maarten De Bock, Maciej Krychowiak, Ralf Koenig, Jakob Svensson, Thomas S Pedersen In magnetic confinement nuclear fusion devices, spectroscopic diagnostics have been widely employed to extract information on the plasma from its radiation. At ITER, the visible spectroscopy reference system (VSRS) will measure various plasma parameters, for example, the effective ion charge Zeff, electron and ion densities and temperatures, etc. This system will collect different types of plasma radiation including the electron-ion bremsstrahlung continuum and line emission due to excitation, recombination and charge exchange processes along a single horizontal line of sight penetrating the plasma core. The VSRS is modelled within the Minerva framework by taking into account the experimental setup and the relevant physics. This model can generate a synthetic data set according to the ITER operational scenarios and infer the plasma parameters from the generated data set. Based on the model, a real-time algorithm for delivering Zeff with its posterior uncertainties for the ITER's first plasma is developed. This algorithm can also be used to provide a proxy for ne in case of missing line-integrated ne measurements from the interferometer diagnostics for plasma control. The model is implemented in a general way within the IMAS infrastructure and can therefore be applied to similar diagnostics in other IMAS-adapted fusion experiments. |
Wednesday, October 19, 2022 3:12PM - 3:24PM |
PO05.00007: Modelling interaction of Runaway electrons with Whistler waves using KORC-AORSA model Yashika Ghai, Donald A Spong, Matthew T Beidler, Diego del-Castillo-Negrete Resonant interactions between high energy runaway electrons (REs) and whistler waves may scatter the REs to higher pitch angles leading to increased RE energy dissipation via synchrotron radiation. DIII-D observations of RE-driven whistler waves [1] suggest launching whistler waves to mitigate the deleterious effects of REs on the plasma facing components via resonant interactions with whistlers. We have numerically studied the interactions of REs with whistler waves in DIII-D and analyzed the change in the energy and pitch angle of the REs due to whistlers using the coupled KORC-AORSA model. In this framework, we follow full orbit RE trajectories using the KORC code in the presence of whistler wave fields from the AORSA code with the DIII-D whistler wave experimental data. The simulation results indicate a dependence of gain in RE energy on the instantaneous energy, pitch angle, whistler field amplitude and the radial location of the REs. Our simulation model can be used to get physical insights into future experiments on whistler waves and REs interactions. |
Wednesday, October 19, 2022 3:24PM - 3:36PM |
PO05.00008: Pellet assimilation and impurity transport in fusion plasma Haotian Mao, Yanzeng Zhang, Xianzhu Tang Pellet injection is a standard technique for fueling and disruption mitigation in tokamak reactors. For thermal quench mitigation in a tokamak disruption, high-Z impurities replace plasma heat flux at the divertor/first wall with volumetric line radiations. This requires large quantity of high-Z impurities to be assimilated into the plasma on a time scale much shorter than the thermal quench duration. Spatial uniformity of the radiation load on the first wall also requires rapid spatial transport and homogenization of high-Z radiators over a flux surface despite the initially local deposition of pellet material. Here we employ the first-principles kinetic simulations to investigate the physics of pellet assimilation and the spatial transport and mix of high-Z impurities in a hydrogen plasma upon pellet assimilation. We find that the kinetic instabilities and collisions play important roles in pellet assimilation, where the tail high-energy electrons can be critical. Another finding is that the assimilated impurities will spread along the field line via propagating fronts, the fastest of which will be the fully ionized impurities that follow the cooling front in the thermal quench [1]. |
Wednesday, October 19, 2022 3:36PM - 3:48PM |
PO05.00009: Conditions for seeing RF condensation in contemporary tokamaks Allan H Reiman, Lanke Fu, Richard Nies, Laszlo Bardoczi, Xi Chen, Nathaniel Fisch, Robert J La Haye, Nikolas C Logan, Joseph T McClenaghan For RF (radio frequency) stabilization of magnetic islands, it is predicted that nonlinear effects associated with RF current condensation can significantly affect the profile of the power deposition and the profile of the RF driven current [1]. We have been investigating the conditions under which the effect is predicted to play a significant role in contemporary tokamaks. To investigate this, we use the OCCAMI code [2], which couples a ray tracing calculation with a solution of the nonlinear thermal diffusion equation in the magnetic island. We have used the code to perform scans investigating the strength of the effect as a function of various parameters in DIII-D, focusing particularly on the predicted effect of varying the parameters in shot 141060, one of a sequence of shots previously used to study RF stabilization of locked islands [3]. Top launch electron cyclotron current drive (ECCD) is of particular interest because of its high current drive efficiency [4]. For top launch ECCD, the nonlinear effects are most pronounced for parameters that make the EC current drive most efficient. That relation is broken by trapped particle effects for outside launch ECCD. |
Wednesday, October 19, 2022 3:48PM - 4:00PM |
PO05.00010: Black-box optimization of massive material injection for disruption mitigation Istvan Pusztai, Hannes Bergström, Peter Halldestam, Oskar Vallhagen, Mathias Hoppe, Tünde Fülöp An effective disruption mitigation system in a tokamak reactor should limit the exposure of the wall to localized heat losses and to the impact of high current runaway electron beams, and avoid excessive forces on the structure. Massive material injection (MMI) as a disruption mitigation scheme is characterized by a large number of parameters, such as when to inject material, in what form and composition, representing a multidimensional optimization problem. We have developed a numerical optimization framework and applied it on simulated disruptions with MMI, representative of ITER. The simulations use the disruption runaway modeling tool DREAM [M Hoppe et al 2021 CPC 268, 108098]. The optimization takes into account the maximum runaway current, the transported fraction of the heat loss and limits on the current quench timescale. With the material deposition profiles fixed, only at lower magnetic fluctuation levels during thermal quench do we find acceptable parameter regimes, while if the injected profiles are also part of the optimization, acceptable optima may be found for a larger range of magnetic perturbations. The global view of the objective function provided by the Bayesian approach is utilized to assess the robustness of the optima. |
Wednesday, October 19, 2022 4:00PM - 4:12PM |
PO05.00011: Modelling and validation of cryogenic pellet formation for the ITER DMS Shattered Pellet Injector Sandor Zoletnik, Miklos Vecsei, Erik Walcz, Tamas Szepesi, Noe Bundschuh, Stefan Jachmich, Uron Kruezi, Michael LEHNEN The ITER Disruption Mitigation System (DMS) plans to use large, 28.5x57 mm (d x L) Hydrogen, Neon and mixture pellets, which have not been used before at such large diameters. To study the process of the pellet fragmentation and to allow testing of key components for the ITER DMS, a support laboratory has been established as part of the ITER DMS Task Force activities at the Centre for Energy Research, Budapest, Hungary. |
Wednesday, October 19, 2022 4:12PM - 4:24PM |
PO05.00012: Thermal Quench in DIII-D locked mode disruptions Henry R Strauss, Brendan C Lyons, Matthias Knolker The cause of tokamak disruptions has not been well understood. |
Wednesday, October 19, 2022 4:24PM - 4:36PM |
PO05.00013: Automatic fitting of SOLPS-ITER predictions to experimental data using Bayesian optimization Christopher Bowman, James R Harrison Matching the predictions of SOLPS-ITER to experimental data provides a means of investigating the role various physical processes play in determining the edge and divertor plasma state, and is a key component of divertor physics studies. This is a time-expensive process, as the modeler must manually inspect the results of each SOLPS simulation and adjust the input parameters to obtain a better match. We present a method for automatic fitting of SOLPS predictions to experimental data based on Bayesian optimisation - a technique designed to minimize the number of model evaluations required to achieve a match with the data. By automating the fitting process, SOLPS can be run continuously (including multiple runs in parallel) to greatly reduce the time required to obtain a good match with experiment. This approach was validated using synthetic edge Thomson-scattering data generated from MAST-U simulations, where parameters defining the anomalous transport coefficient profiles were optimized in order to match SOLPS predictions to the synthetic Thomson-scattering data. We present results of these synthetic tests in addition to results of applying the method to actual MAST-U data. Our method is not specific to MAST-U, and can be applied to any tokamak simulated in SOLPS-ITER. |
Wednesday, October 19, 2022 4:36PM - 4:48PM |
PO05.00014: Kinetic simulation of DIII-D pedestal fueling asymmetry with synthetic diagnostics George J Wilkie, Florian M. Laggner, Seung Hoe Ku, Robert Hager, Michael Churchill, Alessandro Bortolon, Choongseok Chang It has been observed on the DIII-D tokamak that ionization is much higher at the high-field side of discharges with counter-current magnetic field and this asymmetry reverses upon swapping the direction of the toroidal magnetic field. This was revealed by the LLAMA diagnostic, which measures hydrogenic Lyman-alpha radiation emitted along several dozen lines of sight that straddle the separatrix. A synthetic version of this diagnostic was incorporated into the DEGAS2 neutral transport solver, and results are sensitive to both the plasma background and the neutral source. Kinetic neutral simulations were thereby performed as a validation mechanism for total-f XGC simulations of the edge plasma turbulence including neoclassical physics, turbulence, and neutral recycling. |
Wednesday, October 19, 2022 4:48PM - 5:00PM |
PO05.00015: Turbulence measurements with a correlation ECE diagnostic in negative triangularity plasmas at ASDEX Upgrade Branka Vanovac, Jörg Hobrik, Thomas Pütterich, Rachel Bielajew, Pablo Rodriguez-Fernandez, Christian Yoo, Garrard D Conway, Anne E White, Tommaso Bolzonella, Francesco Sciortino, Tim Happel Negative triangularity plasmas, in the absence of a transport barrier, show a reduction of fluctuation levels and improved confinement. Relative fluctuation levels are reported to be reduced in experiments [1,3], and modeling [2]. At ASDEX Upgrade, the negative δ scenario with 600 kA plasma current is established, and unfavorable configuration is identified as an essential ingredient in avoiding H-mode operation [4]. |
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