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 PP11: Poster Session VI: InPerson, Hall A (2:003:30pm) and Virtual Poster Presentations (3:455:00pm)

Hide Abstracts 
Room: Exhibit Hall A and Online 

PP11.00001: MFE: DIAGNOSTICS Session Chairs: 

PP11.00002: Laboratory tests of pulsed CO_{2} laser collective Thomson scattering for measurements of divertor ion temperature Tomu H Hisakado, Tsuyoshi Akiyama, Thomas N Carlstrom Measuring the ion parameters is essential for divertor operations and for validation of divertor simulation codes. Collective Thomson scattering (CTS) is a diagnostics method that measures the ion temperature of a plasma. CTS measurements are challenging because of the inherently small Doppler shift and scattering signals that are difficult to detect. In this work, a heterodyne detection scheme is implemented to measure spectrum broadening of less than a few GHz, which is expected from the ion temperature of divertor plasma. A unique optical collection scheme that is designed to collect the scattered light efficiently using an Axicon lens is demonstrated. The axicon lens is used to collect the scattered light emitted within an annular crosssection from the scattering volume. The efficiency and performance of the heterodyne detection scheme and annular collection approach were demonstrated using a Transverse Excited Atmosphericpressure (TEA) CO_{2} laser with a pulse energy of 160 mJ at = 10.59 mm. Using a pulsed CO_{2} laser, feasibility of the heterodyne detection system is demonstrated. *Supported by the U.S. DOE under Contracts DESC0019079. 

PP11.00003: Development and experimental results of a new dispersion interferometer system, Single Crystal Dispersion Interferometer with a single detector on KSTAR Donggeun Lee, K.C. Lee, J.W. Juhn, Jayhyun Kim, Michael LEHNEN, Larry R BAYLOR, Jaeseok Lee, Ghim Y.c. Dispersion interferometers using an acoustooptic modulator (AOM), capable of suppressing phase shifts associated with mechanical vibrations, have been used widely in fusion research. We have developed a dispersion interferometer system using not only a single nonlinear crystal but also with a single detector so that the beam paths of the first and second harmonics are exactly same from the beam source to the detector. Thus, our dispersion interferometer removes a possible source of errors due to different beam paths of the harmonics around the AOM and detectors, if multiple detectors were used. The new dispersion interferometer system using an Nd:YAG laser with a fundamental wavelength 1064nm has been installed to measure line integrated densities of KSTAR discharges, especially during shattered pellet injection (SPI). Since SPI results in more than one order higher density and density gradient (order of 10^{22} m^{2}) compared to conventional tokamak plasmas, using a shortwavelength laser is beneficial where our new design of the dispersion interferometer becomes valuable. We introduce the new dispersion interferometer system and its measurement results from KSTAR. The experimental results are compared with measurements from the KSTAR TCI (twocolor interferometer) system, which is a routine measurement system for electron density in KSTAR but with a weakness of frequent fringe jumps right after SPI. 

PP11.00004: Neutron reflectometry for insitu surface characterization of plasmafacing components Carli S Smith, Matthew S Parsons, Jean Paul Allain, Camilo Jaramillo Correa Measuring the evolution of plasmafacingcomponents (PFCs) in a tokamak or stellarator environment is extremely challenging, in part due to the difficulty in establishing insitu techniques to diagnose materials during irradiation under a controlled setting and measure the evolution of the plasmamaterial interface (PMI). To address this challenge, we study diagnostics which rely on neutrons to characterize fusionrelevant PFC materials during plasma exposure. Proofofconcept modeling for neutron reflectometry (NR) indicates that changes in nearsurface material composition nearsurface due to deuterium implanted in pure W (19.35 g/cm3) at 500–1000 eV can be detected by NR at fluences as low as 10^{16} cm^{2}. Fluences of 10^{17}, 10^{18}, and 10^{19} cm^{−2} are distinguishable from each other, and differences for larger fluences must be detected at higher q values. NR was also modeled for D implantation at 1000 eV for various dispersionstrengthened W materials. At each fluence, the reflectivity curves are qualitatively similar regardless of the composition. Differences between the curves as a function of dispersoid concentration are due to the differences in the scattering lengths of the dispersoids. We conclude that the range of incident angles needed to capture relevant features depends on sample density. This result will be important for designing future experiments, to ensure that the relevant features are captured. Given the observed, large changes in NR spectra as a function of fluence, it is expected that NR will be an effective technique for the insitu diagnosis of PFCs during plasma irradiation. A multidiagnosis system, which will be implemented and tested at the NIST Center for Neutron Research, has been developed to perform insitu NR experiments. 

PP11.00005: Measurement of the Number Density in Pulsed (Gas/Plasma) Jets using a 2Dimensional, SecondHarmonic, Dispersion Interferometer Cameron T Chavez, Andrew Egly, Ivan Sepulveda, Frank J Wessel A (twocolor) secondharmonic, dispersion interferometer (SHDI) is under development that uses a commonmode, singlebeam path to measure a sample's dispersivephase shift. The phase shift exists between the primary 1064 nm beam, Δt = 0.6 ns, 200 μJ, and its 532 nm second harmonic. Postsample, the primarybeam phase information is transferred to a second, secondharmonic beam, and the dispersivephase change is eventually measured between the two SH beams. Achromatic telescopes, before and after the sample, provide a 5X beam magnification/demagnification, which allows for largearea illumination, A ≤ 10 cm^{2}. The use of these telescopes unfortunately introduces a sizeable ``noise" background present on all measurements, as a radiallysymmetric, dispersivephase shift (Δφ > 2π radians). This phase noise is quantified and subsequently removed from all sample measurements using various digital techniques. The instrument has now been tuned to measure dispersivephase changes as low as 10^{2} radians, at spatial resolutions of order, Δ x ≈ 0.1 mm using samples that include: fusedsilica objects (wedge, planoconcave and planoconvex lenses) and pulsedjets of argon (gas and plasma). For the latter, the minimum measurable linedensity product is, ∫n_{gas}dl ~10^{15 }cm^{2} and number density, n_{gas} ~ 10^{1719}cm^{3} and for plasma is, ∫n_{plasma}_{ }dl ~10^{15 }cm^{2} and n_{plasma} ~ 10^{1416}cm^{3}. Design enhancements are currently underway to extend the SHDI performance to provide a higher noiserejection ratio, S/N ≤ 10^{2.8}, largerarea imaging, A ~10 100 cm^{2}, and higher, framecapture rates, fps ~ 0.1  1 kHz. 

PP11.00006: Application of a conceptual electron temperature fluctuation diagnostic based on soft Xray imaging to simulations of tokamak turbulence Xiang Chen, Juan Ruiz Ruiz, Jon C Rost, Nathan T Howard, Walter Guttenfelder, Jeff Candy, Jerry W Hughes, Robert S Granetz, Anne E White The measurements of temperature fluctuations is important for understanding transport that determines the fusion gain of tokamaks. A new electron temperature fluctuation diagnostic based on soft Xray imaging has been proposed and has been proven feasible on a simplified model with artificial fluctuations in a circular poloidal cross section[1] and on a more realistic model using fluctuations generated from gyrokinetic simulations in a real Dshape poloidal cross section in NSTXU. However, the fidelity of the reconstruction of the latter model is lower compared to the former toy model. The applicability of the diagnostic can be sensitive to a number of factors such as the nature of the fluctuations(ITG, ETG...), the configuration of the tokamak, and the plasma conditions in equilibrium(electron density/temperature profile etc.). In this work, we run gyrokinetic simulations for several cases to obtain fluctuation data and then feed it into the diagnostic model to assess the quality of fluctuation reconstructions. The final goal of this work is to fully understand what conditions are favored by the diagnostic, and possibly for those unfavorable conditions, what measures can be taken to improve the quality of reconstructions. 

PP11.00007: Progress in conceptual design of a Heavy Ion Beam Probe diagnostic for the T15MD tokamak Filipp Khabanov, Mikhail A Drabinskiy, Leonid Eliseev, Alexander V Melnikov, Georgiy Sarancha, Nikita Vadimov, Nikolai Kharchev The Heavy Ion Beam Probe (HIBP) diagnostic is proposed for the T15MD tokamak (R=1.48 m, a=0.67 m, A=2.2, B_{t}≤2 T, I_{pl}≤2 MA) located at NRC “Kurchatov Institute”, Moscow. Two similar HIBP systems will be installed in different poloidal crosssections 90 degrees shifted around the torus. The arrangement will allow studying both poloidal and toroidal correlations of the plasma electric potential and electron density. The probing ions trajectories in the magnetic field of the tokamak are calculated with the 4th order RungeKutta method implemented in the HIBPSOLVER code. Based on the calculations results, detector grids (plasma regions accessible for measurements) are obtained, and the probing beam attenuation in the plasma is estimated. The concept of a double secondary beamline is proposed to detect secondary ions from both peripheral and central regions of the plasma column. In starting T15MD discharges with B_{t}=1 T, I_{pl}≤1 MA a Tl^{+} probing beam with the energy E_{b}<320 keV can provide measurements in a wide radial range (0.3<ρ<1) in the upper quarter (LFS) of the plasma crosssection. Additionally, the formation and focusing of the diagnostic beam in the injector is simulated, the values of focusing and extracting voltages are determined to obtain a quasiparallel beam. 

PP11.00008: Multicomponent Spectra Estimation with Deep Learning Gilson Ronchi, Elijah H Martin, Cornwall H Lau A wide range of plasma diagnostics rely on the spectral analysis for inference of plasma properties and behavior. In optical emission spectroscopy the collected light is an integrated measurement along a lineofsight and the resulting spectrum can be modeled by a sum of distinct components. When high RF power is applied to the plasma, like in Lower Hybrid Current Drive (LHCD), the emission spectrum of Deuterium and Hydrogen can be substantially modified by the presence of the RF electric field. That, in combination with the Zeeman effect due to the equilibrium magnetic field, Doppler and Stark broadening, results in a complex spectrum. Theoretical modeling of those effects can be computationally expensive, and the fitting can be challenging if the initial guess of the spectrum parameters is not close to the optimal solution. We present the use Deep Neural Networks (DNN) to estimate the physical parameters used to model the WEST spectra. The DNN estimation provides at least x100 computational speedup and can be used both as a direct estimation of the RF electric field or as an initial guess for a more refined model fitting. 
Author not Attending 
PP11.00009: Novel MultiEnergy Soft XRay Camera in the WEST Tokamak: First Data and Synthetic Diagnostic Oulfa Chellai, Luis F DelgadoAparicio, Didier Vezinet, Tullio Barbui, Remi Dumont, Kenneth W Hill, Philippe Malard, Brentley C Stratton, Novimir A Pablant, Patrick D VanMeter During the C6 campaign, the tungsten (W) Environment in Steadystate Tokamak (WEST) 

PP11.00010: Magnetic island temperature perturbation reconstruction in mixed second and third harmonic electron cyclotron emission conditions Euichan Jung, Max Austin, Laszlo Bardoczi, Allan H Reiman The electron cyclotron emission (ECE) diagnostic is one of the prevailing methods to measure electron temperature in tokamaks. However, the ECE diagnostic is limited in a low toroidal field condition, where multiple ECE resonance layers exist in the plasmas. Because the resonance layers with different locations emit the same frequency waves, it complicates the estimation of spatially resolved electron temperature based on the wave frequency [1]. Here we present a technique to reconstruct the ECE signal associated with magnetic island perturbation in mixed multiple harmonic ECE conditions. The method utilizes the time dependence of magnetic island perturbations, which is absent in the other resonance layers, to extract the data. The attenuation of perturbations caused by the absorption in the other layers is also considered by calculating their optical thickness [2]. We successfully obtained the temporal evolutions of electron temperature perturbation profiles in the 2/1 magnetic island in mixed second and third harmonic ECE environments in the DIIID tokamak. 

PP11.00011: Improved Realtime Equilibrium Reconstruction with Kinetic Constraints on DIIID and NSTXU Ricardo Shousha, John R Ferron, Zichuan A Xing, Andrew O Nelson, Keith Erickson, Egemen Kolemen We report on the improvements to realtime (RT) equilibrium reconstruction by including kinetic constraints which more robustly reflect both the pressure and current profiles including pedestals. Since not all quantities of interest in tokamak plasmas can be measured directly, RT equilibrium reconstruction codes are used. However, plasma internal profiles remain largely unconstrained when only data from magnetics are used. For algorithms depending on profile accuracy, it is crucial to include data from measurements internal to the plasma. The inclusion of pressure profile fits has been shown to significantly improve the reconstructed pressure profile. The robustness has been improved by adding buffers for the CER, and TS data. Even though the pressure profiles consistently exhibit the pedestal, the current density does not consistently show the bootstrap peak. To address this, RT equilibrium reconstruction has been extended to receive current density constraints. These are calculated using the Sauter model. An RT Thomson system is being implemented on NSTXU, paving the way for improvements to be ported and evaluated in realtime once possible. 

PP11.00012: Wavenumber Sensitivity of the NSTXU Poloidal Highk Scattering System Xianzi Liu, Calvin W Domier, Jon Dannenberg, Yilun Zhu, Jagadishwar R Sirigiri, Yang Ren, Brentley C Stratton, N C Luhmann A 693 GHz, 8channel, poloidal highk collective scattering system is under development for the National Spherical Torus eXperiment Upgrade (NSTXU) device. It will replace the previous 280 GHz, 5channel, tangential scattering system [1] to study highk electron density fluctuations, thereby providing a measurement of the k_{θ}spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. A tool is under development to calculate the wavenumbers which can be measured and the range of r/a which can be covered in NSTXU. In the previous work, the tool is limited to placing the interaction regions on the midplane and it helps on evaluating the initial design and motivating the new receiver optical design to achieve better performance. The new version of the tool is able to place the interaction regions above or below the mid plane, so larger scattering angle and thus larger fluctuation wavenumber can be achieved. Simultaneously, according to the magnetic field experimental data, it can take the effect of magnetic pitch angle into consideration. We use this tool to evaluate the wavenumber sensitivity of the NSTXU poloidal highk scattering system. 

PP11.00013: MachineLearning Design Optimization and Tomographic Inversion of 2D Fiber Optic Bolometer Array Seungsup Lee, Morgan W Shafer, Matthew L Reinke, Qiwen Sheng, Xiaoli Wang, Ming Han, David C Donovan New inversion schemes are demonstrated to assess the feasibility of a novel 2D fiberoptic bolometer (FOB) array. A recent test showed that the FOB is comparable to a resistive bolometer performance and avoids electromagnetic interference by using FabreyPérot resonator system to encode small temperature changes related to the incoming power. With these advantages and its compact size, an array was designed using a Bayesian global optimization algorithm with CHERAB library. The algorithm efficiently optimized six design parameters with nonlinear results. Six synthetic radiation profiles were used to calculate the cost for the optimization. Tomographic inversion methods for the optimized design were developed using an iterative method with regularization and neural networks (NN). The regularizations were higher costs as further away from the separatrix and lower costs along the similar flux values. 20,000 partially randomized synthetic radiation profiles were used to train the NN methods. The sensitivity matrix of the design was used with a measurement as an input for the “only” NN method. A hybrid method used the result of the iterative method with a simple regularization as an input for a NN. 

PP11.00014: Development of Spatial Heterodyne Spectroscopy for ion temperature and rotation measurements during transient events in DIIID Ryan Albosta, Benedikt Geiger, George McKee, Raymond J Fonck, Marcus G Burke, Damian Jilk, Samuel Stewart To validate models that describe the transition from the low to the high confinement mode in tokamaks, as well as the evolution of edge localized modes [Cathey et al (2020)] [Snyder et al (2002)], high speed measurements of ion temperature/rotation and plasma current profiles are of particular interest. At the DIIID tokamak, the Spatial Heterodyne Spectroscopy (SHS) technique has been applied successfully to investigate fast changes of the edgelocalized magnetic field which contains information on the current profiles. Here, we present an upgraded SHS system with replaced optics, a new lownoise CCD detector, and a modified optical filter, which can be additionally used to study ion temperatures and plasma rotation by observing chargeexchange emission of C^{6+} ions. Thanks to the interferometric method utilized, both the required high spectral resolution (0.1 nm) and high photon throughput (etendue of 0.64 mm^{2}sr) can be achieved, allowing for high quality measurements with subms time resolution. The modified device will be optimized for 110 kHz lowuncertainty measurements for comparison with previous SHS edge current analysis, as well as with the upcoming installation of 4 new beamemission spectrometers designed to improve on the previous edgecurrent data. 

PP11.00015: Synthetic Diagnostic Development to Calculate Spatial Resolution of Beam Emission Spectroscopy and Charge Exchange Imaging Samuel Stewart, Benedikt Geiger, George R McKee, David R Smith, Aidan Edmondson, Michael J Gerard, Xiang Han, Zheng Yan Beam Emission Spectroscopy (BES) and Charge eXchange Imaging (CXI) enables fast, spatially resolved density measurements by targeting the beam activated component of main ion or impurity line radiation. These measurements allow lowk to midk turbulence (0.51.5 cm^{1}) to be characterized. The light is spatially localized to the crossing between the neutral beam and the lineofsight of a fiber imaged in the plasma. The extent of the finite volume defined by this crossing determines maximum channel packing and therefore the spatial resolution of the diagnostic. The spatial extent has several main sources: finite spot size of an imaged fiber, finite beam width, optics etendue, finite lifetime effect, and transformation to field aligned geometry. The Point Spread Function (PSF) and Spatial Transfer Function (STF) of the diagnostic were calculated and integrated into pyFIDASIM, a synthetic diagnostic for the BES and CXI systems at DIIID. The calculated PSF and STF were validated against preexisting codes with good agreement. Using varied sightlines and fiber arrangements, an optimal configuration was determined for high resolution BES operation. Additionally, various density profiles were considered to identify an optimal plasma condition for studying core turbulence using BES. 

PP11.00016: Progress towards an innovative ion energy analyzer for electric potential diagnosis of fusion plasmas Peter J Fimognari, Thomas P Crowley, Diane R Demers Knowledge of the electric potential as a function of location and time in magnetically confined plasmas can advance understanding of the electric field and its effect on transport. A diagnostic heavy particle beam can be used to obtain such measurements, as well as fluctuations of potential and density in the interior of hot plasmas. To determine the electric potential within the plasma accurately, the difference in energy of the injected particles and detected ions must be precisely measured. Ion energy analyzers commonly achieve this by deflecting the ions with an electric field provided by a pair of flat, parallel electrodes. We are developing an innovative ion energy analyzer that employs cylindrical annulus sector electrodes rather than flat electrodes. It simultaneously measures the incoming angle of the beam and the deflection by the electrodes in order to determine the ion energy. This novel combination is key to obtaining equilibrium plasma potential measurement resolution of .01% of the beam energy. This design makes more efficient use of the electric field region (than traditional flat parallel plates having a single biasvoltage), reduces the maximum electrode voltage required, and lowers overall cost. Important features of the analyzer's design and characterization and initial measurements made with the analyzer will be discussed. Portions of this work were done at the Wisconsin Plasma Physics Laboratory (DoE award number DESC0018266) and on the Madison Symmetric Torus. 

PP11.00017: Comparison of Signal Resolution from Two Plasma Sources under Various Gas Sampling Conditions for Optical Emission Spectroscopy Chloe Benton, Chris Marcus, Theodore M Biewer, Chris Klepper, David A Rasmussen The role of the ITER diagnostic residual gas analyzer (DRGA), is to measure the composition of the exhaust gases leaving the tokamak within a onesecond response time. The current DRGA design comprises an instrumented, highvacuum chamber, including a plasma cellactivated optical emission spectroscopy arrangement, referred to as an optical gas analyzer (OGA). It is used to measure both the hydrogen and helium isotopic content as well as other gas species. In the determination of which plasma cell and OGA configuration is optimal, various gas leak mixtures were produced and analyzed in a laboratory setting to determine the measurements with the highest signal resolution. These mixtures, comprising various concentrations of hydrogen (H2), deuterium (D2), and helium (He), were selected because they are relevant to the gas species expected in the ITER tokamak. The mixtures were leaked into a test chamber at DRGArelevant, steadystate sampling pressures. Initially, the OGA analyses were done using the Optix System in its commercial configuration: plasma cell (inverted magnetron geometry) and integrated spectrometer. In additional tests, the emission from the plasma cell was coupled to an IsoPlane™ spectrometer via an optical fiber. This latter configuration was also tested concurrently using the traditional OGA, a Penninggeometry cold cathode gauge, coupled to the same spectrometer. The measurements were carried out in steady state and over a range of gas sampling pressures. A preliminary assessment of the Optix™ plasma cell for the ITER OGA application will be presented. 

PP11.00018: Measuring Electron Temperature Profiles and Detecting NTMs in ITER Using ECE Joseph P Ziegel, Saeid Houshmandyar, William L Rowan, Francois Waelbroeck, Thomas Watts, Max Austin This poster describes the effects of physics issues on interpreting electron cyclotron emission (ECE) diagnostics, and shows how simulated ITER plasma scenarios that are perturbed with magnetic islands can be used to test ECE detection of neoclassical tearing modes (NTMs). These areas of focus help determine the design of the ECE system. ECE diagnostics are planned for ITER as a tool to measure plasma electron temperature with high spatial and temporal resolution, and to detect NTMs. Physical limitations including frequency cutoffs and harmonic overlap can hinder the ability to interpret ECE [1]. In high temperature plasmas, relativistic shift and broadening of the ECE must be considered to accurately reconstruct electron temperature spatial profiles [2]. Accounting for these effects allows ECE diagnostics to be used for accurate measurement of the equilibrium electron temperature profile, and fluctuations about this equilibrium. One such fluctuation is caused by fast radial transport of heat across magnetic islands [3]. ECE diagnostics can detect periodic fluctuations in electron temperature due to rotating magnetic islands to determine the existence and location of NTMs [4]. Fast and accurate detection of NTMs is necessary for avoidance of disruptions. 

PP11.00019: MFE: EDGE AND PEDESTAL Session Chairs: 

PP11.00020: DataDerived Operational Boundaries and Scaling of RMP ELM Suppression Priyansh Lunia, Carlos A PazSoldan, Nils Leuthold, Wolfgang Suttrop, Matthias Willensdorfer, JongKyu Park, Nikolas C Logan, Min Woo Kim Suppression of edgelocalized modes (ELMs) by application of resonant magnetic perturbation (RMP) fields has been demonstrated in many tokamaks, however, the access criteria are not fully understood. Linear discriminant analysis (LDA), a classifier that projects data onto a linear axis that maximizes the distance between class means, is performed on a dataset of discharges from the ASDEX Upgrade tokamak including ELMy and ELMsuppressed phases. Treating this analysis as a classification problem, an LDA model using equilibrium, control, and plasma parameters is trained with a predictive accuracy of >90%. The decision boundary for determining a discharge’s classification as ELMy or suppressed is derived and compared to known experimental threshold conditions. Scaling laws for confinement time are extracted from a multidevice database consisting of RMP ELMsuppressed Hmode discharges from ASDEX Upgrade, DIIID, and KSTAR. These are compared to previously derived Hmode and Lmode laws. Including rotation data in addition to previously used quantities improved the overall goodnessoffit, especially so for singledevice data. This work provides a further understanding of the parameter space required for ELMs to be suppressed by RMPs and the confinement quality expected therein. 

PP11.00021: Modeling high radiation fraction Lmode plasmas in multiple configurations Haley S Wilson, Andrew O Nelson, Carlos PazSoldan The use of noble gas impurities as radiators in fusion scenarios can reduce powerhandling demands in reactors and keep power well below the Hmode threshold power. We develop 0D and 1D models to show a reduction in power to the scrape off layer while maintaining relatively high power in the core and exhibiting improved Lmode performance compared to nonradiative regimes. We use these models to lever negative triangularity in tokamaks, which can improve confinement and thus correct some deficiencies of Lmode operation. The 1D radiative Lmode tokamak model is compared to data measured in recent argonbased radiation feedback control experiments on DIIID for model validation. We extend our analysis to compare the efficacy of radiators between plasmas of varying densities, magnetic fields, and aspect ratios in stellarators. We find that at reactor values radiative impurities reduce power to the first wall with minimal fuel dilution. We build off the 1D scenarios using the STEP code for selfconsistent operating points, supporting results from the 0D and 1D models. This work shows the benefits of radiative impurities in stellarator and tokamak configurations and the feasibility of Lmode tokamak reactors for commercial fusion, specifically with respect to power handling. 

PP11.00022: Progress with the fullF continuum edge gyrokinetic code COGENT Mikhail Dorf, Milo Dorr, Debojyoti Ghosh, Justin R Angus COGENT is an Eulerian gyrokinetic code being developed for edge plasma modeling. The code is distinguished by the use of a highorder finitevolume discretization combined with mapped multiblock grid technology. Our recent work is focused on performing hybrid kinetic ion  fluid electron electrostatic microturbulence simulations in model and realistic divertor geometries. The simulation model describes the ion scale ion temperature gradient (ITG) and resistive drift and ballooning modes as well as neoclassical ion physics effects. The role of Xpoint geometry is explored by comparing crossseparatrix simulations with counterpart calculations performed in a toroidal annulus geometry. Preliminary results demonstrate formation of an Erwell and a density pedestal in the regime of suppressed turbulence for the case of a model singlenull geometry. Rapid progress is concurrently being made toward including electromagnetic effects. The hybrid model has been extended to include lowbeta effects, e.g., shearAlfven waves. Also, a fluid MHD module, which captures finitebeta effects and can take advantage of the fieldaligned grid technology, has been added to the suit of COGENT tools. 

PP11.00023: Electrostatic driftkinetic simulations of edge localized mode heat pulses in the tokamak scrapeoff layer Vasily I Geyko, Ilon Joseph, Mikhail Dorf, Milo Dorr, Debojyoti Ghosh For a tokamak operating in highconfinement (Hmode), edgelocalized modes (ELM) determine the peak particle and heat fluxes delivered to the divertor. Parallel heat transport is studied within a onedimensional drift electrostatic approximation using continuum gyrokinetic code COGENT. We adopt a test problem setup and simulation parameters used by previous authors^{1}, where the ELM is modeled as a heat and particle source at the midplane of the scrapeoff layer. The time evolution of particle and heat fluxes on the target plate is found and compared to results from previous works. The main focus of the research is on the impact of boundary conditions on the heat flux evolution. We considered several modifications of the commonly used logical and insulating sheath boundary conditions and analyzed the overall system behavior. We also investigated different modifications of the gyrokinetic Poisson equation in order to mitigate fast electrostatic shear Alfvén wave and to achieve better quasineutrality conservation. The results of the presented models are in qualitative agreement with previous works. 

PP11.00024: Investigation of plasma turbulence in tokamak divertor and its implications for plasmamaterial interactions Maxim Umansky, Bruce I Cohen, Ilon Joseph Turbulent fluctuations in the tokamak divertor region are important for the plasmafacing components since plasmamaterial interaction processes, such as sputtering, are strongly nonlinear. In this study, a fluid edge plasma turbulence model SOLT3D is used for investigation of divertor plasma turbulence and plasma interaction with the material surfaces. The model, implemented in the BOUT++ framework [1], includes equations for collisional fluid plasma and neutral gas, with sheath boundary conditions on the divertor target plates. The computational domain represents the edge plasma region of a tokamak in a “rectified” geometry. The model supports basic fluid plasma instabilities relevant to the SOL and divertor: the drift resistiveballooning mode instability, driven by the magnetic curvature and the radial gradient of plasma pressure, and the conductingwall mode instability, driven by the endplate sheath boundary conditions and the radial gradient of plasma temperature. Comparison with linear dispersion relations and some existing nonlinear results demonstrates excellent consistency. Results for simulated plasma turbulence in the divertor region are presented, and implications of turbulent fluctuations for plasmamaterial interactions are discussed.
[1] Dudson et al., Comput. Phys. Commun. 180, 1467–1480 (2009).


PP11.00025: Numerical modeling of MHD/turbulence and their role in setting divertor heat flux width in WidePedestal QHmode plasmas Zeyu Li, Xi Chen, Darin R Ernst, Patrick H Diamond, Xueqiao Xu, Huiqian Wang, Nami Li Widepedestal QHmode (WPQH), a stationary, quiescent Hmode with pedestal width larger than EPED prediction discovered on DIIID in recent years is featured with low edge rotation and good Hmode confinement. The MHD and turbulence of WPQH are identified using BOUT++ [1]: a) a low frequency, lowk peelingballooning mode that rotates in the ion diamagnetic drift (IDD) direction; b) a higher frequency, intermediatehigh k driftAlfven wave that propagates in the electron diamagnetic drift (EDD) direction; which are consistent with BES/DBS diagnostics. Correlation between amplitude of edge turbulence and the divertor heat flux width is observed experimentally. The role of different modes in setting the divertor heat flux width is studied numerically using BOUT++ 6field reduced MHD module. By varying the pedestal profiles, it has been found that the IDD mode amplitude increases with a steepened T_{i} profile and extends radially across the pedestal, broadening the divertor heat flux width. Simulations predict divertor heat flux width increases with the fluxsurfaceaveraged turbulence intensity flux at separatrix. Further, the sheathlimited SOL character of WPQHMode is reproduced in the simulation. ([1] Zeyu Li et al 2022 Nucl. Fusion 62 076033) 

PP11.00026: Neutrals modulated intrinsic rotation in tokamaks Robert W Brzozowski, Timothy J StoltzfusDueck The toroidal rotation of a tokamak plasma can stabilize instabilities and is consequently of interest. Present devices are often heated by neutralbeam injectors, which can apply a large toroidal torque, while future reactors will primarily rely on isotropic fusion reactions. Thus, understanding the rotation in low appliedtorque scenarios is important. Strong transportdriven scrapeoff layer (SOL) plasma flows are present even in lowtorque discharges and are felt by chargeexchanged (c.x.) SOL neutrals, which have velocities characteristic of the local ions. Having high crossfield mobility, neutrals can transport this momentum into the pedestal. We extend a recent reformulation of the modulatedtransport model [StoltzfusDueck 2012] to include neutrals. The ion distribution function couples to the neutrals via a short c.x. step expansion, treating the neutrals as c.x. dominated. The theory retains key edge features (turbulent transport, drift orbits, ion loss cone, etc.) and allows arbitrary neutral densities. Compared to the intrinsic rotation driven by the interplay of ion drift orbits and inhomogeneous turbulence, the neutrals' effect is modest under realistic conditions. Future work will address the finite c.x. step and its role in the momentum transport of the SOL flows. 

PP11.00027: Discovery of microturbulent homoclinic tangle near magnetic Xpoint from the XGC totalf electromagnetic simulation Choongseok Chang, SeungHoe Ku, Michael Churchill, Ralph Kube, Robert Hager, Hanqi Guo, Jong Choi, David Pugmire, Scott Klasky The outermost confinement in a diverted tokamak reactor is designed to be at the magnetic separatrix surface, which, however, can easily be distorted into wild lobe or finger structures, called homoclinic tangle, by small nonaxisymmetric internal or external perturbations that could allow plasma to leak out around the magnetic Xpoint region. In the past, transient MHDdriven and stationary RMPdriven homoclinic tangles have been found. Recently, it has been discovered from electromagnetic edge simulations in the totalf gyrokinetic code XGC that a highfrequency, intrinsic turbulent homoclinic tangle can be formed by microturbulence even in the absence of MHD instabilities or RMPs. The turnover frequency of this intrinsic homoclinic tangle is resonant with the electron kinetics and can easily produce an extra source of electron heat transport across the last confinement surface towards divertor plates, possibly making an intrinsic connection between the pedestal and heatexhaust to divertor. The turbulent homoclinic tangle is found to have a nonnegligible widening of the divertor heatload width on the fullcurrent ITER, but a negligible effect on the present tokamak plasma in a normal Hmode operation. Detailed properties of the turbulent homoclinic tangle will be presented. 

PP11.00028: Theory of nonlinear ELMs as reconnection bursts Fatima Ebrahimi New results on the rise and nonlinear relaxation of PeelingBallooning ELMs (EdgeLocalized Modes) will be presented. The formation of current sheets and the transition to 3D currentsheet instability is demonstrated through fully nonlinear resistive MHD simulations of PB ELMs in DIIID discharges. Largescale axisymmetric current sheets, as well as smallscale poloidally extending current sheets, are formed as the coherent PB ELM filaments nonlinearly evolve. A model for the magnetic selforganization during nonlinear ELMs is presented (arXiv:2110.09706). Work supported by DOE. 

PP11.00029: Gyrokinetic penetration of resonant magnetic perturbations into tokamak pedestal and core Robert Hager, SeungHoe Ku, Alessandro Bortolon, CS Chang, Shaun R Haskey, Qiming Hu, Florian M. Laggner Suppression of ELM crashes using a set of external resonant magnetic perturbation (RMP) coils is planned in ITER and could be critical for its success. So far, only special MHD and fluid codes have been used to understand the penetration of RMPs into the pedestal and core plasma while neglecting or simplistically modeling important kinetic physics. We report the first successful simulation of gyrokinetic RMP penetration in a realistic tokamak geometry, including the separatrix, using the totalf gyrokinetic particleincell code XGC that simulates neoclassical physics, neutral particle recycling and electromagnetic turbulence together. We study a DIIID RMP ELMsuppressed Hmode discharge [S. Gu et al., Nuclear Fusion 59, 026012 (2019)] and compare the gyrokinetic penetration calculation against M3DC1’s MHD results. We discuss the possible existence of magnetic islands and stochastic magnetic perturbations due to RMPs at the pedestal top and deeper into the core plasma as implied by experimental observations, and how the gyrokinetic density pumpout and electron/ion thermal transport compare with the experimental observations. 

PP11.00030: Totalf XGC study of electromagnetic turbulence effect on divertor heatload width Seung Hoe Ku, Robert Hager, Choongseok Chang, Amil Sharma, Michael Churchill, Aaron Scheinberg Understanding the underlying physics of the divertor heatload width, λ_{q}, is one of the most important issues for reliable operation of ITER. Previously, predictions from the totalf multiphysics simulation in XGC agreed with the “Eich” allmachine regression formula #14, but predicted 12 times wider turbulenceenhanced λ_{q }for the fullcurrent ITER [1]. However, the simulations were electrostatic, and the electromagnetic turbulence effect remained as a question. Recently, an electromagnetic algorithm utilizing the mixedvariable and pullback transformation methods was installed on the totalf gyrokinetic code XGC [2]. XGC has been simulating the electromagnetic physics while retaining all the totalf capabilities that selfconsistently include neoclassical physics, turbulence physics, neutral particle recycling, heat and torque sources, nonlinear FokkerPlanck collisions, logical sheath, etc. Here, we report the heatflux width study for DIIID and ITER Hmode plasmas using electromagnetic XGC simulations. XGC finds that the electromagnetic effect makes little difference to the divertor heatload width in DIIID, but makes a noticeable widening of λ_{q }in ITER. Data analysis and physics details will be presented. 

PP11.00031: Neoclassical transport in strong gradient regions of large aspect ratio tokamaks Silvia Trinczek, Felix I Parra, Peter J Catto, Iván Calvo, Matt Landreman Applicability of standard neoclassical theory in transport barriers is limited because of sharp gradients of temperature, density, and radial electric field. We have developed a new neoclassical approach that sets the scale length in transport barriers to be the ion poloidal gyroradius. This ordering implies that the poloidal component of the ExBdrift becomes of the order of the poloidal component of the typical ion parallel velocity, and the trapped particle region is shifted. Using large aspect ratio and low collisionality expansions, we derive equations describing the ion transport of particles, parallel and perpendicular momentum, and energy. Previous work which only accounted for strong gradients in density and electric field or neglected the mean parallel velocity gradient is extended by keeping the poloidally varying part of the electric potential and by allowing the temperature gradient to have the same scale length as the density gradient. We find that a neoclassical ion particle flux requires parallel momentum input. Due to the nonlinear character of the equations, we can show that for certain sources and boundary conditions there are no solutions. 

PP11.00032: Quantitative measurements of ion orbit loss from gyrokinetic simulations Hongxuan Zhu, Timothy J StoltzfusDueck, Robert Hager, Seung Hoe Ku, Choongseok Chang Ionorbit loss is considered to have important impact on the radial electric fields Er in the tokamak edge. In neoclassical equilibria, collisions can scatter ions into the loss orbits and generate a steadystate radial current, which may drive the edge Er away from the confinedregion neoclassical value without orbitloss. To quantitatively measure this effect, an ionorbitflux diagnostic [1,2] has been implemented in the axisymmetric version of the totalf gyrokinetic particleincell code XGC [3,4]. The validity of the diagnostic is demonstrated by studying the collisional relaxation of Er in the core plasmas. Then, the ion orbitloss effect is numerically measured in the edge plasmas in the DIIID geometry. It is found that the effect of the collisional ion orbit loss is more significant for an Lmode plasma compared to an established steady Hmode plasma. 

PP11.00033: Insight into MHD simulation of DIIID QHmode saturation mechanism using power transfer analysis Jacob R King, Eric C Howell, Xi Chen, Guanying Yu, Yilun Zhu Progress towards full understanding of Hmode operation regimes without edge localized modes (ELMs) requires the ability to simulate nonlinear fluctuation dynamics. Specifically, we study the dynamics of edge harmonic oscillations and broadbandMHD during DIIID standard and widepedestal quiescent Hmode [Chen Nucl Fusion 2016]. The twofluid, extendedMHD NIMROD code [Sovinec et al., J Comp Phys 2010] is used with a multispecies collisionality formulation that incorporates the carbon impurity. Fluctuations produced in nonlinear MHD simulations are dominated by low frequency and low wave numbers akin to the observed dynamics in DIIID [Pankin et al., Phys Plasmas 2020; King et al., Phys Plasmas 2017]. The amplitude of the saturated dynamics are dependent on the amplitude of the underlying sources. As the strength of the underlying drive is varied, a spectral powertransfer diagnostic [Howell et al. Phys Plasma 2022] is applied to interpret the fluctuation saturation mechanism. A synthetic diagnostic is applied to compare the simulation with recent electroncyclotron emission imaging measurements. 

PP11.00034: Transport barrier for spinning blobs in magnetically confined plasmas Junyi Cheng, James R Myra, Scott E Parker, Seung Hoe Ku, Robert Hager, Choongseok Chang In this work, we use the fullf gyrokinetic particleincell code XGC [1] to investigate the blobs in the electrostatic limit. The blobs are seeded in the core region close to the separatrix with the realistic magnetic field from CMod Hmode discharge. We found the blob with a large amplitude has a stable shape with a large spin and a small radial motion. We also found the spinning blob with a certain amplitude in the midplane is split into two blobs in the separatrix region: the inner blob has a bounce motion (switch between the negative and positive radial velocity in a certain radial region), and the outer blob moves outward radially. It is characterized as a transport barrier for spinning blobs. 

PP11.00035: Enhanced Electron Confinemet in the Lithium Tokamak Experiment (LTX) Scrape off Layer Akash Shukla, Gregory W Hammett, Manaure Francisquez, David R Hatch, Ammar Hakim Fluid simulations of the scrape off layer are unable to capture the effects of trapped particles on confinement, which can be important. We use the Gkeyll computational framework, the first successful fullf continuum electromagnetic gyrokinetic code on open field lines to explore particle and heat confinement in the LTXSOL.Here, we conduct 3 dimensional (1 spatial and 2 velocity dimensions) and 5 dimensional (3 spatial and 2 velocity dimensions) gyrokinetic simulations on open field lines with parameters representative of the LTX scrape off layer to investigate enhanced electron confinement observed in the LTXSOL. 

PP11.00036: Effect of plasma shaping on MAST and MASTU pedestal stability Koki Imada, Xi Chen, Andrew Kirk, Matthias Knolker, Thomas H Osborne, Samuli Saarelma, Philip B Snyder, Howard R Wilson Modern tokamaks can operate in highconfinement (H)modes, in which a steep edge plasma pressure gradient is established, creating a "pedestal". However, Hmodes are subject to a class of explosive edge localized modes (ELMs), which could cause serious damages to the vessel walls of large tokamaks, like ITER. Large ELMs must therefore be mitigated or suppressed. 

PP11.00037: Edge modeling and simulation of Plasma Injector (Pi3) plasmas with lithium walls Leopoldo Carbajal, Aaron Froese, Celso Ribeiro, Carl P Dunlea, Stephen J Howard, Rouslan Ivanov, Maxim Umansky, Thomas D Rognlien General Fusion works towards commercial power generation through magnetized target fusion (MTF) [M. Laberge, J. Fusion Energy 38, 199–203 (2019)]. Target plasmas in this MTF scheme use a spherical tokamak (ST) generated through coaxial helicity injection by a Marshall gun into a liquid metal cavity, which compresses the plasma for a few milliseconds until the plasma reaches ignition. The plasma injector (Pi3) is a noncompressing experimental device at General Fusion with solid lithium walls used to study and to improve target plasmas. In this work we present results of the edge modeling and simulation of Pi3 plasmas using the UEDGE code [T.D. Rognlien et al., J. Nucl. Mater. 196–198, 347 (1992)]. We evolve the plasma for a few milliseconds to study the effect of neutral hydrogen and neutral and partially ionized lithium on the plasma dynamics and on the mechanisms for energy transport and deposition to the walls. We compare simulated profiles of plasma density and electron temperature to experimental measurements from a movable triple Langmuir probe in Pi3. We also compare simulated hydrogen and lithium line radiation and measurements of a visible camera in Pi3, finding good qualitative agreement between simulation and experiment.


PP11.00038: Observation and Characterization of EHOlike modes during the InterELM periods of typeI ELMing DIIID Hmode Discharges Tanmay Macwan, Kshitish Kumar Barada, Terry L Rhodes, Santanu Banerjee, Lei Zeng, Zheng Yan, Richard J Groebner Edge harmonic oscillations (EHOs) are normally observed in quiescent Hmode (QHmode) plasmas. Reported here for the first time are the observations of EHOlike modes during the interELM period of regular typeI ELMing Hmode discharges of the DIIID tokamak. The observed modes, with a character similar to that of EHOs, are being investigated for the role they may play in particle transport during the interELM period. ELITE calculations show that the MHD stability is close to the peeling boundary in the interELM period, similar to QHmode pedestal. The EHOlike modes (~10 kHz and its harmonics) are observed during each interELM period in the measurement of density fluctuation (ñ) by Doppler backscattering (DBS) and beam emission spectroscopy, with similar modes observed by magnetic probes and in the ion saturation current measurements by Langmuir probes. The DBS measurements confirm that the EHOlike modes are pedestal localized, i.e., they weaken towards the separatrix and the pedestal top. Analysis of several discharges indicate a critical electron pedestal pressure gradient following an ELM crash above which the EHOlike modes are excited. 

PP11.00039: MFE: STABILITY Session Chairs: 

PP11.00040: Experiments to overcome velcoity limitations in centrifugally confined plasmas. Remignton R Reid, Jenny R Smith Traditional magnetic mirrors are appealing because of their comparably simple geometry which lends itself to costeffective construction. However, magnetic mirrors suffer from several inherent problems that make them poor choices for confining and heating plasmas. The chief concerns are the losscone instability which continuously saps hot particles from the trap and the interchange instability which effectively transports hot plasma from the core of the trap to the edges where it is lost to the walls. Centrifugal confinement schemes address these concerns with the addition of supersonic poloidal rotation which can effectively shut off the losscone. In addition, velocity shear in the flow may mitigate or even turn off the interchange instability if high enough rotation speeds can be achieved. Previous experiments have verified the efficacy of centrifugal confinement but have been unable to achieve sufficient rotation velocities to entirely shut down the interchange modes. The rotation velocity in these experiments was limited by the CriticalIonizationVelocity (CIV) instability which manifested at the ceramic insulators. We are begining a seris of exoeriments to to verify that the CIV is the limiting factor in supersonic plasma centrifuges and to explore the concept of vacuum insulation to avoid the presence of cramic insulators which may catayze the CIV instability. 

PP11.00041: Minimization of Poloidal Viscosity in Tokamaks Using the FLOW Code Ian F Gustafson, Luca Guazzotto Extensive experimental evidence shows that the presence of poloidal flow in tokamaks can dramatically improve transport properties. However, theory shows that these flows are damped by poloidal viscosity. In this work, ideal magnetohydrodynamic equilibria are calculated via the FORTRAN code FLOW [1] and a postprocessor is used to estimate the poloidal viscosity. A norm of the viscosity is then minimized over the input parameters of the calculation, i.e. the input free functions for FLOW, which are associated with intuitive physical quantities. To achieve this minimization, the FLOW code has been functionalized and wrapped within a Python script for easy use with an opensource parallel minimization package. Here, we present and compare equilibria with minimized poloidal viscosities for various FLOW input free functions, plasma shapes, sonic regimes, and definitions of poloidal viscosity. We also compare our numerical results to those of an analytical minimization, and find that we can further reduce the poloidal viscosity by up to an order of magnitude with respect to the analytic result. 

PP11.00042: Validation of MARSF Modeling of 3D RMP Plasma Response and Testing of Reduced Surrogate Models Xuan Sun, Yueqiang Liu, Lang L Lao, Carlos A PazSoldan MARSF, a simulation code which models 3D magnetohydrodynamics in tokamak plasmas, is applied to resonant magnetic perturbation (RMP) discharges in DIIID. Understanding these 3D RMP plasma responses in simulation is important for controlling the edge localized mode (ELM). Experimental validation datasets for plasma response are available in DIIID, such as Thomson scattering (TS) and charge exchange recombination (CER) which both measure the displacement of the plasma boundary and the internal displacement at certain toroidal locations. This work focuses on validating the MARSF computed plasma boundary displacement based on the linear resistive fluid model, complementary to most of the previous studies in DIIID where magnetic probe measurements were used for comparison. Furthermore, the ability to validate against vertical and horizontal plasma boundary displacements allows systematic investigation of "mixing" of these two geometric components – an important aspect in terms of the geometric sensitivity of both measured and modeled results. A range of experiments, scanning both the plasma and RMP coil parameters, are simulated. The results (i) confirm the predictive capability of the MARSF model for 3D response in tokamak plasmas, and (ii) help expand the available perturbed 3D equilibrium database constructed using MARSF. This database has also been analyzed utilizing various model order reduction techniques, including singular value decomposition (SVD) combined with neutral networks (NNs). In particular, it is found that the first 5 SVD eigenstates are capable of representing ~95% of the database with a relative error of <10%. 

PP11.00043: Error field source identification in early ITER plasmas Matthew C Pharr, Carlos A PazSoldan, JongKyu Park, Nikolas C Logan, Yuri Gribov, Nils Leuthold Above a critical threshold, error fields in toroidal magnetic confinement schemes can be disastrous for maintaining a high energy density fusion plasma. These 3D fields break toroidal symmetry, cause a loss of confinement, and may spawn instabilities leading to disruption. Their possible origin and optimal correction is a topic of pertinent interest for study in planning the operation of future fusion experiments. We conduct a study on linear error field source modeling using GPEC to analyze the n=1 sources from the tilting and shifting of poloidalfield and other coils, and calculate the ideal correction current in the ITER midplane error field correction coils. We consider multiple different early operational scenarios that will be relevant to early campaigns in ITER. We present results in the form of error fields from each scenario and their dominant mode overlaps, as well as the ideal current and phase in the correction coils. Such research is necessary to gain an understanding of how the error fields will behave at higher currents, where it is too risky to measure directly via compass scans due to the increased risk of damage due to disruption. 

PP11.00044: Investigation of negative triangularity plasma in terms of the n=0 resistive wall mode Junhyuk Song, Carlos A PazSoldan, Andrew Oakleigh Nelson, Jungpyo Lee Recently, negative triangularity (NT) plasmas have shown advantages over positive triangularity (PT) counterparts, including reduced electron heat transport and strong core performance concomitant with an Lmode edge. Despite these benefits, NT plasmas suffer from reduced elongation due decreased vertical stability. We have developed an n=0 resistive wall mode instability code (AVSTAB  Axisymmetric Vertical STABility), which calculates the marginally controllable elongation given a tokamak feedback parameter, to optimize the elongation of NT plasmas. NT equilibria generated with ECOM show increased Shafranov shifts compared to PT references, with more elongated inner flux surfaces which grow vertical instabilities. Poloidal beta has an opposite effect in NT and PT in terms of its influence on the marginally controllable elongation, which is increased with high poloidal beta only in the negative case. Interestingly, the conversed triangularity of a wall and plasma demonstrates elevated marginally controllable elongations for both negative and positive configurations. The feedback parameter of AVSTAB is improved for poloidal modes to reproduce various experimental results, including KSTAR discharges copper passive plates to control vertical instabilities. 

PP11.00045: Selforganization and confinement in tokamak plasmas with very low edge safety factor Noah C Hurst, Brett E Chapman, Abdulgader F Almagri, Brian S Cornille, Stephanie Z Kubala, Karsten J McCollam, John S Sarff, Carl R Sovinec, Jay K Anderson, Daniel J Den Hartog, Cary B Forest, Mihir D Pandya, Winston S Solsrud There has long been interest in understanding tokamak behavior for edge safety factor q(a) < 2, in part due to the strong scaling of energy confinement with plasma current. We report internal measurements and nonlinear MHD modeling for very low safety factor, steady, Ohmic tokamak plasmas spanning 0.8 < q(a) < 3. The experiments are conducted in MST (a = 0.5 m, R = 1.5 m, B_{T} = 0.13 T), where the disruptive kink instability typically encountered at q(a) = 2 is mitigated passively by the closefitting, thick, conducting shell. A family of selforganized q(r) profiles is discovered in which q(0) ~ 1 as q(a) decreases toward 1, such that the flat core region expands outward toward the wall. Internal electron density and temperature measurements also exhibit increasingly broad, flat profiles. The experimental results are compared to nonlinear MHD simulations with q(a) ≥ 1.5 using the NIMROD code with a similar Lundquist number S = 10^{5}, which also show q(0) relaxing toward unity. Experimental data show that periodic sawtooth behavior gives way to irregular fluctuations, and electron energy confinement drops as q(a) decreases below 2. Interesting nonlinear mode coupling behavior near and below q(a) = 1 is also discussed. 

PP11.00046: Nonlinear simulation with strong Internal transport barrier and weak External transport barrier under the BOUT++ GyroLandauFluid code Pengfei Li, Xueqiao Xu, S. Ding, Andrea M. Garofalo


PP11.00047: Progress on a fast and robust solver for ideal MHD stability in stellarator geometry Caira Anderson, Adelle Wright, Benjamin Faber, David Bindel


PP11.00048: Linear equations for stellarator local MHD equilibria around irrational and rational flux surfaces Felix I Parra, Ivan Calvo, Wrick Sengupta, Jose Manuel GarciaRegana, Antonio GonzalezJerez Building on previous work [1, 2, 3], we develop a new set of linear equations to determine the magnetic geometry coefficients needed for local gyrokinetic simulations on a flux surface of interest. The inputs required for the model are the shape of the flux surface, the radial derivative of that shape and four constants. One possible choice for these four constants is the pressure gradient, the gradient of the toroidal flux, and the rotational transform and its radial derivative at the flux surface of interest. When we apply our equations to rational flux surfaces, we find that, for flux surfaces to exist, two conditions must be satisfied. One of the conditions is the wellknown Hamada condition [4], but the other has not been discussed in the literature to our knowledge. 
Author not Attending 
PP11.00049: Machine learning methods for probabilistic lockedmode predictors in tokamak plasmas Dylan P Brennan, Cihan Akçay, John M Finn We have extended the model of Ref.[1], including a resistive wall and an error field. This leads from 3rd order to 5th order, with the RPRW stability index Delta(t,rw) taking the place of the RPIW index Delta(t) of [1]. This model also includes quasilinear saturation by finite island width. The error field and the applied torque are the control parameters. The normalized order parameters are determined from the variables of the 5th order ODE system. As in [1], we have applied machine learning (ML) methods, starting with clustering algorithms used to classify into locked (L) and unlocked (U) states. The normalizations greatly aid in this step. In terms of the 2D control parameter space, there is a region (L') of only L states, a region (U') of U states, and a hysteresis region (H'), where both L and U states occur. The second step is to use the classification into L and U to determine the locking probability p(L). We find that a neural network (NN) scheme gives a good estimate of p(L). We have computed the internal and external fields from the measured fields, and used these to search for a signature of incipient locking in H'. We have also explored adding a new layer to the NN, and used it with much more sparse data to update p(L). 

PP11.00050: Nearaxis expansion of weakly quasisymmetric fields to all orders: numerical implementation Lanke Fu, Eduardo Rodriguez, Amitava Bhattacharjee


PP11.00051: Current singularities on rational surfaces including pressure effects YiMin Huang, Stuart R Hudson, Joaquim Loizu, Yao Zhou, Amitava Bhattacharjee Nonaxisymmetric ideal magnetohydrodynamic equilibria with a continuum of nested flux surfaces and a continuous rotational transform generically exhibit singular currents on rational surfaces. These currents have two components: a surface current ($\delta$function in radius) that prevents the formation of a magnetic island and an algebraically divergent PfirschSchl\"uter current when a pressure gradient is present across the rational surface. At an adjacent flux surface of the rational surface, the traditional treatment gives the PfirschSchl\"uter current density to scale as $j \sim 1/\Delta \iota$, where $\Delta \iota$ is the difference of the rotational transform between the two flux surfaces. If the distance $x$ between flux surfaces is proportional to $\Delta \iota$, the scaling relation $j \sim 1/\Delta \iota \sim 1/x$ will lead to a paradox that the PfirschSchl\"uter current is not integrable. In this work, we investigate this issue by considering the pressuregradientdriven PfirschSchl\"uter current in the HahmKulsrudTaylor problem, which is a prototype for singular currents arising from resonant perturbations. We show that because of the $\delta$function current at the resonant surface, the neighboring flux surfaces are strongly packed with $x\sim (\Delta \iota)^2$. Consequently, the PfirschSchl\"uter current $j \sim 1/\sqrt{x}$, making the total current finite, thus resolving the paradox. 

PP11.00052: MHD simulation of different sawtooth crash models with comparison to DIIID experiments Dingyun Liu, William R Fox, Sayak Bose, Zheng Yan, George R McKee, Stephen C Jardin, Hantao Ji, Yilun Zhu, Guanying Yu Core electron temperature drops rapidly during the sawtooth crash in tokamak plasmas, which causes heat loss and may lead to fast particle losses or even a disruption. Several models have been proposed for the fast relaxation, including (1) fast magnetic reconnection provided by twofluid effects or the plasmoid instability; (2) growth of highermodenumber pressure driven instabilities. We have performed 3D MHD simulations of the sawtooth crash for different models with the M3DC1 code. The magnetic field, parallel current density profile, electron density and electron temperature have different behaviors in the original Kadomtsev’s resistive reconnection model, (1) the extended model with twofluid effects, and (2) the quasiinterchange model with highermodenumber instabilities. The 2D poloidal structures of electron density and temperature evolution are compared with that near the q=1 surface during sawtooth crashes in DIIID measured by Beam Emission Spectroscopy (BES) [Bose et. al. submitted to Rev. Sci. Instrum. (2022)] and Electron Cyclotron Emission Imaging (ECEI) to distinguish between these models. 

PP11.00053: Resonant layer responses to 3D magnetic perturbations across linear, twofluid, driftMHD regimes Jace C Waybright, JongKyu Park 3D magnetic perturbations arising in a tokamak can induce complex plasma responses near the 

PP11.00054: Simulations of plasma flow evolution of an axisymmetric tokamak using a ChapmanEnskoglike (CEL) kinetic closure approach in NIMROD Joseph R Jepson, Chris C Hegna, Eric D Held, Eric Howell


PP11.00055: Impact of poloidal mode spectrum on 3D plasma response at various triangularities Brent L Ford, Chris C Hegna, Tyler B Cote, Brendan C Lyons, Shuai Gu, Carlos A PazSoldan In this work, we study the effects of the poloidal mode spectrum on 3D plasma response to externally applied magnetic perturbations (MPs) for DIIID plasmas as a function of triangularity. There is growing evidence that 2D plasma shaping plays a critical role in determining the plasma response to the MPs, limiting access to the ELM suppression regime for cases of sufficiently high or low triangularity. Starting from kinetic EFIT reconstructions, the SEGWAY framework provides perturbed equilibria for varied triangularity which in turn implies both direct changes in the poloidal harmonic coupling and indirect changes of the plasma profiles. The GPEC code then provides the plasma response to various MPs configurations, including variations of the applied poloidal mode spectrum as well as the perturbation amplitude. In order to fully understand the dependence of the plasma response as triangularity changes, it is necessary to characterize both the kink and tearing components of the plasma response. GPEC enables direct analysis of the kink response through 3D edge displacement calculations and spectral composition, and provides insight into the tearing response through the rational currents and Chirikov parameters from the effective island widths associated with these currents. 

PP11.00056: Strengthening the EFIT Solver for Burning Plasmas Torrin A Bechtel, Joseph T McClenaghan, Lang L Lao, Scott E Kruger, Jarrod Leddy, Samuel W Williams, Oscar Antepara, Alexei Pankin, William H Meyer, Steven A Sabbagh EFIT is one of the most extensively used equilibrium reconstruction code in the world. Although robust, EFIT plasma reconstructions will face new challenges in the burning plasma era. These include adapting to new operating regimes and relying on diagnostics that can survive in a harsher, radioactive environment. These stricter plasma control scenarios have motivated exploration of machine learning techniques to improve the quality of realtime equilibrium reconstructions. In order to train these new methods, a database of solutions is required which carefully tracks all constraints and fits performed by EFIT. To support these new developments, we are also improving the core GradShafranov solver. Changes include clearly separating devicespecific coding, improving code portability, developing a continuous development pipeline with automatic regression testing, and ensuring threadsafety in preparation for GPUdevelopments. Using extremelyportable OpenMP and OpenACC directives, we have been able to improve the performance of EFIT using GPU hardware. For the subroutines tested we have observed 40 times speedup across multiple GPU vendors. New options have also been added to assist with creation and analysis of database results. Access to these new techniques is made widely available with Gitlab hosted documentation [https://efitai.gitlab.io/efit/] and integration with the OMFIT framework [https://omfit.io] and existing workflows. 

PP11.00057: Overview and Progress of the EFITAI Project Scott E Kruger, Lang L Lao, Cihan Akcay, Torrin A Bechtel, Y. Q Liu, Joseph T McClenaghan, David Orozco, David P Schissel, Sterling P Smith, Xuan Sun, Eric Howell, Jarrod Leddy, Sandeep Madireddy, Jaehoon Koo, Samuel W Williams, Oscar Antepara, Alexei Pankin, Daniel Greenhouse The EFITAI project is creating a modern advanced equilibrium reconstruction code suitable for tokamak experiments and burning plasmas. Key elements of the EFITAI framework include: 1. improved optimization and data analysis capabilities using a MLenhanced Bayesian framework, 2. a ModelOrderReduction (MOR) version of the twodimensional (2D) Grad Shafranov equation solver using a neural network, and 3. a MOR version of threedimensional (3D) perturbed equilibrium reconstruction tool. The success of ML relies on large amounts of quality data. To enable this, we have created a large database of curated EFIT equilibria, which has required developing new curation techniques. We will present results of training EFITMOR on both magnetic and MSE reconstructions and discuss the applicability of EFITMOR for RT control and as initial conditions for EFITAI. The core solver, now called EFITAI, has been substantially improved in portability, performance, and testing, and is ready for use in production environments. Bayesian approaches using Gaussian Process techniques offer a way of accurately and efficiently providing the experimental inputs into EFITAI without the manual efforts required for removing bad data or avoiding overfitting. We include work on using new kernels and likelihood functions to improve accuracy of prior methods used within the fusion community. 

PP11.00058: EFITAI Database Creation and Storage for Machine Learning David Orozco, Scott E Kruger, Sterling P Smith, Lang L Lao, Cihan Akcay, Alexei Pankin, Torrin A Bechtel The desired application of Machine Learning (ML) and Data Science techniques to advance fusion research has motivated the need for high quality and open access databases. A EFITAI database has been assembled and curated: a collection of multiple equilibrium reconstructions for a variety of tokamak discharges. The database features the entirety of the 2019 DIIID campaign (approx. 2500 discharges) and contains 3 different types of EFIT reconstructions: 1. with magneticsonly constraints; 2. with magnetics + MSE(Motional Stark Effect) constraints; and 3. with OMFITautomated kinetic constraints (for a subset of shots). The database is currently being used for training of equilibrium reconstruction neural networks aimed at improving real time reconstructions. To incorporate Findable, Accessible, Interoperable, and Reusable (FAIR) data principles, the data was organized according to the ITER IMAS (Integrated Modeling and Analysis Suite) data schema (ontology), and then stored as selfdescriptive HDF5 binary files that will be made publicly available. This mapping to IMAS was carried out within the OMFIT framework [https://omfit.io], leveraging the functionalities of the OMAS library [https://gafusion.github.io/omas]. A collection of validation scripts ensures the quality of the training dataset by verifying that all necessary data is available, the equilibria have low GradShafranov equilibrium error, and the equilibrium reconstructions match experimental diagnostic signals. To track different versions of EFIT data generated for this database construction, this work utilized Git and the Opensource Data Version Control (DVC) system, which was developed intentionally for Data Science and Machine Learning projects. Work supported by the US Department of Energy DESC0021203, and DEFC0204ER54698. 

PP11.00059: MultiDiagnostic Classification of Alfvén Eigenmodes using Multimodal Machine Learning Andrew Rothstein, Azarakhsh Jalalvand, Alvin V Garcia, Max Austin, William W Heidbrink, Egemen Kolemen Realtime Machine Learning based control on tokamaks requires efficient data processing and featurization of highfrequency diagnostics. By using multiple highfrequency diagnostics, we can create a multimodal representation that yields a better classification of Alfvén Eigenmode (AE) activity. Previous work has used a database of 1000 labeled DIIID shots to look at individual Electron Cyclotron Emission (ECE) channels and classify four main types of AE activity: Lowfrequency modes (LFMs), Betainduced Alfvén eigenmodes (BAE), ReversedShear Alfvén eigenmodes (RSAE), and Toroidal Alfvén eigenmodes (TAE). 

PP11.00060: Electron Density Profile Regulation with Pellet Injection using Selftrigger Model Predictive Control Lixing Yang, Sai Tej Paruchuri, Eugenio Schuster Precise control of the plasma density, which will be crucial for nextgeneration tokamaks, can be achieved by both pellet injection (core actuation) and gas puffing (edge actuation). Successful regulation of the density profile demands considering the discretetime effect of pellet injection on the plasma dynamics during control synthesis by modeling both the size of the pellet and the injection rate. While gas puffing is a continuoustime process, actuation of the gas valves is prone to lags and delays that also must be incorporated into the model used for control synthesis. An observerbased, selftriggered, Model Predictive Control (MPC) strategy is developed in this work for active regulation of the density profile in tokamak plasmas. A controloriented model that integrates the discretetime nature of pellet injection is first developed. This model is the core not only of the MPC algorithm but also of an observer that aims to estimate and correct the potential error between the model prediction and the actual system. Moreover, the proposed MPC algorithm is based on a selftriggered scheme, which reduces computational efforts by solving the optimization problem only when necessary. The effectiveness of the proposed control scheme is demonstrated in higherdimensionality nonlinear simulations. 

PP11.00061: MFE: HEATING Session Chairs: 

PP11.00062: Timedomain modeling of plasma sheaths on RF antenna surfaces Thomas G Jenkins, David N Smithe, James R Myra, J. C Wright, Atul Kumar, Matthew J Poulos A nonlinear, multiparameter subgrid model for plasma sheaths [1] has been implemented in the Vorpal finitedifference timedomain code. Physically, such sheaths form near plasmamaterial interfaces; our focus will be on the plasmafacing surfaces of RF antennas (used for heating or profile control) in fusion devices. Large sheath potentials on antenna surfaces may arise due to rectification of the sheath by RF electromagnetic fields, and these high potentials are associated with undesired plasmasurface interactions such as sputtering (wherein highZ atoms are ejected from metallic antenna surfaces by bombarding ions falling through the sheath). 

PP11.00063: Reduced model for energetic ion tail formation by ion cyclotron range of frequency power Paul T Bonoli, Samuel Frank, Donald B Batchelor, Jungpyo Lee, Nicola Bertelli, David L Green, Francesca M Poli, John C Wright High fidelity simulation capabilities for selfconsistent minority ion heating, such as the combined AORSACQL3D model [1] tend to be impractical for implementation in time dependent integrated modeling frameworks because of their computational requirements. Here we revisit previous work [2, 3] where TORIC and CQL3D were coupled iteratively through a quasilinear diffusion coefficient formulated in the ion finite Larmor radius (FLR) limit in TORIC and through the nonthermal ion distribution from CQL3D. The TORIC solver employs a reduced model for the ion conductivity valid in the FLR limit, thus greatly reducing the computational requirements relative to AORSA. The Pythonbased Integrated Plasma Simulator (IPS) [4] will be used to couple TORIC and CQL3D thus providing the test of a workflow that could be used in an integrated modeling calculation. 

PP11.00064: Verifying raytracing/FokkerPlanck lowerhybrid current drive simulations with a new selfconsistent fullwave/FokkerPlanck model Samuel Frank, Jungpyo Lee, John C Wright, Ian Hutchinson, Paul T Bonoli The raytracing/FokkerPlanck (FP) simulations used to model lowerhybrid current drive (LHCD) often fail to reproduce experimental results, especially in experiments where the LHCD is weakly damped. Here, we determined whether or not "fullwave" effects, such as diffraction and interference, and breakdown of the raytracing approximation could explain the discrepancies seen between experiments and simulations. To do this, we performed some of the largest RF simulations ever (~2 million CPU hours), in which we directly solved the plasma Helmholtz equation for nonMaxwellian distribution functions in tokamak geometry using the TORLH fullwave fieldsolver coupled to the CQL3D FokkerPlanck solver. These simulations determined that raytracing accurately captures the features of the exact Helmholtz equation solution. Diffraction was quantified, and its effect was found to be smaller than other broadening mechanisms such as finite launcher spectral width. Breakdown of raytracing near cutoffs and caustics was also found to not result in important deviations from fullwave results. These results provide the first definitive verification of raytracing/FP simulations of LHCD used for tokamak reactor design against fullwave solutions. 

PP11.00065: Using the Stix Finite Element RF Code to Investigate the PowerPhasing Scan on Alcator CMod Christina Migliore, Mark L Stowell, John C Wright, Paul T Bonoli Ion cyclotron range of frequency (ICRF) power plays an important role in heating and current drive in fusion devices. However, experiments show that in the ICRF regime there is a formation of a radio frequency (RF) sheath at the material and antenna boundaries that influences sputtering and power dissipation. Methods to mitigate the formation of the RF sheath have been studied through the means of optimizing the ICRF antenna. A powerphasing scan was done on Alcator CMod in which the amount of power was changed on the inner versus outer two straps of the 4 strap antenna showed a minimization of enhanced potentials and impurities around fractions between ~0.5 to 0.8. New capabilities in the realm of representing the RF sheath numerically now allow for these kind of experiments to be simulated. Given the size of the sheath relative to the scale of the device, it can be approximated as a boundary condition (BC). A new parallelized coldplasma wave equation solver called Stix implements a nonlinear sheath impedance model BC formulated by J. Myra 2015 ~\footnote{J. Myra, et al., Phys. Plasmas 22, 062507 (2015)} through the method of finite elements in pseudo2D using the MFEM library [http://mfem.org]. This research will discuss the results of Stix's rectified potential values simulating this powerphasing scan done on Alcator CMod. 

PP11.00066: Development progress for a farSOL anisotropic fluid transport solver Rhea L Barnett, Mark L Stowell, Jeremy D Lore, David L Green, Lin Mu, Xiaozhe Hu, Dylan Copeland Fluid transport in fusion plasmas can be highly anisotropic due to the strong confining magnetic field, with diffusion coefficients D_{}/D⟂ ranging from 10^{3} to 10^{9}. Although a field aligned mesh can be used to avoid error pollution in the crossfield direction, in the far scrapeoff layer (SOL) a geometry conforming grid is required to resolve complicated radio frequency (RF) antenna structures. A new fluid plasma solver MAPS (MFEM Anisotropic Plasma Solver) is being developed to simulate the farSOL plasma using unstructured meshes, where high order finite elements are used to address the highly anisotropic behaviour. The ion and neutral continuity, ion parallel momentum, and the ion and electron temperature equations are solved using the Symmetric Interior Penalty Discontinuous Galerkin (SIPG) method with arbitrary order. The time integration uses a highorder singly diagonal RungeKutta (SDIRK) method with PID controlled timestep selection. Novel preconditioning methods have also been implemented for solving the linear system in highly anisotropic cases. Initial benchmarking efforts for the MAPS code in 1 and 2D will be presented. We will also discuss future applications of the MAPS code, including coupling to an MFEMbased RF solver to investigate issues in the antenna nearfield region of the plasma. 

PP11.00067: RAYS, a simplified code for exploration of design options for a modern ray tracing code Donald B Batchelor, Mark R Cianciosa Ray tracing is a method for obtaining approximate solutions to the wave equation in nonuniform media which, if applicable, can be orders of magnitude less computationally demanding than direct solution of the wave equation. While there have been great strides in full wave solution of RF fields in fusion relevant plasmas, geometrical optics (or ray tracing) is still an important tool for analysis of experiments and will continue to be needed in the workflows of wholedevice models. The present code is a complete rewrite and considerable simplification of the venerable RAYS code. The primary objectives are 1) to provide flexibility for exploration of different code organization strategies, modern programming paradigms, and modern computer architectures, and 2) to build in modularity at every level so as to enable A/B comparisons between different implementations of kernel functions, such as differential equation solvers, equilibrium models, dispersion relation models and approaches to generating the Hamiltonian derivatives. Criteria we will be targeting include: ease of use, flexibility  easy support for multiple geometries, dispersion models, equilibrium models, extensibility  ease of adding new features without disturbing existing ones, verifiability  ease of comparison with simple situations for which rigorous answers are available, speed and accuracy. We will present comparisons between different implementations of ODE solvers, derivative computation methods, and equilibrium models. 

PP11.00068: A new RF Ray Tracing code using auto differentiation Mark R Cianciosa, Donald B Batchelor To design a fusion pilot plant or simulate an ITER pulse, a highfidelity, wholedevice simulation capability including RF heating is needed. Ray tracing is a method to determine to deposition location of RF power or the originating location of the emission in a plasma medium. Adapting legacy codes to modern HPC systems is challenging due to GPU incompatibility and a lack of abstraction. Errors transcribing derivatives of complex dispersion relations pose a challenge when attempting to extend existing or develop new codes. Auto differentiation technology eliminates this error and has emerged as a preferred method for abstracting backend resources from front end equations in machine learning applications. We present a new ray tracing code built from a pure C++ auto differentiation framework. This approach results in a modern extensible code that can adapt to current and future HPC systems and embed within other codes. New physics is added by simply providing expressions for the dispersion relation and equilibria. The framework then performs symbolic computations to convert these into optimized expressions for the differential equations that can be solved to trace a ray. This new ray tracer shall be validated against expected analytic expressions for simple dispersions functions. 

PP11.00069: Analytical and numerical modeling of RF sheath boundaries in ICRF heating experiments Matthew J Poulos, Nicola Bertelli, Syun'ichi Shiraiwa Sheath potentials formed on the material surfaces of plasma facing components are dramatically enhanced by the application of radiofrequency (RF) power in the ioncyclotron (IC) range of frequencies. The resulting rectified sheath potentials lead to several important effects such as the sputtering of impurities from the wall material and the formation of convective cells. An analytical model is presented to describe the selfconsistent enhancement of the sheath potential together with the global electromagnetic field sourced by an ICRF antenna. Explicit formulas are obtained, yielding the sheath voltage in the antenna near field for varying input power. Nonlinear features associated with RF sheathplasma interactions are elucidated and their importance for experimental regimes is assessed. DC effects are incorporated into the model and their importance in sheath regulation is highlighted. Utilizing the finite element code PetraM, highfidelity modeling of RF sheath rectification due to ICRF in the WEST tokamak is conducted, including realistic antenna geometry and plasma parameters. 

PP11.00070: Nonlinear RF rectified sheath based on magnetic scalar potentials in PetraM Syun'ichi Shiraiwa, Nicola Bertelli A new formulation to describe the RF induced radiofrequency sheath boundary, which is suitable for a large 3D simulation, is discussed. We start from linear asymptotic, socalled thick sheath, model. In this limit, B_{n}=0 and D_{n} = 0, where B_{n} and D_{n} are normal component of magnetic field and displacement current. Therefore, it is closely related to the DB boundary recently discussed in other fields. In order to use this nonstandard form of boundary condition in a regular RF finite element method based on the H(curl) edge elements, we introduce a magnetic potential to describe curlfree vector field on the sheathplasma boundary, which is then used to apply an inhomogenous Neuman boundary condition. The sheath potential is obtained by integrating a Poisson equation. This approach is further extended to a nonlinear sheath regime, which is characterized by nonzero D_{n}. Since the sheath potential is already obtained, D_{n }is readily computed using the Ohm’s law and the nonlinear sheath impedance (Myra PoP 2017). This D_{n }is fed to RF solver through another magnetic scalar potential which is used to define the divergencefree component of magnetic field on the sheathplasma boundary. An actual implementation in PetraM RF solver and detail is discussed in the poster presentation. 

PP11.00071: Benchmark of the linear and nonlinear RF rectified sheath boundary conditions implemented in the PetraM FEM platform with the previous results obtained with the rfSOL code Nicola Bertelli, Syun'ichi Shiraiwa, Matthew J Poulos, James R Myra The ICRF antenna and the plasma waves propagating in the SOL can drive several hundredvolt rectified sheath potentials at the plasma material interfaces. These potentials can cause erosion and sputtering of high Zimpurities, which may contaminate the core plasma leading to radiative collapse. For this reason, the implementation of the RF sheath boundary conditions (BC) in the RF solvers is a crucial step to improve ICRF modeling. Linear and nonlinear RF sheath BCs have been recently implemented in the PetraM FEM platform and a benchmark activity is presented in this work with the previous results obtained with the rfSOL code. We focus on the 2D cases with both 90degree angle and oblique angle between the background magnetic field and the surface. Moreover, a comparison of the shaped wall on the RF sheath effects is also performed investigating the impact of the variation of the angle between the magnetic field and the surface. Finally, a comparison with the rfSOL code of a 2D circular tokamak crosssection with a limiter protrusion is also presented showing the role of the of the conversion from fast to slow waves on the sheaths. In all cases analyzed, an excellent agreement is found in the nonlinear regimes between the two models. 

PP11.00072: Results from integrated modeling of RFinduced ponderomotive effects on edge/SOL transport David N Smithe, Thomas G Jenkins, Maxim Umansky, Andris M Dimits, Thomas D Rognlien Fast timescale RF fields in the scrapeoff layer result in slow timescale ponderomotive forces which can perturb the local density profiles near the RF antenna structures. We have coupled the Vorpal (FDTD EM+plasma solver) and UEDGE (2D edge plasma transport) codes in a manner enabling numerical study of these ponderomotive terms and their effects on edge/SOL transport and profiles, and present results from studies with the coupled codes. 

PP11.00073: Noisefree largetimestep RF plasma modeling with the spider stencil Carl Bauer, John R Cary, Thomas G Jenkins, David N Smithe We present an explicit (no matrix inversions) finitedifference timedomain 

PP11.00074: An Efficient and Effective FEM Solver for Diffusion Equation with Strong Anisotropy David L Green, Xiaozhe Hu, Jeremy D Lore, Lin Mu, Mark L Stowell The Diffusion equation with strong anisotropy has broad applications. In this project, we discuss numerical solution of diffusion equations with strong anisotropy on meshes not aligned with the anisotropic vector field, focusing on application to magnetic confinement fusion. In order to resolve the numerical pollution for simulations on a nonanisotropyaligned mesh and reduce the associated high computational cost, we developed a highorder discontinuous Galerkin scheme with an efficient preconditioner. The auxiliary space preconditioning framework is designed by employing a continuous finite element space as the auxiliary space for the discontinuous finite element space. An effective line smoother that can mitigate the highfrequency error perpendicular to the magnetic field has been designed by a graphbased approach to pick the line smoother that is approximately perpendicular to the vector fields when the mesh does not align with anisotropy. Numerical experiments for several benchmark problems are presented to validate the effectiveness and robustness. 

PP11.00075: FullWave: Hybriditerative full wave solver with implicit time stepping algorithm* Nikolai Barov, Liangji Zhao, JinSoo Kim FARTECH, Inc. has been developing the FullWave code, a hybriditerative full wave solver, to model rf waves in hot plasmas including the nonlocal hot plasma responses. The code uses configuration space to discretize wave equations and calculate the nonlocal hot plasma dielectric response[1]. Plasma dielectric responses are calculated without approximations by solving the linearized Vlasov equation using the method of characteristics. Our recently developed hybrid iterative algorithm[1] significantly increases spatial resolution of the RF fields when compared with other stateofart full wave codes based on direct solvers. FullWave has successfully simulated ECRH waves in tokamaks[2]. To extend the capability to lower frequencies such as LowerHybrid and Helicon waves, an implicit algorithm using CrankNicolson time stepping is being implemented. We will present FullWave 1D and 2D simulation results for Lower Hybrid and Helicon waves. 
Author not Attending 
PP11.00076: Sensitivity of Synthetic Phase Contrast Imaging Measurements to the Parallel Wavenumber Spectrum of Helicon Waves at DIIID Severin S Denk, Cornwall H Lau, Alessandro Marinoni, Robert I Pinsker, Miklos Porkolab, Jon C Rost Comprehensive fullwave modeling has been performed in preparation for experiments at the DIIID tokamak with the goal of validating theoretical predictions for helicon waves [1] via measurements from a phase contrast imaging (PCI) diagnostic [2]. The workflow consists of a 2D, highlyresolved, cold plasma, finite element model covering the plasma edge, and 2D calculations of the plasma core with the All ORders Spectral Algorithm (AORSA) full wave code [2], the stateoftheart model for predicting power absorption and current drive for helicon waves. To predict PCI measurements the helicon path has to be resolved in 3D, which is achieved by stacking calculations of up to 30 toroidal mode numbers. The helicon path is sensitive to the coupled toroidal mode number spectrum of the antenna, which is an area of active study. Our modeling shows that the PCI measurements will provide an indirect measurement of the antenna spectrum. 

PP11.00077: Radiation pressure of radio frequency waves on plasma turbulence Abhay K Ram, Kyriakos Hizanidis It has previously been shown that radio frequency (RF) electromagnetic waves are partially scattered when propagating through density fluctuations in the edge region of fusion devices. The scattering affects the flow of wave energy to the plasma core. Conversely, the radiation pressure due to the RF waves can affect plasma turbulence. We determine the radiation force on incoherent fluctuations using Kirchhoff's tangent plane approximation and Fresneltype scattering analysis. The force on a coherent filamentary structure is determined using the Maxwell stress tensor. The filament is assumed to be cylindrical with its axis aligned along the ambient magnetic field. The two approaches share similar physical outcomes. For waves in the electron cyclotron range of frequencies, filaments with densities higher than the background density are pulled in towards the RF source, while those with lower densities are pushed away. The radiation force is large enough to impact the motion of filaments, and could possibly be observed in experiments. This suggests the possibility of utilizing RF waves to modify some aspects of edge turbulence. 

PP11.00078: Machine learning models for inverse and lateral problems of lower hybrid current drive Gregory M Wallace, Zhe Bai, Talita Perciano, Nicola Bertelli, Syun'ichi Shiraiwa, Wes Bethel, John C Wright This presentation describes the development of machine learning models to solve the inverse and lateral problems for lower hybrid current drive (LHCD) simulations. The inverse problem in physics involves solving for the set of causal factors that result in a set of observations. Recent work [Wallace et al, JPP 2022] has shown that machine learning surrogate models can accurately reproduce the current density and power absorption profiles calculated by GENRAY/CQL3D (a suite of raytracing/Fokker Planck solvers) given a set of 0D input parameters describing the plasma shape, temperature, density, and LH waves based on a database of simulations. In the inverse problem context, the observations are current density and power absorption profiles calculated by GENRAY/CQL3D, and the causal factors are the input parameters to the codes. An analogous problem, which we call the lateral problem, relates one output of GENRAY/CQL3D (e.g. the hard Xray emission synthetic diagnostic) to another output (e.g. the current density profile). This presentation focuses on the application of MLbased models to the inverse and lateral problems in situations where analytic or iterative solutions are impractical. 

PP11.00079: New injection scheme and experimental results for improved heating efficiency of electron cyclotron heating in the LHD Masaki Nishiura, Ryoma Yanai, Toru I Tsujimura, Hiroe Igami, Yasuo Yoshimura, Naoki Kenmochi, Hiromi Takahashi, Yoshinori Mizuno, Toshiki Takeuchi, Shin Kubo We proposed a new electron cyclotron heating (ECH) system injected from a high field side in the Large Helical Device (LHD). We expect that a highly reliable and functional ECH system enhances plasma parameters and performs various physics experiments. The conventional EC beams cause the refraction in plasmas because of an oblique injection against magnetic fields [1], even if the electron density is below the cutoff density. The new method suppresses the refraction effect by directing the injected EC beam normal to the magnetic surfaces of the LHD. The suppression is confirmed by a raytracing calculation (TRAVIS code). We have designed and installed the new injection system in the LHD. From the plasma experiment, the straight propagation of the EC wave from the new injection system leads to the effective heating on the magnetic axis, even though the 77 GHz EC wave from the existing injection system refracts in the same shot. However, the new system suffers from the reflected wave to the gyrotron. In the present experiment, the gyrotron's output power and pulse length are limited so that the oscillation does not stop. We will discuss the solution for the next campaign. 

PP11.00080: Startup of tokamak plasmas using electron cyclotron waves – theory and modelling. Panagiotis C Papagiannis, Panagiotis C Papagiannis, George E Anastassiou, Christos Tsironis, Kyriakos Hizanidis, Abhay K Ram Electron cyclotron wave power is being used for initiating neutral gas ionization during the startup phase of ITER. The EC field is launched as a spatially localized Gaussian beam propagating through the gas. Stray electrons, energized by their cyclotron resonance interaction with the beam, impact ionize gas atoms and molecules creating additional electrons. When a sufficient number of electrons are present, an avalanche process is initiated giving rise to a partially ionized plasma. The lead up to the avalanche phase is modelled by the nonlinear interaction of seed electrons with the beam in the presence of a static, homogeneous magnetic field. The analytical crosssections for impact ionization and elastic electronneutral collisions are included in the simulations as we follow the dynamics of each electron. The time required to trigger an avalanche and also the electron density growth rate, depend on the beam power, its spatial width and polarization, the direction of propagation, and the pressure of the neutral gas. We will present detailed results that follow from our studies. 

PP11.00081: Noninductive current drive by DC helicity injection via magnetic flux rope merging in VEST JongYoon Park, Taekyoung Kim, Taehee Eom, Y.S. Hwang The Local Helicity Injection (LHI) technique is a noninductive startup and currentdrive method for Spherical Torus that deals with the limitedcentralinductiveflux swing. The recent LHI technique begins by discharging 3D helical magnetic flux ropes. To use the LHI technique as a startup, the seed plasma should be formed by 3D magnetic flux ropes. With this seed plasma, the plasma current can be driven further via LHI and the Taylor relaxation process that convert the localized injected helicity into global helicity and macroscopic plasma current. In achieving the seed plasma from 3D helical flux ropes, it has been suggested by NIMROD simulation that the merging of flux ropes undergoing external kink mode plays an important role. However, experimental conditions for both the merging and LHI have yet to be suggested and validated, resulting in the possibility of operational failure. Here, the two magnetic field conditions are suggested for successful LHI operation. The total vacuum magnetic field strength is the key to the merging of flux ropes, resulting in a limited radial operating range in ST for a given discharge power. After forming seed plasma via the merging of flux ropes, the proper vertical field is the key to injecting helicity as it adjusts the proximity between seed plasma and flux ropes. Only when these two conditions are met, a peaked radial profile of ion temperature is observed with noninductively driven plasma current, which means that magnetic reconnection is a crucial component of helicity injection with high proximity. 

PP11.00082: Wave Coupling and Propagation from the Helicon Antenna in LAPD Joshua J Larson, Bart Van Compernolle, Robert I Pinsker, Troy Carter Lowpower (~100 W) ‘helicon’ (fast waves in the lower hybrid range of frequencies) experiments were conducted on the LArge Plasma Device (LAPD) at UCLA to study wave propagation and coupling properties with a 10element combline traveling wave antenna. The antenna was constructed using modules from the DIIID lowpower Helicon antenna. The parameter space explored included: background magnetic field (0.7 – 2 kG), plasma density (~10^{10} – 10^{12} cm^{3}), imposed n_{} (2 – 4), and launcher angle with respect to B_{0} (0 – 45 degrees). Across the range of densities there are times during the discharge where both the fast (helicon) and slow (‘lower hybrid wave’) branches may simultaneously propagate in the plasma core. Propagating waves are observed in locations and times during the discharge that agree with the expected wave dispersion relation. These experiments verified important properties of the antenna design. Unidirectional launch along the long axis of the machine and control of the parallel wavelength of the waves propagating in the plasma are demonstrated. 

PP11.00083: Behavior of RF sheath admittance across Ion Cyclotron Resonance analyzed with fluid theory and largescale ParticleinCell simulations Mikhail Rezazadeh, James R Myra, Logan Meredith, Davide Curreli The next generation of tokamaks (SPARC, ARC, FNSF, DEMO) and several current tokamaks (WEST, etc.) operate with ICRHonly as auxiliary heating technique, because it transfers power directly to the ions, and it involves the cheapest RadioFrequency (RF) actuators. However, RF sheaths are associated with increased levels of impurities and other drawbacks such as hotspot formation. RF sheaths not only form on the ICRH antenna itself, but on farfield electrically connected surfaces. In this study, we highlight an interesting case where the cyclotron frequency of ions is on par with the frequency of an RF sheath in an oblique magnetic case. Due to the 1/R scaling of the magnetic field in a tokamak, such cases are possible in front of material surfaces placed in proximity of the radial location of the ICRH resonance. The problem has been analyzed using largescale ParticleinCell simulations using the hPIC2 code and semianalytical fluid models. We found that the combination of RF sheath rectification and cyclotron resonance generate trends of the RF sheath impedance analogous to the classical driven damped harmonic oscillator, where charge density damps ion admittance. We show that the resulting resonance can lead to increased ion flux at the wall and localized material sputtering. 

PP11.00084: MFE: TRANSPORT, TURBULENCE Session Chairs: 

PP11.00085: Flow topology and Lagrangian conditional statistics in edge plasma turbulence Benjamin Kadoch, Diego DelCastilloNegrete, Wouter Bos, Kai Schneider To understand the role of coherent structures (e.g., vortices, "blobs", and zonal flows) in the plasma edge, we present a study of the relationship between flow topology and Lagrangian statistics in the Hasegawa–Wakatani model. The topology is characterized using the Okubo–Weiss criterion that splits the flow into elliptical (strong vorticity), hyperbolic (strong deformation), and intermediate (transition) regions. The Lagrangian statistics is computed by tracking ensembles of particles over hundreds of eddy turnover times in statistically stationary turbulence. Particle "trapping" and "flights", induced by coherent structures and known to play a key role in anomalous transport, are quantified using residence times statistics. It is shown that the probability density functions (pdfs) of the residence time conditioned to elliptic and hyperbolic regions exhibit algebraic decaying tails. However, in the intermediate regions the pdf exhibits exponentially decay. The pdfs of the Lagrangian velocity, acceleration, and density fluctuations, conditioned to the flow topology, are also computed along with the density flux spectrum, which characterizes the contributions of different length scales. 

PP11.00086: Coupled continuum gyrokinetic and kinetic neutral simulations in shaped scrapeoff layer scenarios Tess Bernard, Federico D Halpern, Manaure Francisquez, Noah R Mandell, James Juno, Gregory W Hammett, Ammar Hakim Interactions between the plasma and neutral particles play a crucial role in determining the exhaust characteristics of tokamak plasmas, and magnetic shaping in the scrapeoff layer (SOL) can have important effects as well. Thus, the coupling of a continuum fullf gyrokinetic turbulence model with a 6D continuum model for kinetic neutrals in the Gkeyll code has been extended to model shaped SOL scenarios. The neutral distribution function is evolved in nonorthogonal fieldline following coordinates for the physical space and orthogonal coordinates for the velocity space. Geometric terms are applied via the streaming term in the Vlasov equation. This coupling is presented in seeded blob simulations with DIIID SOL parameters. Magnetic shear and flux expansion decrease radial blob velocities by increasing poloidal blob velocities and shearing the blobs apart more quickly. Including neutral interactions can also decrease radial blob velocities while increasing blob coherence. Thus, it is important to include both magnetic geometry and neutral interactions to accurately model blob dynamics in gyrokinetic SOL simulations. 

PP11.00087: Topology analysis of electromagnetic fields during plasma startup in tokamaks MinGu Yoo, YongSu Na At plasma startup phase, external electromagnetic fields are applied in a tokamak to ionize prefilled neutral gas molecules, resulting in an electron avalanche. Based on the traditional Townsend avalanche theory, various methods have been developed to evaluate the quality of external electromagnetic fields. However, it was recently revealed (Yoo 2018 Nat. Commun. 9 3523) that the avalanche process is completely different from the Townsend avalanche because a strong electric field generated by the plasma spacecharge reduces the avalanche growth rate and causes the dominant turbulent E×B transport. Considering the important selfgenerated electric field effects, we propose a novel topology analysis method (Yoo 2022 PPCF 64 054008) that can very easily predict the overall plasma evolution in complex electromagnetic structures. The topology analysis method is verified with particle simulation results for various electromagnetic configurations. The main plasma locations observed in simulations are successfully predicted by the topology analysis. The topology analysis method will be of great help in designing reliable startup scenarios in ITER and future fusion reactors. 

PP11.00088: Transition from ITG to MTM linear instabilities near pedestals of parameterized Hmode plasmas Joseph T McClenaghan, Tim Slendebroek, Gary M Staebler, Brian Grierson, Orso M Meneghini, Sterling P Smith, Galina Avdeeva, Kathreen E Thome, Lang L Lao, Jeff Candy, Walter Guttenfelder Investigation of linear gyrokinetic ionscale (k_{θ }ρ_{s} =0.3) most unstable modes near pedestals of parameterized Hmode plasmas using CGYRO finds a transition from Ion Temperature Gradient (ITG) to microtearing mode (MTM) dominance is predicted as the density is increased to slightly above the Greenwald density limit for DIIID sized tokamak. This transition (n_{MTM}) has a weak dependence on radial location in the region near the top of the pedestal (ρ=0.70.9), which allows probing single radii to examine the scaling of n_{MTM} with global parameters. The critical n_{MTM} is found to scale with plasma current. Additionally, increasing the minor radius by decreasing the aspect ratio and increasing the major radius are found to reduce n_{MTM}. However, any relationship between n_{MTM }and density limit physics remains unclear as n_{MTM} increases relative to the Greenwald density with larger minor radius and with larger magnetic field, suggesting the MTM transport may be less important for a reactor. Additionally, n_{MTM} is sensitive to the pedestal temperature, local electron and ion gradients, and the current profile. The stability of MTMs is then examined in DIIID and NSTX Hmode experiments. It is found that MTMs are predicted to become unstable deeper into the pedestal top on DIIID when the density is increased and energy confinement is reduced relative to empirical scaling expectations, supporting the results of the parametrized study. 

PP11.00089: A new flexible gyrofluid linear eigensolver Gary M Staebler, Emily A Belli, Jeff Candy Gyrofluid equations are velocity space moments of the gyrokinetic equation. Special gyroLandaufluid closures have been developed to include the damping due to kinetic resonances fit to the collisionless local response functions. This damping allows for accurate linear eigenmodes to be computed with a relatively low number of velocity space moments compared to gyrokinetic codes. An analysis of the published gyroLandaufluid closure schemes finds that the Onsager symmetries of the resulting quasilinear fluxes are not preserved. Onsager symmetry guarantees that the matrix of diffusivities is positive definite, an important property for a transport model. A new, simpler scheme for regularizing the gyrofluid equations that preserves the Onsager symmetry and is scalable to higher velocity space moments has been developed. Linear eigenmodes from the new system of equations are verified with gyrokinetic results. The new linear gyrofluid eigensolver (GFS) will be used to extend the TGLF quasilinear transport model so that it can compute the energy and momentum fluxes due to parallel magnetic fluctuations, completing the transport matrix. The GFS equations do not use a bounce average approximation. The GFS equations are fully electromagnetic, with general flux surface magnetic geometry, pitch angle scattering for electron collisions and subsonic equilibrium rotation. The Onsager symmetries enable output of the offdiagonal contributions to the fluxes separating diffusion and convection terms. This will be particularly helpful to multiion species plasmas transport studies. 

PP11.00090: Progress on Transport Studies in the Spherical Tokamak (ST) Pi3 at General Fusion Inc Celso Ribeiro, Russ Ivanov, Carl Dunela, Filiberto Braglia, Ivan Khalzov, William Young, Patrick Carle, Akbar Rohollahi, Xiande Feng, Kelly Epp, Adrian Wong, Kathryn Leci, Aaron Froese, Ryan Zindler, Daymon Krotez, Calum Macdonald, Matt Herunter, Leopoldo Carbajal, Alexander D Mossman, Michel Laberge, Neeraj Kumar, Joshua Hawke The ST Pi3 is a mediumsize device in operation at General Fusion Inc. aiming to guide the ST Pi4 (currently under construction) and the Fusion Demonstration Plant (FDP) to be constructed at the Culham Laboratory site, UK[1]. 

PP11.00091: Investigation of Temperature Screening of Neoclassical Impurity Transport in High Rotational Tokamak Plasmas Hyeonjun Lee, Emily A Belli, Jeff Candy, Jungpyo Lee A recent study [1] shows that the temperature screening of impurity neoclassical transport depends on the impurity collisionality nonmonotonically, which is verified numerically and analytically. This tendency is determined dominantly by the impurity particle flux component proportional to the main ion temperature gradient, and the component coefficient is sensitive to inverse aspect ratio [1] and toroidal rotation speed [2]. The analytical models of the coefficient of the main ion temperature gradient were derived under the assumptions such as low rotational plasmas [1, 3] or small inverse aspect ratio [3]. In this work, we investigate the analytical model for nonmonotonic dependency of the coefficient on the collisionality by extending the limit to the highrotational plasmas and compare the results with NEO [34] simulations. The neoclassical impurity transport model is applied to interpret the KSTAR Tungsten impurity measurements [2]. 

PP11.00092: Effect of turbulence on impurity transport in the edge and SOL region Shrish Raj, Nirmal Bisai, Vijay Shankar, Abhijit Sen


PP11.00093: Effect of electrode biasing on radial particle and energy fluxes in the edge and SOL regions Vijay Shankar, Nirmal Bisai, Shrish Raj, Abhijit Sen Electrode biasing (EB) can modify the plasma turbulence in the edge and SOL regions in a tokamak. This can influence a number of transport processes such as particle and heat exhausts, material recycling etc., that can impact the particle and energy confinement time as well as the heat load on the limiter/divertor plates. We report on numerical simulation studies done in the presence of positive as well as negative EB in the edge region . The simulation results show a reduction of the radial particle and energy fluxes at all the radial positions. The positive biasing increases the fluctuation level of the density and electron temperature but the particle and energy fluxes decrease. We have estimated the fluctuation levels as a function of electric field shear in the presence of positive and negative biasing. We have also investigated the SOL layer thickness as a function of the biasing voltages and calculated the maximum particle and energy densities on the limiter/divertor plates. Such data have been further used to estimate the particle and energy loads (in the parallel direction) on the material plates in the SOL as a function of the radial electric field shear. As these fluxes depend on the blob fraction , therefore, this fraction has been calculated as a function of the radial electric shear obtained from these EB simulations. The fluxes behave nonlinearly with shear. The numerical data have been used to estimate the poloidal wave vector (k_{y}) spectra and it is found that EB shifts the turbulence towards lower k_{y }modes. These results have been correlated with the blob fraction as a function of EB and radial electric field shear. 

PP11.00094: Theory and simulations of microtearing mode using BOUT++ code Kaixuan kaixuan, Xueqiao Xu, Ben Zhu, Nami Li, Chao Dong Microtearing mode (MTM) has been suggested as one of the potential driving mechanisms crucial for pedestal plasma turbulence transport [1]. Recently, the classical Hazeltine electric conductivity model [2] has been extended to include radial variation by Larakers et.al. [3]. We revisited this derivation, derived dispersion relations in various limiting cases, and compared them with different MTM models in the literature. We found that the general electric conductivity reduces to Drake model [4] in both the collisional limit and the semicollisional limit limits with a Lorentz gas collision operator. We also found that if the electron inertia term is retained in Hassam’s fluid MTM model [5], the result is consistent with Drake and Larakers models in the collisional limit. Based on extended Hassam model, the BOUT++ sixfieldtwo fluid model has been extended to include the MTM. The preliminary fluid simulation results with MTM will be presented. 

PP11.00095: Gyrokinetic study of transport in the ScrapeOff Layer with SPARCrelevant parameters Miguel Calvo Carrera, Noah R Mandell, Nuno F Loureiro As fusion devices approach reactorscale conditions, it is crucial to manage the heat poured into its walls and divertor. Due to the high temperatures of burning plasmas, fluid theory becomes unreliable not only in the core, but also in boundary plasmas. For this reason, firstprinciples gyrokinetic theory and modeling is important for understanding turbulent transport from the core to the edge and scrapeoff layer (SOL) of burningplasma reactors. This poster will present results obtained using the gyrokinetic code Gkeyll to perform simulations in a simplemodel helical geometry with SPARC's characteristic magnetic field, temperature and density. In particular, we have studied the evolution of the temperature and density profiles and the distribution of the heat flux along the divertor when we vary the pitch angle of magnetic field lines in the SOL. These profiles are determined by the competition of transport across the field lines, dominated by the interchange instability and stabilized by sheath and FLR effects; versus the transport along the field lines, determined by the time that thermal particles take to reach the divertor plates from the midplane. Analytical work and numerical simulations support the conclusion that by decreasing the pitch angle, the resulting increase in the connection length will reduce the stabilization from sheath effects. This makes interchangedriven transport more predominant, resulting in broader profiles and a larger pressure gradient scale length. 

PP11.00096: Diagnosing Magnetic Reconnection in Tokamak Scrapeoff Layer Simulations Juan Manuel Lazaro, Nuno F Loureiro, Noah R Mandell Magnetic reconnection in the scrapeoff layer (SOL) may have several impacts on the operation of a tokamak, such as increased plasma flows and changes to the magnetic topology. In this work, we analyze data from the Gkeyll electromagnetic gyrokinetic code, using simulations that model the SOL of the National Spherical Torus Experiment at high beta parameters. These simulations exhibit magnetic fluctuations δB_{⊥}/B ∼ 1%, making this an interesting regime to look for indicators and effects of magnetic reconnection. Among these indicators is a locally large current, which allows the frozen flux constraint of ideal magnetohydrodynamics to be broken. Similarly, we look for regions of β_{kin} ∼ 1, where β_{kin} is the ratio between the kinetic energy of E×B flows in the plasma and the energy stored in B_{⊥} fluctuations. If reconnection does happen at these sites, this would indicate a large energetic impact. Finally, we look for saddle points in the parallel magnetic vector potential A_{∥}, which correspond to the characteristic Xpoint magnetic topology in the perpendicular plane. Reassuringly, many of these indicator conditions highlight similar regions and times which will allow automated detection of reconnection in the SOL. This is also the first step in assessing the role of reconnection in SOL turbulence and transport. 

PP11.00097: GX: a GPUnative gyrokinetic turbulence code for tokamaks and stellarators Noah R Mandell, William D Dorland, Ian G Abel, Nathaniel Barbour, Braden Buck, Rahul Gaur, Patrick S Kim, Tony Qian The GX code is a GPUnative radiallylocal deltaf gyrokinetic turbulence code that uses pseudospectral methods in both configuration (Fourier) and velocity (HermiteLaguerre) space. At high resolution GX is a standard gyrokinetic code, but it can also be successfully run at low resolution (particularly in velocity space) in lieu of uncontrolled approximations, since in the lowest velocityresolution limit the system corresponds to established gyrofluid models. We demonstrate the robust convergence properties of the model via nonlinear benchmarks against established gyrokinetic codes in both tokamak and stellarator geometries. Coupled with efficient use of GPU computing architectures, GX produces a performance advantage over other gyrokinetic approaches in many cases. GX has been coupled to the Trinity transport solver, which uses a multiscale approach to solve for timedependent radial profiles of density, temperature, etc. Turbulent fluxes are obtained from GX calculations, neoclassical fluxes are obtained from a drift kinetic solver, and external sources and edge boundary conditions are supplied by the user. Using the Trinity+GX system, we demonstrate the ability to solve for the timedependent evolution of core fusion reactor profiles without resorting to reduced models. 

PP11.00098: Linear stability of ultrahighbeta (beta ~ 1) equilibria Rahul Gaur, William D Dorland, Ian G Abel The power density of tokamaks scales with the plasma beta as beta^2 which makes highbeta operation an attractive choice for future highpower tokamak devices. beta ~ 1 configurations have previously [Hsu. et al. PoP 96] been explored by solving the GradShafranov equation in the limit epsilon/(beta q^2) << 1. We extend this by obtaining exact global equilibria numerically. However, various instabilities may limit the utility of such equilibria. To that end, we present an infiniten, idealballooning and linear gyrokinetic analysis of various equilibria for tokamaks. We find that alpha_MHD >> 1 is large enough to make them "secondstable" to the ideal ballooning mode. Next, we examine their stability to the two major sources of electrostatic turbulence: ITG and TEM, using the initial value code GS2. To understand the trend with a changing beta, we compare these equilibria with an intermediatebeta (beta~0.1) and a lowbeta (beta~0.01) equilibrium at two different radial locations: the inner core (Normalized radius rho = 0.5) and the outer core (rho = 0.8) for two different triangularities: delta = 0.4 and delta = 0.4. We find that the ultrahighbeta equilibria are stable to both the ITG and TEM over a wide range of gradient scale lengths (R/L_T and R/L_n). Next, we perform a linear electromagnetic study of all the nominal local equilibria to explore the possible effects of Kinetic Ballooning Modes (KBMs). We find that all the highbeta equilibria become more unstable than their lowbeta counterparts in the inner core but turn out to be much more stable than both the low or intermediate beta equilibria in the outer core. We also find that the negativetriangularity highbeta equilibria do not show any signs of KBMs. Using a gyrokinetic code for linear electromagnetic studies can be relatively expensive. Therefore, as an alternative, we numerically solve the KBM equations of Tang et al. as a reduced model for KBMs and compare the results with GS2. 

PP11.00099: MachineLearning Closures of the Kinetic Moment Hierarchy in the Context of Landau Damping Nathaniel Barbour, William D Dorland, Noah R Mandell, Rahul Gaur, Madox C McGraeMenge, Jacob R Pierce, Mark Almanza, Jason Chou, E. Paulo Alves, Frederico Fiuza, Nuno F Loureiro A common approach to understanding microscale dynamics in fusion plasmas is to study the time evolution of the kinetic distribution function. Recently, the GyrokinetX (GX) code demonstrated an efficient method of analysis in the gyrokinetic limit [1]. By taking fluid moments of the fundamental equations (integrating the fundamental equations over velocity space with orthonormal basis weights), it is possible to derive a hierarchy of coupled equations with an attractive feature: nearlocality in velocity space. We aim to improve the fidelity of lowresolution simulations by integrating a machine learning algorithm into a numerical solver to develop an artificial closure of the moment hierarchy. We demonstrate the successful application of this method to a variation of the canonical problem of Langmuir wave damping in an unsheared slab, studied by Landau [2] and revisited by Hammett and Perkins with analytic closures [3]. The promising results of our method suggest that machinelearned closures of the full moment hierarchy may be possible to achieve. We are also investigating whether we can develop this approach into an interpretable model. 
Author not Attending 
PP11.00100: A comparison of kinetic and fluid approaches to ITG turbulence using the gyrokinetic code GX Braden Buck, William D Dorland, Noah R Mandell Following optimizations to reduce neoclassical losses, turbulent transport will be the dominant mode of transport in modern stellarator designs. The geometric properties of the threedimensional confining magnetic field that influence the behavior of turbulence are not wellunderstood. In an analytic model developed by Hegna, Terry, & Faber (2018), specific geometric quantities of the confining magnetic field that influence the turbulence associated with the Ion Temperature Gradient (ITG) instability have been identified. This analytic model is constructed using a threefield fluid model. To gain an understanding of the limitations and shortcomings that this may impose on the rest of their model, we compare a threefield fluid model against a kinetic model in gyrokinetic calculations of quantities associated with ITG turbulence. We do this by using the unique gyrokinetic solver GX, which employs an algorithm that reduces to a threefield fluid model at lowvelocity resolutions and converges to an Eulerian approach at highvelocity resolutions. We demonstrate that a fluid approach used for turbulencerelated calculations will suffer from inaccuracies in low collisionality environments, which are typical in modern tokamaks and stellarators. 

PP11.00101: Implementation of the NonTwisting Flux Tube in the Gyrofluid Code GX Jacob M Halpern, Jason Parisi, Justin Ball, Tony Qian Simulating microturbulence in fusion plasmas involves gyrokinetic codes that average over the fast perpendicular gyromotion timescale. The computational expense is further reduced through a “flux tube” domain, which uses a field aligned coordinate system to match the structure of the underlying turbulence [1]. At the outboard midplane, the perpendicular domain is rectangular and the normal/binormal directions are several gyroradii in length. Due to magnetic shear, the perpendicular cross section twists into a parallelogram and can damp certain types of turbulence. In this work, we implement a nontwisting flux tube in the pseudospectral code GX [2]. We build off a previous study [3] that redefines the binormal spatial coordinate and subsequent normal wavenumber grid to maintain a rectangular cross section at all poloidal locations. We will review the code alterations and compare the findings and runtimes of conventional and nontwisting flux tubes for both linear and nonlinear benchmarks. 

PP11.00102: Radial Distributions of QuasiCoherent Mode in T10 Ohmic and ECRheated plasmas Mikhail A Drabinskiy, Leonid G Eliseev, Philipp O Khabanov, Alexander V Melnikov, Nikolay K Kharchev One of the most important problems in magnetic confinement fusion is the anomalous level of the energy and particle losses caused by the plasma turbulence. It has been shown that, at the T10 tokamak (R = 1.5 m, a = 0.3 m), the major contribution to the turbulent particle flux is given by the density oscillations in the 50150 kHz frequency range corresponding to the QuasiCoherent mode (QCmode). In this study radial distributions of the QCmode in the Ohmic and ECRheated plasmas are presented (B0 = 2.2 T, Ipl = 230 kA, and ne ≈ 1·1019 m3, PECRH ≤ 2.2 MW). The measurements were carried out in the wide radial range 0.3 < ρmeas. < 1 using Heavy Ion Beam Probe (HIBP) diagnostic which is capable of detecting midscale (kpol < 3 cm1) plasma potential and density fluctuations. The most pronounced changes of QCmode during ECRH appear in the core plasma region with ρ < 0.5. ECR heating causes the gradual decrease of the QCmode frequency from f = 90±50 kHz in the OH stage to f = 20±10 kHz in the 2.2 MW ECRH stage. The direction of the QCmode poloidal rotation remains the same during both Ohmic and ECRheated stages despite the radial electric field change from Er = 80 V/cm in the OH stage to Er = +20 V/cm in the ECRH stage. 

PP11.00103: Analyzing the nature of impurity transport coefficients in tokamaks using the coupled TRANSPAurora impurity transport framework Amrita Bhattacharya, Francesca M Poli, Francesco Sciortino The study details a new framework coupling TRANSP[1] with the impurity transport code Aurora[2],for impurity transport analyses with interpretive runs in TRANSP.The TRANSPAurora framework is developed for better deducing impurity distributions,over current TRANSP impurity models,in an evolving fusion plasma discharge.The framework requires providing Aurora with inputs from a TRANSP run including waveforms of NCLASS[3] calculated impurity transport coefficients.Individual impurity charge state distributions are obtained from Aurora by solving the coupled impurity transport equations for these states with atomic data from ADAS[4] database.The net impurity distribution is estimated next and matched with experimental data.The steps are reiterated for different times into the discharge.Agreement between simulated and experimental impurity distributions yield better estimates of impurity transport coefficients,effective charge state,and radiation losses.The framework is applied here for KSTAR and NSTX discharges. 

PP11.00104: Plasma transport by turbulent homoclinic tangles in diverted tokamak plasmas Ralph Kube, Michael Churchill, Seung Hoe Ku, Jong Choi, CS Chang Electromagnetic turbulence can generate a fluctuating homoclinic tangle of magnetic field lines around the magnetic Xpoint, destroying the last confinement surface (magnetic separatrix surface) in a diverted tokamak plasma. In this work we implement a passive tracer particle diagnostic to study plasma transport in turbulent homoclinic tangle structure. Turbulent electric and magnetic fields obtained from the totalf XGC gyrokinetic simulations are used to push tracer particles. Particle and energy transport by the homoclinic tangle in present tokamaks will be compared with those in fusion power production ITER plasma. Implication to diverter heatload footprint will be discussed. 

PP11.00105: Neoclassical transport due to resonant magnetic perturbations in DIIID and NSTX Priyanjana Sinha, Nathaniel M Ferraro, Emily A Belli We investigate the role of neoclassical physics in particle and energy transport during the application of resonant magnetic perturbations (RMPs) to suppress the edge localised modes in a tokamak. The drift kinetic code NEO is used to evaluate the neoclassical transport in DIIID plasmas where RMPs are applied. The magnetic field given as an input to NEO is calculated using extended MHD code M3DC1 and includes nonlinear resistive plasma response in realistic geometry, dissapiation, and sources. 

PP11.00106: Stabilizing Effects of Negative Triangularity on MicroinstabilityDriven Turbulence Jessica L Li, Michael Cole, Allan H Reiman, Mike Zarnstorff Negative triangularity shaping of tokamak plasmas has been shown to improve confinement both experimentally and numerically. This is theorized to be due to stabilization of ionscale microinstabilities, leading to the suppression of turbulent transport. We investigate the stability properties of collisionless iontemperaturegradient (ITG), trappedelectronmode (TEM), and kineticballooningmode (KBM) instabilities in axisymmetric equilibria. The global electromagnetic gyrokinetic code XGC is used to simulate updown symmetric positive and negativetriangularity geometries of DIIIDlike equilibria at varying temperature and density profiles and plasma beta. We compare critical gradients, growth rates, and stability boundaries of these collisionless microinstabilities to study the strength and extent of the negativetriangularitydriven stabilization mechanism in different regimes. At low beta, kinetic electron simulations show that both ITG and TEM are linearly stabilized by negative triangularity. We also compare critical gradients for ideal ballooning modes with those for KBM instabilities and assess the significance of negative triangularity effects within experimental operating regimes. 

PP11.00107: Turbulence in stellarators with precise quasisymmetry Richard Nies, Felix I Parra We study the turbulence properties of the recently obtained stellarator configurations with precise quasisymmetry [1] using the gyrokinetic code stella [2]. The linear growth rates and nonlinear turbulence levels in multiple flux tubes are compared, using both adiabatic and kinetic electron models. We furthermore investigate whether, in a regime of strongly driven ion temperature gradient turbulence, the quasisymmetric configurations exhibit critical balance scalings similar to tokamaks [3]. Finally, we study the nonadiabatic response of passing electrons [4], which is significant in the precisely quasisymmetric configurations [1] due to their low magnetic shear, affecting both the linear growth rates at low binormal wavenumbers and the saturated turbulence levels. 

PP11.00108: Understanding and Controlling Imodes through Cross Phase Control David E Newman, Paul W Terry, Raul Sanchez, Jose Miguel Reynolds Barredo, Dempsey Rogers The Imode and similar new transport regimes offer good confinement properties with reduced density limit issues and potentially better control. While a number of different mechanisms have been identified for the formation and maintenance of enhanced confinement regimes few if any allow enhanced confinement in one channel but not another which is seen in the Imode. We have proposed differential crossphase modification as a possible mechanism for different transport in different channels and investigate control tools. Simple dynamical models have been able to capture a remarkable amount of the dynamics of the core and edge transport barriers found in many devices. By including in this rich though simple dynamic transport model a simple model for cross phase effects, due to multiple instabilities, between the transported fields such as density and temperature, we can investigate whether the dynamics of more continuous transitions such as the Imode can be captured, understood and controlled. First we look at the cross phase in a more fundamental model then we investigate the use differential electron and ion heating to control the Imode regime in the simpler model and we demonstrate the ability to stay in the Imode without slipping into the Hmode regime. 

PP11.00109: Sustainability and Dynamics of Transport Barriers Near the Density Limit Mikhail A Malkov, Patrick H Diamond Numerous studies have demonstrated that an edge shear layer generated by drift waves collapses when the adiabaticity parameter α = k^{2} V^{2}_{th} /ων is decreased below α_{crit} ∼ 1 . We have investigated the role of this parameter and the initial density contrast in the formation and dynamics of transport barriers. This study is relevant to the fate of shear layer and transport barriers near the density limit. We use the HasegawaWakatani model, assuming the starting density profile formed after, e.g., a pellet or supersonic neutral beam injection, or other means of buildup. In this setting, no shear flow is initially imposed but created by the drift waves generated by the density gradient. The density profile then relaxes under the competition between the turbulent transport and its suppression by the shear flow. The relaxation dynamics generically go through a staircase phase, wherein the initial density step splits into two smoother steps separated by a flat density region. This process is accompanied by the shear flow formation and suppression of the turbulent transport. The final spread of the transport barrier depends on the adiabaticity α and the initial density contrast, Δn. Turbulent fronts propagate at approximately the same speed in both directions from the initial localization of the transport barrier, depending on the density contrast Δn and adiabaticity α. 

PP11.00110: Gyrokinetic modeling of impurities during the Hmode pedestal interELM buildup Scott E Parker, Qiheng Cai, Stefan Tirkas, Neeraj Kumar, Yang Chen, Gabriele Merlo, Shaun R Haskey, Brian Grierson We study profiles from the DIIID Hmode interELM buildup phase that show hollow Carbon and electron profiles. These experimental results are interesting because inward impurity flux may be partially responsible for the electron density buildup. We have carried out linear gyrokinetic simulations using the GENE code in the fluxtube limit and study the pedestal top in the range of ??_{tor}=0.80.95 where closedfluxsurface calculations are valid. We find ITG and TEM modes most unstable in the ionscale range and ETG most unstable in the electron scale range. Quasilinear calculations indicate that the anomalous particle transport is dominated by ITG or ionscale modes with phase velocity in the ion diamagnetic direction. The quasilinear calculations show negative particle fluxes for both electrons and Carbon. These results are being compared to neoclassical calculations using the NEO code. We use these linear and quasilinear calculations as a scoping tool for nonlinear GEM simulations. Understanding the impurity transport, especially if impurity fluxes are inward, is critical for future fusion reactors where highZ impurities may not fully ionize in the core leading to significant radiative power loss. 

PP11.00111: Transport of Particles, Electron Energy, and Turbulence in Strong InterchangeType Turbulence Kenneth W Gentle The Helimak is an approximation to the infinite cylindrical slab with a size large compared with turbulence transverse scale lengths, but with open field lines of finite length. A pressure gradient in unfavorable magnetic curvature is unstable to interchangetype modes, leading to large amplitude nonlinear fluctuations similar to those in a tokamak SOL. A novel magneticallybaffled probe cluster permits full characterization of the turbulence, including density, temperature, and true plasma potential fluctuations as well as radial transport of all quantities across the full plasma profiles. Despite the short coherence lengths, the level of saturated turbulence and transport cannot be inferred from local parameters. The fluxes of density and temperature turbulence (quadratic in the dimensionless fluctuation amplitudes) are generally small, less than 10m/s, less than 25% of those of the density/thermal fluxes themselves and insufficient in both magnitude and sign to explain the large turbulent amplitudes seen in linearly stable regions of the pressure profile. The transport statistics of the turbulence are unusual. The Helimak is now at Shenzhen University. 

PP11.00112: Quasilinear Gyrokinetic Modeling of Reduced Transport in the Presence of High Impurity Content, Large Gradients, and Large Geometric α Cole D Stephens, David R Hatch, Michael T Kotschenreuther, Swadesh M Mahajan, Jonathan Citrin, Clarisse Bourdelle Pelletfueled tokamak discharges lead to large gradients that can destabilize electrostatic microinstabilities, thereby driving anomalous turbulent transport [1]. However, large gradients can also lead to large geometric α, a stabilizing parameter in certain regimes [2]. The resulting transport is inherently constrained to be ambipolar; in effect, these large gradients can make this flux constraint impossible to satisfy, resulting in stabilization and the reduction of turbulent transport [3]. Due to the high computational cost of nonlinear gyrokinetic simulations, using a reduced turbulent transport model is ideal for predictive modeling. We test the extent to which the gyrokinetic quasilinear code QuaLiKiz [4] can reliably predict anomalous transport in pelletfueled discharge regimes to determine parameters that lead to turbulent transport reduction. We use the gyrokinetic code GENE [5], based on first principles, as a point of comparison for QuaLiKiz. Unlike GENE, QuaLiKiz uses many approximations to ensure computational tractability. In particular, QuaLiKiz assumes a Gaussian eigenfunction, uses sα geometry, and only captures electrostatic fluctuations. We test, and in some cases, relax these approximations to ensure accurate predictions in pelletfueled discharge scenarios. 

PP11.00113: Simulations of TemperatureGradientDriven Trapped Electron Modes on HSX Gavin W Held, Benjamin Faber, Chris C Hegna The ongoing upgrade to the HSX stellarator at University of WisconsinMadison will provide access to higher core electron temperatures and larger electron temperature gradients. The inherent geometric properties of HSX combined with strong electron heating will likely destabilize temperaturegradientdriven trapped electron modes (TEM). Fluxtube gyrokinetic simulations have been performed using the GENE code to study microturbulence characteristics at the larger temperature gradients and temperature ratios. A notable feature of the nonlinear simulations are distinct, long wavelength electrostatic potential structures. These structures show strong similarities with structures observed previously in densitygradientdriven TEM simulations for HSX [1]. 

PP11.00114: Implementing general moment equations for parallel closures in NIMROD Hankyu Lee, Andrew Spencer, Eric D Held, JeongYoung Ji At low collisionality, valid parallel closures can be obtained by solving the first order drift kinetic equation. A previous study solved the drift kinetic equation in NIMROD code and calculated neoclassical quantities in an axisymmetric tokamak [1]. In this study, general parallel moment equations [2] are implemented in NIMROD for obtaining parallel closures. The parallel closures are applied to timedependent fluid equations in NIMROD. The convergence of the numerical solution is shown by increasing the number of moments of the system. As a benchmark test, ion parallel flow calculations are compared to the previous study [1]. 

PP11.00115: CrossPhase Analysis of ITG and ETG Particle Transport for Understanding I Mode Paul W Terry, David E Newman The tokamak I mode has proved difficult to explain because it is not clear how an anomalous heat flux is suppressed while the particle flux remains robust. We investigate details of transport crossphases in a model with L and I mode representations, since cross phases can differ from one regime to another. We assume L mode is dominated by ITG turbulence and I mode by ETG turbulence, as suggested by observations, and calculate the respective particle fluxes from kinetic theory. To enable analytic calculations, flow shear is not included but is accounted for by assuming that the shearing rate is larger in I mode and tends to reduce all fluxes. Nonadiabatic particles govern transport; in ITG they are trapped electrons and require collisions to produce radial transport, even in hot plasmas. This gives a ▽Tdriven pinch that offsets outward diffusion, weakening particle transport in L mode. The nonadiabatic ions of ETG are collisionless, with nonzero transport requiring an ion spectrum feature to create a magneticdrift resonance. If ITG is a subdominant instability in I mode all flux terms are outward, yielding more robust particle transport than in L mode. The requirement of an ion frequency is discussed in relation to linear and nonlinear effects in the frequency spectrum. 

PP11.00116: MHD triggered GAM in ADITYAU tokamak Kaushlender Singh, Harshita Raj, Tanmay Macwan, Suman Dolui, Ankit Kumar, Bharat Hegde, Ashok Kumawat, Pramila Gautam, Rohit Kumar, Suman Aich, Laxmikanta Pradhan, Ankit Patel, Kalpesh Galodiya, Kaushal Patel, Kumarpalsinh A Jadeja, Lavkesh Lachhvani, Rakesh Tanna, Joydeep Ghosh Plasma turbulence is known to be one of the strong driving mechanisms of energy and particle transport which can degrade the plasma confinement in tokamaks. Hence, it is important to understand different physical processes which drive and control turbulence. It has been observed that the selfgenerated axissymmetric structures such as zonal flows play a key role in controlling the turbulence and associated transport [1, 2]. Lowfrequency zonal flows (LFZF) and highfrequency geodesic acoustic mode (GAM) have been observed and studied in several toroidal devices [2]. The effect of MHD modes on GAMs is also an important aspect that is being explored in several experiments in devices like TCABR and STORM tokamak [3,4]. 

PP11.00117: ASTRO: ASTROPHYSICAL PLASMA Session Chairs: 

PP11.00118: Magnetically Driven Jet Studies on the Big Red Ball Joseph R Olson, Priyadarshini Rajkumar, Jeremiah Kirch, Karsten J McCollam, John P Wallace, Hui Li, Cary B Forest Magnetically driven jets are commonly observed originating from active galactic nuclei. These jets are launched and collimated in regions much smaller than the current resolution limits of observations, so the details of this process remain elusive. We are developing experiments on the Big Red Ball (BRB) at the Wisconsin Plasma Physics Laboratory (WiPPL) to explore propagation dynamics and stability of magnetically driven jets. Such experiments would differ from the previous studies in that the fastmoving jets will be propagating in a pressurized plasma background (vs vacuum). Extensive prior theoretical and numerical studies suggest this background pressure will markedly impact the jet propagation. Our work will focus on studying the shock and precursors formed between the magnetized jet and the unmagnetized background plasma and on how the development of the kink instability could depend on the strength of the background pressure. We will characterize the jet condition via temporally and spatially resolved diagnostic measurements of the magnetic field strength, electron and ion densities, temperatures, and velocities. The experiments will be guided by and interpreted with the aid of 3D MHD simulation and theoretical analysis carried out at LANL. 

PP11.00119: Novel parallelkinetic perpendicularfluid model for highly magnetized (relativistic) plasmas James Juno, Ammar Hakim, Jason M TenBarge, Alexander A Philippov, Ian G Abel Many plasma systems, from pulsar magnetospheres to magnetic confinement devices, are highly magnetized. However, the derivation of large magnetization asymptotic models applicable to this wide variety of plasmas is challenging. Relativistic energies and strong flows both complicate the asymptotics and even if the derivation can be made sufficiently rigorous, the subsequent equations may resist easy discretization via standard numerical methods, especially when one includes the geometry necessary to correctly model the plasma of interest, e.g., fieldline following coordinates for magnetic confinement devices or general relativistic effects for extreme astrophysical systems. 

PP11.00120: Cosmic Ray Injection in a Realistic Galactic Disk Roark S Habegger, Ellen G Zweibel Cosmic rays and magnetic fields provide a significant contribution to the energy density of the Milky Way's interstellar medium (ISM). Through the Parker instability, these nonthermal components compress the thermal ISM into clumps near the disk's midplane and create magnetic lobes perpendicular to the midplane. However, the Parker instability takes a long time, >200 Myr, to develop through linear perturbations to an isothermal slab under vertical hydrostatic equilibrium. The vertical equilibrium is disrupted in a shorter time, ~100 Myr, when triggered by cosmic ray injection from energetic events like supernovae. But even this time is long enough to suggest larger scale phenomena (e.g. galactic rotation) could minimize the observational traces of the effects of cosmic rays and magnetic fields. However, this reasoning neglects the possibility the injection drives change in a shorter time when coupled with other dynamical phenomena in a multiphase ISM. To understand if this coupling is possible, we use 3D ideal magnetohydrodynamic simulations to study the movement of a buoyant, cosmic ray loaded magnetic flux tube in a realistic galactic disk. These are local simulations of a Cartesian slab, representing a patch of a galactic disk. Comparing different simulation runs, we examine how the buoyant flux tube's movement changes when including the effects of (1) galactic rotation, (2) density waves, (3) clumpy ISM structure, and (4) multiple ISM phases. Simulation methodology and preliminary results will be presented. 

PP11.00121: Hear Me Roar: Whistler Lion Roars in highβ plasmas of galaxy clusters Francisco Ley, Drake Miller, Ellen G Zweibel, Mario A Riquelme Lion roars are shortlived, low frequency, righthand polarized whistler waves generated by anisotropic electrons trapped in low magnetic field regions of nonlinear mirror modes. They are observed in lowbeta plasmas near the Earth and the solarwind. In the intracluster medium (ICM) of galaxy clusters the mirror instability can also be excited by turbulent shearing and compression, given the high values of plasma β, and we found preliminary indications of lion roars also present in those ambient conditions (Ley et al. 2022). We perform fully kinetic particleincell (PIC) simulations of a highβ plasma subject to a continuous amplification of B(t) to study the nonlinear stages of the mirror instability and the ensuing excitation of whistler lion roars. We see that, as mirror modes reach nonlinear amplitudes, whistler lion roars start to emerge with subdominant amplitudes and quasiparallel propagation. We characterize their wave properties and the population of electrons that excite them, with results consistent with previous works. Within our parameter space, we argue that whistler lion roars are a concomitant feature of mirror instability even at highβ, and therefore expected to be present in astrophysical environments such as the ICM. We discuss the implications of our results on electron thermal conduction models in the ICM such as whistlerregulated MHD (Drake et al. 2021). 

PP11.00122: Rotating magnetic field to emulate a pulsar magnetosphere in BRB Rene Flores Garcia, Karsten J McCollam, Jeremeiah J Kirch, Steven P Oliva, Cary B Forest We are building a dipolar rotating magnetic field (RMF) system with the intention to emulate the magnetosphere of an obliquely rotating pulsar and demonstrate production of an outgoing plasma wind at the Wisconsin Plasma Physics Laboratory (WiPPL). The driver consists of an orthogonal pair of Helmholtzlike RMF drive coils resonated at ~6 kHz and two tubebased amplifiers for generation of sine and cosine coil currents of amplitude 30 kAturns. The coils will be placed at atmospheric pressure in an aluminacoated fiberglass pressure vessel at the center of BRB. A power of 150 kW per channel will be fed to the drive coils from transmission lines running through a support pedestal coaxial with BRB. Fuel gas will be puffed from outlets at the BRB equatorial plane, and the RMF will ionize the gas. The experimental hardware is in development. Coupling transformers are partially done. Transmission line hardware is finalized and assembly is pending. Winding the RMF coils is in process. Vacuum tests qualified the vessel to be used in BRB. The pressure vessel is currently being painted with alumina to protect the fiberglass surface. Our next major step is to test the RMF drivers at full power prior to going into BRB. Future steps include implementing the gas puff system and initial plasma tests. 

PP11.00123: On motion of a particle in a strongfield magnetic bottle Mikhail V Medvedev Compact astrophysical sources like neutron stars and magnetars possess extremely strong magnetic fields. Radiative cooling of plasma particles in their magnetospheres can be short compared to the plasma dynamical time. Such magnetospheres are observed to produce strong flares, which indicates production of relativistic electrons and, possibly, positrons. How does the particle distribution change as these particles propagate in the magnetospheric 'magnetic bottle'? Here we discuss the motion of a relativistic 'larmor particle' in a straight magnetic bottle subject to synchrotron energy loss. 

PP11.00124: Extended solution of the dipolar neutron star vacuum fields Rui P Torres, Fabio Cruz, Thomas Grismayer, Ricardo A Fonseca, Luis O Silva Neutron stars are usually assumed to be perfect spherical conductors with a predominant intrinsic dipolar magnetic field anchored to their stellar surface. When including General relativity in the vicinity of compact objects, Maxwell's equations are modified, leading to changes in the exterior vacuum solution of compact neutron stars. In this regime, approximate solutions were obtained up to first order in the framedragging frequency parameter [e.g. L.Rezzolla et al, MNRAS 322 (2001)]. These corrections are usually considered for the electric field but are neglected for the magnetic field. Our extended solution includes the full firstorder correction on both electromagnetic fields. We tested the validity of the derived solution by prescribing it as an initial value problem to twodimensional particleincell simulations. We discuss the relevance of this solution to particleincell simulations, highlighting the differences to previously proposed solutions. Finally, we address future possible extensions of this work. 

PP11.00125: Study of Burgerslike turbulence driven by resistive instabilities in a flux tube Alexander Velberg, Lucas Shoji, Muni Zhou, Nuno F Loureiro We present results from a study of the nonlinear dynamics of kinklike resistive instabilities in a flux tube in reduced MHD. Simulations were performed using the pseudospectral code Viriato, in which a screw pinch equilibrium with a low safety factor (q) on axis was initialized. Due to having q < 1 throughout much of the system, the equilibrium is linearly unstable to a variety of poloidal and toroidal (m and n) resistive modes at the q = m/n rational surfaces, which we confirm via linear analysis. For certain initial perturbations of m=1, high n modes we find that the nonlinear coupling of multiple linearly unstable modes drives turbulence in the system via the excitation of larger m and n tearing modes. This turbulence can be characterized by the formation of current sheets, resulting in a Burgerslike turbulent spectrum with a magnetic energy power law E_{M }~ k^{2} and a kinetic energy power law E_{K}_{ }~ k^{1}. These results may have implications for the study of astrophysical jets as well as tearing mode turbulence in reversed field pinches. 

PP11.00126: Generation and amplification of magnetic field due to RayleighTaylor instability in a twofluid plasma Liang Wang, Chuanfei Dong, Manasvi Lingam We present twodimensional simulations of the RayleighTaylor instability in a twofluid plasma using the Princeton code, Gkeyll. In these simulations, the corresponding fluid moment equations are evolved for the electron and ion species. Initially, each species is in a separate hydrodynamic equilibrium, and the initial electromagnetic field constitutes the vacuum solution. Perturbations are then applied to the electron and ion fluids, which give rise to a magnetic field due to the Biermann battery effect. The field is further amplified in the nonlinear stage via a dynamolike effect, followed by a slow decay as the forcing weakens. We investigate the magnetic field's growth and decay and their dependence on the mass of the lighter species (i.e., electrons). Implications for the dynamo in threedimensional configurations will also be discussed. 

PP11.00127: Longterm evolution of electron acceleration in high Mach number shocks with MHDPIC simulations Alisa Galishnikova, Anatoly Spitkovsky The questions of longterm evolution of shock waves in supernova remnants and the interplay between shocks and cosmic rays (CRs) remain under active investigation. We use a hybrid magnetohydrodynamicparticleincell (MHDPIC) approach to study electron acceleration in quasiparallel shocks. The method treats CRs as particles, while the thermal electronion plasma is described as a fluid by MHD equations. We implement a novel injection prescription based on the selfconsistent reflectivity of the shock, which we determine by tracing test particles through the MHD turbulence in the shock upstream. This approach allows us to study the longterm evolution of the particle acceleration and the upstream turbulence, particularly substantial in quasiparallel shocks, on macroscopic scales, which are unachievable with the PIC method. We find that larger upstream turbulence confines accelerated particles closer to the shock, and leads to changes in the reflected particle fraction. As a result, the shock reaches a selfconsistent particle injection level which is independent of the numerical parameters. Such selfregulation of injection is likely important in the strongly nonlinear turbulence of supernova remnant shocks. 

PP11.00128: Simulation study of particle reflection and injection in magnetized collisionless shocks Jhonnatan Gama Vazquez, Alexis Marret, Frederico Fiuza Collisionless shocks are common in astrophysical plasmas and are known to be important in the acceleration of both highenergy electrons and protons. While diffusive shock acceleration is well established, particle injection into the nonthermal tail remains an important puzzle, particularly for electrons. In this work we present the results of one and twodimensional particleincell simulations of magnetized collisionless shocks to study how the properties of the shock reflected and injected particles depend on the plasma parameters, namely the Alfvénic and sonic Mach numbers and the orientation of the ambient magnetic field with respect to the shock normal. 

PP11.00129: Quasicylindrical kinetic simulations of particle acceleration in relativistic magnetized jets Gabrielle Guttormsen, Frederico Fiuza, E. Paulo Alves The mechanisms by which relativistic magnetized jets from AGN produce nonthermal particles and radiation remain a longstanding puzzle. Recent largescale 3D particleincell (PIC) simulations show that the onset of hydromagnetic instabilities in jets can lead to efficient nonthermal particle acceleration [1,2,3]. However, these simulations are computationally expensive, as they need to capture large dynamic ranges to understand how acceleration mechanisms might scale to and operate at astrophysically relevant system sizes. 

PP11.00130: Magnetic energy dissipation and gammaray emission in energetic pulsars Hayk Hakobyan, Alexander Philippov, Anatoly Spitkovsky Some of the most energetic pulsars exhibit rotationmodulated gammaray emission in the 0.1 to 100 GeV band. The luminosity of this emission is typically 0.110% of the pulsar spindown power (gammaray efficiency), implying that a significant fraction of the available electromagnetic energy is dissipated in the magnetosphere and reradiated as highenergy photons. To investigate this phenomenon we model a pulsar magnetosphere using 3D particleincell simulations with strong synchrotron cooling. We particularly focus on the dynamics of the equatorial current sheet where magnetic reconnection and energy dissipation take place. Our simulations demonstrate that a fraction of the spindown power dissipated in the magnetospheric current sheet is controlled by reconnection at microphysical plasma scales and only depends on the pulsar inclination angle. We demonstrate that the maximum energy and the distribution function of accelerated pairs is controlled by the available magnetic energy per particle near the current sheet, the magnetization parameter. The shape and the extent of the plasma distribution is imprinted in the observed synchrotron emission, in particular, the peak of the observed spectrum and the cutoff. We study how the strength of synchrotron cooling affects the observed variety of spectral shapes. Our conclusions naturally explain why pulsars with higher spindown power have wider spectral shapes and, as a result, lower gammaray efficiency. 

PP11.00131: The Effects of Relativistic Shearflows and Kelvin Helmholtz Instability on the Magnetic Reconnection Rate in the Magnetically Dominated Regime Sarah Peery, YiHsin Liu In this study we explore the behavior of magnetic reconnection in the relativistic (magnetically dominated) regime, in the presence of relativistic shearflows, and a guide field. To do this we use a 2D fully kinetic PIC code, and SweetParker (1957) scaling analysis. Inplane shearflow suppresses reconnection, as found by Cassak and Otto (2011), but at high flow shear the Kelvin Helmholtz instability can induce reconnection. The presence of the guide field reduces the inplane Alfven velocity in relativistic reconnection and allows the transition between suppressed to driven reconnection to happen at lower flow speeds. 

PP11.00132: Spectral studies of PIC simulations of multistreaming plasmas Michael C Sitarz, Mikhail V Medvedev, Alexander A Philippov Interpenetrating plasma beams is unstable to electromagnetic instabilities such as the Weibel filamentation instability and others. Astrophysical systems with high energy density content, such as in collisionless shocks of gammaray bursts and supernova explosions, are the locations where the beamplasma Weibel instability naturally occurs and affect plasma dynamics and observable electromagnetic radiation. Here we study the case of a collisionless, unmagnetized system with mildly relativistic counterstreaming beams of equal density with PIC simulations using TRISTANMP code. We developed the spectral analysis software used at the postprocessing stage. Here we present the timedependent spectral analysis in the omegak space of the plasma modes present in the system as it evolves. We discuss various properties the excited plasma modes. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700