Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Plasma Physics
Monday–Friday, October 30–November 3 2023; Denver, Colorado
Session PP11: Poster Session VI:
Poster

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Room: Plaza ABC 

PP11.00001: DIIID AND CONVENTIONAL TOKAMAKS II


PP11.00002: Ion orbit losses and tokamak improved confinement in negative and positive triangularity Linda E Sugiyama Ion orbit losses through the plasma edge are a pervasive, but often neglected, component of tokamak edge confinement. Orbit losses, especially from near a plasma boundary Xpoint, are known to be be able to drive a nearedge annulus of negative radial electric field E_{r}. Losses are enhanced at higher temperature T_{i}. Strong radial shear of the ExB velocity reduces turbulent transport and allows a strong edge pressure gradient to form. Negative and positive triangularity (NT and PT) have very different edge ion orbits. PT maximizes particle trapping (mirroring reversal of the parallel velocity), leading to more and wider banana orbits, while NT minimizes mirroring. In some NT shapes, the orbit effects of strong NT at a single Dcorner can strongly suppress Hmode onset for quite small geometric changes, when added to the other NT properties. PT plasmas with lower ``subHmode'' levels of improved confinement tend to have reduced ion trapping and banana width; their weaker E_{r} and E_{r} shear make it hard to reach full Hmode. In nonaxisymmetriy, ion orbits in some stellarator helical fields could enhance Xpoint losses and maybe related to the widely observed density pumpout seen in tokamaks with small nonaxisymmetric magnetic perturbations. 

PP11.00003: Role of neutral particles on pedestal structure for Hmode experiments in DIIID Julio J Balbin Arias, Saskia Mordijck, Theresa M Wilks, Laszlo Horvath, Tomas Odstrcil, Ryan A Chaban, Aaron M Rosenthal, Jerry W Hughes, Alessandro Bortolon, Florian M. Laggner


PP11.00004: Measurement of edge turbulence in negative triangularity plasmas with phase contrast imaging on DIIID Jon C Rost, Alessandro Marinoni, Kathreen E Thome, Miklos Porkolab Sweeps of the upper triangularity (δ_{U} in [0.4,0.2]) in negativetriangularity [1] discharges have been performed with fixed lower triangularity (δ_{L}=0.2) with a variety of plasma parameters_{ }, providing a platform for the study of the edge turbulence. The Phase Contrast Imaging diagnostic [2] provides measurements of lineintegrated edge turbulence with good wavenumber resolution and wide frequency bandwidth and is especially sensitive to the turbulence in the sheared edge region of highperformance plasmas. The spectra of the ionscale turbulence seen in negative triangularity discharges, even without auxiliary heating, is similar to that seen in plasmas with significant edge shear such as Hmodes rather than Lmode plasmas. Two instability regimes were identified, corresponding to pure ohmic heating and moderate beam heating. With no auxiliary heating, the turbulence both above and below the midplane was sensitive to the upper triangularity. The edge turbulence in plasmas with moderate beam heating was independent of the upper triangularity. This demonstrates that the good performance edge observed in negativetriangularity plasmas is robust and persists over a variety of parameters and turbulence regimes. 

PP11.00005: Controlled lowZ melting experiment in DIIID tokamak Dmitry L Rudakov, Tyler W Abrams, Igor Bykov, Gregory Sinclair, Jonathan D Coburn, Robert D Kolasinski, Dinh Truong, Charles J Lasnier, Adam McLean, Filippo Scotti, Konstantinos Paschalidis, Svetlana Ratynskaia, Panagiotis Tolias, Richard A Pitts, Zana Popovic, Jun Ren, Robert S Wilcox Controlled melting of aluminum (Al) was performed in the lower divertor of DIIID, and the molten surface deformation was modeled with the MEMENTO code [1]. The experiment was largely motivated by using Al as a proxy for beryllium in ITER. Three Al blocks sized 1×1 cm in the toroidal and poloidal directions, with the top surface angled at ~32 degrees towards the incident plasma heat fluxes, were exposed under steady Lmode discharge conditions using the Divertor Material Evaluation System (DiMES) manipulator. During the exposure, Al samples were imaged by visible and infrared (IR) cameras, and the current through them was measured via a shunt with resistance of ~0.15 Ω. Heat fluxes incident on the angled surfaces were inferred from IR data aided by SMITER field line tracing. The block exposed to the incident heat flux of ~10 MW/m^{2} for ~1 sec achieved the intended shallow melting. MEMENTO code was able to qualitatively reproduce the surface deformation profile and the melt onset timing, but detailed comparison was impeded by the unknown thermophysical properties of the sample due to strong oxidation. Crosssectional analysis of the molten surface for improved comparison is in progress. 

PP11.00006: Observations of energetic ion driven ion cyclotron emission and high frequency Alfvén eigenmodes in negative triangularity plasmas in DIIID Jesus J Serrano, Neal A Crocker, Troy A Carter, Kathreen E Thome, Shawn X Tang Observations are presented for an investigation of energetic ion driven coherent ion cyclotron emission (ICE) and subcyclotron high frequency Alfvén eigenmodes (hfAE) in negative triangularity shaped plasmas in DIIID obtained with a set of loops inside the vacuum wall with sensitivity to radio frequency emission at frequencies f < 200 MHz. This investigation contributes to a better understanding of the observed waves so that in the future, such observations can be used to diagnose the energetic ion population. In a 2023 negative triangularity campaign, many experiments were conducted which provided a rich data set for examining ICE and hfAE characteristics on plasma parameters in negative triangularity shaped plasmas. The ICE was observed to occur at low harmonics of the central ion cyclotron frequency and the dominant harmonic varied with plasma conditions but tended to be low (l ≈ 2). Frequency splitting was observed for some ICE harmonics, as well as hfAEs. Analysis showed that in some case the splitting was the result of the formation of propagating wave packets, suggestive of nonlinear dynamics. Work supported by US DOE under DEFC0204ER54698 and grant # DESC0020337. 

PP11.00007: Radiation Dependence of Divertor Leg Length in Detachment on DIIID Morgan W Shafer, Adam McLean, Anthony W Leonard, Filippo Scotti Experiments performed on DIIID demonstrate that while increasing the outer leg length distributes radiation over a larger volume, the increased leg length does not prevent an eventual collapse of the Xpoint temperature at high density. Accommodating divertor radiation requires understanding the dissipation processes that takes place along a flux tube. Smaller corevolume plasmas in the open divertor were used to extend the poloidal leg length, L_{pol}, to 38 and 55 cm for two injected powers (8.3 MW and 5.4 MW). Gas puffing was used to increase the plasma density to the point of detachment to test the radiation volume required in the convective limit and extend beyond existing stabledetachment temperature gradient measurements (200eV/m for 15cm L_{pol}). The higher L_{pol} cases show a lower detachment onset density, but only by ~5%. The normalized confinement, H_{98}, drops from 1.2 before detachment and drops below one and continues to reduce as the divertor is driven deeper into detachment. Radiated power is found to extend along the outer leg in detachment for all cases. Despite the extended radiating volume, the CIII radiation pattern is found to peak strongly at the separatrix near the Xpoint in the detached limit, indicating a 78 eV electron temperature at the Xpoint. 

PP11.00008: Turbulence and Transport Dependence on rho* and Isotope Mass in HMode Plasmas on DIIID George R McKee, Elizabeth Perez, Colin Chrystal, Kathreen E Thome, Rongjie Hong, Nathan T Howard, Filipp Khabanov, Xijie Qin, Terry L Rhodes, Lothar Schmitz, Zheng Yan Normalized longwavelength (k_{⊥}ρi<1) density fluctuation amplitudes are found to scale approximately linearly with the normalized local ion gyroradius, ñ⁄n~ρ* in ITERlike ELM’ing Hmode plasmas on DIIID; ρ_{I} was systematically varied both via a ρ* scan in deuterium as well as by changing isotope mass in matched hydrogen and deuterium plasmas. Interestingly, confinement is found to increase at smaller ρ* as ρ* is varied within a single ion species (deuterium), consistent with gyroBohm predictions. However, when ρ* is reduced by changing isotope mass (D>H), confinement degrades, counter to simple gyroBohm predictions, potentially indicating that the dimensionless electrontoion mass ratio is important to confinement scaling. Comprehensive measurements of the spatiotemporal turbulence properties, obtained with 2D Beam Emission Spectroscopy, are compared as the local ion gyroradius is altered via magnetic field and/or isotope variation. The turbulence radial correlation length is found to scale with ρ_{I} in the deuterium ρ* scan, but not in the isotope scan. These turbulence measurements and analysis will be compared with linear and nonlinear gyrokinetic simulations to help resolve the conundrum of ρ* scaling of confinement and the isotope effect. 

PP11.00009: Analysis on the Effect of Main Ion Density on HighZ Impurity Transport in the Scrapeoff Layer of DIIID Using Collector Probes Seth H Messer, Jeremy D Mateja, Jake H Nichols, Jonah D Duran, Shawn A Zamperini, Gregory Sinclair, David C Donovan, Tyler W Abrams, Tomas Odstrcil, Jun Ren, Ezekial A Unterberg, Peter C Stangeby, Dmitry L Rudakov, David Elder Experimental results from the 2022 tungsten (W)coated Small Angle Slot (SASVW) divertor campaign at DIIID indicate that while core plasma density is increased approaching detachment in the unfavorable (ion B×∇B out of the divertor) toroidal magnetic field (B_{T}) direction, W concentration at the midplane farScrapeoff Layer (SOL) is reduced while core W concentration increases. To better understand highZ impurity transport and contamination of the core, an experiment was performed including a series of uppersinglenull Lmode discharges in each B_{T} direction. The discharges incrementally increased the plasma density, (lineaveraged density = 3.154.35e19 m^{3}), which approaches and slightly exceeds the divertor detachment threshold. W deposition measurements using doublesided, graphite Collector Probes (CPs) inserted at the outer midplane farSOL revealed a 75% decrease in W areal density over the scan when operating in the unfavorable B_{T} direction. Observations of flattened W deposition profiles allude to increased radial transport with increasing Soft Xray (SXR) imaging data from the same discharges shows core W content that increases by 77% over the same scan. Both W core content and CP deposition changed marginally with the onset of (partial) divertor detachment. 

PP11.00010: Deuterium retention in LiD codeposits in the DIIID tokamak Maria Morbey, Florian Effenberg, Shota Abe, Alexander Nagy, Tyler W Abrams, Alessandro Bortolon, Dmitry L Rudakov, Ryan T Hood, Laszlo Horvath, Jun Ren, Michael Simmonds, Dinh Truong, Thomas W Morgan Deuterium (D) retention in lithium (Li) codeposits was studied in DIIID by injecting Li powder at 1.530 mg/s into Hmode plasmas with and without 3D fields applied. When Li is injected, a decrease in the Lyα signal intensity is observed, indicating a decrease in the ionization source related with a reduction of the recycling coefficient due to D uptake by Li. Two sets of samples were exposed to the plasmas through DiMES, each consisting of seven samples, including: 1.6 μm of deposited W on graphite, polished stainless steel samples, several coated with 300 nm, and 600 nm Li layers, and a Si sample with microtrenches. Observations with HRUV showed a substantial increase in Li emission during injection and confirmed that prelithiated samples were not significantly eroded. Ion fluxes of ΓD+= 4.3 6.1x1020 D/m2 s were measured with Langmuir probes at DiMES. Considering the injected Li amount and assuming that 10% deposits outside of the OSP, the thickness of the lithium layer is estimated to be 4 nm. In postmortem NRA spectra, Li and D peaks are observed in most samples, confirming codeposition took place. TDS shows D retention in prelithiated and SS samples. Results from postmortem analysis of the LiD codeposits with SIMS, XPS, NRA, and EBS will be presented and discussed. 

PP11.00011: Simultaneous Regulation of the Electron Temperature and Safety Factor Profiles for DIIID using Optimal Control Methods Shira Morosohk, Zibo Wang, Sai Tej Paruchuri, Tariq Rafiq, Eugenio Schuster A controller has been designed to simultaneously regulate the electron temperature (T_{e}) and safety factor (q) profiles on DIIID. Future scenario development efforts will require the capability to control both kinetic and magnetic profiles to achieve high performance plasmas while maintaining MHD stability. Optimal control solutions for the regulation of the Te and q profiles individually has been demonstrated for DIIID [1, 2]; the controller presented here aims to extend these results by controlling both profiles at the same time. The controller is synthesized based on the linearized electron heat transport and magnetic diffusion equations. Using this model, the Linear Quadratic Integral (LQI) controller is designed to minimize the integrated error between the actual and target profiles. The controller has been tested in nonlinear simulations using the Control Oriented Transport Simulator (COTSIM). Predictive simulation results demonstrate the effectiveness of this controller in regulating both the electron temperature and safety factor profiles simultaneously by using the available heating and current drive sources. 

PP11.00012: Heat flux width scaling and detachment in high heat flux experiments on DIIID Auna L Moser, Alan W Hyatt, Charles J Lasnier, Anthony W Leonard, Adam McLean, Tom Osborne, Filippo Scotti, Morgan W Shafer, Huiqian Wang, Theresa M Wilks, Jonathan H Yu A multitokamak scaling predicts narrowing heat flux widths and increasing heat flux density in reactors well beyond the limits which existing armor materials can sustain. However, more recent experiments suggest that broadening effects observed at higher scrapeofflayer (SOL) pressure might change how the divertor heat flux profiles scale, easing this heat flux challenge. Experiments at the DIIID tokamak use a range of plasma current (I_{p} =1.01.9 MA) and neutral beam heating power (P_{inj}=816 MW, for a powerintoSOL of P_{SOL}≈510 MW) Hmode discharges to investigate the physical processes that may limit the maximum parallel heat flux into the divertor. Analysis of infrared camera measurements in the divertor shows heat flux broadening between ELMs at the outer target in the P_{SOL}=10 MW case compared to the 5 MW case at I_{p}=1.9 MA. Density scans provide data both attached and detached conditions, with detachment onset in the high power case at about 59% the Greenwald limit. Detached cases at I_{p}=1.9 and P_{SOL}=10 MW give some of the highest normalized divertor parameters achieved on DIIID, with neutral ionization length, heat flux width, and Lyman mean free path length within factors of ≈2.53.2 compared to that expected in a reactor. 

PP11.00013: Identification of Multimode Interactions of Magnetic Fluctuations by Faradayeffect Polarimetry in DIIID QHmode Plasmas Rachel A Myers, Brett E Chapman, Karsten J McCollam, Mihir D Pandya, John S Sarff, Ruifeng Xie, Thomas E Benedett, David L Brower, Jie Chen, Weixing Ding Measuring nonlinear tearing mode (TM) coupling with high m/n near the magnetic axis can aid in understanding neoclassical TM seeding, growth, and decay mechanisms. For this tracking we use the Radial InterferometerPolarimeter (RIP), which is sensitive to coreresonant magnetic fluctuations on DIIID and has detected TMs well before they appear on the edge sensing coils [Pandya, DPP invited talk 2021]. Here we employ RIP to analyze the impact on preexisting TMs of multiple, emerging MHD modes that are never detected by the coils. We focus on plasmas in QHmode, where infrequent ELMs make TMs more clearly identifiable. In one example, RIP detects an n=3 mode coupled to both an n=2 mode and a lowerfrequency intermittent mode. The n=3 mode loses up to 98 percent of its energy during the coupling, while the other two modes grow. When the intermittent mode disappears, the n=3 mode begins to grow robustly. All three modes are resonant near the magnetic axis, and their interaction is only visible using RIP. In another example, the edge coils show an n=2 mode apparently dissipating in the absence of other modes, but RIP shows instead that it loses energy through coupling to higherorder modes. 

PP11.00014: 2023 Status of the ECH System on DIIID Perry Nesbet, Nikolai de Boucaud, Yuri A Gorelov, Clayton Gray, William Grosnickle, Rigo Brambila, Antonio C Torrezan, Michael P Ross, Esteban Bagdy, Xi Chen, Jared Squire, Marc Barsanti, Adrianus C Sips The Electron Cyclotron Heating (ECH) system on DIIID currently consists of five nondepressed collector 110GHz Communications and Power Industries (CPI) gyrotrons which combine to inject a total of 3.2 MW of RF power into the plasma via eight transmission lines and four equatorial launchers. The available ECH power increased by 700 kW from last year after the refurbished gyrotron "Han" was successfully commissioned and added to operations earlier this year. Additionally, two more 110GHz CPI gyrotrons will be joining operations by the start of the FY24 plasma campaign, potentially increasing the available ECH power to over 4.5 MW. The first gyrotron, "NASA", is a refurbished depressed collector gyrotron that is currently undergoing the testing and conditioning process at DIIID. The second gyrotron, "Thor", is a new nondepressed collector gyrotron that is scheduled to arrive at DIIID this summer after undergoing repairs by the manufacturer that interrupted its conditioning process at DIIID earlier this year. Furthermore, DIIID is also expected to receive its first two new depressed collector gyrotrons from Thales in 2024 and 2025, which are each designed to generate a maximum power of 1 MW at a frequency of 117.5 GHz. 

PP11.00015: Upgrading DIIID to Close the Gaps to Future Fusion Reactors Craig C Petty The DIIID program is pursuing an ambitious plan to rapidly close critical design gaps to a Fusion Pilot Plant (FPP), including integrating performance and exhaust solutions, addressing plasma interacting material and technology issues through an expanded R&D effort, and resolving a high fusion gain path to ITER and a pulsed/steadystate FPP. Key to the DIIID approach is major facility upgrades to access reactorrelevant physics regimes with increased flexibilities. A staged divertor program will allow for more plasma shaping, and higher current and density, to enable more reactorrelevant coreedge integration. The electron cyclotron heating (ECH) will be increased to 10 gyrotrons, with an extension to 20 gyrotrons by 2028, to furnish lowtorque electron heating and profile control, while new reactorrelevant solutions for efficient offaxis current drive will be pioneered by highfieldside lower hybrid current drive, helicon waves and top launch ECH to enable FPP steadystate scenarios. Additional proposed facility upgrades include an expanded set of 3D coils, and disruption mitigation and materials testing capabilities. An exciting option for a negative triangularity path is being assessed. Together these elements will enable reactor solutions to be pioneered and projected with confidence. 

PP11.00016: Flow, Mode Effects That Seed Neoclassical Tearing Modes James D Callen, Robert J La Haye, Ted Strait This poster discusses how perturbations seed a robustly unstable neoclassical tearing mode NTM) by exceeding a "gate." In the NTM instability equation the destabilizing bootstrap current drive d_NTM is approximately 3 (j_boot / j_parallel). It is balanced by an ion polarization current that produces a stabilizing flow dependent gate function F (f_m). The polarization current gate function in the plasma is proportional to the difference between the frequencies of the NTM instability mode and the radial electric field toroidal reference frame. In the DIIID ITER Baseline Scenario (IBS) discharge 174446, the NTM drive d_NTM is about 0.5 and the ion polarization width w_pol of 2.7 cm is about twice the ion banana width. The NTM is unstable when the NTM drive exceeds the stabilizing gate in the island evolution equation: d_NTM > (w_pol^2 / w^2) F (f_m). Here, the island width w (cm) equals 3 B_rms(G)^1/2, where B_rms(G) is a transient external Mirnov signal (e.g. ELM). When the gate function is closed [F(f_m) equals 1], growing NTMs are seeded in 174446 if B_rms > 1.8 G (w > w_pol / d_NTM^1/2 simeq 4 cm). However, if the gate function F (f_m) is reduced because flow differences are reduced, NTM growth can be seeded by a slightly smaller B_rms, w. 

PP11.00017: Manipulating density pedestal structure to improve coreedge integration towards low collisionality Huiqian Wang, Rongjie Hong, Xiang Jian, Terry L Rhodes, Lei Zeng, Anthony W Leonard, Xinxing Ma, Jon Watkins, Jun Ren, Brian A Grierson, Morgan W Shafer, Filippo Scotti, Tom Osborne, Dan M Thomas, Saskia Mordijck, Florian M. Laggner, Laszlo Horvath By leveraging the benefits of lowdensitygradient pedestal in the closed divertor, DIIID has achieved a promising coreedge integrated scenario plasma which integrates a hightemperature, lowcollisionality (n^{*}_{ped}<1) pedestal with a partially detached divertor. With a closed divertor and high heating power, strong gas puffing moves the pedestal peak density radially outward and reduces the density gradient in the pedestal region. These leads to a significant separation between density and temperature pedestals and result in high η_{e}  well above the stability threshold. Concomitantly, measured electron turbulence (kr_{s}>1) is enhanced at pedestal and strongly correlated with the high η_{e}. Nonlinear CGYRO simulations found a similar instability as seen in experiment driving significant heat transport that could broaden the pedestal to be wider than the EPED scaling. The wide temperature pedestal facilitates the achievement of hightemperature lowcollisionality pedestal. Simultaneously, the outward shift of the density pedestal facilitates access to detached divertor conditions with low temperature and low heat flux towards target plate. Experiments also found that higher plasma current, strong shaping and higher heating power are beneficial for this promising coreedge scenario plasmas. 

PP11.00018: Characterization of the radiated power operational space in negative triangularity plasmas at DIIID Austin Welsh, Livia Casali, David Eldon, Tomas Odstrcil, Andrew O Nelson, Ray Mattes, Tyler B Cote, Carlos A PazSoldan, Hang Si, Kathreen E Thome We report on the first experiments and related edge modeling performed to assess the integration of core performance with power exhaust in diverted negative triangularity plasmas. A database with a wide parameter range in terms of radiated fraction, Greenwald fraction, power, density, and current has been collected, indicating a core radiated power fraction up to 0.85 obtained through the injecting of mantle radiators such as Kr, Ar, Ne. Krseeded discharges exhibit an increase in β_{N} with increases in both radiation fraction and Greenwald fraction, while Ne seeding leads to a reduction of β_{N} for f_{rad} > 0.5. Scoping studies with SOLPSITER modeling guided the location choice of seeding during the experiments, and interpretive SOLPSITER modeling with multiple impurity species will be presented showing the effects of the experimental scanned parameters, edge impurity transport, and divertor characteristics. 

PP11.00019: Measurements and SOLPSITER Modelling of Pumping Experiments in DIIID Robert S Wilcox, Morgan W Shafer, John M Canik, Shaun R Haskey, Jeremy Lore, Huiqian Wang Carefully selecting crossfield transport coefficients, particle and energy sources, and particle removal rates to reflect experimental conditions is shown to improve agreement between boundary plasma and neutral modelling using the SOLPSITER code and experimental measurements from Langmuir probes and pressure gauges in Hmode plasmas in the DIIID tokamak. However, modifying diffusive transport coefficients to match upstream plasma profiles alone is shown to result in a significant underprediction of target plasma fluxes in the cases explored. This result holds regardless of whether diffusive transport is expressed as poloidally symmetric or given a ballooning structure. Using ion temperature measurements from main ion charge exchange to determine ion thermal transport is also shown to enable agreement of upstream kinetic profiles between SOLPS and measurements, whereas the model finds measurements of impurity ion temperature to be inconsistent with other profile inputs. This work identifies boundary plasma model deficiencies and enables proper model validation exercises as models are improved. 

PP11.00020: Limiting factors for achieving peelinglimited pedestals in present devices Theresa M Wilks, Thomas H Osborne, Matthias Knolker, Philip B Snyder, Morgan W Shafer, Florian M. Laggner, Jerry W Hughes An optimized pedestal regime called the SuperH Mode is leveraged to access peeling limited pedestals and study limitations on the integrated tokamak exhaust and performance gap. Analysis of DIIID experiments demonstrates separatrix and midpedestal collisionality as key parameters in determining the state of both the pedestal and the divertor regions. Experiments were performed on DIIID to determine the conditions where peeling and ballooning modes become strongly coupled. Primary actuators for these experiments included D<span style="fontsize:10.8333px">2 puffing to match pedestal density in semiopen and closed divertors as well as varied strike point location to change the pumping efficiency in the divertor. Pedestal structure is modified by fueling and pumping such that the closed divertor requires higher gas puffing for a matched pedestal density due to the higher pumping efficiency. Due to ~2x increased pumping efficiency in the closed divertor configuration, approximately 5x higher fueling rates were required to achieve similar pedestal conditions as the open divertor. The difference in pumping efficiency and fueling for the same pedestal density indicates a change in pedestal particle transport, which leads to ~5x lower collisionalities at the separatrix and ~10x lower at midpedestal, allowing access to a peelinglimited pedestal. 

PP11.00021: Overview of High Field Side Lower Hybrid Current Drive Experiment at DIIID Stephen J Wukitch, Mirela Cengher, Ivan Garcia, Jeff Doody, Rick Leccacorvi, Evan Leppink, Yijun Lin, Mohamed Mohamed, Sam Pierson, James Ridzon, Grant Rutherford, Andrew Seltzman, Rui Vieira, Tom Guzman, Dan Kellman, Chris Murphy, Robert I Pinsker, Kyle Teixeira High field side lower hybrid current drive (HFS LHCD) is a potential tool for efficient, off axis current drive. From simulations, efficient offaxis current at r/a~0.60.8 with peak current density up to 0.4 MA/m^{2} and 0.4 MA/MW coupled is achievable for target DIIID discharges. From the HFS, LH waves are expected to have improved accessibility and single pass absorption due to favorable wavenumber upshift. A compact coupler utilizes a traveling wave, 4way splitter and a multijunction to distribute power poloidally and toroidally, respectively, and imbedded matching structures to maximize performance. Laser Powder Bed Fusion (LPBF) GRCop84, a high strength, thermal and electrical conductivity copper alloy, is used for the coupler and invessel waveguides allowing for embedded RF elements and waveguides with precise twists and bends. Klystron commissioning has begun and the klystrons have been conditioned up to 20 kW into dummy load for short pulse. The invessel waveguides and coupler have been assembled on the DIIID vessel mockup and are expected to be installed in 2023 vent. Initial HFS edge density measurements suggest the coupling is quiescent and within range the coupler was optimized. The latest results and system status will be presented. 

PP11.00022: Analysis of Final Loss Events due to Vertically Unstable Runaway Electron Beams in DIIID Jamie L Xia, Alexander F Battey, Hari P Choudhury, Oak A Nelson, Carlos A PazSoldan, Jayson L Barr, Nicholas Eidietis, Eric M Hollmann, Andrey Lvovskiy, Daisuke Shiraki Runaway electrons (REs) in tokamak fusion plasmas pose a significant challenge. A noncollisional technique called the 'benign termination strategy' shows promise for RE beam termination with minimal firstwall heating. This work analyzes RE vertical displacement event (VDE) experimental data from DIIID tokamak benign termination experiments and simulation with the TokSys code suite. This research aims to investigate correlations between experimental parameters related to equilibrium evolution and parameters associated with final loss events and MHD instabilities, which can provide valuable insights on accessing and optimizing the benign termination strategy . Equilibrium evolution analysis examines plasma stability in plasma current (IP)/ plasma minor radius (aminor) and edge safety factor (qa)/internal inductance (li) spaces to gain insight on what influences the final loss events. Derivative metrics are applied to assess the speed of VDEs and its effect on access to the final loss event. Comparisons are made between experimental EFITs and simulated TOKSYSderived EFITs. Analysis of bursts and final loss events includes the hard xray (HXR) loss duration, correlation with burst duration and time into current quench. This research enhances understanding of the crucial plasma compression phase and which details are most crucial for accessing the final MHD loss event, improving confidence in the benign termination strategy for RE beams. 

PP11.00023: Emulation of ITER Axisymmetric Control Characteristics on DIIID Zichuan A Xing, Jayson L Barr, SangKyeun Kim, Michael L Walker D3D is well suited to provide a testing ground for remaining unknowns in ITER control and exception handling. Control software have been developed to emulate ITERlike control characteristics aimed at enabling D3D to act as a scaled model for ITER development. Currently, we focus on the emulation of the magnetic control characteristics, which is implemented in two ways dependent on experimenter’s choice. A static method uses a model linearized around a scaled ITER plasma. First, a linearized model is used to calculate the ITER coil current dynamics from the power supply voltage. Then the ITER coil currents are mapped to D3D coils. Finally, a D3D current feedback controller achieves the currents calculated. The alternate method instead calculates the expected ITER field, and then calculates in realtime, the D3D coil currents that best achieves the D3D scaled equivalent. Simultaneously, vertical control characteristics are emulated by using active control to slow down the vertical instability growth rate to the ITER timescale. The emulation has been tested in D3D vacuum shots, and in control simulations. The development of a standin ITER controller is ongoing to enable the first experiment of emulated ITER control on D3D. 

PP11.00024: Dependence of EC toroidal injection angle on effective EC assisted startup James J Yang, Adrianus C Sips, Michael L Walker, Peter C de Vries, Joyeeta Sinha, HyunTae Kim, Fenton Glass, Max Austin, Michael Van Zeeland, Jeffrey L Herfindal, Morgan W Shafer, Andrew O Nelson, Claudio Marini, Alan W Hyatt, Francesca Turco, Robert I Pinsker The effect of electron cyclotron (EC) wave toroidal injected angle on the quality of preplasma for the EC assisted startup is studied experimentally at DIIID in support of ITER. The Deuterium alpha filterscope signal shows for the first time that the postreflection, second pass absorption efficiency depends heavily on the toroidal injection angle and results in the change in preplasma density and temperature that is necessary for a successful startup. A 110 GHz, extraordinarymode polarized EC wave is injected into the DIIID vacuum vessel aimed for the second harmonic resonant absorption at a poloidally oblique angle from the upper outboard launcher. The toroidal injection angle is systematically scanned from radial to 20 degrees offradial angle. It has been reported previously that the EC beam is absorbed at least twice at the resonance radius due to the reflection near the inboard midplane. The DYON and RT4 simulations indicate that the power absorption efficiency changes with the toroidal injection angle and explains the experimental observation qualitatively. This result provides valuable data to validate models and optimize ITER's startup strategy, where the EC assist is necessary and EC is designed to be injected at a toroidally oblique angle. 

PP11.00025: Modeling dissipative divertor designs for DIIID with variations in wall baffling and pump location Jonathan H Yu, Roberto Maurizio, Robert S Wilcox, Andreas M Holm, Steven L Allen, Wilkie Choi, Max E Fenstermacher, Anthony W Leonard, Adam McLean, Filippo Scotti, Morgan W Shafer In the upcoming DIIID 5year plan, a deepbaffled dissipative divertor with a long outer poloidal leg length of ~50 cm is planned, with the aim to provide data to constrain models for predicting radiation and detachment processes in a fusion pilot plant. The plasma boundary codes SOLPSITER and UEDGE are used to evaluate designs of this dissipative divertor for plasmas with up to 25 MW of heating power, focusing on the effects of baffle geometry (including particle drifts) and pump location on the divertor solution. Crossfield transport coefficients are tuned to match the heat flux width from the ITPA scaling and the pedestal shape of a recent 16 MW DIIID plasma. Increasing divertor baffling in the scrapeofflayer (SOL) better confines neutrals in the divertor, but the overall effect is small for detached solutions, with just 5 to 10% electron density increase in the divertor farSOL when the baffling is approximately conformal to SOL flux surfaces. Increased baffling in the private flux region (PRF) restricts neutrals sourced at the inner divertor from reaching the outer divertor leg through the PFR, and compresses neutrals at the Xpoint. Moving the pump location upstream from the divertor target reduces pump throughput for a given upstream separatrix density, but increases the local density near the target and thus dissipation, highlighting a robust tradeoff between the ability to exhaust particles and dissipate power. 

PP11.00026: Investigating the dependence of a LongLeg, Dissipative LowField Side Divertor on HighField Side Divertor Leg Length in DIIID Using UEDGE Simulations Including Drift Flows Andreas M Holm, Jonathan H Yu, Robert S Wilcox, Filippo Scotti, Thomas D Rognlien, Marvin E Rensink, Menglong Zhao, Roberto Maurizio, Steven L Allen UEDGE simulations of uppersingle null plasmas with a 50 cm baffled lowfield side (LFS) divertor leg, including drift flows in the favorable direction, predict a 25% decrease in LFS target separatrix electron temperature (T_{e,LFSt,sep}) and a 5% increase in LFS midplane separatrix electron density when the highfield side (HFS) divertor leg length is reduced from 20 cm to 15 cm. The simulations indicate E_{θ}×B radial drift flows through the private flux region are responsible for the observed T_{e,LFSt,sep}dependence on HFS divertor leg length. Simulations in the unfavorable drift direction predict a negligible impact on LFS divertor conditions as the HFS divertor leg length is reduced from 20 cm to 15 cm. In the unfavorable drift direction, the drift flows are directed towards the pump, increasing the particle removal rate. Consequently, T_{e,LFSt,sep} increases by 15% and 50% compared to the favorable drift direction for 20 cm and 15 cm HFS divertor leg lengths, respectively, for the same boundary conditions. The long legged, baffled divertor of the DIIID Staged Modular Divertor program will explore the feasibility of a largevolume dissipative divertor, by increasing the LFS divertor volume without internal magnetic field coils, without degradation of core plasma performance. 

PP11.00027: Density turbulence measurements by using fast sweep reflectometry in DIIID Lei Zeng, Terry L Rhodes, William A Peebles, George R McKee The fast RF frequency sweep reflectometry, with the stateofart capability of electron density radial profile measurement, is able to determine the density turbulence radial profile by the analysis of reflectometer phase fluctuations^{1}. In DIIID, the ordinary mode launch/receive phase fluctuations have been used to derive the radial profile of n_{e} fluctuations analytically. The calculated radial wavenumber range of the turbulence is from ~1 cm^{1} to ~10 cm^{1}, which is limited by the Bragg scattering condition. Initial turbulence measurement results by this technique in various DIIID plasma conditions, such as LH mode transition and the wide pedestal QH mode to standard QHmode transition, are obtained. In a typical Lmode plasma the relative fluctuation level (δn/n) varies from ~1% in the core (rho < 0.6) to more than 10% in the edge. A significant reduction in δn/n is observed when Hmode occurs. The comparison with other turbulence diagnostics, e.g., DBS and BES, has shown reasonable qualitative agreement (e.g., with BES showing ~4% and reflectometry showing ~5% at rho=0.9 for a QH mode plasma). The analysis of turbulence fluctuations via extraordinary mode reflectometer phase fluctuations is comparatively more challenging and will also be presented. 

PP11.00028: Pellet Fueling Research on DIIID Daisuke Shiraki, Larry R BAYLOR, Andrew Dvorak, Steve Meitner, John B Caughman Core fueling by pellet injection will be an essential technique for sustaining burning plasma scenarios in ITER and in a fusion pilot plant. The physics of core pellet fueling is an area of active study on DIIID, with current emphasis on understanding the interaction of the core fueling process with edge and boundary phenomena that are also essential for a highperformance plasma scenario. Interactions of concern include the possible return or onset of edgelocalized modes due to perturbation of the edge pedestal, and the effects on stability of the divertor plasma detachment. Modeling of the magnetohydrodynamic stability of the pedestal under the pellet particle source, and a series of upgrades to the DIIID pellet injection system to enable experimental study of such interactions, are underway. The ability to vary pellet mass and delivery location, with absolutely calibrated mass measurements, allows for flexible variation and quantitative analysis of the pellet particle source. These capabilities and future upgrades to increase pellet injection rates to levels relevant for divertor detachment studies, along with planned approaches for modeling the detachment response to the dynamics of the pellet particle source, are described. 

PP11.00029: Connecting DIIID and NERSC to support DIIID Operations through Kinetic Equilibrium Analysis Sterling P Smith, Torrin A Bechtel, Severin Denk, Earl W DeShazer, Andrew O Nelson, Laurie Stephey, Zichuan A Xing, Oscar Antepara, Eli Dart, Raffi Nazikian, Samuel W Williams The CAKE (Consistent Automatic Kinetic Equilibrium) OMFIT workflow to reconstruct magnetic equilibria in the DIIID tokamak with kinetic constraints has been automated to run in the NERSC realtime queue, connected to DIIID via the ESnet network. These reconstructions had been carried out on the DIIID local cluster, Iris, but took too long to make an impact on control room decisions. Optimizing the time to solution on NERSC’s Cori system (launched via the NERSC Superfacility API), with its greater parallelization possibilities, resulted in a run time for less wellconverged cases of 22 minutes. Further improvements in runtime are anticipated in moving the workflow to Perlmutter at NERSC and improving the method for finding the optimal EFIT internal spline knot locations, including more parallelization. The solutions are written back into DIIID’s MDSplus data management system and are then available to the entire DIIID team, including visualization through the omas library. 

PP11.00030: Error Field Identification through Torque Balance on a Saturated Island Edward J Strait, Yanzheng Jiang, Qiming Hu, Jeremy M Hanson, Nikolas C Logan, Carlos A PazSoldan Measurement of the electromagnetic torque on a magnetic island could be an attractive method for error field identification in the early (PFPO1) phase of ITER operation. Previous DIIID experiments [1,2] have demonstrated the principle of this approach using a stationary island, while recent developments in magnetic data analysis [3] allow the field of a rotating island to be distinguished from that of the wall currents induced by its rotation. In a recent experiment, a slowly rotating n=1 magnetic perturbation forced a saturated magnetic island to rotate, thus sampling all toroidal phases periodically in a single discharge. The phase and amplitude of the error field are inferred from analysis of the torque balance on the island, including torques from the error field, the applied magnetic perturbation, and the wall currents induced by rotation of the applied perturbation and the island. Results will be compared with those from more conventional methods.  Refs.: [1] E.J. Strait, NF 2014; [2] D. Shiraki, NF 2014; [3] R.M. Sweeney, PoP 2019 

PP11.00031: Overview of Results from the DIIID Negative Triangularity Campaign Kathreen E Thome, Max Austin, Alan W Hyatt, Alessandro Marinoni, Andrew O Nelson, Carlos A PazSoldan, Filippo Scotti, Jayson L Barr, William Boyes, Livia Casali, Colin Chrystal, Tyler B Cote, Siye Ding, Xiaodi Du, David Eldon, Darin R Ernst, Andrea M. Garofalo, Rongjie Hong, Filipp Khabanov, Gerrit J Kramer, Charles J Lasnier, Priyansh Lunia, George R McKee, Adam McLean, Saskia Mordijck, Michio Okabayashi, Olivier Sauter, Lothar Schmitz, Daisuke Shiraki, Samuel Stewart, Yuki Takemura, Dinh Truong, Tom Osborne, Huiqian Wang, Theresa M Wilks, Menglong Zhao In early 2023, a dedicated multipleweek experimental campaign was conducted to qualify the negative triangularity (NT) scenario for future reactors on the DIIID tokamak after previous initial promising experiments on TCV and DIIID. During this campaign, high confinement (H_{98y,2}≥1), high current (q_{95}<3), and high normalized pressure plasmas (β_{N}>2.5) were achieved at highinjectedpower in strongly NTshaped discharges with δ_{avg}=  0.5. The experiments with a lower outer divertor Xpoint shape covered a wide range of DIIID operational space (plasma current, toroidal field, electron density and pressure) in contrast to other highperformance ELMsuppression scenarios that have narrower operating windows. Also demonstrated was high normalized density (n_{e}/n_{GW}≤2), particle confinement comparable to energy confinement, a detached divertor without impurity seeding, and high core radiation fraction. Plasmas with strong NT maintained a nonELMing NTedge with an electron temperature pedestal, exceeding that of typical Lmode plasmas, whereas plasmas with reduced δ_{avg}~  0.18 transition into Hmode. These results are promising for a NT fusion pilot plant and further results on performance, stability, transport, scenario development, and coreedge integration will be presented. 
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PP11.00032: Spectroscopic Neutral Density Measurements of the DIIID Divertor and Comparison to Modeling Dinh Truong, Filippo Scotti, Adam McLean, Fenton Glass, Robert S Wilcox, Jeffrey L Herfindal, Menglong Zhao, Galen G Burke, Andreas M Holm, Steven L Allen Initial divertor neutral density (n_{D}) measurements in an experiment exploring the role of neutrals on detachment in DIIID indicate that n_{D} during Lmode, attached condition is ~25  35% of the local electron density. Neutral density measurements in tokamaks are critical to characterize particle sources and energy loss mechanisms in the plasma edge. Neutral densities are derived from calibrated lineintegrated Deuterium Balmer alpha (D_{α}) brightness, using local n_{e} and T_{e} measurements to determine the photon emissivity coefficients and a characteristic emissivity decay length along the line of sight from UEDGE simulations. The n_{D} obtained is an upper estimate of the atomic density due to contributions from molecular dissociative excitation and recombination processes. To unravel the relative contributions, the derived D_{α} emissivity and n_{D} are compared to DEGAS 2, which calculates neutral (atomic and molecular) densities and emissivities from measured profiles. Atomic densities obtained with this technique and interpreted by DEGAS 2 are validated using Lymanalpha measurements, which have negligible contributions from molecular processes. By sweeping the outer strike point past the diagnostic lineofsights, this measurement technique can be extended into 2D. 

PP11.00033: Temperature fluctuation measurements in negative triangularity plasmas in ASDEX Upgrade Rachel Bielajew, Branka Vanovac, Michael G Dunne, Thomas Pütterich, Tim Happel, Dirk Stieglitz, Davide Silvagni, Garrard D Conway, Jörg Hobrik, Nathan T Howard, Pablo RodriguezFernandez, Matthias Bernert, Christian Yoo, Anne White Negative triangularity (NT) experiments in TCV [1] and DIIID [2] have shown Hmode level confinement without Edge Localised Modes (ELMs), setting a path for NT as an operating scenario for burning plasmas. At ASDEX Upgrade, NT plasmas with δ_{av} < 0.2 can be achieved, and these plasmas can undergo the L to Hmode transition depending on ∇B drift configuration and heating power [3]. In this work, we present Correlation ECE measurements in NT plasmas of T_{e} fluctuation spectra, fluctuation amplitude, and correlation lengths in the outer core and the edge. We compare powermatched discharges with low (δ_{av} ≈ 0) and moderate (δ_{av} ≈ 0.2) average triangularity. At moderate δ_{av}, the plasma enters Hmode with ELMs. The low δ_{av} discharge stays in Lmode for the same heating power, contrary to the current understanding that higher negative δ_{av} means Hmode avoidance. Hmode phases of ECRHheated and NBIheated NT plasmas are also compared. An increase in T_{e} fluctuation amplitude with radius is observed in both plasmas, but the details of spectral features differ. Initial gyrokinetic simulations are performed for the ECRH and NBI discharges in the outer core and pedestal top. 

PP11.00034: ECEImaging characterization of edge magnetic islands affecting pedestal transport and stability in a netzero torque plasma Calvin W Domier, Guanying Yu, Zeyu Li, Tyler B Cote, Gerrit J Kramer, Yilun Zhu, Neville C Luhmann Characterization of a m=5, n=1, and f~0.53 kHz rotating island at the pedestal top (psiN~0.89) of a netzero torque lowcollisionality, wide pedestal QHmode is presented. The characterization is made with ECEImaging and other diagnostic systems at the DIIID tokamak. The magnetic island is observed to exert a profound effect on the pedestal structure and the axisymmetric peelingballooning mode stability. Though the discharges have no Resonant Magnetic Perturbation (RMP) applied, the observations of edge island and peeling mode serve to improve the understanding of EdgeLocalizedMode (ELM) suppression with 3D fields. As the edge island grows, the pedestal pressure ceases increasing and holds relatively unchanged until a large ELM is triggered after ~ 100 ms. The island rotation also displays a clear modulation on the amplitude of the peeling mode, which eventually grows to a large amplitude and triggers the ELM. These observations suggest that an edge magnetic island plays a complicated role in RMPELM suppression. Though it enhances the pedestal transport that benefits ELM suppression, the rotation of the island also periodically excites a high frequency (~50 kHz) ELMtrigger peeling mode, which can be a result of the 3D field effect on the peeling mode stability boundary. 

PP11.00035: Wall current compensation for rotating magnetic perturbations through the magnetic diagnostic response function Yanzheng Jiang, Mattew J Overton, Edward J Strait, Qiming Hu The method of magnetic diagnostic response function (MDRF) [1] is well suited to estimating the magnetic fields of wall currents induced by rotating resonant magnetic perturbations (RMP). The MDRF provides a set of time dependent Green’s functions for the magnetic diagnostics, obtained by fitting magnetic measurements with individual coils energized at varying frequencies. The wall current field from RMP is then predicted by the response functions when using the RMP coil currents with arbitrary waveforms. These predictions will be validated by vacuum shots with rotating RMP fields in DIIID. The wall current field from the rotating RMP is separated in magnetic signals to evaluate the effect of the wall currents on electromagnetic torque analysis of magnetic islands. The present work can provide the wall currents compensation in error field identification experiments, which use a rotating RMP field to drive rotation of an n=1 magnetic island. Additionally, this work will benefit the analysis of other experiments with timevarying applied fields by accounting for the effects of induced currents in the wall and other conducting structures. 

PP11.00036: Bayesian inference of axisymmetric plasma equilibria Sehyun Kwak, Jakob Svensson, Oliver P Ford, Lynton Appel, Youngchul Ghim We present a Bayesian approach for inferring axisymmetric plasma equilibria from measurements of the magnetic field and plasma pressure. This method delivers a set of posterior solutions for plasma current and pressure distribution that align with the given measurements and satisfy magnetohydrodynamic (MHD) force balance. In this method, the toroidal plasma current and magnetic field coils are modelled as a collection of axisymmetric currentcarrying beams. The remaining parameters, such as plasma pressure and poloidal current flux, are represented as a function of poloidal magnetic flux, determined by a twodimensional distribution of axisymmetric current. The profiles of plasma pressure and poloidal current flux are modelled as Gaussian processes, and their smoothness is determined according to Bayesian model selection based on the principle of Occam's razor. The force balance constraint derived from MHD is taken into account at every plasma current beam. Experimental observations collected by diagnostics are compared with predictions from the predictive (forward) models. The complex, highdimensional posterior probability distribution is explored by using a novel algorithm leveraging the Gibbs sampling scheme. The method is developed within the Minerva framework and applied to the JET tokamak experiment. 

PP11.00037: Enhancing Machine Learning of the GradShafranov Equation with EFIT's Green's Function Tables Joseph T McClenaghan, Cihan Akcay, Torrin A Bechtel, Xuan Sun, Lang L Lao, Sandeep Madireddy, Scott E Kruger, OrsoMaria O Meneghini This work presents a method for predicting plasma equilibria in tokamak fusion experiments and reactors. The approach involves representing the plasma current as a linear combination of basis functions using Principal Component Analysis of plasma toroidal current densities (J_{t}) from the EFITAI equilibrium database. Then utilizing EFIT's Green's function tables, basis functions are created for poloidal flux (ψ) and diagnostics generated from the toroidal current. First, the predictive capability of a least squares technique to minimize the error on the synthetic diagnostics is employed. Results show that the method achieves high accuracy in predicting ψ and moderate accuracy in predicting J_{t} with median R^{2} = 0.9995 and R^{2} = 0.973, respectively. A simple neural network (NN) is also employed to predict the coefficients of the basis functions. The NN demonstrates better performance compared to the least squares method with median R^{2} = 0.9997 and 0.988 for J_{t }and ψ respectively. The robustness of the method is evaluated by handling missing or incorrect data through the least squares filling of missing data, which shows that the NN prediction remains strong even with a reduced number of diagnostics. Additionally, the method is tested on plasmas outside of the training range showing reasonable results. 

PP11.00038: Towards a high fidelity tokamak pulse simulator Jin Myung Park, Gary M Staebler, Kyungjin Kim, Rhea L Barnett, John Canik, Cami S Collins, Ehab M Hassan, Jeremy Lore, Phil. B Snyder, Robert S Wilcox A range of efficient and robust IPSFASTRAN integrated modeling workflows has been developed to predict time evolution of tokamak plasma discharges from plasma current rampup to termination. The TGLF quasilinear transport model is employed in the core region with the new 3D saturation model SAT2 for the Ohmic Lmode current rampup, where the boundary conditions are given at the separatrix. The coupled EPED/SOLPSITER modeling predicts selfconsistent profiles in the pedestal and SOL/divertor regions during the Hmode phase of discharge flattop. Testing with TGLFSAT2 against the ITER demonstration discharges on DIIID reproduces the magnetic flux consumption and time evolution of the internal inductance during the plasma current rampup reasonably well, which strongly depends on accurate estimation of the electron temperature profile and electrical conductivity in the outer radius region. Recent progress on the PredictFirst approach will be discussed to design an optimum access to high β_{N} Advanced Tokamak scenarios on DIIID. 

PP11.00039: Multifidelity neural network representation of gyrokinetic turbulence Tom F Neiser, Orso Meneghini, Sterling P Smith, Joseph T McClenaghan, Tim Slendebroek, David Orozco, Brian Sammuli, Gary M Staebler, Joseph B Hall, Emily A Belli, Jeff Candy This presentation will introduce a multifidelity neural network model of gyrokinetic turbulence GKNN0, which has been trained and validated against a database of 5 million TGLF simulations and 5000 linear CGYRO simulations with experimental input parameters from the DIIID tokamak. The first half of the presentation will review the TGLF saturation rules  SAT0, SAT1, SAT2  and present a big data approach to validating both the linear model of TGLF and the saturation rules using experimental data from the DIIID and MASTU tokamaks. As a highlight, the TGLF model is shown to accurately reproduce both experimental and quasilinear CGYRO fluxes for electrostatic turbulence, and the SAT2 model shows improved accuracy compared to SAT1 at capturing physics of trapped electron modes and the instability threshold of kinetic ballooning modes. The second half of the presentation will focus on database generation and benchmarking of a singlefidelity, retrained TGLFNN and a multifidelity GKNN0. The training database uses synthetically extended data from DIIID as input, and both single and multifidelity models show good convergence within a fluxdriven transport solver. The big data validation approach allows efficient extensions of the training database, positioning GKNN0 as a fast and accurate surrogate model of gyrokinetic turbulence. 

PP11.00040: Prediction of kinetic profiles of DT plasma using the TGYRO transport code in the JET DTE2 discharges Nan Shi, Gary M Staebler, Emily A Belli, Joseph T McClenaghan, HyunTae Kim, Fulvio Auriemma, Krassimir Kirov JET DTE2 experiments have demonstrated the highestever fusion energy production. Prediction of transport in these discharges has been made using the TGLF and NEO models in TGYRO transport code. A new model TGLFSAT2 [1] of the saturated 3D fluctuation spectrum fit to a large set of nonlinear CGYRO turbulence simulations was developed to address discrepancies uncovered by validation with JET deuterium discharges. The predicted kinetic profiles of DT plasma using TGYRO have been validated by the JET DTE2 experiment and were found to be an accurate predictor when using the measured boundary values at r/a=0.85. TGYRO predicts the temperature profiles well for a wide radial window, except for a minor discrepancy in T_{i} in the plasma core. The electron density profiles n_{e} are underpredicted by 20% at midradii for both baseline scenarios and hybrid scenarios. 

PP11.00041: MHD AND STABILITY


PP11.00042: Developing novel group theoretical algorithms for evaluating MHD stability in complex geometry Caira Anderson, Adelle M Wright, David S Bindel, Benjamin J Faber We present recent progress on the development of a new code for evaluating linear (global) ideal MHD stability in stellarator geometry, using Julia’s high performance mathematical libraries. Here, we focus on the exploration of novel algorithms, based on representation theory of finite groups, that serve the dual purpose of (i) reducing the complex, global problem to simpler eigenvalue problems over the invariant subspaces of symmetry groups in stellarators and; (ii) minimize the impact of spectral pollution, allowing accurate location of continuous spectra and discrete eigenvalues for scalable, highperformance calculations. 

PP11.00043: Equilibrium βlimits dependence on bootstrap current in classical stellarators Antoine Baillod, Joaquim Loizu, Zhisong Qu, Hugo P Arbez, Jonathan P Graves While it is important to design stellarators with high magnetohydrodynamic (MHD) stability βlimit, it is also crucial to ensure that good magnetic surfaces exist in a large range of β values. As β increases, pressuredriven currents perturb the vacuum magnetic field and often lead to the emergence of magnetic field line chaos, which can worsen the confinement and is the cause of another kind of βlimit, the socalled equilibrium βlimit. In this paper, we explore numerically the dependence of the equilibrium βlimit on the bootstrap current strength using the Stepped Pressure Equilibrium Code (SPEC). We develop a diagnostic to determine whether or not magnetic islands are expected to participate significantly to radial transport, and we build an analytical model to predict the expected equilibrium βlimit, which recovers the main features of the numerical results. This research opens the possibility to include additional targets in stellarator optimization functions, provides additional understanding on the existence of magnetic surfaces at large β, and is a step forward in the understanding of the equilibrium βlimit. 

PP11.00044: FIRST tokamak in progress Marty Chou, Lin Shih, C. T. Hsu, K. C. Shaing, H. K. Lee A conceptual design of FIRST (Formosa Integrated Research Spherical Tokamak) is in progress. The scientific goals of the device are to perform research on (1) high β plasmas, (2) high bootstrap current density fraction (preferably 100%) operation, (3) the possibility of improved neoclassical ion confinement and the possibility of suppressed turbulent fluctuations, and (4) the maneuverability of particle transport. Here, β is the ratio of the plasma pressure to the magnetic field pressure. These goals are consistent with the desirable features of tokamak fusion energy reactors, i.e., configurations with good plasma confinement but with ash removability without sacrificing plasma β and without the need of the noninductive external current drive for steady state operations. Thus, a tokamak can be an intrinsically steady state plasma confinement concept when its collisioonality parameter ν_{* }< 1. Here, ν_{* }is the ratio of the effective collision frequency to the bounce frequency of the trapped particles. To achieve high β plasmas but with acceptable economic consequences, the device will be a low aspect ratio tokamak. The targeted aspect ratio is in the vicinity of 1.5. The magnetic field will be in the range of 0.1T to 0.5T (or higher when it is upgraded). Plasma minor radius is 30cm and elongation is 2.5 with a positive triangularity parameter. The stability property, and the β limit of the equilibrium with a high bootstrap current density fraction of the design together with the relevant physics, and the future plan will be reported. 

PP11.00045: FLIPEC, an Ideal MHD freeboundary equilibrium solver for plasma with flows in axisymmetric geometries. Gonzalo FernandezTorija Daza, Jose Miguel Reynolds Barredo, Raul Sanchez, Victor Tribaldos Macía, Alberto Loarte The ability of calculating ideal MHD equilibria is needed not only during the design of a magnetic fusion device, but also in its normal operation. In the case of tokamak axisymmetric configurations with significant plasma flow, the plasma edge is maintained fixed as the code searches for the equilibrium in the majority of codes. However, plasma flows may induce changes such as displacements of the position of the Xpoint, the magnetic axis or the shape of the plasma boundary, to name a few, that cannot be quantified properly in a fixedboundary setup. In this contribution we present a new equilibrium code and its most significant and recent upgrades. In this context, FLIPECode was written to obtain freeboundary axisymmetric ideal MHD equilibria for arbitrary plasma flows. Particularly, the freeplasmaboundary scheme has been previously applied to 3D, nonaxisymmetric configurations in the absence of flow within the SIESTA equilibrium code. 

PP11.00046: MultiModal analysis of linear MHD response to resonant magnetic perturbations in DIIID plasmas Brent L Ford, Tyler B Cote, Chris C Hegna, Brendan C Lyons, Shuai Gu The impact of plasma triangularity on the plasma response to 3D magnetic perturbations for DIII D plasmas is investigated to understand its role in suppression of edge localized modes. Evidence suggests the dynamics of ELM suppression can be significantly altered by the 2D plasma shaping, namely triangularity, to the point where suppression may not be achieved [1]. By varying triangularity, pedestal density, and plasma beta using the SEGWAY framework, and calculating the 3D plasma response with GPEC, we examine the combined effect of 2D plasma shaping and 3D perturbations on ELM suppression. Preliminary results show qualitative agreement between the triangularity dependence of the kink response from GPEC and that of a related study using MARSF[2]. Using singular value decomposition techniques, we analyze changes in dominant mode harmonics to assess the dependence of plasma response on plasma shaping. This comprehensive study identifies key factors influencing the response, providing valuable insights for optimizing plasma configurations and control strategies. [1] PazSoldan C. et al, Nucl. Fusion 59, 056012 (2019). [2] S. Gu et al, Nucl. Fusion 62 076031 (2022). 

PP11.00047: Gyrokinetic modeling of neoclassical tearing modes using the electromagnetic Xpoint Gyrokinetic Code (XGC) Thomas Gade, Robert Hager, Choongseok Chang Neoclassical tearing modes in tokamak plasmas are an active area of research due to their impact on global plasma stability. They have been mainly studied with magnetohydrodynamic (MHD) codes due to the relatively smaller computational cost compared with kinetic models. The downside of fluid methods is the approximate treatment of kinetic effects such as collisional parallel or turbulent crossfield transport through simple fluid closures and turbulence models. In contrast, this work uses the electromagnetic totalf gyrokinetic particleincell code XGC to model low toroidal mode number ("lown") tearing modes using a recently installed hybrid spectral/finiteelement field solver that provides higher accuracy and greater numerical stability for lown modes than XGC's standard field solver. We present verification studies of lown tearing mode physics using XGC's deltaf option against linear eigenvalue solvers and MHD codes. Using XGC's totalf algorithm, we study neoclassical tearing modes in a single firstprinciples kinetic model without relying on fluid closures or coupling to other codes. 

PP11.00048: Nonlinear saturation of nonresonant ideal long wavelength instabilities and application to sustained hybrid operational regimes Jonathan P Graves, Margot CosteSarguet, Isabel Krebs A new theory is presented unifying the nonlinear saturation of nonresonant n=m=1 internal kink modes with reverse shear [1], and nonlinearly saturated n=m=1 quasi interchange modes with an extended region of very low shear [2]. The generalised set of new equations also describes n=m>1 modes [3] with arbitrary nonresonant qprofiles. By explicitly evaluating the nonlinear effect of these modes to, and on, the magnetic flux, it is possible to analytically quantify the effect of the 3D magnetic structures on the qprofile. Over the initial phase of the resistively diffusing plasma scenario, the associated growing 3D magnetic perturbations are assumed to cause strong crossfield transport. Under these conditions the plasma will cease to resistively diffuse, and the modes cease to grow, so that the hybrid regime can in principle be sustained, possibly in line with previous ideas concerning a magnetic flux pump [4]. The picture remains robust to potential kinetic corrections of core instabilities in the weakly collisional regimes of future tokamak reactors. 

PP11.00049: Fluctuationinduced electromotive forces in currentdriven tokamak sawtooth relaxation Karsten J McCollam, Brett E Chapman, John S Sarff, Carl R Sovinec, Rachel A Myers, Mihir D Pandya, Ruifeng Xie We show via nonlinear MHD modeling a causal relationship between the fluctuationinduced 'dynamo' EMF and the cyclic equilibrium profile relaxation in currentdriven tokamak sawtooth activity. Sawteeth have been of keen interest in tokamak research (see Jardin et al. 2020, Heidbrink & Victor 2020, e.g.), and we highlight the role of dynamo EMF in impulsive sawtooth magnetic relaxation. Using the NIMROD code, we perform nonlinear zerobeta 3D viscoresistive MHD simulations initialized with q profiles reaching just below 1 on axis. This leads to currentdriven sawtooth cycles, originally described by Kadomtsev. A dynamo EMF, the spatial average of the nonlinear product of velocity and magnetic fluctuations in Ohm's law, arises naturally in the relaxation process. In 3D simulations, with fluctuations of multiple toroidal mode numbers included, the dynamo EMF is localized to the core near the q=1 surface and is correlated in time with quasiperiodic bursts in fluctuation amplitudes, driving the core q profile above 1, a change of several percent, during the corresponding crash events. Comparing these cases to the quiescent equilibria in 2D simulations highlights the causal character of the dynamo EMF in the sawtooth dynamics. Details of the fluctuation dynamics are observed to vary with the location of the q=1 surface. For example, for larger q=1 radius, a subsequent oscillation in n=1 energy occurs after the main n=1 crash, possibly reflecting partial rather than complete reconnection in the main crash. 

PP11.00050: Error field predictability and consequences for ITER Matthew C Pharr, Carlos A PazSoldan, Nikolas C Logan, Nils Leuthold, JongKyu Park We conduct a linear study of n=1 error fields due to tilted and shifted misplacements of central solenoid and poloidal field coils within tolerance. Error fields in magnetic confinement fusion can cause large, sometimes sudden, losses in confinement, which has severe consequences for fusion performance. Their origin and optimal correction therefore remains a topic of pertinent interest for study in planning future magnetic confinement devices. We thus begin with an analysis of the necessity of error field correction for daily operation in ITER using updated scaling laws for the error field penetration threshold. We then investigate the optimal correction of each error field using the error field correction coils as well as the RMP ELM coils. We also consider the predictability of error field overlap across early planned ITER scenarios and, as measuring error fields in high power scenarios poses risks to the device, the potential for extrapolation to the ITER Baseline Scenario (IBS). We find that some error field sources extrapolate well to IBS, while others do not and could benefit from careful metrology. 

PP11.00051: Improving SIESTA numerical convergence JoseMiguel ReynoldsBarredo, Raul Sanchez SIESTA is a well known ideal MHD non linear equilibrium solver [1] capable of finding solutions that may exhibit rather complicated topologies including both magnetic islands and stochastic regions. Recently, it was extended to be capable of providing freeplasma boundary solutions as well [2]. In this work, various advances targetting the improvement of the numerical convergence of SIESTA towards the equilibrium are presented. These advances will be of use, not only for increasing the computational efficiency for cases that SIESTA already solves with ease, but to significantly improve the performance of SIESTA in configurations where convergence is slow, is plagued by plateaus of apparently no convergence or simply fail to converge. To achieve this, it has been developed a new second order advance for both p and B perturbations (currently, it is only first order) that allows to improve the equivalence between the MHD energy variation and the work associated with the force for any given displacement. By carefully discretizing the resulting advance equations, this equivalence can be made exact for the pressure term (up to machine accuracy) and second order accurate in the displacement for the magnetic field term.This equivalence has the additional associated benefit of ensuring a fully symmetric Jacobean down to machine precision. Analytical results and first numerical tests will be presented. 

PP11.00052: Investigation of changes induced in the MHD spectrum by the presence of magnetic islands/stochastic regions with the SIESTA 3D MHD equilibrium code Raul Sanchez, JoseMiguel ReynoldsBarredo SIESTA [1] is a well known 3D MHD equilibrium solver that is capable of finding ideal MHD equilibrium solutions without assuming the existence of nested toroidal magnetic surfaces everywhere in the plasma volume. As a result, SIESTA solutions that exhibit both magnetic islands and stochastic regions are possible. In addition, SIESTA uses Eulerian coordinates in which the pressure and magnetic field response to arbitrary plasma displacement can be easily calculated. SIESTA also estimates the local Hessian of the problem (i..e, the derivative of the force with respect to the local displacement) at each step of its nonlinear iteration towards equilibrium since it is often used as preconditioner for the linear problem that must be solve at each step. Once the equiilibrium is reached, the Hessian is available and the study of its eigenvalues/eigenvectors allows to explore and quantify the ideal MHD stability properties of the reached solution. In this work we will use this capability to characterise the changes that are induced in the MHD ideal spectrum, with respect to that of neighbouring solutions that assume nested tori everywhere, by the presence of islands/stochastic regions, their size and location, for both tokamak and stellarator configurations. [1] Hishman SP, Sanchez R and Cook, CR. Physics of Plasmas 18, 062504 (2011). 

PP11.00053: Analysis of KelvinHelmholtzlike instabilities in strongly rotating tokamak plasmas Celine Schaumans, Jonathan P Graves, Howard R Wilson Toroidal rotation in tokamak plasmas has been shown to stabilize several performancelimiting instabilities. However, for toroidal flows of the order of the ion sound speed a new rotation and rotation sheardriven KelvinHelmholtzlike instability can grow [1]. Experimental evidence for this mode may have been observed in previous NSTX data. The experiments indicate that gradients in density coexisting with sonicordered flows could play an important role in its drive [2]. In [1], only strong gradients in plasma rotation were considered. 

PP11.00054: Status and overview of the Wisconsin HTS Axisymmetric Mirror experiment Dmitry Yakovlev, Jay K Anderson, Michael R Brown, Jan Egedal, Benedikt Geiger, R.W. Harvey, Mykola Ialovega, Jeremeiah J Kirch, Ethan E Peterson, Yuri V Petrov, Jonathan D Pizzo, Tony Qian, Kunal Sanwalka, Oliver Schmitz, John P Wallace, Mason Yu, Cary B Forest The Wisconsin HTS Axisymmetric Mirror (WHAM) is a magnetic plasma confinement experiment developed by UWMadison. The setup, with its 17Tesla superconducting magnets and classrecord volumetric density of heating power (3MW/40l) will explore the performance limits of simple axisymmetric mirrors by capitalizing on better understanding of MHDstable operation of such systems and on the significant technological advances of recent years. The goals of the experiment include achieving the socalled classical mirror ion confinement regime that could be upscaled to Q ~ 1 fusion power gain factor in the upcoming nextgeneration device. A major part of the experimental program is devoted to plasma microstability, that was previously seen as a major obstacle to unlocking the full potential of simple mirrors. As a critical piece a larger fusion program, the experiment will also provide valuable data for advanced mirror concepts such as the axisymmetric tandem mirror reactor. 

PP11.00055: Bifurcation of radial electric field in tokamak edge pedestal in response to resonant magnetic perturbations Ping Zhu, Fangyuan Ma, Jiaxing Liu, Xingting Yan The radial electric field E_{r }can significantly influence the transport and stability of plasma in tokamak edge pedestal, as well as the plasma response to resonant magnetic perturbations (RMPs). Through the radial force balance, the radial electric field E_{r} can be determined from toroidal and poloidal flows, along with the pressure profiles. In presence of RMPs, the nonresonant neoclassical toroidal viscosity torque is able to drive toroidal rotation in the edge pedestal due to large diamagnetic drifts, in addition to the resonant electromagnetic torque on a rational surface. Both torques depend on the radial electric field E_{r}, which may eventually settle into a steady state through the torque balance. In this work, we solve for the steady state E_{r} in presence of RMPs through numerical iterations, based on the plasma response computed from the modified Rutherford equation or the MHD simulations using the NIMROD code. Mostly due to the existence of multiple neoclassical offset rotation roots in certain parameter regimes, the steady state E_{r} in the edge pedestal region tends to be multiplevalued as well, demonstrating bifurcation behaviors and suggesting potential mechanisms underlying the edge pedestal processes that rely on the plasma response in E_{r} to RMPs. 

PP11.00056: ANALYTIC TECHNIQUES IN MFE


PP11.00057: Adjoint methods for Transport Equations Ian G Abel, Rahul Gaur Gyrokinetic simulations of plasma transport have been the workhorse of numerical understanding of magnetically confined plasmas for nearly two decades. With increasing focus on designing the core of a fusion pilot plant, the focus of simulations has moved from highly accurate verification and validation simulations to the task of trying to design 

PP11.00058: Basis Dispersionlet Bispectral Analysis Derek A Baver Ritztype bispectral analysis^{1} is a class of techniques that use statistical correlations in turbulence fluctuation data to infer the underlying model equations. This offers a novel approach to theoryexperiment comparison, and more recent algorithms can additionally infer profile functions or topological boundaries from fluctuation data. Out of this class, basis dispersionlet analysis is a technique in which model equations are represented using waveletlike operators, or dispersionlets. This offers a compromise between accurate modeling of dispersion relations, as with the basis function method, and accurate modeling of profile functions, as with the basis operator method. 

PP11.00059: GPUcapable RF Ray tracing using a domainspecific compiler Mark R Cianciosa, Donald B Batchelor, Wael Elwasif Designing an optimized fusion pilot plant requires rapid prediction of wholefacility performance. Highfidelity models such as full wave radiofrequency (RF) for determining power deposition profiles require too much time and resources to explore a vast array of design parameters. Geometric optics, commonly called ray tracing offer a faster approach to determine such models. However, legacy codes have not been built to exploit the hardware architectures of modern computers and their graphical processing units (GPUs). To compound the problem, GPU coding is not compatible between different manufacturers. Without proper abstraction, codes written for the CUDA architecture of Summit need to be rewritten to support the AMD architecture of Frontier. We present a new ray tracing code built using a graph computational framework. Physics equations are compiled into a graph of mathematical operations. Transformations of that graph apply auto differentiation to build ray update expressions. Reductions of the graph to reduce the problem to its simplest form. This graph of operations can be just in time (JIT) compiled to an optimized GPU or CPU kernels for a specific architecture. Using this framework, we demonstrate correct fully 3D ray behavior for realistic tokamak geometries for different plasma dispersion functions. 

PP11.00060: Numerical nearaxis expansion of weakly quasisymmetric MHS equilibria to all orders Lanke Fu, Amitava Bhattacharjee, Eduardo Rodriguez Quasisymmetric stellarators can achieve tokamaklike neoclassical confinement without driven current. However, QS equilibria are notoriously hard to construct. It is widely believed that isotropic pressure MHS equilibria with global QS may not exist. When expanded in effective minor radius, the governing equations become overdetermined at the 3rd order.[1] This does not forbid the existence of special solutions, as recent optimization works have indeed produced equilibria with precise QS.[2] It also does not apply to anisotropic equilibria. Rodriguez and Bhattacharjee has shown that adding a pressure anisotropy allows the expansion of global weak QS equilibria to any order.[3] This expansion is likely divergent,[4] but its optimal truncation and higher order behavior remain unclear. 

PP11.00061: Implementation of the logical sheath boundary condition in the COGENT code Vasily I Geyko, Ilon Joseph, Mikhail Dorf Accurate modeling of the boundary sheath layer in plasma simulation necessitates addressing the finescale features of the sheath region. These scales are typically much smaller than the characteristic length scales of the plasma bulk, therefore including a sheath region in a numerical model would significantly increase the cost of simulations. To overcome these difficulties, the logical sheath boundary condition (BC) is used where the sheath is replaced by a boundary potential that reflects fast electrons and enforces the total electron and ion current through the boundary to be equal. Implementation of the logical sheath BC in the finite volume COGENT code requires assigning proper values of the probability distribution function (PDF) in the ghost cells, since the fluxes on the boundary cell faces are computed based on the values of the PDF in nearby cells. This procedure depends on the advection scheme used in the code and has been implemented and tested it for first and third order upwind schemes. When electrons are reflected by the sheath potential, it inevitably yields to formation of a sharp interface of the PDF in the velocity space. That in turn leads to Gibbs oscillations when high order advection schemes are used. Different approaches for smearing the interface and mitigating the oscillations are discussed. 

PP11.00062: ThinCurr, TokaMaker and friends: Opensource fusion modeling tools for engineering, analysis, and education Christopher J Hansen, Alexander F Battey, Anson Braun, Francois Logak, Sophia Guizzo, Sander Miller, Daniel A Burgess, Carlos A PazSoldan The PSITet [1] and PSITri [2] code bases have been merged into a common framework of reusable infrastructure for fusionrelevant simulation tools based on finite element methods on unstructured grids. In addition to the existing 3D forcefree ideal MHD equilibrium [3] and 3D timedependent extended MHD [4] tools, two additional capabilities have been added: 1) A 3D thinwall current modeling tool named “ThinCurr” [5] that is being used to study nonaxisymmetric currents in 3D device structures (eg. ports and REMCs) and as an alternative to fourierbased current potential formulations in stellarator coil optimization. 2) A 2D static and timedependent GradShafranov equilibrium tool named “TokaMaker”, that is designed to be a userfriendly and open tool for device design, control development and education. The core framework provides common capabilities to all tools, including: meshing directly from CAD models, access to scalable linear and nonlinear solvers, extensible finite element representations, parallelization via OpenMP+MPI, and 3D visualization through VisIt and similar tools. Information and development plans for ThinCurr, TokaMaker, and the full toolkit will be presented. 

PP11.00063: An anisotropic hybrid structuredunstructured mesh approach enabling PIC simulations of the ScrapeOffLayer Md Fazlul Huq, Logan T Meredith, Onkar Sahni, Davide Curreli In this research, we introduce an anisotropic hybrid structuredunstructured mesh approach for ParticleInCell (PIC) scheme based kinetic simulations of the ScrapeOffLayer (SOL) for cases with nontrivial wall shapes. The steep gradient of the electrostatic potential results in an anisotropic solution variation, e.g., in the plasmasheath region, for which using a uniform mesh, or even a nonuniform/graded isotropic mesh, leads to an excessively large mesh. To address this challenge, we propose an anisotropic hybrid mesh approach. This approach employs a structured or layered anisotropically refined mesh, including near the nontrivial wall shapes, and smoothly transitions into a relatively coarse unstructured triangular mesh with rapid gradation for regions with a marginal solution variation. The anisotropic layered mesh uses a much smaller mesh size in the direction of the solution variation, e.g., mesh size of the Debye length in the wallnormal direction in the sheath region, while using a larger mesh size in the other directions. The effectiveness of the proposed approach is demonstrated through kinetic simulations of largescale SOL using the hPIC2 code on multiGPU computers. 

PP11.00064: GITRm: A 3D Unstructured Meshbased Particle Tracking Code for Global Impurity Transport in Fusion Devices Dhyanjyoti D Nath, Vignesh V Srinivasaragavan, Timothy R Younkin, Md Fazlul Huq, Davide Curreli, Zachary J Bergstrom, Aritra De, Jerome Guterl, Mark S Shephard, Onkar Sahni GITRm is a 3D unstructured meshbased Monte Carlo particle (neutral atom and ion) tracking code for global impurity transport in fusionrelevant devices. It is designed to target complex wall geometries, including nonaxisymmetric local features such as bumpers, probes, etc., and account for their interactions with the plasma. It is capable of resolving the gyromotion of impurity particles in 3D. It is built on the PUMIPic infrastructure that is designed to be performant on multiGPU computers. It uses strongly graded and anisotropic elements to efficiently and accurately represent the plasma fields from multiple sources, especially in a 3D/volumetric fashion. The sheath electric field can be calculated analytically or obtained from a sheath simulator. For example, procedures have been developed in GITRm to integrate a sheath mesh on which an electric field has been calculated from the particleincell based kinetic code hPIC2. Furthermore, the capabilities of GITRm have been extended to simulate multiple impurity species simultaneously and their interactions with different material surfaces including mixed surfaces. Results of the impurity transport simulations will be shown for multiple cases such as the ITER and DIIID geometries including local features. 

PP11.00065: Contour Method for Resistive Evolution of GradShafranov Plasma Equilibrium and Its Application to MTF Studies at General Fusion Ivan Khalzov, Victoria Suponitsky We present a numerical code based on a contour method, which is developed at General Fusion (GF) for simulating magnetized plasma dynamics. The goal of this code is to model the existing GF plasma experiments and to guide the design of future GF magnetized target fusion (MTF) systems, in which metal liner compresses compact toroid plasma. The method assumes that the tokamaklike plasma goes through a sequence of axisymmetric GradShafranov equilibria, which are linked together through the transport processes. The plasma is represented as a set of nested contours (flux surfaces), each of them encloses a fixed amount of plasma particles and corresponds to some values of poloidal flux Ψ_{c}, toroidal flux Φ_{c} and entropy S_{c}. The contours are reconstructed as levels of poloidal flux function Ψ(r,z) on 2D Eulerian quadrilateral mesh. At every time step, the code alternates between 1D transport substep, where updated values of Ψ_{c}, Φ_{c} and S_{c} are calculated using contour averaged transport equations, and 2D GradShafranov substep, where new equilibrium mesh function Ψ(r,z) is found by iterations. The main advantage of this code is its speed: the time step is limited by a large resistive diffusion timescale and not by a small Alfven timescale as in usual MHD codes. The code can be generalized to include moving boundaries of plasma domain, which is especially useful in modeling MTF systems. Verification of our code against open source code MHD OpenFOAM and comparison of results with ongoing GF experiments will be demonstrated. 

PP11.00066: Testing multispecies MHD algorithms within the acceleratorenabled NIMROD code Jacob R King, Eric C Howell Multispecies MHD simulation is critical to fusionenergy applications such as coreedge integration with a radiating detached divertor; disruption mitigation through impurity injection; and burningplasma physics with multiple fuel species and fusion byproducts. Hierarchical models for multicomponent MHD that include closures for a diffusion velocity or evolving a momentum equation for each species are described. The NIMROD code uses a mixed implicit, semiimplicit leapfrog algorithm for single and twofluid (electrons and a single ion species) simulations. A semiimplicit operator in the momentum equation is essential for numerical stability for the single and twofluid models. Approaches to generalize the semiimplicit operator for multiple momentum equations are tested. These capabilities are implemented within a version of the NIMROD MHD code that incorporates device accelerated computing through OpenACC and abstract types as enabled by modern Fortran. 

PP11.00067: Modeling neoclassical impurity transport with the fullf gyrokinetic code COGENT Alexey R Knyazev, Mikhail Dorf, Sergei I Krasheninnikov In recent years, various collision operator models have been implemented in numerous gyrokinetic codes to simulate Coulomb collisions in tokamak plasmas [1–7]. Because of high computation cost, only some gyrokinetic codes [9,10] include the correct collision operator, typically referred to as the FokkerPlanck operator. Instead, recent reports [2–7] focus on implementing increasingly complex reduced collision operators and extending these operators for the case of unlike species. Proposed models differ in physical properties, and have different scopes of use. In particular, some recent implementations of unlike collisions (e.g., [9,10]) produce no thermal force, which is important for impurity transport in the tokamak edge [11,12]. 

PP11.00068: Implementing general moment equations for parallel closures in NIMROD Hankyu Lee, J. Andrew Spencer, Eric D Held, JeongYoung Ji Implementing an advanced closure module significantly extends the capability of MHD fluid codes such as NIMROD [1]. NonMaxwellian parallel moment equations are implemented in NIMROD to obtain parallel closures. To derive the moment equations, we take moments of the firstorder drift kinetic equation using orthogonal velocity polynomials. The system of parallel moment equations is then solved using 2D finite elements in the poloidal plane, considering an axisymmetric magnetic field. To overcome the memory limit associated with large problem sizes, the GMRES algorithm is used without the need for explicit matrix construction. The solution is shown to converge as the system size increases. The steadystate results are compared to analytic results using the momentFourier approach, which involves expanding moments and quantities related to the magnetic field in terms of Fourier series [2]. 

PP11.00069: Highorder finite element arbitrary LagrangianEulerian resistive magnetohydrodynamics coupled to a multiphysics code Philip Mocz


PP11.00070: A GradShafranovlike equation for quasisymmetric stellarators Nikita Nikulsin, Wrick Sengupta, Rahul Gaur, Amitava Bhattacharjee The nearaxis expansion has been a successful analytical model for stellarators; however, it cannot account for shear in quasisymmetric devices easily. To get around this issue, we previously considered a large aspect ratio expansion of the 3D equilibrium equations, which, when combined with quasisymmetry, gives a GradShafranovlike equation*. However, the large aspect ratio expansion only allows quasisymmetric stellarators that can be obtained from a tokamak by applying a toroidallyvarying vertical shift to each poloidal plane, thus excluding rotatingellipselike shaping. A more general GradShafranovlike equation can be obtained by expanding the magnetic field around a curlfree vacuum field. In order to make the problem tractable, we apply a subsidiary expansion of the vacuum field around a purely toroidal vacuum field. In this subsidiary expansion, the zeroth order corresponds to the large aspect ratio model previously considered, and corrections allow us to overcome some of the limitations. We then compare the analytical solutions to numerical results from VMEC. We also consider the construction of a stellarator salpha model from the present equilibrium model. 

PP11.00071: Plasma control system design and disruption forces modelling with the opensource platform ERMES Ruben Otin, Tim C Hender, Xia Guoliang, Oliver Bardsley, James Paterson Plasma control is essential for the correct operation of a magnetic confinement nuclear fusion reactor. The plasma must be properly shaped and positioned to make possible the generation of fusion energy. Control systems are composed of a set of coils interacting with this plasma through magnetic fields. These fields can be distorted by the different components of the reactor. These perturbative effects must be considered during the design phase and be adequately compensated to guarantee the successful performance of the machine. Also, in the event of losing control of the plasma, we need to calculate the induced forces to design the supporting structures accordingly and avoid damage. 

PP11.00072: Timeresolved biphase signatures of quadratic nonlinearity observed in coupled eigenmodes on the DIIID tokamak Gregory Riggs, Mark E Koepke, William W Heidbrink, Michael Van Zeeland, Donald A Spong We report the detection of quadratic coupling between toroidicityinduced Alfven eigenmodes (TAEs) on submillisecond time scales (~750 μs). Identification of phasecoherency between multiple TAEs and nonlinearlygenerated modes is facilitated by waveletbased bicoherence analysis of timeseries from inductive coils, taken from 4 DIIID shots heated by neutral beam injection (NBI). A threepoint scan of beam power (3, 4, and 5MW) compares coupling in different regimes of fastion drive. 

PP11.00073: Finding Magnetic Surfaces via a Single Trajectory Max Ruth, David S Bindel Many important qualities of nuclear plasma confinement devices can be determined via the Poincare plot of the magnetic field return map. These qualities include the locations of the invariant circles (magnetic flux surfaces), chaotic regions, and magnetic islands. The convergence rate of ergodic averages has been shown to successfully categorize these orbits, but many iterations of the return map are needed to implement this directly. Recently, it has been shown that a weighted average can be used to accelerate the convergence, resulting in a useful method for categorizing trajectories. 

PP11.00074: On Magnetic Compression in Gyrokinetic Field Theory Bruce D Scott The issue of finite magnetic compressibility in lowbeta magnetised plasmas is considered within the gyrokinetic description. The gauge transformation method of Littlejohn is used to obtain a Lagrangian which contains this effect additionally. The field theory version obtains a system model which guarantees exact energetic consistency. Gyrocenter drifts under this model are considered within a ChewGoldbergerLow MHD equilibrium allowing for pressure anisotropy. The contributions to the current divergence balance, hence the dynamics, due to the difference between the curvature and gradB drifts and to the compressibility are shown to cancel up to corrections of order beta. This recovers an earlier result with the same conclusion within linear theory of kinetic ballooning modes. 

PP11.00075: Unstructured Mesh tools for Fusion Energy System Simulation Codes Mark S Shephard, Cameron W Smith, Jacob Merson, Usman Riaz, Aditya Yogesh Joshi Historically fusion plasma simulation codes have employed structured grid methods that are effective for dealing with simplified geometric regions. However, structured mesh methods are not well suited for the design of the geometrically complex components of the upcoming commercial fusion energy systems such as divertors, baffles, RF antennas, etc. Therefore, a substantial number of the developers of fusion energy system simulation codes are employing unstructured mesh methods. This poster will present a set of tools developed to support unstructured mesh fusion energy system simulation codes. The poster will present: 

PP11.00076: Kinetic effects on plasma flow in the magnetic mirror Mikhail Tyushev, Andrei Smolyakov, Peter Yushmanov, Ales Necas, Roelof Groenewald This work describes the results of quasitwodimensional kinetic modeling of plasmas in the magnetic mirror using ParticleinCell methods. The driftkinetic equations of motion for electrons and ions were implemented into the EDIPIC code [1]. The effects of the inhomogeneous magnetic field are included by varying the cell's volume and using the modified Poisson equation corresponding to the flux tube approximation. The electron collisions are included using the Langevin approach. Results of full kinetic simulations are compared with fluid analytical theory and quasineutral simulations. The role of the boundary sheath on the total potential drop is investigated at different expansion ratios in full mirror and expander only configurations. The simulations were performed in full selfconsistent (full electron and ion dynamics) and reduced models with fixed potential and/or fixed ion density. The effects of electron collisions on the electron flux into the loss cone were studied and compared with earlier analytical and computational results [24]. The role of electrons trapped in the expander region and the effects of inherent PIC numerical noise are investigated in different regimes. 

PP11.00077: Scenario Planning in Tokamaks by Integrating Freeboundary Equilibrium and Fast Transport Solvers into a Modelbased Optimization Scheme Xiao Song, Zibo Wang, Brian R Leard, Tariq Rafiq, Eugenio Schuster Modelbased optimization in tokamaks has the potential of successfully generating feedforwardcontrol policies capable of achieving an advanced scenario characterized by weak magnetic shear, electron internal transport barriers (eITBs), and an unfavorable plasma configuration. The optimization scheme integrates freeboundary equilibrium (FBE) and fast transport (FT) solvers, enabling efficient trajectory planning for the powers of available heating and current drive systems (H&CDs) and the currents of the poloidalfield (PF) coils. In the FBE solver, the toroidal current density is parameterized by using polynomials based on the normalized poloidal flux function. This parameterization is constrained by the plasma current prescribed by the designer and the poloidal beta computed by the FT solver. The FT solver, utilizing different transport and source models while leveraging the equilibrium configuration computed by the FBE solver, provides solutions for the electron heat transport equation (EHTE) and the magnetic diffusion equation (MDE). The optimization scheme takes into account limitations imposed on actuators and the plasma state, including the requirement to maintain q_{min} above specific thresholds to avoid associated MHD instabilities. Optimized evolutions are determined for the PFcoil currents and the H&CD powers of the EAST tokamak to illustrate the effectiveness of the proposed method. 

PP11.00078: Electromagnetic gyrokinetic mode simulations in XGC with an improved finitegrid stable implicit particleincell algorithm Benjamin J Sturdevant, Luis Chacon, SeungHoe Ku, Mark F Adams, Choongseok Chang An implicit particleincell method for electromagnetic gyrokinetics using parallel velocity as a coordinate has been developed in the XGC code as a means of avoiding the Ampère cancellation problem for longwavelength MHDtype modes [1]. Here, we present an improved formulation for the implicit method, based on the work in [2], which demonstrates robust stability properties with respect to both finitegrid and temporal instabilities. We demonstrate the ability of the scheme to simulate various electromagnetic modes such as the shear Alfvén wave, kinetic ballooning modes [3], and lown cylindrical tearing modes [4]. Finally, we study the performance of the scheme by evaluating the cost of solving the system of equations arising from the implicit discretization. 

PP11.00079: PINCHES AND HOHLRAUM PHYSICS


PP11.00080: Magnetic field distribution estimations with Zeeman splitting spectroscopy at the radial phase of the PF400J device Gonzalo Avaria, Miguel Escalona, Cristian Pavez, Gonzalo Jimenez, Julio Valenzuela, Hugo M Ruiz, Leopoldo Soto Discharge current measurements in Plasma Focus discharges are usually made with inductive probes such as Rogowskii coils, which present the disadvantage that it cannot determine the current circulating through the plasma column. This indetermination makes it more difficult to estimate plasma characteristics such as the temperature inside the column through the Bennett relation. 

PP11.00081: Xray Spectroscopic Studies of Multimaterial Twisted Wire Hybrid Xpinches Nathaniel G Chalmers, Mouad Damir, Joshua Luoma, Ahmed T Elshafiey, David A Hammer The Hybrid XPinch (HXP) has been shown to be an excellent point source of Xray emission on the XP pulsedpower machine for radiography, producing Xray radiation with photon energies up to 4keV ^{1}. Spectroscopic analysis of xpinch dynamics has shown Lshell line emission during the compression phase, followed by a ~10ps continuum burst, with many emission lines in the expansion phase^{2}. Current studies are exploring the use of multimaterial twisted wire HXPs to produce two temporally spaced Xray bursts, while also investigating the possibility of using this load configuration to produce line radiation in different soft Xray energy bands at the time of micropinch formation. This study is utilizing the 450 kA peak current XP pulsed power generator with a rise time of 60 ns (10 to 90%). Its goal is to determine if the multimaterial twisted wire HXP load configuration can predictably produce temporally spaced xray sources within the desired soft Xray energy bands through material selection. 

PP11.00082: Upgrades To LLNL's MJOLNIR Dense Plasma Focus (DPF) Power Flow Region and Mounting Structure James K Walters, Luis Frausto, Michael Anderson, Paul M Campbell, Christopher Cooper, Andrea Schmidt There is an updated design for the Lawrence Livermore National Laboratory’s Megajoule Neutron Imaging Radiography (MJOLNIR) Dense Plasma Focus (DPF) machine. 

PP11.00083: Yield scaling and operating conditions for highest observed neutron yield shots above 3.5 MA on MJOLNIR DPF Christopher Cooper, Anthony J Link, Clement S Goyon, Enrique Anaya, Paul M Campbell, Steven F Chapman, Owen B Drury, Don Max, Jaebum Park, Sophia V Rocco, Kurt Walters, Amanda Youmans, Andrea Schmidt MJOLNIR DPF requires high yield neutron pulses to perform flash neutron radiography with more neutrons contributing to a better image. Commissioning MJOLNIR above 3.5 MA requires operational modifications to take advantage of the higher current to produce higher yields. 

PP11.00084: Neutron Anisotropy Measurements on MJOLNIR Dense Plasma Focus Clement S Goyon, Anthony J Link, Amanda Youmans, Rick Anaya, Justin R Angus, Paul Campbell, Steven F Chapman, Christopher Cooper, Owen B Drury, Drew Higginson, Luis Frausto, Sheng Jiang, Matthew M McMahon, Jaebum Park, Sophia V Rocco, James K Walters, Andrea Schmidt Dense plasma focus (DPF) Zpinches are compact pulse power driven devices consisting of two coaxial electrodes, separated by an insulator, and filled with a lowdensity gas. MJOLNIR is a dense plasma focus (DPF) located at LLNL being developed to produce a neutron source for flash neutron radiography which has produced neutron pulse when driven with > 3.8 MA. DPFs produce neutrons through a combination of thermal and beamtarget processes. Results will be on inferred neutron fluence angular distribution and energy spectrum from time of flight and activation detectors. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DEAC5207NA27344. LLNLABS 851333 

PP11.00085: Anode Implosion Radius Effects on Dense Plasma Focus Performance Anthony J Link, Enrique Anaya, Justin R Angus, Paul Campbell, Steven F Chapman, Christopher Cooper, Owen B Drury, Clement S Goyon, Drew Higginson, Luis Frausto, Sheng Jiang, Don Max, Matthew M McMahon, Jaebum Park, Sophia V Rocco, Kurt Walters, Amanda Youmans, Andrea Schmidt Dense plasma focus (DPF) Zpinches are compact pulsed power driven devices consisting of two coaxial electrodes, separated by an insulator, and filled with a lowdensity gas. MJOLNIR is a dense plasma focus (DPF) located at LLNL being developed to produce a neutron source for flash neutron radiography and has produced greater than 10^12 neutrons when driven with up to 3.8 MA. Producing a neutron source for radiography requires both a bright neutron pulse as well as the neutrons emanating from a small volume. Simulation and experimental results will be presented on neutron yield, and stagnation characteristics for anodes with a variety of implosion radii, the radius at which the implosion starts for both the 100 kA and 3 MA DPFs at LLNL. 

PP11.00086: Meeting Flash Neutron Radiography Requirements with the MegaJoule Neutron Imaging Radiography (MJOLNIR) DPF Andrea Schmidt, Enrique Anaya, Michael Anderson, Justin R Angus, Steven F Chapman, Christopher Cooper, Owen B Drury, Luis Frausto, Clement S Goyon, Drew Higginson, Sheng Jiang, Anthony J Link, Don Max, Matt McMahon, Jaebum Park, Sophia V Rocco, James K Walters, Amanda Youmans, Paul C Campbell A dense plasma focus (DPF) is a compact coaxial plasma gun which completes its discharge as a Zpinch, producing short (<100 ns) pulses of ions, Xrays, and/or neutrons. In 2018, LLNL constructed and brought into operation the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF, which is designed for flash neutron radiography. This device has achieved neutron yields of up to 1.2e12 neutrons/pulse at 3.7 MA peak current and 1.2 MJ stored energy, with a measured neutron spot size as small as 3.8 mm FWHM. Higher stored energy (up to 2 MJ) commissioning is underway. The MJOLNIR team recently performed an assessment of the DPF's ability to meet neutron radiography requirements for dynamic experiments, including 1.0e13 yield, and 1 mm spot size FWHM. Further spot size improvements may be achieved through the use of noble gas dopants, a reentrant cathode, and control of the anode's implosion radius. Further yield improvements may be obtained with anode shaping and an onaxis gas jet that creates a differential gas load. We present progress so far on these metrics, and potential paths forward for meeting these requirements. 

PP11.00087: Optimization of the Neutron Source Size for Dense Plasma Focus using ParticleInCell Simulations Sheng Jiang, Anthony J Link, Enrique Anaya, Justin R Angus, Paul Campbell, Steven F Chapman, Christopher Cooper, Owen B Drury, Clement S Goyon, Drew Higginson, Luis Frausto, Don Max, Matthew M McMahon, Jaebum Park, Sophia V Rocco, Kurt Walters, Amanda Youmans, Andrea Schmidt The dense plasma focus (DPF) devices can serve as portable neutron sources for radiography when deuterium is utilized as the filling gas. Improving the resolution of the radiography system relies on reducing the size of the neutron source generated by DPF. In this study, we employ the particleincell (PIC) code Chicago^{1} to simulate different anode shapes at varying pressures. Our findings reveal that both the implosion radius and the slope angle of the anode significantly influence the size of the pinch column during stagnation. This aspect has a considerable impact on the neutron source size, particularly in the early stages of the neutron production process. Additionally, the pressure of the filling gas determines the collisionality of the pinch plasma, which further affects compression. We will present a detailed comparison of these factors. 

PP11.00088: FLASH Simulations of a GasPuff Xe Liner Staged ZPinch Edward C Hansen, Fernando Garcia Rubio, Marissa B Adams, Milad Fatenejad, Kasper Moczulski, Paul Ney, Hafiz U Rahman, Adam Reyes, Emil Ruskov, Victor Tranchant, Petros Tzeferacos The staged Zpinch (SZP) is a pulsedpower–driven magneto inertial fusion concept under development at MagnetoInertial Fusion Technology, Inc. (MIFTI) [1,2]. There are now several SZP variations in the literature, but they all use a high atomic number liner. In this work, we focus on FLASH simulations of a lowdensity gaspuff Xe liner, driven by the pulsedpower Z machine at Sandia National Laboratories, imploding on DT fuel. This configuration differs from previous ones in a crucial way: the thermal losses in the fuel are dominated by thermal conduction rather than radiation. Therefore, if the fuel can be sufficiently magnetized, thermal conductivity and losses can be reduced. We include comparisons with results from the MACH2 code and show that there is a significant difference in fuel magnetization resulting in discrepancies in convergence ratios (CR) and stagnation. Despite this, both codes’ results are encouraging as fuel ion temperatures > 15 keV are achieved. The 1D FLASH results reach CR > 300, which is likely to be experimentally unattainable, and we see Rayleigh Taylor instability (RTI) growth in 2D simulations. We hypothesize that an applied axial magnetic field would help the fuel retain heat and improve stability, resulting in a CR that could be achieved experimentally. 

PP11.00089: Simulation of XRay Spectra in MultiMaterial MicroPinches Joshua Luoma, Ahmed T Elshafiey, Nate Chalmers, David A Hammer The dynamics of micropinch formation is often investigated through timeresolved measurements of xray emission, including L and Kshell lines. Previous studies of singlematerial micropinches have measured Lshell emission during compression and a continuum burst at stagnation, followed by L and Kshell emission during expansion [1]. A micropinch containing multiple materials offers the opportunity to tailor the xray spectra so line emission occurs at key times during the compression phase. Simulations of multimaterial micropinches are presented for several candidate materials to determine the best combinations for future experiments. The dynamics of the micropinch is handled with the XMHD code PERSEUS and the output is coupled to SPECT3D, a radiation transport code. The combination of codes predicts the observable xray spectra during the compression stage of the micropinch. These results will inform ongoing experimental efforts on the XP pulsed power driver at Cornell University’s Laboratory of Plasma Studies. 

PP11.00090: Comparison of hydrodynamic and kinetic simulations of an ICF hohlraum surrogate Steven Anderson, Luis Chacon, Andrei N Simakov Recently, Le Pape et. al studied the plasma interpenetration in a surrogate hohlraum environment [1]. Using 3$omega$ (351nm) laser light, they drove counterpropagating carbon and gold plasmas both in vacuum and with a lowdensity He4 gas fill, and found the presence of the gas fill significantly inhibited interpenetration of the gold and carbon. In this work, we present computational studies of this experimental setup using both 2D (axisymmetric) hydro simulations with xRage [2,3] and 1D kinetic simulations with the VlasovFokkerPlanck code iFP [4,5]. We compare both to the experimental measurements of inferred plasma temperature and relative number fraction, as well as directly to the reported experimental Thomson Scattering spectra. Contrary to naïve expectation, we find that iFP reproduces the gasfill results (which ought to be more “hydro like”) better than xRage, and vice versa for the vacuum results. We hypothesize this is due to significant 3D hydrodynamic effects in the vacuum case (e.g., plasma “fingering”), which are less present in the gasfill case. Further, the gasfill case presents kinetic interpenetration and mix of the He4 into the carbon and gold, which is not well represented in a hydro code. 

PP11.00091: Nonlocal nonMaxwellian electron distributions in radiating laserplasmas Kevin H Ma, Mehul V Patel, Eric Johnsen At laser irradiances relevant to ICF, steep temperature gradients lead to nonlocal electron thermal transport. The electron heat flux from the nonlocal anisotropy f_{1} of the electron distribution function (EDF) alters the selfemission from the laserheated plasma. This deviation of f_{1} from classical to nonlocal is caused by the deviation of the isotropic component of the EDF, f_{0}, from Maxwellian. Consequently, this work considers both the nonlocal heat flux from f_{1} and the nonMaxwellian distortion from f_{0} on the plasma’s selfemission. 

PP11.00092: Abstract Withdrawn


PP11.00093: Delayed shock breakout from aluminum samples in a halfraum due to hot electron beaming from the LEH window Mordecai D Rosen, Alastair S Moore, William A Farmer, Michael S Rubery, Peter M Celliers, Matthew P Hill, Marius Millot, Matthias Hohenberger, Mordecai ( E Rosen, Steven Ross, Weston Montgomery, Clay Henning, Otto L Landen We have shot gas filled Au halfraums at the National Ignition Facility with a sample on the back wall. With Au samples we measure radiation burnthrough to assess opacity and equation of state at 300 eV. The Dante instrument measures halfraum drive via xray emission through the laser entrance hole (LEH). To more accurately assess the drive at the sample position, we measured shock breakout from Al samples. The shock broke out 1 nsec later than expectations based on a drive that matched the Dante. We attribute that discrepancy to hot electrons beaming from the LEH window, and preheating the back surface of the Al samples. This causes motion of that back surface, which delays the shock breakout. We quantify this effect by measuring the time resolved hard xrays produced by those hot electrons, and analytically calculate a 6 eV preheat. Simulations show that precisely such an amount leads to the observed 1 nsec delay in shock breakout. Future experiments will eliminate this preheat by using a small prepulse to blow down the LEH window before it is illuminated by the high power pulse. 

PP11.00094: ASTROPHYSICAL PLASMAS


PP11.00095: Evidence of suppressed beamplasma instabilities in a laboratory analogue of blazarinduced pair jets Charles D Arrowsmith, Gianluca Gregori, Francesco Miniati, Subir Sarkar, Brian T Huffman, Alexander A Schekochihin, Archie F Bott, Jack W Halliday, Sam Iaquinta, Nikolaos Charitonidis, Pascal Simon, Alice Marie Goillot, Ilias Efthymiopoulos, Vasiliki Stergiou, Stephane Burger, Robert Bingham, Raoul M Trines, Tristan Davenne, Tom Hodge, Pablo J Bilbao, Filipe D Cruz, Luis O Silva, Nelson Lopes, Daniel J Haberberger, Dustin H Froula, Hui Chen, Raspberry Simpson, Tammy Ma, Brian Reville, Thibault Vieu, Jon Tomas Gudmundsson We report on an experimental platform at the HiRadMat facility, within CERN’s accelerator complex aimed at recreating a laboratory analogue of ultrarelativistic blazarinduced pair jets propagating into the intergalactic tenuous plasma. More than 10^{13} electronpositron pairs are produced by irradiating a target with 440 GeV protons from the Super Proton Synchrotron. The pair yield and plasma extent are orders of magnitude larger than currently achievable at laser facilities, producing for the first time pair plasma conditions necessary for the study of relativistic kinetic plasma instabilities. In our experiment, the pair beams are remarkably stable as they propagate through 1m of plasma. We compare the results with theory and particleincell simulations, which predict that the growth of kinetic instabilities is strongly suppressed when nonidealized beam conditions are assumed, such as the inclusion of a small transverse temperature. An experimentally inferred growth rate, when scaled to blazar's jets, is comparable to the inverseCompton cooling time of the pairs on the cosmic microwave background. Given that a cascade of GeV inverseCompton scattered photons is not observed from blazar's jets, our results imply that such an absence must be the related to the presence of intervening magnetic fields in the intergalactic plasma of primordial origin. 

PP11.00096: Extended Magnetohydrodynamic Effects on Dynamics and Stability of Magnetically Driven High Energy Density Plasma Jets Dalton A Lund, Eric S Lavine, Charles E Seyler A novel experiment resembling a planar plasma gun has been developed to produce magnetically driven highenergydensity (HED) plasma jets on the 1 MA, 220 ns rise time COBRA generator at Cornell University. The experimental setup consists of a central pin electrode that injects a single gas puff on axis, surrounded by a second annular electrode with a continuous gas injection slit. A permanent ring magnet is housed within the central electrode to provide an initial poloidal magnetic field which links the two electrodes. In this way, the experiment mimics a magnetized central object such as a star or blackhole surrounded by a rotating accretion disk. The resulting freeboundary, high aspect ratio plasma jets strongly resemble naturally occurring astrophysical jets. Here, we investigate extended magnetohydrodynamic (XMHD) effects on jet dynamics and stability via the ability to have the cathode as the central pin electrode and anode as the annular electrode or vice versa with the added flexibility to reverse the polarity of the background poloidal magnetic field independently of the cathode and anode. Measurements of densities, temperatures, velocities, and magnetic fields are collected using Thomason scattering, Bdot probes, Faraday rotation, laser interferometry, and optical spectroscopy. The experimental results are supported by 3D modelling using PERSEUS an XMHD code; simulation results are used to study the evolution of canonical fields, flux tubes, and helicity in the plasma jets. 

PP11.00097: The electron cyclotron maser instability in laser ionized plasmas Thales Silva, Pablo J Bilbao, Luis O Silva We propose the use of laserionized plasmas as a way to probe the electron cyclotron maser instability in the laboratory. Due to the conservation of canonical momentum, the laser imprints its polarization in the momentum distribution function of the electrons [1]: the distribution after the laser passes the region is closely connected to the laser vector potential at the ionization instant. Therefore, circularly polarized lasers can generate ringshaped distribution functions [2]. Recent results have shown that these distributions may be much more common in astrophysical plasmas than previously thought [3]. 

PP11.00098: Characterization of the nonaxisymmetric MHD mode in the Princeton magnetorotational instability experiment using simultaneous velocity and magnetic field measurements Yin Wang, Erik P Gilson, Fatima Ebrahimi, Jeremy Goodman, Hantao Ji We report comprehensive experimental and numerical characterization of the recently identified magnetohydrodynamic (MHD) instability in a modified TaylorCouette experiment using Galinstan as the working fluid [Wang et al., Nat. Commun. 13, 4679 (2022)]. In the experiment, the inner cylinder, outer cylinder and upper (lower) endcaps corotate independently at an fixed angular velocity ratio Ω_{1}:Ω_{2}:Ω_{3}=1:0.1325:0.55, creating a hydrodynamically stable (quasiKeplerian) flow in the bulk of the container. Coils surrounding the outer cylinder provide a uniform magnetic field Bi along the rotation axis. We used Hall probes and ultrasound velocimetry to simultaneously measure the radial magnetic field B_{r} and azimuthal velocity u_{φ} at different azimuths in a single run. The B_{r} measurements were made on the inner cylinders surface at different heights, and u_{φ} measurements were made from the outer cylinder at the midplane. The nonaxisymmetric instability is observed in B_{r} and u_{φ}. It has an exponential growth at its onset and a dominant azimuthal wavenumber m=1. The instability is global with a radially uniform rotation frequency (angular phase velocity), and an axial phase velocity as well. Our numeral simulations reproduce the experimental findings, and further reveal that the nonaxisymmetric instability contributes to outward radial angular momentum transport, as with the magnetorotational instability. Possible mechanisms for the instability are also discussed. 

PP11.00099: Advancing MultiScale Physics Modeling in Strongly Magnetized Relativistic Plasmas: A SubCycling Approach of Analytic Particle Pusher Guangye Chen, Federico Fraschetti, Fan Guo, Chengkun Huang, Patrick Kilian, Nicole L Ronning Modeling multiscale physics in astrophysical and laboratory plasmas with strong magnetic fields for particle acceleration poses challenges for conventional explicit relativistic ParticleinCell (PIC) simulations that employ the leapfrog scheme. The leapfrog scheme utilizes a fixed time step for both fields and particles, which works well when the time step determined by the field solver (CFL condition) is the smallest timescale of the simulation. However, in the presence of a strong magnetic field, a gyromotion timescale may be even smaller than the CFLdetermined time step. To address this issue, we propose a particle subcycling approach [1] by employing a known analytical solution of particle motion in arbitrary constant electromagnetic fields [2] to construct approximate solutions with nonuniform fields. By incorporating the analytic particle pusher with subcycling, our method enables significant improvements in achievable scales within the kinetic model for systems with strong magnetic fields, surpassing the limitations of standard approaches. We demonstrate the effectiveness of the proposed particle pusher in test particle problems and the PIC algorithm through standard benchmark tests such as Landau damping and 2stream instabilities. Additionally, we compare the performance of the new algorithm with standard PIC simulations on problems spanning a range of magnetization strengths from relatively weak to strong regimes. Overall, our study presents a novel approach to address the challenges of multiscale physics modeling in plasmas with strong magnetic fields, offering improved capability and accuracy. 

PP11.00100: DiscontinuousGalerkin Representation of the MaxwellJuttner Distribution Grant R Johnson, James Juno, Ammar Hakim Accurately projecting the MaxwellJuttner (MJ) distribution onto a discrete simulation grid can be a challenge for relativistic kinetic continuum simulations. This arises from the finite velocity bounds of the domain which may not capture the entire distribution function, as well as errors introduced by projecting the function onto a discrete grid. Here we outline a procedure for projecting the MJ in a Discontinuous Galerkin scheme, which itself adds complication in calculating nonlinear quantities on the grid. By computing the moments of the projected distribution function, using GaussLegendre quadrature for nonlinear quantities, and iterative correcting moments calculated by this procedure they converge, we can correct for these inaccuracies in the discrete projection. The result is a method that accurately captures the distribution function and ensures the moments match the desired values to machine precision. 

PP11.00101: The Large Scale Impact of Localized Cosmic Ray Injection Roark S Habegger, Ellen Zweibel Supernova explosions are a major driver of galaxy evolution, and cosmic rays are a major component of that driving. This 'cosmic ray feedback' presents a challenging multiscale problem in galaxy simulations. The supernova explosions on small scales (<< 1pc) which accelerate cosmic rays eventually produce the background of cosmic rays streaming throughout a galactic disk. They also affect the vertical structure of a galactic disk on large scales (> 1kpc). We examine the connection of cosmic ray production by supernovae to the vertical structure of a galactic disk using galactic patch simulations in the Athena++ code. We randomly place pointlike injections of cosmic rays in the midplane of a 1kpc^{2} patch of a galactic disk. These injections disrupt the vertical hydrostatic equilibrium on large scales. We observe significantly different results when using random, pointlike injections instead of a constant cosmic ray flux. 
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PP11.00102: Saturation of the Tayler instability in a rotating, stratified plasma Adrian E Fraser, Evan H Anders, Jim Fuller, Suoqing Ji, Laurène Jouve, Daniel Lecoanet, Ellen Zweibel As stars evolve beyond their corehydrogenburning phase, angular momentum conservation forces their contracting cores to spin up and their expanding envelopes to spin down. However, observations show a much smaller coreenvelope rotation difference than expected, indicating anomalous transport of angular momentum between the core and envelope. One proposed source of this transport is MHD turbulence driven by the TaylerSpruit dynamo, which might provide significant transport despite the rotating and strongly stratified nature of these plasmas. However, conflicting reduced models have been put forth to predict the efficiency of this transport and how it varies with properties of the star. These conflicting predictions stem from different assumptions regarding the saturation mechanism of the Tayler instability, a key element of the TaylerSpruit dynamo. 

PP11.00103: Entity: Architectureagnostic General Coordinate (QED)(GR)PIC Code for Simulating Astrophysical Plasmas Hayk Hakobyan, Benjamin Crinquand, Alisa Galishnikova, Jens F Mahlmann, Alexander A Philippov, Arno Vanthieghem, Muni Zhou Over the past decade, particleincell (PIC) has become the preferred method for simulating plasma physics in the vicinity of compact astrophysical objects. However, there is currently no publicly available code that encompasses all the necessary radiationplasma coupling processes and can effectively model largescale systems. In this presentation, I will introduce Entity, a stateoftheart opensource PIC code specifically designed for extreme astrophysical plasmas. Built upon the Kokkos framework, Entity boasts efficient implicit multiarchitecture portability, including GPU utilization. Notably, the code incorporates advanced algorithms to handle diverse radiationplasma coupling phenomena, such as Compton scattering, electronpositron pair production, and annihilation. Entity is constructed within a general coordinate system defined by metric functions, enabling it to successfully tackle global models of compact object magnetospheres. These models necessitate algorithms operating on noncartesian grids (e.g., spherical, cubedsphere) with varying densities, and even encompassing full general relativity. To enhance usability, Entity is packaged with a runtime GUI based on OpenGL for realtime data visualization and a Pythonbased postprocessing framework. 

PP11.00104: Neutralchargedparticle Collisions as the Mechanism for Accretion Disk Angular Momentum Transport Yang Zhang, Paul M Bellan The matter in an accretion disk must lose angular momentum when moving radially inwards but how this works has long been a mystery. By calculating the trajectories of individual colliding neutrals, ions, and electrons in a weakly ionized 2D plasma containing gravitational and magnetic fields, we numerically simulate accretion disk dynamics at the particle level [1]. As predicted by Lagrangian mechanics, the fundamental conserved global quantity is the total canonical angular momentum, not the ordinary angular momentum. When the Kepler angular velocity and the magnetic field have opposite polarity, collisions between neutrals and charged particles cause: (i) ions to move radially inwards, (ii) electrons to move radially outwards, (iii) neutrals to lose ordinary angular momentum, and (iv) charged particles to gain canonical angular momentum. Neutrals thus spiral inward due to their decrease of ordinary angular momentum while the accumulation of ions at small radius and accumulation of electrons at large radius produces a radially outward electric field. In 3D, this radial electric field would drive an outofplane poloidal current that produces the magnetic forces that drive bidirectional astrophysical jets. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. Quantitative scaling of the model using plausible disk density, temperature, and magnetic field strength gives an accretion rate of 3 × 10^{−8} solar mass per year, which is in good agreement with observed accretion rates. 

PP11.00105: The Structure of the Beginning of the Universe  Point Circle Structure Han y yong Quan The radiation radius of any object is equal to the speed of light divided by the angular velocity of the object's rotation. R=c/ ω, R is the radiation radius, c is the speed of light ω It's angular velocity. When the rotational speed of an object is equal to the speed of light, the radiation radius is equal to the radius of the object. The highspeed rotation of air can create a vacuum inside, without air. Dense solids that rotate at the speed of light can also form a vacuum inside them, free of matter. Due to the constant speed of radiation and the speed of light, the radiation radius must exist inside objects that rotate faster than the speed of light. When a dense object far exceeds the speed of light, the radiation radius R tends to be infinitely small, similar to a point. Due to the object's rotation speed far exceeding the speed of light, the internal vacuum of the dense object, the outer circle, is bound to be extremely large, and there is a radiation circle with a very small radius inside  a point, forming a point circle structure. At this point, the entire matter of the universe is concentrated on this dot and circle structure, and the universe is about to perish and start a new universe. 

PP11.00106: The Effect of Heat Transport on Compressible Fluctuation Dynamo in Multitemperature Plasmas Abigail Armstrong, Adam Reyes, Edward C Hansen, Ananya Mohapatra, Eric Blackman, Archie F Bott, Petros Tzeferacos The existence of magnetic fields of dynamical significance, as measured through astronomical observations, poses several questions regarding the mechanisms behind their origin, the processes that result in their amplification, and how they maintain their magnitudes. Fluctuation dynamo, wherein turbulent motions drive the amplification of small seed magnetic fields to magnetic energies that are a nontrivial fraction of the turbulent kinetic energy, is one of the leading theories to account for the observed magnetic fields. First numerically demonstrated in the foundational work of Meneguzzi et al.,[1] several numerical studies have explored fluctuation dynamo in magnetized turbulence in different regimes, but few have ventured beyond the constant diffusivity magnetohydrodynamics (MHD) ansatz. The recent experimental demonstration of fluctuation dynamo [2, 3] at the Omega Laser Facility has brought about the urgent need for such excursions, which will lay the theoretical foundations to understand the mechanism when plasma effects are prevalent. To start exploring plasma conditions that are relevant to laserdriven, high energydensity (HED) plasma turbulence, the onetemperature, isothermal, resistiveMHD ansatz broadly used in current theoretical and numerical models must be relaxed (for a recent review, see Rincon [4]). Leveraging FLASH’s new extended MHD and HED physics capabilities, we present the first set in a series of simulations that explore how threetemperature physics affect the workings of fluctuation dynamo in HEDrelevant plasma conditions. 

PP11.00107: Whistler Lion Roars within Mirror Modes in Galaxy Clusters Francisco Ley, Ellen Zweibel, Drake Miller, Mario A Riquelme Lion roars are bursts of whistler waves associated with low magnetic field regions of mirror modes. They are observed in plasmas near Earth, Saturn and the solar wind. In the intracluster medium (ICM) of galaxy clusters, mirror instability is also expected to be excited, but it is not yet clear whether whistler lion roars can also be present in this highβ environment. In this work, we perform fully kinetic particleincell simulations of a plasma subject to a continuous amplification of the mean magnetic field to study the nonlinear stages of the mirror instability and the ensuing excitation of whistler lion roars under ICM conditions. Once mirror modes reach nonlinear amplitudes, a simultaneous excitation of whistler lion roars and ioncyclotron waves (IC) is observed, with subdominant amplitudes and quasiparallel propagation. We show that the underlying mechanism of excitation is the pressure anisotropy of electrons and ions trapped in mirror modes with losscone type distributions. We observe that IC waves play an essential role in regulating the global ion pressure anisotropy at nonlinear stages. We argue that lion roars are a concomitant feature of mirror instability even at high β, therefore expected to be present in the ICM. We discuss the implications of this work on the ICM turbulent heating via magnetic pumping. 

PP11.00108: Wave Interactions and Turbulence in Highβ Collisionless Plasmas Stephen P Majeski, Matthew W Kunz, Jonathan Squire Employing numerical simulations and analytic theory, we investigate the nature of hydromagnetic wave interactions and their effects on magnetized turbulence within highβ, collisionless plasmas. In particular, the interactions of parallelpropagating Alfvén waves with acoustic and other Alfvén waves are studied using a CGLMHD framework with Landaufluid heat fluxes. We find that strong modifications can occur to Alfvénwave packets on timescales comparable with their linear propagation in response to the spatially varying pressure anisotropy generated by other modes. These interactions have consequences for our understanding of magnetized turbulence in environments such as the intracluster medium of galaxy clusters and blackhole accretion flows. With this physics borne in mind, we reexamine the interaction between compressive and Alfvénic fluctuations in a turbulent cascade, as well as the ability of Alfvén waves to establish a weak cascade parallel to the guide magnetic field (otherwise forbidden within standard MHD). Our conclusions are further tested using hybridkinetic particleincell simulations, which selfconsistently capture feedback from kinetic microinstabilities such as firehose and mirror. 

PP11.00109: MHD turbulence and the dynamo problem John V Shebalin Finding the origin of global magnetic fields around stars and planets is called ‘the dynamo problem.’ These global magnetic fields arise from layers of turbulent plasma that can be modeled as a spherical shell of magnetofluid in which magnetohydrodynamic (MHD) turbulence occurs due to convection. Ignoring compressibility, the problem reduces to examining incompressible MHD turbulence in a spherical shell. Velocity and magnetic fields and represented by orthogonal function expansions whose coefficients form a dynamical system. Assuming that the magnetofluid is ideal (no dissipation), we can apply equilibrium statistical mechanics based on the ideal invariants of incompressible MHD. For a rotating system, the ideal invariants are energy and magnetic helicity; if there is no rotation, cross helicity is also an invariant. Expectation values such as means and variances of the dynamical variables are then calculated and tested numerically using Fourier codes, since the statistical mechanics for a spherical shell and a periodic box are equivalent. Expectation values mostly agree with numerical time averages, but there is a surprise: Although all mean values are predicted to be zero, the largestscale modes have dynamical mean values that are large and quasistationary. This ‘broken ergodicity’ is due to a dynamically broken symmetry. Here, we review the theory and computation that lead to this solution of the dynamo problem, as well as discuss its applicability to real MHD turbulence. 

PP11.00110: Turbulent nonlinear dynamics of magnetic flux ropes in reduced magnetohydrodynamics Alexander Velberg, Lucas Shoji, Muni Zhou, Nuno F Loureiro Magnetic flux ropes are integral to the dynamics of many plasma physics phenomena, including coronal heating, astrophysical jets, and 3D magnetic reconnection. While interactions between multiple flux ropes play an important role in some of these systems, the evolution of a single flux rope under its own dynamics is also relevant. We present results from numerical simulations of magnetic flux ropes in reduced magnetohydrodynamics, in which resistive instabilities of the flux rope result in a turbulent nonlinear state where the intense current sheets associated with unstable modes produce a magnetic energy spectrum E_{M} ~ k_{⊥}^{2}. We show that the number of linearly unstable rational surfaces is an important parameter for determining the fraction of magnetic energy available to the turbulence and discuss the mechanisms by which the system can be maintained in a quasisteady nonlinear state accompanied by dissipation of a large fraction of the initial magnetic energy. This work may have implications for the study of particle acceleration in astrophysical systems, as well as plasmoids in 3D magnetic reconnection. 

PP11.00111: Simulations of the Radiative Collapse of Plasmoids in Extreme Astrophysical Environments Simran Chowdhry, Rishabh Datta, Jack D Hare, Nuno F Loureiro In extreme HED astrophysical environments such as black hole coronae, jets and pulsar magnetospheres, radiation is an important signature of reconnection that modifies the energy partition, leading to cooling instabilities such as radiative collapse. Initial theoretical work done by Uzdensky and McKinney [Uzdensky & McKinney, 2011] describes radiative reconnection using a modified, compressible SweetParker model, but this model does not include the effects of the plasmoid instability, which serves as a trigger for fast reconnection and forms magnetic islands or “plasmoids” [Loureiro et. al., 2007]. Simulations of the reconnection layer generated by a dual exploding aluminium wire array, using the Eulerian 3D resistive MHD code GORGON [Ciardi et. al., 2007], showed the formation and collapse of plasmoids in the presence of radiative cooling. Additionally, it was found that larger plasmoids collapse before smaller plasmoids. The presented work aims to elucidate the underlying mechanism of plasmoid collapse using AthenaPK, an astrophysical MHD code, whilst considering all terms involved in the balance of power density, including radiative loss, thermal conduction and ohmic heating, in a more fundamental geometry. 

PP11.00112: Simulation study of energy partition in nonrelativistic collisionless shocks Jhonnatan Gama Vazquez, Alexis Marret, Frederico Fiuza Collisionless shocks are common in astrophysical plasmas and are known to be important for the magnetic field amplification and acceleration of both high energy electrons and protons. While diffusive shock acceleration is well established, particle injection into the nonthermal tail remains an important puzzle. In this work we present the results of largescale onedimensional particleincell simulations of magnetized, non relativistic, collisionless shocks to discuss how the properties of the injected particles depend on the plasma parameters, namely the Alfvénic Mach numbers and the orientation of the ambient magnetic field with respect to the shock normal. Quasiparallel and quasiperpendicular shocks are analyzed. We analyze electron heating and the development of a nonthermal power lawlike tail in the energy spectra, finding that quasiparallel shocks with high Mach number are the most efficient in terms of injection to the highest energies. Reflected particles exchange energy through waveparticle interactions, exciting modes in the upstream and promoting electrons heating. We analyze the nature of these modes and compute the ratio Te/Ti. We analyze individual trajectories of the most energetic particles to discuss how they achieve nonthermal energies. 

PP11.00113: Spectral studies of the Weibel turbulence via PIC simulations Michael C Sitarz, Mikhail V Medvedev, Alexander A Philippov Unmagnetized plasmas with (interpenetrating) plasma beams are highly unstable to electromagnetic instabilities such as the Weibel filamentation instability. Highenergydensity plasmas in astrophysical systems are ubiquitous, and are present in collisionless shocks of gammaray bursts and supernova explosions, for instance. These are the locations where the beamplasma Weibel instability naturally occurs. It affects plasma dynamics and observable electromagnetic radiation. Here we investigate collisionless, unmagnetized, counterpropagating plasmas with PIC simulations using TRISTANMP code. We developed a spectral analysis software suite which we now use at the postprocessing stage. Here we present the timedependent spectral analysis in the omegak space and the angledependence of the plasma modes present in the system as it evolves in time. Various properties the excited plasma modes are discussed. 

PP11.00114: LOW TEMPERATURES PLASMA APPLICATIONS


PP11.00115: Spectral characterization of the Hall Effect thruster operation on argon propellant Oleg Batishchev, Alexander Hyde, James Szabo We continue noninvasive characterization of the BHT200 Hall Effect Thruster performance. First, vacuum EUV spectra of the HET's operation on Ar propellant are collected and the emission lines of plasma species including natural impurities are identified. Next, FUVMUV spectrum is examined for notorious boron nitride lining erosion products as a function of the discharge parameters. Finally, the upgraded highresolution NUVNIR system [1] is used to measure the axial velocity of Ar ions along the plasma plume. New results are compared to the old data [2,3] of the thruster operating on Xe and Kr propellants. 

PP11.00116: Evaluation of Plasma Flow and Acceleration Effect Using Rotating Magnetic Field Current Driving Method in Magnetic Nozzle Takeru Furukawa, Daisuke Kuwahara, Shunjiro Shinohara Rotating Magnetic Field (RMF) current driving is utilized to form Field Reversed Configuration (FRC) in the field of nuclear fusion research [1] and accelerate plasma in electrodeless Radio Frequency (RF) plasma propulsion [2]. The RMF plasma acceleration is proposed for performance improvement of the RF plasma thruster by increasing an electromagnetic force under a magnetic nozzle [3]. The RMF method drives an azimuthal electron current owing to the nonlinear Hallterm effect, and the additional force is generated in the presence of the external divergent magnetic field. 

PP11.00117: Preliminary concept for an electrodeless Magnetic Reconnection Thruster (eMRT) Kush Maheshwari, Jungkyun Kim, Hantao Ji, Yevgeny Raitses, Jongsoo Yoo, Fatima Ebrahimi, Masaaki Yamada Advanced thrusters are needed for deep space missions to Mars and beyond. Critical issues for such thrusters include (1) how to generate large thrusttopower at (2) sufficiently high specific impulse with (3) long lifetime and (4) flexibility in propellant. To address these challenges, we are exploring a new electrodeless Magnetic Reconnection Thruster (eMRT), which will use asymmetric, inductivelydriven magnetic reconnection outflows to provide spacecraft thrust. Not requiring electrodes would mitigate electrode erosion, which is a key constraint on the lifetime of magnetoplasmadynamic (MPD) and Zpinch thrusters–other candidates for these missions. 

PP11.00118: Nanosecond dielectric barrier discharge aircraft ice protection system Andrey Starikovskiy, Manny Rios The Earth's atmosphere contains lots of water vapor at every level. Liquid water droplets in clouds can be below the freezing point, a matter phase state with the thermodynamic name of "supercooled". It so happens that all aircraft flying at subsonic speeds into clouds in these conditions collect ice on every forward exposed structure. The big engineering challenge is to design and develop ice protection systems that use the least amount of engine power, which at this point is why, numerically, the number of iceprotected aircraft is the minority compared to overall global number of aircraft. This paper presents results of numerical modeling of nanosecond surface dielectric barrier discharge (nsSDBD) for aircraft ice protection system using a heat release in highly nonequilibrium pulsed plasma. The major attention is paid to the effects based on ultrafast (on nanosecond time scale at atmospheric pressure) local heating of the gas, since at present the main successes in ice protection using gas discharges are associated with namely this thermal effect. The mechanisms of ultrafast heating of air at high electric fields realized in these discharges, as well as during the decay of discharge plasma, are analyzed. 

PP11.00119: Development and Analysis of a Multiscale Numerical Model for Ionic Electrospray Emission Amin Taziny, Iain D Boyd Electrospray thrusters, a rapidly evolving class of electric propulsion devices, hold significant potential for enhancing the efficiency of miniaturized spacecraft. These thrusters operate by applying an electrostatic field to a liquid ion source, from which ions are extracted and accelerated, thereby generating thrust. Despite their high propulsive efficiency, particularly those operating in a purelyionic emission regime using roomtemperature molten salts (ionic liquids), their broader adoption has been limited. This is primarily due to various uncharacterized failure modes that impede their reliability in missioncritical applications.This study aims to address this gap by developing a comprehensive, multiscale numerical model of a purely ionic emitting electrospray thruster. The model is designed to guide future thruster design optimization and enhance their reliability. The methodology involves an electrohydrodynamic meniscus model that links upstream geometric and fluid properties to the current emitted at the interface. A dual direct simulation Monte Carlo and particleincell approach, a method that simulates the movement of ions within the plume, is then implemented. Preliminary results indicate that this model can successfully predict the behavior of these thrusters under various conditions. This understanding can help identify key design parameters that influence thruster performance and reliability. By illuminating the dependencies of emission characteristics, this research provides valuable insights into potential strategies for mitigating electrospray failure mechanisms. 

PP11.00120: Investigation of PlasmaInduced Magnetic Flux Compression on Induced Current in a Stator Coil Within Different Magnetic Field Configurations Ian Wagner, Gabe Xu In this experiment we investigated the effect of magnetic flux compression using different magnetic field geometries on induced current in a solenoidshaped stator coil. A laserproduced plasma (LPP) was created to induce magnetic flux compression. In this experiment, a pulsed Nd: YAG laser with a wavelength of 532 nm was focused through a planoconvex lens and fired at a graphite target within a solenoidal stator coil in a vacuum chamber. The stator coil was placed in between two permanent block magnets and contains 22 turns of wire. The block magnets are arranged in different positions to analyze how different magnetic field configurations affect current produced during magnetic flux compression. These configurations include axial, transverse, and magnetic cusp geometries. The experiment was carried out in a pressure range of 10^{4} Torr to 250 mTorr and used a laser energy of 200 mJ. A Pearson coil was connected to an oscilloscope and was used to detect current induced in the stator coil during the LPPinduced magnetic flux compression. 

PP11.00121: Laser produced plasma expansion into high magnetic field gradients. Zachary K White, Gabe Xu, Saikat Chakraborty Thakur, Edward Thomas Laser produced plasmas expanding into background magnetic fields is a good analogue for many plasma phenomena. We have extended our previous work by initiating a laser produced plasma expansion into a nonuniform, high gradient background magnetic field. The highly uniform magnetic fields produced by the Magnetized Dusty Plasma Experiment (MDPX) were combined with the field of 2” x 2” cylindrical permanent magnet to create our desired fields within a vacuum chamber pumped to pressures of ~ 4 mTorr. We captured the emission from the laser ablating a solid carbon fiber sheet with an ICCD camera, and the input laser energy, applied MDPX field, and camera gate delay time relative to the laser pulse were all varied. Increasing laser energy led to a broadening of the plasma emission transverse to the magnetic field and increasing the applied MDPX field led to a focusing of the plasma emission. Varying the camera gate delay allowed us to observe the dynamics of the expansion, and the resultant gradient field also lead to a much longer confinement time than that of laser produced plasmas expanding directly transverse to the applied magnetic field with the emission lifetime lasting upwards of 10 μs. Additionally, the plasma emission seemed to have two distinct components with one fast lived component reaching maximum expansion within 1 μs and another slower component reaching maximum expansion at > 10 μs. 

PP11.00122: GasBubble Mixing Improves Liquid Treatment with Cold Atmospheric Plasma Ha Nguyen, Haoyu Cheng, Yuting Wu, Yoann Choy, Benjamin B Minkoff, Thao T Nguyen, Mark P Richards, Michael R Sussman, Hau D Le, J. Leon Shohet This research addresses the treatment uniformity of liquid (TUL) treated with cold atmospheric plasma (CAP), a key challenge in plasmaliquid interactions. In CAP treatment of liquids, it is crucial to render the effects of CAP on all parts of a liquid sample such as protein solutions. Existing methods have limited effectiveness due to the restricted liquid diffusion of shortlived reactive species into liquid, complexities of liquid samples and their interface with plasma, and variations in plasma parameters. Consequently, either the liquid surface is overtreated, or its bottom part is rarely modified, resulting in undesirable outcomes. In this work, we used the controlled hydrodynamics of gas bubbles rising in the liquid as a method to improve liquid mixing for enhanced TUL treated with CAP generated on the liquid surface. Proofofconcept experiments were performed using various liquids containing organic molecules, including bromophenol blue, terephthalic acid, coumarin, and myoglobin. We employed our CAP technology called PlasmaInduced Modification of Biomolecules (PLIMB) [1,2] and integrated it with a gasbubble mixing system to treat these benchmark liquids. Our preliminary results demonstrated that TUL was significantly improved with this mixing process. Furthermore, the mixing facilitated faster modification of these molecules with PLIMB, substantially reducing treatment time. Overall, we anticipate that the coupling of any CAP device and gasbubble mixing presents an innovative approach [3] to enhance CAPbased liquid treatment, with potential applications to both engineering and basic research on plasmaliquid interactions, shedding light on transport phenomena of multiple phases. 

PP11.00123: Enhanced NeutronInduced Damage Testing through Plasma Window Technology Joshua Blatz, Ross F Radel, Tye T Gribb, Preston J Barrows, Todd Kile One of the greatest needs in the development of today’s fusion technology is the ability to test neutroninduced damage to components relevant to proposed fusion sources. There are no available sources that can generate both the neutron flux and relevant energy spectrum necessary. This has forced researchers to utilize simulation and lower energy sources to approximate component response. 

PP11.00124: Optimizing UV/VUV Transmission Through Capillaryarray Windows From Utilizing Statistical Experimental Designs Haoyu Cheng, Ha Nguyen, Leon J Shohet Capillaryarray windows have gained interest in semiconductor industries for plasmaassisted materials processing applications. They enable the transmission of desired optical radiation such as UV/VUV photons to the processing chamber while protecting the target sample from producing damage by bulky debris, thus leading to enhanced quality of plasma processing. Here, we report a new approach in which a capillaryarray window can show its efficacy over conventional solid thin films in the transmission of UV and VUV photons in an ECR plasma reactor. By benchmarking windows of varying capillary size and thickness as a key factor of three levels (nanometersized pore, micrometersized pore, and millimetersized pore), we demonstrated that the transmission could achieve as high as 58.93%. This optimized transmission can be attained by carrying out a factionalfactorial design to examine the interaction of various factors, namely, pore diameter, window thickness, window area, and incident angle of radiation properties. In addition, the windows can hold pressure differentials from 10^{6} torr to 20 mtorr and 20 mtorr to 760 torr without mechanical failure. The capillaryarray windows also survived the tests of differential pressure of several hundred psi. Overall, our approach to use capillary windows for plasma UV/VUV transmission in a processing chamber with differential vacuum levels is very promising. 

PP11.00125: Understanding the effect of magnetic field configuration on preferential transport of impurities in PISCESRF Gayatri D Dhamale, Matthew J Baldwin, MD SHAHINUL ISLAM, Atul Kumar, Marlene I Patino, Wouter Tierens, Juergen Rapp Helicon plasma sources driven by the radio frequency of 13.56 MHz have proven to be an efficient way of producing high density plasma (n_{e }≥ 10^{19} m^{3}) in linear plasma devices^{1–3}. Such devices are being built to study the plasmamaterial interaction under fusion reactor relevant conditions. A helicon source when operated under high RFpower^{1} was found to generate impurities originating from its vacuumwindow (e.g. Al_{2}O_{3}, AlN, Si_{3}N_{4}) as a result of the strong rectified sheath voltage on the ceramic. Previous studies revealed that the helicon window is eroded by deuterium and oxygen^{1}. However, selfsputtering of Al or Si could contribute significantly. The present study reports on the transport of the released impurities towards the plasma upstream side in PISCESRF device^{2}. Deposition of the Alimpurities were traced at various locations of the vacuum vessel. A strong deposition of Al was observed on the upstream side walls when the magnetic field is terminated at the sides wall in a “cusp” configuration. The physics of the impurity generation and its transport in PISCESRF will be presented and corroborated with modeling of the RF sheath, plasma, neutral and impurity transport for various magnetic field configurations. 

PP11.00126: Ion Velocity Distribution Function Effects on Atomic Layer Etching in a RF Discharge Brian Jensen, David B Graves RF Discharges are used in a range of systems with notable applications in semiconductor processing [1], surface treatment [2], medicine [3], and water purification [4]. In this work, we model RF discharges through 1D PIC simulations and measure ion velocity distribution functions (IVDF) at the surface of a substrate immersed within the plasma. We implement the resulting IVDFs into molecular dynamics (MD) simulations to more accurately study substrate etching [5]. We discuss differences between our MD results and prior MD simulations which assumed a delta function IVDF of incident ions. Our analysis considers various plasma compositions (eg. argon) and substrate materials (eg. silicon). 

PP11.00127: Magnetohydrodynamics Modeling of Electrothermal Instability Development on Electrically Pulsed Conductors Seth E Kreher, Christopher L Rousculp, Bruno S Bauer, Aidan W Klemmer The evolution of a conductor driven by multimegaampere current pulses from solid metal to thermal plasma is of great interest when designing imploding liner inertial confinement fusion experiments, magnetically driven flyer plates for material science tests, and electrical initiators for high explosives. The electrothermal instability (ETI) propagates unstable temperature perturbations in the conductor that deform the metal and limit its ability to carry current. They can develop from axial machining perturbations and resistive inclusions/voids in the metal—both of which divert the current and lead to preferential Joule heating. The resistive MHD code FLAG is used to model electrically thick rods driven by the ~1 MA, ~100 ns Mykonos current driver as well as thin wires and hollow liners with equivalent current densities to interpret experimental results showing ETI growth.


PP11.00128: Measuring Tungsten Fuzz Growth with Transient Grating Spectroscopy Andrew T Lanzrath, Angus Wylie, Sara E Ferry, Kevin B Woller, Michael P Short Tungsten is a candidate material for plasma facing components (PFCs) in magnetic confinement fusion (MCF) power plants and will be used for the first wall and divertor of ITER and Commonwealth Fusion System’s SPARC tokamak. When exposed to high temperatures and helium (He) plasmas, a nanostructured layer called fuzz forms on the originally smooth tungsten surface, which changes the local material properties and could potentially contaminate MCF plasmas. Transient grating spectroscopy (TGS) is a nondestructive, picosecond time scale characterization technique that reveals the material’s elastic properties, thermal diffusivity, and energy dissipation by measuring the decay of acoustic waves and temperature gratings on the surface of the material created from a laserinduced transient diffraction grating. Polished tungsten samples heated to 800°C will be exposed to a 13.56 MHz He plasma in the Dynamics of ION Implantation and Sputtering Of Surfaces (DIONISOS) experiment to show that the thermal diffusivity decreases with increasing fuzz production from two different TGS measurements. Scanning electron microscopy will confirm the fuzz microstructure evolution as a function of the plasma fluence. The first measurement will be taken on a benchtop TGS after He plasma irradiation, and the second will be in realtime on the Plasma Insitu Ion Irradiation TGS (PI^{3}TGS), which is installed on the DIONISOS beamline. Agreement between the benchtop and insitu TGS measurements would point to the necessity for a diagnostic to detect the onset and severity of fuzz growth in future MCF devices using tungsten PFCs. 

PP11.00129: Computational Investigation of Ion Energy Angle Distribution within Trench Structures using the hPIC2 ParticleinCell Code Andrew Liu, Logan T Meredith, Davide Curreli Plasmamaterials interactions are sensitive to a plasma's ion energyangle distribution (IEAD). Accurately characterizing the IEAD of a processing plasma can aid the use and development of pattern transfer methods used in high aspect ratio etching for MEMS and integrated circuits. In particular, the variation in ion flux in different areas of a microstructure can cause variation in etch rates. hPIC2, a GPUaccelerated electrostatic particleincell code, is able to simulate plasmas in unstructured finite element meshes using the finite element C++ library, MFEM. This is used to model the geometry of various trench structures often found in etching process flows, enabling a spatially varying IEAD output. We investigate the effect of varying plasma parameters and aspect ratios on the IEAD incident on trench surfaces. 

PP11.00130: Sheath models for thermionically cooled surfaces in twotemperature plasmas Kal Monroe, Iain D Boyd Electron transpiration cooling (ETC) is a proposed thermal management technique for the leading edges of hypersonic vehicles. This technique leverages the wellunderstood property of thermionically emitted electrons by carrying away heat energy at the surface as potential and kinetic energy. Computational fluid dynamics (CFD) modeling approaches for this phenomenon have developed emissive boundary conditions for ETC. These account for spacechargelimited emission to accurately determine the level of electron emission from the surface. However, CFD modeling approaches for ETC have only considered the thermionic emission from a negatively biased surface. In reality, emitted electrons are expected to travel downstream of the emission point and reattach to the vehicle surface and redeposit their energy. In this work, we propose an approach to model electron absorption downstream of the thermionic emitter at a positively biased surface. Physics of an electron sheath near a positively biased anode in a 2T quasineutral plasma are investigated and electron absorption treatment is discussed. Comparison of CFD prediction of the reabsorption model to an ETC experimental investigation is underway. 

PP11.00131: Direct measurements and spectroscopic analysis of secondary electron emission from carbon foams Angelica Ottaviano, Yevgeny Raitses, Gary Wan, Evan T Ostrowski, Shota Abe, Bruce E Koel, Richard E Wirz Secondary electron emission (SEE) from plasmafacing components can significantly impact the performance of many devices such as electric propulsion thrusters, plasma gun components, fusion device first walls, divertors, and bias electrodes. To this end, materials with geometrically complex morphologies have been found to be effective at suppressing SEE yield compared with flat surfaces. SEE measurements of carbon foams and flat graphite are presented and agree with recent experimental and analytical findings. An optimal geometric configuration for reticulated carbon foams showing up to to 45% reduction of SEE yield compared with flat graphite was also determined. SEE angular measurements also revealed a loss of angular dependence for carbon foams with < 100 geometric features, as has been shown in previous studies of tungsten nanofuzzes. A doublepass cylindrical mirror analyzer (CMA) typically used for Auger electron spectroscopy was also used to study the SEE spectra from foams compared to flat graphite surfaces. This analysis revealed that generation of true (0 – 50 eV) SEs may be enhanced by up to 5% from foam surfaces compared to flat graphite surfaces, and that foams may suppress backscattered secondary electrons by > 80%. These results can inform the basic SEE physics and design space of plasmafacing components, particle accelerator walls, electron microscopy, and RF components for multipactor effect mitigation. 

PP11.00132: Optimization of Additively Manufactured Plasmafacing Surfaces with Consideration of Plasma Infusion Effects Graeme T Sabiston, Richard E Wirz While volumetrically complex materials (VCMs) have shown to be robust when exposed to plasmafacing environments, this study seeks to examine the performance of additively manufactured VCMs and investigate their capability to volumetrically conduct current. This research builds upon advanced ionsolid interaction simulation codes and optimization algorithms to determine optimal VCM designs that seek to minimize sputtering erosion. Optimized VCM geometries have demonstrated a reduction in sputter yield by approximately 80%; these complex designs have been realized only through the advanced capabilities of the additive manufacturing process. This research also seeks to understand the transport mechanisms of electrical current through VCMs, a critical factor for determining the currentbearing capacity of highpower cathodes. This investigation underlines the potential of VCMs to bolster durability in applications such as nuclear fusion, plasma electrodes, and space propulsion, thereby pushing the boundaries of current technological capabilities. 

PP11.00133: Effects of Oxides on Hydrogen Uptake and Release in DispersionStrengthened Tungsten Carli S Smith, Robert D Kolasinski, Martin NietoPérez, Xing Wang To further our understanding of hydrogen (H) retention in PFCs, it is important to consider tungstenoxide systems. Oxides form naturally on the surface of tungsten (W) due to the strong chemical affinity. This effect becomes more prominent in extreme environments e.g., in fusion reactors. As materials are exposed to the plasma, they will experience erosion and redeposition, which could significantly modify fuel retention. Therefore, the topic of oxidative mechanisms for hydrogen retention warrants further discussion. In collaboration with Sandia National Lab, we will elucidate how both the partial coverage of oxygen (O), as well as the presence of oxide thin films, affects H chemisorption and uptake in dispersionstrengthened tungsten (DSW) samples. We will be using W1%ZrC, W5%TiC, and W10%TiC to compare the effects of different dispersoids on O and H interactions in W. We will apply low energy ion scattering (LEIS) and direct recoil spectroscopy (DRS) to investigate how the partial coverage of O affects H chemisorption on the surface, as well as xray photoelectron spectroscopy (XPS) and Auger spectroscopy to characterize both the material’s chemical and elemental composition before and after dosing. We will then grow oxide films on the materials to further investigate the effects of oxides on these surfaces. Subsequently, we will perform ellipsometry insitu with deuterium (D) plasma exposure to obtain optical properties in real time. Finally, we will use LEIS and DRS again to quantify the chemisorbed H and D under the presence of these thicker oxide layers. 

PP11.00134: Development of the ParticleMesh, MaterialInteraction ParticleInCell Code Package (PEMMICAN) for the Simulation of Plasma Facing Component Wall Effects Alex Somers, Leigh Winfrey, George K Larsen, Holly B Flynn The vapor shielding effect occurs when a plasma impinges on a surface, depositing energy and inducing vaporization, leading to interaction with the impinging plasma. This plasmavapor interaction results in an overall reduction of the energy deposited at the material surface. The ParticleMesh, Material Interaction Particle in Cell code package (PEMMICAN) was developed to simulate vapor generation as a result of plasma energy deposition on tungsten, iron, carbon, and lithium targets. PEMMICAN is also capable of simulating plasmavapor interaction between a tungsten vapor and a deuteriumtritium plasma via electron impact ionization and radiative recombination. The development and verification of PEMMICAN is presented in this paper. The underlying model implemented in PEMMICAN is described and relevant theory is discussed. Verification tests are presented, including measurement of simulated electron and ion gyrofrequencies and Larmor radii, electrostatic repulsion, E⨯B drift, gradB drift, spatial and temporal stability analysis, vaporization mechanics, and electron impact ionization and recombination mechanics. Good agreement between the underlying model and simulation results were found. Notably, near exact agreement was found between simulated electron and ion Larmor radii in a strong magnetic field and the corresponding analytical value. Concluding thoughts, current efforts, and future work are discussed. 

PP11.00135: MINICONFERENCE SHOCKS


PP11.00136: A new hybrid: kinetic ions with parallelkineticperpendicularmoment (pkpm) electrons James L Juno, Ammar Hakim, Jason M TenBarge, Gregory G Howes, Collin R Brown The hybrid kinetic formalism, wherein one retains the complete Vlasov dynamics for some number of ion species while reducing the electron dynamics to a fluid model, is a workhorse simulation model for the plasma community, especially in applications to collisionless shocks. However, a known deficiency of this approach for collisionless shock applications is one must prescribe the ultimate temperature partition of the shock downstream between electrons and ions. Such a partition is fraught with difficulties due to the complex nonequilibrium dynamics of the shock, with the electrons typically undergoing significant nonadiabatic heating through their kinetic response to, for example, parallel electric fields which develop in the shockwave. 

PP11.00137: Investigation of the Ion Reflection Rate at QuasiPerpendicular Shocks Eli D Monyek, Hadi Madanian, Narges Ahmadi, Karlheinz J Trattner Particle reflection at collisionless shocks plays an important role in the dynamics of the shock layer. In this study we investigate the rate of ion reflection from quasiperpendicular shocks under different upstream conditions. We use insitu observations from NASA’s Magnetospheric Multiscale (MMS) Mission during 225 shock crossings as these shocks provide a wide range of parameters. For each event, different ion populations, including the solar wind and reflected ions are identified in the data, and associated plasma moments for each population are determined. We then looked at correlations between shock and plasma parameters, and ion reflection rate. These parameters include: ΙBΙ amplification rate, Alfvénic Mach Number (M_{A}), the shock angle (Θ_{BN}), upstream plasma density (n_{Up}), temperature, and velocity. We find that the reflection rate is not constant, and increases with the Alfvénic mach number and the magnetic amplification rate across the shock. This information will help further the understanding of the solar wind and how it interacts with our magnetosphere. 

PP11.00138: Electron acceleration mechanisms in magnetic reconnection and flux ropes in the Earth's quasiparallel bow shock Naoki Bessho, LiJen Chen, Michael Hesse, Jonathan Ng, Lynn B Wilson, Julia Stawarz Recent shock observations by NASA’s Magnetospheric Multiscale (MMS) have revealed numerous reconnecting current sheets in the Earth’s bow shock. Magnetic reconnection can produce energetic particles, but the role of reconnection in shock heating and acceleration remains to be investigated. 

PP11.00139: Reconnection diffusion region in a shock ramp LiJen Chen, Jason R Shuster, Richard Denton, Yi Qi, Hadi Madanian, Jonathan Ng, Ari Le, Adam J Stanier, Naoki Bessho, Craig J Pollock, Daniel Gershman, James L Burch We present a new possibility based on observations of a reconnecting current sheet that occurs within the ramp of a bow shock at Earth. Observed reconnection signatures include electron jet reversals, intense electron heating, inward and outward convecting magnetic fluxes, and features of electron distribution functions consistent with those in a fully developed electron diffusion region at the terrestrial magnetopause. The observations suggest that reconnection can contribute substantially to electron heating at collisionless shocks in planetary and astrophysical systems, and potentially has largescale impact on the shock structure and function. 

PP11.00140: Conditions of structural transition from collisionless electrostatic shock to doublelayer structure Minh N Ly, Takayoshi Sano, Youichi Sakawa, Yasuhiko Sentoku In unmagnetized plasmas, collisionless shocks can be sustained by electrostatic potential alone when electron temperature is significantly larger than ion temperature. These shocks, known as collisionless electrostatic shocks (CES), can be generated in laboratory settings through the interaction between intense lasers and nearcritical density targets. Another structure having a similar presence of localized electrostatic potential is doublelayer structure (DL) which has been frequently observed in space plasmas. Using particleincell (PIC) simulations, we investigate the formation of CES at the interface between two plasma slabs with varying pressures and reveal a natural transition from CES to DL. From the numerical results, we identify that the transition to DL occurs when the initial density ratio between the two plasma slabs exceeds 40, independent of the temperature ratio. Motivated by this result, we propose a new model based on previous CES studies to also describe DL dynamics. In addition, our model successfully explains the transition observed in PIC simulations, providing new insights into the physics of CES and DL in space and laboratory plasmas. 

PP11.00141: Hydrodynamic Shock Modifications by the Heat Flux of NonThermal Particles Colby C Haggerty, Damiano Caprioli, Paul A Cassak, Mahmud Hasan Barbhuiya, Lynn B Wilson, Drew L Turner Collisionless plasma shocks are a common feature of many space and astrophysical systems and are sources of highenergy particles and nonthermal emission, channeling as much as 20% of the shock's energy into nonthermal particles. The generation and acceleration of these nonthermal particles have been extensively studied, however, how these particles feedback on the shock hydrodynamics has yet to be fully treated. This work presents the results of selfconsistent, hybrid particleincell simulations that show the effect of selfgenerated nonthermal particle populations on the nature of collisionless, quasiparallel shocks, which contribute to a significant heat flux upstream of the shock. Nonthermal particles downstream of the shock leak into the upstream region, taking energy away from the shock. This increases the compression ratio, slows the shock, and flattens the nonthermal population's spectral index for lower Mach number shocks. We incorporate this into a revised theory for the jump conditions that include this effect and show excellent agreement with simulations. The results have the potential to explain discrepancies between predictions and observations in a wide range of systems, such as inaccuracies of the predicted arrival times of coronal mass ejections and the conflicting radio and xray observations of intracluster shocks. These effects will likely need to be included in fluid modeling to predict shock evolution accurately. 

PP11.00142: Understanding the Breakdown of the Bell Instability in the Limit of High Cosmic Ray Current Density Emily R Lichko, Damiano Caprioli, Siddhartha Gupta A critical component to explaining the observation of cosmic ray acceleration at supernova remnants is the nonresonant Bell's instability, where the relative drift between the thermal ions and the cosmic rays lead to the amplification of magnetic fields necessary to accelerate particles with diffusive shock acceleration. In order to extend our understanding of particle acceleration in other astrophysical systems, and to inform limitations on the amount of heating possible from the Bell instability in supernova remnants, in this work we investigate the instabilities present in the high cosmic ray current density limit, where the assumptions underlying the Bell instability break down. Despite the increase in the free energy in the particles, in this limit significantly less magnetic field amplification is observed. We discuss the saturation of the instabilities in this regime, how they scale with respect to the sources of free energy in the system, and, critically, their relevance for the injection of electrons into the process of diffusive shock acceleration. 

PP11.00143: Experimental Observations of Electrode PlasmaSurface Chemistry in AirBreathing Gridded Ion Thrusters Patrick Crandall, Richard E Wirz Electrode surfaces inside airbreathing electric propulsion (ABEP) plasma discharges are exposed to reactive oxygen and nitrogen species which can form insulating layers and quickly degrade thruster performance. Previous literature has shown titanium and stainless steel both have potential for mitigating electrode surface degradation, but limited analysis of electrode surfaces was performed (Lotz 2013, Tejeda and Knoll 2023). In this work, stainless steel and titanium electrodes are tested in a radiofrequency (RF) gridded ion thruster running on nitrogen and oxygen. Surface layer growth and composition are analyzed via SEM and EDS imaging. Material recommendations which limit electrode performance degradation in ABEP thruster electrodes are made. 

PP11.00144: Imaging Refractometry Technique Development Alexander Rososhek, Bruce R Kusse, William M Potter, Eric S Lavine, David A Hammer The imaging refractometry technique is a valuable diagnostic tool for studying high energy density plasmas. Density fluctuations in these plasmas are challenging to measure, particularly in gaspuff Zpinch implosions where turbulence is thought to be present [1,2,3]. After its introduction [4], the technique has been further developed at Cornell’s Laboratory of Plasma Studies for diagnosing imploding gaspuff Zpinch plasmas using a 40 mJ, 150 ps, frequency doubled Nd:YAG laser pulse at 1064/532 nm. To obtain timeresolved wavenumber spectra a visible light streak camera is being used along with a ~150 mJ, ~12 ns, frequency doubled NdYLF laser pulse at 532 nm. 

PP11.00145: Characterization of Circular Arc Electron Source for Air Ionization in a SelfNeutralizing AirBreathing Plasma Thruster Anmol Taploo, Vikas Soni, Halen Solomon, Marshal McCraw, Li Lin, Jake Spinelli, Steven P Shepard, Santiago Solares, Michael Keidar Nowadays interest in airbreathing plasma propulsion for very low earth orbit applications is increasing. To this end, airbreathing plasma thrusters utilize incoming air as a propellant that is ionized and then consequently accelerated to produce thrust. This talk will present a unique concept for airbreathing plasma thrusters in which ionization and acceleration occur without slowing incoming air. In addition, by varying electron energy it has been demonstrated that both positive and negative ions can be extracted. This configuration could potentially eliminate the complexity of using a collimator reducing the drag. Typically, an airbreathing plasma thruster would require an external neutralizer to inject electrons for ion beam neutralization while a selfneutralizing airbreathing plasma thruster utilizes both positive and negative ions to achieve beam neutralization. This talk focuses on the ionization aspects of airbreathing thrusters through the development of radial magnetized arc electron source. This source consists of a circular configuration of a metallic arc plasma source coupled with a positively biased grid to extract electrons and control electron energy. It was demonstrated that radial electron source leads to enhanced ionization of airflow. The effect of external parameters on the source showed that the shape and size of arcing regions/intensity varied. While the grid underwent deposition of about 600 microns, the conductance was observed to increase/saturate with time and bias voltage indicating an electrically "selfhealing material 
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