Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session CO03: DIII-D TokamakLive Streamed
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Chair: Theodore Biewer, ORNL Room: Ballroom 100 C |
Monday, October 17, 2022 2:00PM - 2:12PM |
CO03.00001: DIII-D: Closing the Gaps to Future Fusion Reactors Craig C Petty The DIII-D program is pursuing an ambitious plan to close critical design gaps to a Fusion Pilot Plant (FPP), including integrating performance and exhaust solutions, addressing plasma interacting material and technology issues, and resolving a high fusion gain path to ITER and a pulsed FPP. Increasing the ECH power to 10 gyrotrons, with an extension to 20 gyrotrons by FY28, will furnish low-torque electron heating and profile control, while new reactor-relevant solutions for efficient off-axis current drive will be pioneered by high-field-side LHCD, helicon waves and top launch ECCD to enable FPP steady-state scenarios. A series of closed, modular divertors will allow the exploration of innovative plasma solutions for combined core and plasma exhaust in high opacity/low collisionality regimes made possible by stronger shaping to maximize the pedestal pressure and density along with a BT rise to 2.5 T. A dedicated material interaction test station will help close gaps in compatible fusion materials. The control and mitigation of plasma transientswill be addressed through a passive runaway electron dissipation coil and installing novel techniques for disruption mitigation (EM launch, hyper-velocity tungsten pellets). An exciting option for a negative triangularity path is being assessed. |
Monday, October 17, 2022 2:12PM - 2:24PM |
CO03.00002: Overview of Recent DIII-D Experimental Results Auna L Moser DIII-D research advances scientific understanding for ITER and future tokamak fusion reactors. Applied resonant magnetic perturbations (RMPs) increase confinement and stabilize peeling ELMs in a newly identified “pump in” regime. Experiments in H plasmas find a critical D fraction is required to maintain RMP ELM suppression. Multimodal plasma response to applied 3D fields explains heat and particle flux structures at the divertor. The benefits of divertor closure disappear in the deeply detached state. High qmin steady state scenarios benefit from broadening the energetic particle profile in a high bootstrap fraction, noninductive plasma. Transport studies quantify the particle pinch and diffusion in the pedestal after edge localized modes (ELMs); others show micro-tearing modes can dominate electron heat transport in ELMy H-mode pedestals. Multi-Z impurity studies show that the ion thermal gradient instability and the ∇n trapped electron mode dictate transport, with a radially varying Z dependence. Radial core transport events seen at reduced mean ErxB shear flow may explain confinement degradation in high-collisionality H-modes. Experiments and theory show that fast ions drive β-induced Alfven eigenmodes, while the newly identified low-frequency Alfven mode is driven by Te. Explorations of a negative triangularity (NT) reactor concept show that fast ions from counter-/co-current neutral beam injection de/stabilizes sawtooth crashes, and that a low-n MHD mode triggers NT ELMs at a critical pressure gradient. |
Monday, October 17, 2022 2:24PM - 2:36PM |
CO03.00003: Transport and stability in sustained high qmin, high βN discharges on DIII-D Juan Huang, Andrea M. Garofalo, Wilkie Choi, Xi Chen, Colin Chrystal, Siye Ding, Xianzu Gong, Qiming Hu, Rongjie Hong, Christopher T Holcomb, Xiang Jian, John Lohr, Jinping Qian, Terry L Rhodes, Qilong Ren, Ted Strait, PengJun Sun, Yanxu Sun, Huiqian Wang, Liang Wang, Zheng Yan, Xinjun Zhang To address the needs for a fusion pilot plan design, DIII-D/EAST joint experiments on DIII-D have demonstrated high normalized beta βN>4, poloidal beta βP>3, toroidal beta βT>3% with qmin>2, q95≤8 sustained for more than six energy confinement times. The excellent energy confinement quality (H98y2~1.7) is achieved with an internal transport barrier (ITB) at high line-averaged Greenwald density fraction, fGW>0.9 (~7×1019 m-3). Gyrofluid (TGLF) modeling of the transport characteristics shows that the beam driven rotation does not play an important role in the high confinement quality. This is consistent with the paradigm that turbulent transport within the ITB region is suppressed by strong alpha-stabilization effect at high βP. The high performance phase can be terminated by fast growing modes triggered near the n=1 ideal-wall kink stability limit by large edge localized modes (ELMs). While the achieved bootstrap current fraction on DIII-D is high (up to 80%), it will be even higher in a reactor at the same βN, q95 and fGW due to the lower collisionality from higher BT and IP. Future experiments will aim to make up the difference in bootstrap current and achieve fully noninductive conditions by using helicon and top launch EC wave injection for additional, efficient off-axis current drive at high density and beta. |
Monday, October 17, 2022 2:36PM - 2:48PM |
CO03.00004: Near-Edge Alfven Eigenmodes in DIII-D high βp plasmas Xiang Jian, Christopher G Holland, Eric M Bass, Siye Ding, Xiaodi Du, Vincent S Chan, Andrea M. Garofalo, Brian A Grierson, Joseph T McClenaghan, Guanying Yu New analysis of a DIII-D high bootstrap current fraction scenario plasma, which is characterized by high q95(q95>6) and a strong large radius internal transport barrier (ITB) at ρ~0.6, demonstrates that the Beta-Induced Alfven Eigenmode (BAE) plays an important role in controlling transport in the outer core region (ρ~0.75). First, multiple fluctuation measurements show evidence for a mode peaking in this region with frequency and wavenumber consistent with characteristics of the BAE. Second, a detailed stability analysis indicates that the BAE is primarily excited by the unfavorable magnetic curvature drive in this region, which lies close to the kinetic ballooning mode (KBM) boundary as is pointed by Staebler[1]. Because the BAE and KBM share the same drive from the bulk thermal plasma, only a small amount of additional free energy is needed to destabilize the BAE. Gyrokinetic simulations predict that the small but finite fast ion fraction at these radii is sufficient to provide this additional drive and robustly destabilizes the BAE. Application of such a theory is also able to reproduce the BAE behavior in shots with similar q95 but the large radius ITB is not established. Finally, nonlinear CGYRO simulations predict that the BAE can efficiently drive experimentally relevant levels of the electron particle flux and electron energy flux. When additional contributions from neoclassical transport and ETG turbulence are considered, the experimental fluxes in all three channels are reproduced within uncertainties. |
Monday, October 17, 2022 2:48PM - 3:00PM |
CO03.00005: Mode structure measurements of ion cyclotron emission and sub-cyclotron modes on DIII-D Genevieve H DeGrandchamp, Jeff B Lestz, Michael Van Zeeland, Xiaodi Du, Kathreen E Thome, Neal A Crocker, William W Heidbrink, Robert I Pinsker We report mode structure measurements of coherent ion cyclotron emission (ICE) and sub-cyclotron modes on DIII-D. In L-mode plasmas, harmonics of the ion cyclotron frequency fci were observed and are localized near the magnetic axis. Sub-cyclotron modes (f ~ 0.5fci) were also observed when BT ≤ 1.25 T. ICE harmonics localized to the plasma edge were observed in H-mode plasmas, with some exceeding the nominal ICE diagnostic bandwidth of f ∈ [0, 100] MHz. Using an orthogonal loop pair, ICE and sub-cyclotron modes were found to be compressionally polarized at the plasma edge. The same ICE harmonics were observed by centerpost and outer wall loops, suggesting that the modes are poloidally extended. Finally, toroidal mode numbers were calculated for core ICE and sub-cyclotron modes. The sub-cyclotron case served as a benchmark, with the measured n ∈ [-24, -18] roughly agreeing with heuristic estimates of n ∈ [-20, -13]. Core ICE mode numbers n ∈ [-10, 5] were measured, which is comparable to measurements made on other machines. |
Monday, October 17, 2022 3:00PM - 3:12PM |
CO03.00006: Modeling the Alfvén eigenmode induced fast-ion phase-space flow measured by an imaging neutral particle analyzer Javier Gonzalez Martin, Xiaodi Du, William W Heidbrink, Michael Van Zeeland, Konsta Sarkimaki, Antti Snicker, Xim Wang, Yasushi Todo An imaging neutral particle analyzer (INPA) provides energy and radially resolved measurements of the confined fast-ion population at the DIII-D tokamak. In recent experiments, it was used to diagnose fast-ion flow driven by multiple, marginally unstable Alfvén Eigenmodes (AEs). Different models are applied to reproduce such measurements. Ad hoc energetic particle diffusivity modeling by TRANSP significantly deviates from the observations. Comparably, reduced modeling, i.e. a combination of NOVA-K and ASCOT5 codes, reproduce some key features of the observed flow, but largely fail to interpret the observed fast ion depletion near the plasma axis. At last, hybrid simulations predict an RSAE consistent with the experiment that redistributes the injected ions. The resulting synthetic INPA images are in good agreement with the measurement near the injection energy. These simulations confirm that the measured flow follows streamlines defined by the intersection of phase-space surfaces of constant magnetic moment μ and constant E' = nE+⍵Pɸ. Nonperturbative effects are required to reproduce the depletion of fast ions near the magnetic axis at the injection energy. |
Monday, October 17, 2022 3:12PM - 3:24PM |
CO03.00007: Model order reduction of magnetic and MSE EFIT reconstructions with neural networks Cihan Akcay, Jaehoon Koo, Sandeep Madireddy, Lang L Lao, Xuan Sun, Yueqiang Liu, Prasanna Balaprakash We present a model order reduction (MOR) of magnetics-only (EFIT01) and magnetics plus motional Stark effect (MSE) EFITs (EFIT02) with neural network (NN) surrogates that have been trained on the 2019 DIII-D data. Our neural networks reconstruct DIII-D equilibria, given an input space comprising the external magnetic data and internal MSE measurements. The output space comprises the poloidal magnetic flux ψ and toroidal current density Jφ on the EFIT rectangular spatial grid; safety factor profile (for EFIT02); global parameters including the normalized beta, internal inductance, axial and edge safety factor; as well as the plasma boundary and quantities related to the magnetic topology such as the X-point locations. Including Jφ in the training imposes the magnetostatic force-balance condition on the NN. A fully-connected multi-layer perceptron (MLP) NN suffices to learn ψ(R,Z). However, various approaches are pursued to reconstruct Jφ concurrently with and from the NN ψ: 1) a convolutional NN that learns Jφ(R, Z) on the grid, 2) an MLP that learns the pressure and poloidal current flux function profiles to calculate Jφ (ψ), and 3) an MLP that learns the coefficients of the basis functions that form the profiles. Note the output space contracts in size to O(104), O(102), O(10)-many features, respectively for these three approaches. The neural network reconstructions for EFIT01 demonstrate good accuracy with an R2>0.99 and R2>0.98 for ψ and JφThis work is supported by the Department of Energy under Award Numbers DE-SC0021203 and DE-FC02-04ER54698 , respectively; and R2~0.98 for the plasma boundary and global quantities, with the exception of internal inductance, which has been challenging for the NNs to learn so far. |
Monday, October 17, 2022 3:24PM - 3:36PM |
CO03.00008: Simulations of multiple shell-pellet injection into DIII-D Valerie Izzo Dispersive shell pellet (DSP) injection, comprising a hollow shell filled with a dispersive payload, remains a viable alternative for disruption mitigation on ITER. DSP differs from SPI in its ability to cool the plasma from the inside out while maintaining edge flux-surfaces—potentially increasing the radiation fraction even with a lower-Z payload, which could reduce the electric field and current quench (CQ) rate. MHD modeling of single DSP injection into DIII-D was validated against experiments, reproducing several observed trends. But ablation calculations for DIII-D and ITER plasmas find that penetration of a DSP into the core of ITER will be challenging. New simulations model two DSPs fired simultaneously into DIII-D. A symmetric case is compared to cases with a difference of 5-10% in velocity. In the symmetric case, both payloads are released near mid-radius and an inside-out thermal quench (TQ) dominated by n=2 MHD instabilities ensues. When the speeds differ, the release of the first payload temporarily halts the ablation of the second shell through the first payload delivery region, resulting in release of the second payload deep in the core. The second pellet is therefore able to "piggyback" on the first—a potential strategy for DSP penetration into the core of ITER. |
Monday, October 17, 2022 3:36PM - 3:48PM |
CO03.00009: Measurements of radiated power by molecular deuterium in the DIII-D divertor Adam McLean, Steven L Allen, Mathias Groth, Andreas Holm, Filippo Scotti, Vlad Soukhanovskii Radiated power from molecular deuterium emissions have been shown to be quantitatively minor compared to calibrated line radiation from deuterium and impurities in both attached and detached divertor conditions in the DIII-D tokamak. Molecular deuterium is a constituent of recycling flux from plasma-material surfaces, in particular in the divertor target region where the flux is the highest. The Lyman-Werner molecular band produced by excitation of D2 is a broad spectral feature in the VUV which complements the Fulcher band in visible wavelengths. Previous results measured in DIII-D with an absolutely calibrated broadband EUV/VUV spectrometer and modeling suggested that the Lyman-Werner band may account for up to 20% of the radiated power from the plasma, however without the ability to resolve the band. This motivated a new, high resolution VUV instrument which was installed on DIII-D and cross calibrated with the original instrument. In experiments, however, the integrated L-W band constituted <2% of total radiated power. Relationship between the VUV and visible Fulcher band emissions with local conditions (Te, ne) are presented, and suggest that the original interpretation of the VUV data underestimated a wide, secondary line profile due to instrumental effects in its detector. |
Monday, October 17, 2022 3:48PM - 4:00PM |
CO03.00010: Investigation of heat flux from non-charged particles in the different divertor closures in DIII-D Jun Ren, David C Donovan, Jon Watkins, Huiqian Wang, Xinxing Ma, Roberto Maurizio, Tom Looby, John Canik, Dmitry L Rudakov, Peter C Stangeby, Dan M Thomas, Rejean Boivin A method of using a combination of flush and recessed surface eroding thermocouple (SETC) was develop in DIII-D to independently measure the heat flux to the first wall armor carried by non-charged particles, qnc, from that carried by charged particles, qch. Comparison of heat flux-carrying components in the open divertor and closed divertor is made for the first time in a tokamak. Measurements at lower open divertor of DIII-D showed that qch dominates in the attached plasma, while in the detachment conditions, qnc can contribute up to 50% of the total heat flux near the separatrix. SOLPS modeling results indicate the 2D radiation profile in the SAS divertor significantly changes with the increase of upstream density, which suggests that the location of peak qnc moves outward along the divertor. The experiments carried out in the SAS-VW divertor suggests the distribution of qnc is largely dependent on the location and the degree of detachment. As plasma density increases, qnc decreases near the separatrix while increasing in the far SOL, which is consistent with the SOLPS simulation. In the far SOL region, qnc may contribute nearly 100% of total heat flux at the divertor surface. Using the new SETC array installed in the SAS-VW divertor, the dependence of qnc on divertor closure, drift direction and divertor detachment will be systemically investigated in the near future. |
Monday, October 17, 2022 4:00PM - 4:12PM |
CO03.00011: Effect of Low-Z Impurity Injection Location and Recycling Coefficient on Tungsten Leakage from the DIII-D SAS-VW Divertor Matthew S Parsons, Gregory Sinclair, Tyler Abrams, Jean Paul Allain Recent SOLPS-ITER and DIVIMP modeling work shows that the injection of low-Z impurities into the plasma boundary is a viable actuator to manipulate tungsten erosion and leakage from the new closed, V-shaped tungsten-coated divertor in DIII-D and ultimately the amount of tungsten ending up in the core. This optimization is driven in part by a balance between the friction force and the ion temperature gradient force acting on tungsten ions in the Scrape-off-Layer (SOL). Critically, the injection of low-Z impurities upstream in the SOL increases frictional forces which prevent tungsten from leaking out of the divertor. New results show that the SOL forces are sensitive to the poloidal location where low-Z impurities are injected, even when these impurities are assumed to be fully recycling. Furthermore, if the electron temperature at the target is initially high then the radiative cooling also results in a reduction of the tungsten sputtering source and in turn the total amount of tungsten reaching the core. The magnitude of the tungsten source is highly sensitive to the recycling properties of the injected low-Z impurities. With significant recycling at the divertor targets, low-Z impurities build up in the slot divertor and increase W sputtering, narrowing the window of operation for mitigation of tungsten leakage. An assessment of which low-Z impurity injection location and species (N vs. Ne) provides the greatest potential for the mitigation of tungsten leakage from the SAS-VW divertor will also be presented. |
Monday, October 17, 2022 4:12PM - 4:24PM |
CO03.00012: Interpretative analysis of SOL carbon transport using isotopic tracers and multiple, far-SOL collector probes on DIII-D Jonah D Duran, David C Donovan, Jake H Nichols, E.A. Unterberg, Shawn A Zamperini, Tyler Abrams, David Elder, Jeremy D Mateja, Jun Ren, Dmitry L Rudakov, Morgan W Shafer, Peter C Stangeby, Douglas Taussig, William R Wampler, Robert S Wilcox, Mike P Zach Experiments with outer strike point injection of isotopically enriched methane (13CD4) in DIII-D L-mode discharges have demonstrated the ability to infer near scrape-off-layer (SOL) impurity density profiles based on: far-SOL collector probe (CP) measurements; a stable isotopic mixing model; and SOL impurity transport modelling. This work enables one of the first in-depth investigations on the source and transport of SOL impurities which could hinder performance of future fusion devices. Modelling by DIVIMP and 3DLIM of 13C SOL evolution is consistent with diagnostic observations and indicates that the buildup of injected impurities on plasma-facing surfaces must be considered while inferring representative impurity distributions. Namely, 13C deposits on the inner and outer targets are shown to contribute 50% at a minimum of the enriched 13C deposition on CPs and to cause poloidal shifting of the impurity density peaks in the near-SOL. This analysis elucidates the importance of source location, connection length, poloidal diffusion, and radial convective velocity of impurities to accurately model and interpret SOL impurity behavior. |
Monday, October 17, 2022 4:24PM - 4:36PM |
CO03.00013: Characterizing Impurity Sourcing and Transport in the High Temperature Boundary of DIII-D Wide Pedestal QH-Mode Plasmas Xinxing Ma, Huiqian Wang, Darin R Ernst, Filippo Scotti, Tyler Abrams, Alessandro Bortolon, Xi Chen, Tomas Odstrcil, Tom Osborne, Dan M Thomas, Dinh D Truong, Jonathan G Watkins Wide Pedestal QH-mode plasms in the DIII-D tokamak show a sheath limited SOL, where electron density and temperature remain nearly constant along field lines. Consequently, parallel gradients are weak and drifts play an essential role in the boundary impurity transport. The first Langmuir probe measurements point to a high sheath temperature with target Te up to 150eV, leading to high carbon self-sputtering. Midplane carbon densities from SOLPS-ITER modeling in a double-null configuration fall far below experimental measurements unless full drifts are activated. The drift-dependent modeling reproduces the carbon density profile just inside the separatrix. The C2+ density near the outer strike point is also consistent with spectroscopic imaging. With the ion B×▽B drift towards the X-point, carbon in the lower divertors is redistributed from the private flux region to the high field side and pushed upstream in the SOL by poloidal E×B drifts. The B×▽B drift dominates the radial transport of upstream carbon. Simulations with reversed toroidal field show a radically different behavior, where carbon accumulates on the low field side in lower divertors, and is pushed towards the high field side in the upper divertors, indicating a strong effect of particle drifts on impurity sourcing. |
Monday, October 17, 2022 4:36PM - 4:48PM |
CO03.00014: MHD Stability and Transport Modeling of Negative Triangularity Plasmas in DIII-D William Boyes, Francesca Turco, Jeremy M Hanson, Gerald A Navratil, Alessandro Marinoni, Alan D Turnbull, Jin Myung Park, Max Austin Recent Negative Triangularity (NT) experiments suggest a new class of reactor scenarios that integrate an L-mode edge free of ELMs with a high-performance fusion core. A NT state without deleterious MHD activity at βN≈3 has been observed in DIII-D. NT plasmas have long been thought to have lower MHD stability limits than similar positive triangularity (PT) plasmas. Ideal MHD simulations of experimental NT equilibria predicting ideal wall limits near βN = 3.5 are detailed. NT tearing stability (PEST3 and RDCON) is compared with that of the PT hybrid scenario at similar βN. The FASTRAN code suite has been used to reproduce MHD and transport consistent kinetic equilibria of DIII-D NT experiments. MHD stability optimization is explored using FASTRAN over scans of current density and pressure profile shapes. DIII-D PCS simulations identify attainable plasma shapes (-0.44 average triangularity, elongation 1.66, 16m3) yielding n=0 growth rates low enough to control in upcoming experiments. These stability and transport results taken together indicate that continuous operation is possible at βN≈3. |
Monday, October 17, 2022 4:48PM - 5:00PM |
CO03.00015: The Importance of Charge Exchange Neutrals for Fueling DIII-D Plasmas Shaun R Haskey, Alessandro Bortolon, Florian M. Laggner, George J Wilkie, Brian A Grierson, Luke Stagner, Colin Chrystal Spectrally resolved passive Balmer-α (Dα, Hα) measurements from the DIII-D sixteen channel edge main-ion CER system confirm the presence of higher energy charge exchange (CX) neutrals (“thermal” neutrals) in addition to the recycling cold neutrals in the edge region of DIII-D plasmas. CX between ions and edge neutrals transfers energy and momentum between the populations giving rise to neutrals with energies approximating the ions in the pedestal region. Multiple CX events in succession provide a pathway of increasing energy and velocity, permitting a neutral to get deeper into the plasma, allowing fueling in what may otherwise be considered opaque scrape off layers. The spectrally resolved measurement provides key information about the density and velocity distribution of these thermal neutrals while avoiding several challenges that are associated with filter based measurements. The neutral dynamics, and dependence on parameters such as ion temperature, density, Zeff, and isotope mass are modeled with the FIDASIM collisional radiative code, which produces synthetic spectra with a shape that is in close agreement with the measurements. The local neutral densities and ionization source rates are determined by matching the intensity of the measured and modeled thermal emission. |
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