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 GI02: Magnetic Confinement Fusion IIILive Streamed
|
Hide Abstracts |
Chair: Carlos Paz-Soldan, Columbia University Room: Ballroom 100 B |
Tuesday, October 18, 2022 9:30AM - 10:00AM |
GI02.00001: Multimodal plasma response to 3D magnetic perturbations and its impact on the divertor heat fluxes Invited Speaker: Stefano Munaretto Observation of changes in the three-dimensional (3D) structure of the heat and particle fluxes at the divertor plates of the DIII-D tokamak, correlated with changes of the poloidal spectrum of applied 3D fields, are explained by the multimodal nature of the plasma response, and this provides new tools for the control of the divertor heat fluxes in ITER and beyond. Detailed comparisons between measured and predicted edge poloidal structure of the plasma response to applied magnetic perturbations in DIII-D highlight the capability of resistive MHD codes to correctly capture the multimodal nature of the plasma response. Singular value decomposition analysis of the magnetic measurements of the plasma response to stationary applied perturbations, combined with resistive MHD simulations performed with the MARS-F code, shows the presence of two dominant modes: one radially localized at the edge that extends to the whole poloidal circumference and one poloidally localized at the low field side midplane that extends radially to the core. Radial profiles of the infrared and D?? emission show a larger 3D structure at the divertor plates when the former mode is dominant and no correlation with the amplitude of the latter. Resistive MHD simulations done with the M3D-C1 code coupled with the field line tracing code TRIP3D confirm the link between magnetic footprints and the edge resonant mode. This mechanism can also explain the observed inability of the error field correction based on the mitigation of the core mode to reduce the presence of 3D magnetic footprints at the divertor in DIII-D L-mode plasmas. Furthermore, this suggests it will be challenging to decouple the RMP-ELM control problem, for which the edge-resonant coupling is a prerequisite, from the divertor heat flux one. |
Tuesday, October 18, 2022 10:00AM - 10:30AM |
GI02.00002: Progress on edge-localized mode suppression via magnetic perturbations in non-nuclear fuels for the ITER pre-fusion power operation phase Invited Speaker: Nils Leuthold During transitions from deuterium (D) to hydrogen (H) plasmas at ASDEX Upgrade a critical D fraction is required to maintain edge-localized mode (ELM) suppression, raising concern over the feasibility of resonant magnetic perturbations (RMPs) as an ELM suppression tool in the ITER PFPO phase. Operating ITER in H-mode requires ELM mitigation or suppression to prevent critical heat loads caused by ELMs. While access to RMP-ELM suppression is well studied in D plasmas, it has yet to be demonstrated in non-nuclear fuels (H, H+He) expected in the ITER PFPO phase. For the first time, attempts have been made to access ELM suppression with RMPs in ITER-like low collisionality H plasmas at DIII-D and ASDEX Upgrade. The DIII-D experiments operated slightly above the L-H power threshold similar to the expected conditions in the ITER PFPO phase. The RMP fields are found to trigger H-L backtransitions in H plasmas, which can be avoided by diluting the H plasma with He. The additional He combined with a weaker density decrease induced by RMPs in H as compared to D plasmas precludes access to a pedestal top density below the known RMP-ELM suppression threshold. At ASDEX Upgrade, RMP-ELM suppression has been achieved with H concentrations of up to ~38%. While the known access criteria for RMP-ELM suppression are still met above this threshold, full ELM suppression is replaced by strong mitigation. The most prominent difference between the H and D plasmas is a change of turbulence characteristics in the pedestal where Doppler reflectometry suggests a significant reduction of turbulence even with small H concentrations. In conclusion, these experiments not only identify issues and raise concern for RMP-ELM suppression in the ITER PFPO phase, but also highlight missing physics in our current understanding of RMP-ELM suppression. |
Tuesday, October 18, 2022 10:30AM - 11:00AM |
GI02.00003: Improved Particle Confinement with Resonant Magnetic Perturbations in DIII-D Tokamak H-mode Plasmas Invited Speaker: Nikolas C Logan Experiments on the DIII-D tokamak have identified a robust regime in which applied resonant magnetic perturbations (RMPs) increase the particle confinement while partially stabilizing the edge-localized peeling modes. RMPs are of interest for the control the rotational shear and/or suppression of edge localized modes (ELMs) for reactor relevant scenarios, however they have hitherto been observed to degrade the particle confinement via the density "pump-out" phenomenon. This work details DIII-D experiments and model calculations showing the surprising result that there is a range of counter-current plasma rotation (induced by neutral beam injection in the direction opposite to the plasma current) where the 3D fields instead increase the particle confinement, resulting in a particle "pump-in" effect. The new density pump-in phenomenon corresponds to a change in the sign of neoclassical particle transport across flux surfaces induced by the toroidal symmetry breaking, as modeled by the Generalized Perturbed Equilibrium Code (GPEC). The pump-in is also preceded by a decrease in the turbulent fluctuation (and presumed turbulent transport) as evidenced by the prompt drop in microwave doppler back scattering measurements of edge ion-scale density fluctuations. The rise in density also corresponds to lower frequency ELMs, however the change in the ELM frequency and amplitude is such that the time-average ELM induced particle transport is unchanged. The full combination of observed phenomena is robust and reproducible across a finite range of counter-Ip rotation (-80 to 0 km/s) in the pedestal top of DIII-D. This pump-in regime has the potential to minimize or even reverse the confinement degradation currently observed in RMP H-mode scenarios. Implications for ITER and fusion reactors will be discussed. |
Tuesday, October 18, 2022 11:00AM - 11:30AM |
GI02.00004: Role of Edge Stochastic Layer in Density Pump-out by Resonant Magnetic Perturbations Invited Speaker: Arash Ashourvan Formation of an edge stochastic layer is shown to cause the pump-out of density as observed in DIII-D plasmas with applied Resonant Magnetic Perturbations (RMPs) but without exhibiting the suppression of Edge Localized Modes (ELM). In these plasmas RMP penetration near the zero-crossing of the radial electric field Er at the plasma foot leads to density pump-out. Using an analytical model that adds the stochastic parallel transport of electrons to the fluid equations, the ambipolar Er and particle flux are calculated simultaneously. In this model the nonambipolar electron flux, driven by the stochastic magnetic field, is predominantly balanced by the nonambipolar perpendicular ion flux, driven by anomalous viscosity, across a narrow stochastic layer in the last ≈ 2% of the plasma minor radius (0.98<ѱn<1). Stochasticity driven enhanced transport causes the flattening of the density profile in the pedestal foot, which leads to the pump-out at the pedestal top. Using the viscosity coefficient calculated by TRANSP, and RMP amplitudes calculated by the TM1 code, the model reproduces the level of RMP driven density pump-out for three plasma discharges for which the pedestal foot is at medium to high collisionality (2≤ν∗sep≤ 30). The experimentally observed inverse density dependence of density pump-out is accurately captured by the model: an increase in collisionality with density in the pedestal foot results in a decrease in stochastic diffusivity, and hence a decrease in the level of pump-out. This improved understanding of pump-out can enhance the capability for predicting the effect of RMP on particle confinement in ITER. |
Tuesday, October 18, 2022 11:30AM - 12:00PM |
GI02.00005: Internal plasma response measurements at the pedestal top in ELM suppressed plasmas in ASDEX Upgrade Invited Speaker: Matthias Willensdorfer Next step fusion devices like ITER require the suppression of edge localised modes (ELMs) to avoid harm to the first wall. One promising method is the use of externally applied non-axisymmetric magnetic perturbations (MPs), but the physics of suppressing ELMs is however to large extent still unclear. |
Tuesday, October 18, 2022 12:00PM - 12:30PM |
GI02.00006: Understanding the ELM trigger and suppression mechanisms in DIII-D negative triangularity plasmas with Electron Cyclotron Emission Imaging Invited Speaker: Guanying Yu First characterization of the Edge Localized Mode (ELM) dynamics and edge turbulence spreading for Negative Triangularity (NT) plasmas has been carried out with the Electron Cyclotron Emission Imaging (ECEI) instrument on DIII-D, which measures the 2-dimensional ECE fluctuations (0-200 kHz) at ΨN ~0.85-1.1. NT plasmas are typically in L-mode as the larger bad curvature region is theoretically predicted to make the edge susceptible to local ballooning modes. However, dedicated experiments on DIII-D found ELMs during H-mode and Limit Cycle Oscillations in NT plasmas at relaxed negative triangularities or low heating powers. It is thus highly desirable to understand the ELM behavior in these plasmas with direct experimental evidence. ECEI observed that the NT ELMs are triggered by a low-n (<5) MHD mode, which displays a clear energy exchange signature across the separatrix during ELM crashes. At δ=-0.2, this low-n mode is triggered at a critical pressure gradient. The energy exchange signature and critical pressure gradient at the ELM agree with an interchange mode driven by the pressure gradient. At δ=-0.4, the plasma first enters an ELMy phase followed by an ELM-free phase at an increased heating power. In the ELM-free phase, ECEI observed that the ELMs are replaced with low-n turbulence, which spreads to the SOL and causes transport across the separatrix. The edge turbulence spreading may also enhance the SOL transport, as a clear interELM divertor heat-flux-width broadening is observed after the turbulence amplitude increases with heating power at δ=-0.2. For both δ=-0.2 and δ=-0.4, the edge turbulence amplitude measured by ECEI and Beam Emission Spectroscopy correlates with the decreasing edge density gradient and rotation shear, suggesting their roles in turbulence enhancement, and the corresponding ELM suppression and divertor heat flux width broadening in NT plasmas. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700