Deeply understanding the plasma response to 3D fields is crucial to optimize tokamak operation, e.g. for ELM mitigation or error field control, and to make robust extrapolations to future devices. To this aim, the response to n=1 rotating fields was measured with unprecedented resolution in ASDEX Upgrade hybrid plasmas with ? up to the no-wall limit. The poloidal structure of 3D boundary distortions is measured along a full poloidal angle by multiple diagnostics (SXR, Lithium beam, ECE-Imaging, HFS/LFS magnetics). It is dominated by non-resonant poloidal harmonics, m>nq, consistent with stable kink/peeling modes amplifying n=1 fields, as predicted by the linear MHD code MARS-K. The internal response is measured from HFS to LFS by multi-chord SXR cameras and interferometers. It peaks in the core, with an m=1 displacement of 1cm. Qualitative agreement is found with ideal MHD codes MARS-K and V3FIT-VMEC, predicting large internal kink response when the safety factor has a minimum just above one, as in these hybrid plasmas. Effects beyond ideal MHD can affect the response profile: MARS-K finds sensible changes in the core when drift-kinetic damping is included, a prediction being tested by comparison with synthetic diagnostics. Two-fluid effects are studied with M3D-C1. The helical core distortion impacts the plasma, strongly braking core toroidal rotation. Associated e.m. and NTV torques are calculated by MARS-K and the stellarator codes DKES/PENTA. To extend the experimental basis for model validation, a comparison is made with 3D response measurements by SXR cameras and high-resolution magnetics in DIII-D high-? plasmas as similar as possible to ASDEX Upgrade. In both experiments the 3D response is largely due to stable ideal kinks, but nonideal effects are predicted to cause sizable changes to its internal profile. Quantitative comparison with experiment is assessing their impact, an important step to validate 3D equilibrium codes.
High-resolution internal measurements of 3D plasma response for model validation in high-beta plasmas
Piovesan P;Marrelli L;Gobbin M;Terranova D;
2015
Abstract
Deeply understanding the plasma response to 3D fields is crucial to optimize tokamak operation, e.g. for ELM mitigation or error field control, and to make robust extrapolations to future devices. To this aim, the response to n=1 rotating fields was measured with unprecedented resolution in ASDEX Upgrade hybrid plasmas with ? up to the no-wall limit. The poloidal structure of 3D boundary distortions is measured along a full poloidal angle by multiple diagnostics (SXR, Lithium beam, ECE-Imaging, HFS/LFS magnetics). It is dominated by non-resonant poloidal harmonics, m>nq, consistent with stable kink/peeling modes amplifying n=1 fields, as predicted by the linear MHD code MARS-K. The internal response is measured from HFS to LFS by multi-chord SXR cameras and interferometers. It peaks in the core, with an m=1 displacement of 1cm. Qualitative agreement is found with ideal MHD codes MARS-K and V3FIT-VMEC, predicting large internal kink response when the safety factor has a minimum just above one, as in these hybrid plasmas. Effects beyond ideal MHD can affect the response profile: MARS-K finds sensible changes in the core when drift-kinetic damping is included, a prediction being tested by comparison with synthetic diagnostics. Two-fluid effects are studied with M3D-C1. The helical core distortion impacts the plasma, strongly braking core toroidal rotation. Associated e.m. and NTV torques are calculated by MARS-K and the stellarator codes DKES/PENTA. To extend the experimental basis for model validation, a comparison is made with 3D response measurements by SXR cameras and high-resolution magnetics in DIII-D high-? plasmas as similar as possible to ASDEX Upgrade. In both experiments the 3D response is largely due to stable ideal kinks, but nonideal effects are predicted to cause sizable changes to its internal profile. Quantitative comparison with experiment is assessing their impact, an important step to validate 3D equilibrium codes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
