Core inductive electric field during sawtooth crashes on DIII-D

Sawtooth crashes on tokamak plasmas exhibit relaxation much faster than resistive time scales via a mechanism not fully understood. Using core magnetic measurements from the Radial Interferometer-Polarimeter (RIP) diagnostic on the DIII-D tokamak, Grad–Shafranov equilibria constrained by internal ma...

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Veröffentlicht in:Plasma physics and controlled fusion 2024-08, Vol.66 (8), p.85009
Hauptverfasser: Benedett, T E, Chen, J, Brower, D L, Ding, W X
Format: Artikel
Sprache:eng
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Zusammenfassung:Sawtooth crashes on tokamak plasmas exhibit relaxation much faster than resistive time scales via a mechanism not fully understood. Using core magnetic measurements from the Radial Interferometer-Polarimeter (RIP) diagnostic on the DIII-D tokamak, Grad–Shafranov equilibria constrained by internal magnetic measurements that have high time resolution ( < 1 µ s) can be computed, allowing analysis of how equilibrium parameters such as safety factor q , current density J , and parallel electric field E ∥ , particularly on-axis, evolve. At the sawtooth crash, on-axis safety factor q 0 is observed to rise by 5% but remain below 1 throughout the cycle, and on-axis current density J 0 is observed to drop by 5%. On-axis parallel electric field E ∥ ( 0 ) is found to be balanced by η J 0 (resistivity times on-axis current density) except during the 200 µ s crash period, where E ∥ ( 0 ) reaches 22 V m −1 , exceeding η J 0 by a factor of more than 2000. These first measurements in tokamak plasmas verify that generalized Ohm’s law is not balanced during the crash by resistive effects alone; this is a finding expected due to the relaxation being much faster than resistive timescales. Measurement of the electric field during the tokamak sawtooth serves to illuminate the physical mechanisms at work.
ISSN:0741-3335
1361-6587
DOI:10.1088/1361-6587/ad5a3a