MHD stability of spherical tokamak equilibria with non-monotonic q-profiles

Jardin, S. C.; Munaretto, S.; Ferraro, N. M.; Kaye, S. M.; Kleiner, A.; Lyons, B. C.

doi:10.1063/5.0191934

Title: MHD stability of spherical tokamak equilibria with non-monotonic q-profiles

Journal Article · Tue Mar 05 00:00:00 EST 2024 · Physics of Plasmas

DOI:https://doi.org/10.1063/5.0191934· OSTI ID:2326041

^[1];

^[2]

Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
General Atomics, San Diego, CA (United States)

Here, we use the 3D MHD code M3D-C to examine the MHD stability and subsequent evolution of NSTX shot 129169. This discharge had a period with a non- monotonic safety-factor profile, q, (reversed shear) which was terminated by a MHD event which abruptly lowered the central safety factor, q₀, and greatly reduced the peakedness of the pressure profile. We show that the equilibrium just before the MHD event occurred was linearly unstable to many pressure-driven infernal modes. Modes with toroidal mode number n ≥ 3 all had rational surfaces very close to the minimum value of q. However, a non-resonant pressure driven (1, 1) mode was also present, and this dominated the non-linear evolution. The final state in the simulation, after the MHD activity subsided, had a reduced and flattened pressure profile and a nearly monotonic q-profile, in qualitative agreement with experimental results. The initial state was also unstable to the resistive interchange criteria in the reversed-shear region, but the final state was stable everywhere. The ”double tearing mode” (DTM) does not appear to play a role in the MHD activity of this discharge. In Appendix A we show that in a torus, the DTM is strongly stabilized by pressure, but it is destabilized in cylindrical geometry (which has been the most extensively analyzed in the literature),

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Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR). Scientific Discovery through Advanced Computing (SciDAC)

Grant/Contract Number:: AC02-09CH11466

OSTI ID:: 2326041

Journal Information:: Physics of Plasmas, Vol. 31, Issue 3; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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