Local measurements of the pedestal magnetic field profile throughout the ELM cycle on DIII-D
New high speed localized measurements of the pedestal magnetic field during the edge localized mode (ELM) cycle of a DIII-D High confinement mode (H-mode) discharge indicate a temporally and spatial complex redistribution of the edge current density profile, jedge. The measurement technique extracts the magnetic field magnitude, B, via the spectral separation of Stark-split neutral beam radiation in the pedestal. Single spatial channel measurements from a novel spatial heterodyne spectrometer are validated in discharges with core current profile changes. The technique measures Stark-splitting changes that imply B changes as small as 1 mT with high time resolution (50 μs). At normalized poloidal flux ψn=1.0, B appears saturated in the inter-ELM period and then rapidly decreases in <200 μs by ∼1%, before edge recycling emission begins to increase. Radially inboard of jedge, B increases at the ELM crash. The behavior is consistent with a rapid collapse of jedge at the ELM crash and subsequent pedestal recovery. In some discharges, at ψn<0.96, changes in B are observed throughout the ELM cycle. In others, B recovers and is relatively stable until a few ms leading up to the next crash. Measurements of B during the H-mode transition show a large increase at ψn=1 with little change at ψn=0.9, consistent with the formation of the edge bootstrap current density peak. The ψn=0.9 spectrum is complicated by predicted changes to the Stark component intensities with density at the L–H transition.
- Research Organization:
- Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- FC02-04ER54698; FG02-89ER53296; FG02-08ER54999; AC52-07NA27344; AC02-09CH11466
- OSTI ID:
- 1895046
- Alternate ID(s):
- OSTI ID: 1890770; OSTI ID: 1903619; OSTI ID: 2202922
- Report Number(s):
- DOE-GA-54698; LLNL-JRNL-836197; TRN: US2310335
- Journal Information:
- Physics of Plasmas, Vol. 29, Issue 10; Conference: 63.Annual Meeting of the APS Division of Plasma Physics, Pittsburgh, PA (United States), 8-12 Nov, 2021; ISSN 1070-664X
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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