Edge turbulence velocity preceding the L-H transition in NSTX

Zweben, S. J.; Diallo, A.; Lampert, M.; Stoltzfus-Dueck, T.; Banerjee, S.

doi:10.1063/5.0039153

Title: Edge turbulence velocity preceding the L-H transition in NSTX

Journal Article · Fri Mar 19 00:00:00 EDT 2021 · Physics of Plasmas

DOI:https://doi.org/10.1063/5.0039153· OSTI ID:1814511

^[1]; Diallo, A. ^[1];

^[1];

^[2]

Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
College of William and Mary, Williamsburg, VA (United States)

The low-to-high mode or L-H transition in tokamaks involves a sudden reduction in the edge turbulence level and decrease in the edge plasma transport. The mechanism for the L-H transition is widely believed to be associated changes in the the poloidal velocity of the edge turbulence. Using a gas puff imaging (GPI) diagnostic, the poloidally averaged poloidal turbulence velocity < V_pol >_pol was measured for a set of 16 shots with L-H transitions in NSTX. These measurements were focused -2 cm inside the separatrix where the relative fluctuation level as seen in GPI decreases significantly and consistently at the transition. Herein, the magnitude of this poloidal velocity preceding the transition varied widely, ranging from |V_pol| ~1-4 km/sec during the last 1 msec before the transition, and the magnitude of the radial gradient also had a wide shot-to-shot range of |grad V_pol| ~ 0.34 to 1.9 km/sec/cm during this same time. The frequency spectrum of < V_pol >_pol during the 30 msec before the transition had a near-coherent peak at ~2-5 kHz, but only in about half of these shots. In general, there were no clear and consistent changes in the poloidal velocity of the turbulence preceding the L-H transition in this database.

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

Sponsoring Organization:: USDOE

Grant/Contract Number:: AC02-09CH11466; SC0019302; AC02 09CH11466; DE‐

OSTI ID:: 1814511

Alternate ID(s):: OSTI ID: 1774985

Journal Information:: Physics of Plasmas, Vol. 28, Issue 3; ISSN 1070-664X

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

Country of Publication:: United States

Language:: English

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