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Title: Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST

Heat flux and plasma flow in the scrape-off layer (SOL) are examined for the inboard poloidal field null (IPN) configuration of the spherical tokamak QUEST. In the plasma current (I{sub p}) ramp-up phase, high heat flux (>1 MW/m{sup 2}) and supersonic flow (Mach number M > 1) are found to be present simultaneously in the far-SOL. The heat flux is generated by energetic electrons excursed from the last closed flux surface. Supersonic flows in the poloidal and toroidal directions are correlated with each other. In the quasi-steady state, sawtooth-like oscillation of I{sub p} at 20 Hz is observed. Heat flux and subsonic plasma flow in the far-SOL are modified corresponding to the I{sub p}-oscillation. The heat flow caused by motion of energetic electrons and the bulk-particle transport to the far-SOL is enhanced during the low-I{sub p} phase. Modification of plasma flow in the far SOL occurs earlier than the I{sub p} crash. The M–I{sub p} curve has a limit-cycle characteristic with sawtooth-like oscillation. Such a core–SOL relationship indicates that the far-SOL flow plays an important role in sustaining the oscillation of I{sub p} in the IPN configuration.
Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;  [1] ; ; ; ;  [2] ;  [3]
  1. RIAM, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan)
  2. IGSES, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan)
  3. National Institute of Fusion Science, Toki 509-5292 (Japan)
Publication Date:
OSTI Identifier:
22490062
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELECTRIC CURRENTS; HEAT FLUX; LIMIT CYCLE; MACH NUMBER; MAGNETIC SURFACES; NEUTRAL-PARTICLE TRANSPORT; PLASMA; PLASMA INSTABILITY; PLASMA SCRAPE-OFF LAYER; SAWTOOTH OSCILLATIONS; SPHERICAL CONFIGURATION; STEADY-STATE CONDITIONS; SUPERSONIC FLOW; TAIL ELECTRONS; TOKAMAK DEVICES