TY - JOUR
T1 - Effect of magnetic shear on edge turbulence in SOL-like open field line configuration in QUEST
AU - Banerjee, Santanu
AU - Zushi, H.
AU - Nishino, N.
AU - Hanada, K.
AU - Idei, H.
AU - Nakamura, K.
AU - Hasegawa, M.
AU - Fujisawa, A.
AU - Nagashima, Y.
AU - Mishra, K.
AU - Tashima, S.
AU - Onchi, T.
AU - Kuzmin, A.
AU - Matsuoka, K.
N1 - Funding Information:
Contributions from the QUEST support staff are gratefully acknowledged. This work is supported by a Grant-in-aid for Scientific Research (A21246139) and Sasagawa Scientific Research Grant (25-203) from the Japan Science Society. One of the authors (SB) would like to thank J Ghosh, R Ganesh, R Dey, S J Zweben. and A Diallo for many useful discussions during the course of this work.
Publisher Copyright:
© 2018 IOP Publishing Ltd.
PY - 2018/6/28
Y1 - 2018/6/28
N2 - Intensity fluctuations are investigated using the fast camera imaging technique in the slab annular plasma as a function of magnetic shear and connection length in the spherical tokamak QUEST. Note that here QUEST is operated as a simple magnetized torus with a tight aspect ratio. Slab annular plasmas feature open magnetic field lines and can mimic the tokamak edge-scrape off layer (SOL)-like plasma attributes reasonably well. Three magnetic shear regimes are realized using three poloidal magnetic field (PF) coil pairs. A whole range of connection lengths (∼∞ ≥ L c ≥ 5.5 m) is scanned by varying the PF strength for a given toroidal field for each magnetic shear regime. For the first time a systematic study of the effect of magnetic shear and field line pitch together on edge-SOL-like plasma fluctuations is being reported. Slab plasmas with intermediate magnetic shear are observed to be more susceptible to generate distinct blobs when L c is reduced by increasing the PF strength. A distinct coherent mode appears only at the lowest magnetic shear slab featuring a deep potential well. Such mode is not apparent at other magnetic shear cases even at the same L c. Finally, with a combination of PF coil pairs, both the features of intermediate and low magnetic shear slabs are shown to be realizable simultaneously. Significantly stronger blobs are observed with such combination of PF mirror ratios in the presence of a coherent mode. This study may provide better insight into the effect of magnetic configuration in the tokamak edge and SOL turbulence and can help in searching for better tools to control cross-field convective intermittent transport in tokamaks.
AB - Intensity fluctuations are investigated using the fast camera imaging technique in the slab annular plasma as a function of magnetic shear and connection length in the spherical tokamak QUEST. Note that here QUEST is operated as a simple magnetized torus with a tight aspect ratio. Slab annular plasmas feature open magnetic field lines and can mimic the tokamak edge-scrape off layer (SOL)-like plasma attributes reasonably well. Three magnetic shear regimes are realized using three poloidal magnetic field (PF) coil pairs. A whole range of connection lengths (∼∞ ≥ L c ≥ 5.5 m) is scanned by varying the PF strength for a given toroidal field for each magnetic shear regime. For the first time a systematic study of the effect of magnetic shear and field line pitch together on edge-SOL-like plasma fluctuations is being reported. Slab plasmas with intermediate magnetic shear are observed to be more susceptible to generate distinct blobs when L c is reduced by increasing the PF strength. A distinct coherent mode appears only at the lowest magnetic shear slab featuring a deep potential well. Such mode is not apparent at other magnetic shear cases even at the same L c. Finally, with a combination of PF coil pairs, both the features of intermediate and low magnetic shear slabs are shown to be realizable simultaneously. Significantly stronger blobs are observed with such combination of PF mirror ratios in the presence of a coherent mode. This study may provide better insight into the effect of magnetic configuration in the tokamak edge and SOL turbulence and can help in searching for better tools to control cross-field convective intermittent transport in tokamaks.
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U2 - 10.1088/1361-6587/aacb69
DO - 10.1088/1361-6587/aacb69
M3 - Article
AN - SCOPUS:85050372690
SN - 0741-3335
VL - 60
JO - Plasma Physics and Controlled Fusion
JF - Plasma Physics and Controlled Fusion
IS - 8
M1 - 085014
ER -