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Dynamo current drive and Alfven wave generated by CHI on HIST

Author: Masayoshi Nagata
Requested Type: Consider for Invited
Submitted: 2014-05-29 02:21:26

Co-authors: T. Hyobu, H. Hirono, T. Hanao, N. Oki

Contact Info:
University of Hyogo
2167 Shosha
Himeji, Hyogo   671-228
Japan

Abstract Text:
The non-inductive current drive or the plasma start-up by the steady-state coaxial helicity injection (CHI) or the transient CHI was demonstrated for spheromak and ST plasmas. The multi-pulsing CHI (M-CHI) experiments have been performed for the purpose of achieving a quasi-steady-state current drive. We have observed a large fluctuation-induced electromotive force during CHI which is capable of generating plasma current in the closed flux region. It is a key issue in this experiment to understand the underlying dynamo mechanism. Detailed measurements of the spatial and temporal dynamics of dynamo electric field and density fluctuations will provide us further understandings of dynamo mechanism. The frequency of the magnetic field and flow velocity fluctuations peaks around 80 kHz during the CHI. The coupling of these fluctuations generates dynamo electric fields based on the parallel mean-field Ohm’s law which is in the two-fluid description. The MHD dynamo arises from the correlation of magnetic and flow velocity fluctuations and the Hall dynamo rises from the coherent interaction of magnetic and current density fluctuations. Note that there is anti-dynamo in the open flux column region where is a helicity source, and dynamo in the closed flux region which drives the toroidal current in core.
We are considering that the dynamo fluctuations could be identified as the low frequency Alfven waves. The Alfven waves propagate radially from the open flux column to the cutoff point around the magnetic axis through the separatrix layer. During the propagation, the shear Alfven wave may be converted to the kinetic Alfven wave (KAW). The ion heating has been observed to increase around the resonance surfaces due to a damping of the Alfven wave.

Characterization: 1.1

Comments:
This is assigned for the US-Japan CT workshop.

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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