26aD29P
低アスペクト比RFP装置RELAXにおける揺動起因起電力の定量的評価
Estimate of Turbulence-Induced Electromotive Force in RELAX
樋口真行，政宗貞男，三瓶明希夫，青木陽祐，長野友幸，軸原健太，中ノ坊俊，坪井涼介，國田智士，牧澤遼，比村治彦
HIGUCHI Masataka, MASAMUNE Sadao, SANPEI Akio, AOKI Yosuke,
NAGANO Tomoyuki, JIKUHARA Kenta, NAKANOBOU Syun,TSUBOI Ryosuke, KUNITA Satoshi, MAKIZAWA Haruka, HIMURA Haruhiko
京都工芸繊維大学
Kyoto Institute of Technology
1. Introduction
The RFP is one of the toroidal magnetic
confinement systems for high β plasmas. The RFP
configuration is characterized by the toroidal fieldreversal at the edge, which causes strong
mageticshear. This toroidal field reversal can besustained (against resistive diffusion) as long as thetoroidal plasma current is sustained. This
characteristic is often referred to as theself-organization. The resistive MHD instabilities
play important roles in the self-organization process,and therefore, electromotive forces arising fromturbulence are important in sustaining the current.
2. Generalized Ohm’s law and turbulence
induced electromagnetic force terms
In the RFP, the reversed toroidal magnetic field issustained as long as the toroidal plasma current issustained. The mechanism for current sustainment
may be interpreted as follows. When we decompose
the physical quantities (such as electric field,magnetic field, velocity field, current density, etc.)
in averaged and fluctuating components, thegeneralized Ohm’s law can be written down as
follows,of simplicity. Interaction between the fluctuating
quantities generates current in the direction of theaverage magnetic field.
3. Experimental Apparatus
As a first step, we are preparing a dynamo probe
to estimate the MHD dynamo term arising frominteraction between velocity and magnetic field
fluctuations in RELAX.
RELAX is an RFP machine with major radius of0.5m and minor radius of 0.25m, the aspect ratio A
being 2. The plasma parameters attained to date areas follows: toroidal plasma current Ip~40-120 kA,
electron density ne~1018-2×1019 m-3, Thomson
electron temperature Te0~100-200 eV. The discharge
duration is ~3.5 ms.
The dynamo probe structure is shown in Fig.1. It
consists of electrostatic triple probes, three triple
probes of Mach probes, and a magnetic probe inside
the ceramic shield. The electrostatic triple probes
provide electric field, electron temperature, andelectron density. Three components of the flow isprovided by the three Mach probes [3].

(1)
where
is the mean (time-averaged) current
density,
the mean electric field, and η theelectric resistivity. The quantities with ~ are thefluctuating components. The bracket < > stands forthe averaging over time. The second term in theright hand side is the MHD dynamo term, arisingfrom nonlinear interaction of fluctuating velocity
and magnetic fields, and the last term, the Hall
dynamo term arising from nonlinear interaction offluctuating current density and magnetic fields. The
diamagnetic dynamo term is neglected for the sakeFig.1. Structure of the complex probe to estimate
the dynamo term.

References[1] S. Shiina et al.: Phys. Plasmas 12 (2005)
080702.
[2] A. Sanpei et al.: J. Phys. Soc. Jpn. 78 (2009)
013501.
[3] M.Nagata et al.: 2013 Proc. 40th EPS Conf. on
Controlled Fusion and Plasma Physics (Espoo,Finland) 37D p5.151.