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Plasma and Fusion Research

Volume 10, 1403084 (2015)

Regular Articles

Three-Fluid Axisymmetric Equilibrium Model and Application to Spherical Torus Plasmas Sustained by RF Electron Heating
Akio ISHIDA, Akira EJIRI1), Yuichi TAKASE1), Naoto TSUJII1), Hiro TOGASHI1), Yusuke YOSHIDA1), Takahiro SHINYA1) and Shintaro TSUDA1)
10-18 Ikarashinishi, Nishi-Ku, Niigata 950-2161, Japan
1)
The University of Tokyo, Kashiwa 277-8561, Japan
(Received 16 July 2015 / Accepted 17 September 2015 / Published 28 December 2015)

Abstract

Radiofrequency (RF) waves could be used for plasma current start-up in spherical torus (ST) reactors, where plasma formation and current drive without the ohmic heating solenoid is required. In such a plasma, the electrons can be represented by two temperature components, i.e. high-temperature low-density electrons and low-temperature high-density electrons. In order to describe the equilibrium of such plasmas, we develop a three-fluid (two electron fluids and one ion fluid) axisymmetric equilibrium model with toroidal and poloidal flows. This model has been applied for the first time to a recent TST-2 discharge, and we have obtained an equilibrium which is consistent with experimentally observed results. It is found that (1) the toroidal current density and pressure are dominated by the high-temperature low-density electron (eh-electron) fluid and (2) the radial force balance for each fluid species is quite different, i.e. the ion fluid is confined by the electric force due to the negative electrostatic potential while the eh-electron fluid pressure gradient force is balanced by the Lorentz force (its toroidal current density times the poloidal magnetic field). These results are different from previous speculations.

Keywords

solenoid-free spherical torus plasma, flowing two-electron temperature plasma, axisymmetric equilibrium, flowing three-fluid equilibrium model

DOI: 10.1585/pfr.10.1403084

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This paper may be cited as follows:

Akio ISHIDA, Akira EJIRI, Yuichi TAKASE, Naoto TSUJII, Hiro TOGASHI, Yusuke YOSHIDA, Takahiro SHINYA and Shintaro TSUDA, Plasma Fusion Res. 10, 1403084 (2015).