Journal Article

Sawtooth characteristics in ohmically heated HT-7 plasma

LING, BILI, SHI, YUEJIANG, LIU, SHENGXIA, HU, LIQUN, WAN, BAONIAN, XU, YI

2003

Overview

The sawtooth activity in an ohmically heated plasma on the HT-7 tokamak has been investigated experimentally using soft x-ray (SXR) diode arrays, magnetic probes and other diagnostics. Its behaviour and occurrence are correlated closely to the discharge conditions such as the electron density $N_{e}$, the electron temperature $T_{e}$, the safety factor $q_a$ on the plasma boundary and the wall condition, etc. Generally speaking, as $N_{e}$ increases, the sawtooth activity grows, becoming stronger with a longer period $T_{s}$, a larger inversion radius $r_{s}$ and a larger amplitude fluctuation $\\Delta I_{sx}/\\bar{I}_{sx}$ on the SXR radiation intensity signal, and evolve from a small to a moderate sawtooth, to a large or even a giant sawtooth. Sometimes, a double sawtooth and a monster sawtooth activity emerge without apparent deterioration of the plasma confinement and without major plasma disruption. During the events, abundant magnetohydrodynamic phenomena are observed, including a long partial sawtooth collapse. In this paper, the general sawtooth behaviour and the dependence of the occurrence of the sawtooth instability on the electron density $N_{e}$ and wall condition have been summarized. Experimental properties of two types of double sawtooth and monster sawtooth activities are also presented and discussed. The set up of the HT-7 tokamak and the main diagnostics available are also briefly described.

• Publisher: Cambridge University Press
• Subject: Exact sciences and technology / Magnetic confinement and equilibrium / Physics / Physics of gases, plasmas and electric discharges / Physics of plasmas and electric discharges / Plasma macroinstabilities (hydromagnetic, eg, kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.) / Plasma macroinstabilities (magnetohydrodynamic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, rayleigh-taylor, etc.) / Plasma physics / Tokamaks / Waves, oscillations, and instabilities in plasmas and intense beams