Magnetohydrodynamic activity in the JFT-2 tokamak with high-power neutral-beam-injection heating

Abstract

Neutral-beam power of up to 1.2 MW injected into the plasma has produced a volume-averaged ⟨β⟩ of up to 2.6% and a central beta β0 of up to 7%, due to the thermal components in the JFT-2 tokamak. In these beam-dominated discharges, the magnetohydrodynamic behaviour was studied. Four types of internal oscillations were observed: i) enhanced sawtooth oscillations with long repetition time and large sawtooth amplitude; ii) round sawtooth oscillations and/or reduced sawtooth oscillations with short repetition time and small sawtooth amplitude; iii) high-frequency oscillations without sawtooth oscillations, and iv) high-frequency oscillations with sawtooth oscillations. The measured beta values are compared with the critical ones as found from high-n ballooning-mode analysis, and the relationship between MHD behaviour and beta values is also investigated.

Possibility of achieving Q > 1 by tritium pellet injection into hot ion mode deuterium plasmas in a large tokamak

“…3(d). These values are close to the ideal MHD beta limit of a circular cross-section tokamak, but they are realistic since in the JFT-2 experiment J3 reached a value of about 2% [22]. It is possible for pellet injection to trigger a disruption; this depends on the injection conditions.…”

“…Note that the original version of our code is a standard tokamak transport code which was used to simulate sawtooth oscillations of NBI heated plasmas in the JFT-2 tokamak [22].…”

Double sawtooth oscillations in the TEXT tokamak

“…This phenomenon may be explained as follows. Frequency doubling occurs in the centre (as is the case for normal sawtooth oscillations [8]) since both m = 1 modes are observed simultaneously. The detector with the tangent radius r s] observes primarily the inner m = 1 mode, and the detector with the tangent radius r s2 observes only the outer m = 1 mode.…”

Classification of disruptions in PBX

“…Recently, beam-heated high-beta plasmas have been obtained in several tokamak experiments [1][2][3][4][5]. These results have motivated theoretical calculations of high-beta stability to external kink modes and ballooning modes [6][7][8][9].…”