Positive voltage spikes in runaway tokamak discharges

Neto, I. El Chamaa; Kuznetsov, Yu.K.; Nascimento, I. C.; Galvão, R. M. O.; Tsypin, V. S.

doi:10.1063/1.874139

Cited by 4 publications

(1 citation statement)

References 5 publications

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“…In reply, the same but opposite plasma current is generated inductively. Modelling the loop voltage spikes as resistive damping of the plasma current, we can estimate the plasma temperature [21,22]. Considering only the spikes of first type, we obtain that indeed the electron temperature should be rather low, i.e.…”

Section: Ratsmentioning

confidence: 99%

New regime of runaway discharges in tokamaks

Galvão

Kuznetsov

Nascimento

et al. 2001

Plasma Phys. Control. Fusion

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A new regime of runaway discharges has been found in TCABR (Tokamak Chauffage Alfvén Brésilien). This regime is obtained by initiating the discharge with low filling pressure and, after the initial current rise, maintaining a large filling rate. The line density reaches a maximum value around 2 × 10 19 m −3 , during the current ramp-up phase, and then drops by a factor of around four in the quasi-stationary phase of the discharge, when a new regime is achieved. The most distinctive features of this regime, as compared to 'conventional' runaway discharges reported in the literature, are (i) maintenance of the runaway discharge, with the plasma current almost entirely provided by the runaway beam, in a cold background plasma and with strong neutral gas injection; (ii) enhancement of the relaxation instability with strong spikes in the Hα emission and loop voltage correlated with sawtooth relaxation of the line density; and (iii) plasma detachment from the limiter. A simple phenomenological model, based upon straightforward particle and energy balance calculations, is proposed to explain the experimental observations. According to this model, the plasma is rather cold and the short pulses of gas ionization and the related density spikes are due to sudden plasma heating caused by the relaxation instability. Furthermore, it seems that the runaway generation for the conditions of the experiments can be explained only if the secondary generation process is invoked.

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Section: Ratsmentioning

confidence: 99%

New regime of runaway discharges in tokamaks

Galvão

Kuznetsov

Nascimento

et al. 2001

Plasma Phys. Control. Fusion

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Recombinative plasma in electron runaway discharge

et al. 2005

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Cold recombinative plasma is the basic feature of the new regime of runaway discharges recently discovered in the Tokamak Chauffage Alfvén Brésilien tokamak [R. M. O. Galvão et al., Plasma Phys. Controlled Fusion 43, 1181 (2001)]. With low plasma temperature, the resistive plasma current and primary Dreicer process of runaway generation are strongly suppressed at the stationary phase of the discharge. In this case, the runaway avalanche, which has been recently recognized as a novel important mechanism for runaway electron generation in large tokamaks, such as International Thermonuclear Experimental Reactor, during disruptions, and for electric breakdown in matter, is the only mechanism responsible for toroidal current generation and can be easily observed. The measurement of plasma temperature by the usual methods is a difficult task in fully runaway discharges. In the present work, various indirect evidences for low-temperature recombinative plasma are presented. The direct observation of recombinative plasma is obtained as plasma detachment from the limiter. The model of cold recombinative plasma is also supported by measurements of plasma density and Hα emission radial profiles, analysis of time variations of these parameters due to the relaxation instability, estimations of plasma resistivity from voltage spikes, and energy and particle balance calculations.

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Runaway-loss induced negative and positive loop voltage spikes in the Aditya Tokamak

et al. 2010

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Negative spikes followed by positive ones in the loop voltage signal during the discharge are observed in the Aditya Tokamak [S. B. Bhatt et al., Indian J. Pure Appl. Phys. 27, 710 (1989)]. These spikes are always accompanied by hard x-ray bursts caused by sudden loss of runaway electrons. The observed growth of m=3 mode seemed responsible for the losses of localized beams of runaway electrons (Eγ∼1–5 MeV) from the plasma region around q=3 magnetic surface. The movement of these runaway electrons during their extraction from inside the plasma induces both positive and negative electric fields at those locations. In this paper, a one-dimensional toroidal electric field diffusion model is used to estimate the induced electric field at the plasma boundary, which matches quite well with the observed spikes in loop voltage in both magnitude as well as its temporal evolution.

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Positive voltage spikes in runaway tokamak discharges

Cited by 4 publications

References 5 publications

New regime of runaway discharges in tokamaks

New regime of runaway discharges in tokamaks

Recombinative plasma in electron runaway discharge

Runaway-loss induced negative and positive loop voltage spikes in the Aditya Tokamak

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