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(EX/P1-01) Study of Current Oscillations and Hard X Ray Emissions in Pre-cursor Phase of Major Disruptions in Damavand Tokamak

R. Amrollahi1), S. Khorasani2), F. Dini2)3)
1) KNT University of Technology, Tehran, Iran
2) Department of Plasma Physics, AEOI, Amirabad, Tehran, Iran
3) Department of Physics, Amirkabir University of Technology, Tehran, Iran

Abstract.  We notice that the hard x-ray activity before disruption consists of a series of spikes, uniformly distributed in time domain forming an orderly periodic series of oscillations at a frequency of 6.0 kHz. Disruption starts with an initial fast rise followed by decay. Current decay occurs in two regimes: the first corresponds to slow decay, in which the current is oscillating and reducing down to $ \sim$70% its max value, and the second corresponds to fast decay, in which it totally vanishes abruptly in about 0.2 ms. In the first regime, the loop voltage also oscillates with considerable amplitude. The frequency of oscillations in the first regime is measured to be also about 6.0 kHz. As well, they follow the oscillation phase of hard x-rays. Thus the micro-instabilities driven by runaway electrons, being responsible for the production of hard x-rays bursts and small current oscillations, play a significant role in the disruption.

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IAEA 2003