A soft X ray imaging system consisting of three arrays of silicon surface barrier diodes is applied to the tomographic analysis of internal plasma perturbations in the T-10 tokamak (R, = 1.5 m, a = 0.32 m). It is found that density limit disruptions in a plasma with a high safety factor at the edge (qa = 3.5-4.5) are associated with joint rotation of the m = 2, n = 1 and m = 1, n = 1 modes, overlapping at the energy quench stage. Electron cyclotron resonance heating is used to prevent density limit disruptions or to recover stable operation of the discharge after the energy quench at the density limit,

The plasma stability and confinement have been investigated through control of the safety factor profile q(r) by the electron cyclotron current drive in the T-10 tokamak. The regimes with dq/dr ∼ = 0 and dq/dr < 0 in the plasma core were obtained. Various types of MHD activity were observed: ordinary sawtooth, saturated sawtooth, humpbacks, hills etc. It was shown that when the minimal value q min increases from q min < 1 to q min = 2 the plasma becomes strongly unstable due to the corresponding MHD activity or passes to the steady-state improved confinement mode. The latter is realized when the electron internal transport barrier (EITB) is formed. The condition for the appearance of the EITB is dq/dr ∼ = 0, where q = m/n lies near a rational value for low m and n.

The self-organization of a tokamak plasma is a fundamental turbulent plasma phenomenon, which leads to the formation of a self-consistent pressure profile. This phenomenon has been investigated in the T-10 tokamak in different experiments, excluding profiles with pronounced transport barriers. It will be shown that the normalized pressure profile can be expressed by the equation p N (r) = p(r, t)/p(0, t), over a wide range of plasma densities. It will also be shown that p N (r) is independent of the heating power and the deposition profile of electron cyclotron resonance heating. Experiments show that p N (r) depends only on the value of q at the plasma edge. During rapid current ramp-ups it has been demonstrated that the conservation of p N (r) is established during a time t c < 0.1τ E , with τ E the energy confinement time. It can be concluded that the self-consistent pressure profile p N (r) in tokamaks is linked to the equilibrium of a turbulent plasma.

This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2011 Nucl. Fusion 51 094019

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