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

Transition to an all-metal wall was realized on T-10 by replacement of graphite limiters with tungsten ones. Light impurity levels remained high and W accumulation in the plasma core was revealed. A movable lithium (Li) limiter was added to investigate the possibility of the limitation of tungsten and light impurity levels in plasma. For the first time, tokamak results on tungsten protection with Li were obtained in OH and ECRH regimes. After lithization the tungsten density in the core dropped more than an order of magnitude, while W influx into plasma decreased 2–4 times. Drastic drops of light impurities in plasma were observed together with improvement of energy confinement time and density limit values. Nevertheless, Li levels in plasma remained low in both OH and ECRH regimes. Li density in the core as low as 0.5% of ne was obtained. Tungsten transport in T-10 plasma was investigated and results on prevention of W accumulation with central ECRH were obtained. Effects of plasma exposure on ITER-grade tungsten plates from limiters were studied. Investigations of density fluctuation with correlation reflectometry confirmed a decrease of fluctuation amplitude on high field side. Modeling showed that this effect can be, to a great extent, explained by the non-locality of reflectometry. Toroidal correlations at a distance of 2.5 m along field lines were studied. Three-wave interaction between geodesic acoustic modes and broad-band turbulence was found by analysis of heavy ion beam probe diagnostics data. The possibility of plasma current control and the prevention of non-thermal electron beams formation at density limit disruption by means of ECR heating and the controlled operation of OH power supply system has been demonstrated. The study of plasma density decay after gas puff switch off during density ramp-up phase in OH regimes and the effect of ‘density pump out’ during ECRH showed that both effects can be explained by the assumption regarding electron transport growth upon reaching marginal pressure profile. A new type of internal transport barrier in the narrow zone near q  =  1 surface has been found.

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 several tokamaks with different methods of heating. It is shown that the normalized pressure profile has a universal shape for a wide class of tokamaks and regimes, if the normalized radius ρ = r/(I p R/κB)1/2 is used. The consequences of this phenomenon for low aspect ratio tokamaks, the optimal deposition of additional heating, fast velocity of heat/cold pulse propagation and the possibility of obtaining a peaked density profile in ITER are discussed.