The velocity of plasma rotation and the potential distributions are measured in the TM-4 device in the Ohmic-heating regime. The potential is negative at the centre of the column, and its magnitude is significantly larger than the ion temperature. At the edge, the potential is positive while the rotation velocities are considerably lower than their neoclassical values.

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.

Since ITER will be a full metallic wall machine, scattered photons from the strong emission in the divertor may distort the emission from the scrape-off layer (SOL). The influence of stray light for visible spectroscopy of H α and Be I emissions in ITER was investigated with a ray-tracing simulation. It was found that the stray light would be always more than one order of magnitude greater than the real signal intensity for H α emission from the SOL. For Be I emission, although the situation was better than the cases of H α measurement, the stray light could be much larger than the real signal from the SOL. In ITER, it will inevitably reduce the stray light somehow for visible spectroscopy. The effect of optical dumps embedded on first walls was investigated with the ray-tracing analysis.

Results of the electron cyclotron current drive experiment at the second harmonic resonance on the T-10 tokamak are presented. High frequency (HF) power up to 1.2 MW was launched from the low field side. A maximum driven current of 35 kA and current drive efficiency ηCD = 0.05 A/W at an electron temperature Tc(O) = 4 keV and a density nc(0) = 1 × 1013 cm-3 were obtained. For low HF power, the current drive efficiency was less than predicted by the linear theory unless the effect of the elliptical polarization from non-perpendicular injection is considered, in which case the efficiency is close to the theoretical value. The experimental dependence of HF on the absorbed HF power indicated a strong increase of ηCD with power. Suppression of sawtooth oscillations and improvement of confinement during electron cyclotron heating has also been demonstrated