Experiments on m=2, n=1 tearing mode suppression and on avoidance of density limit disruptions by electron cyclotron resonance heating (ECRH) were performed on the T-10 tokamak. Partial suppression of the m=2, n=1 mode by the high frequency (HF) power deposition in the vicinity of the q=2 surface was observed. Development of external kink modes with HF power injection can result in m=2, n=1 mode destabilization under specific operating conditions. ECRH suppresses m=2, n=1 mode activity at extremely high values of electron densities and prevents the density limit disruptions practically independently of EC resonance position. Complete compensation of the additional peripheral heat losses near the density limit by ECRH should be responsible for this result. No effect of electron cyclotron current drive (ECCD) on m=2, n=1 mode stability has been observed because of insufficient values of HF driven current in the vicinity of the q=2 surface under the operating conditions of the experiment

Our understanding of the physics of internal transport barriers (ITBs) is being furthered by analysis and comparisons of experimental data from many different tokamaks worldwide. An international database consisting of scalar and 2-D profile data for ITB plasmas is being developed to determine the requirements for the formation and sustainment of ITBs and to perform tests of theory-based transport models in an effort to improve the predictive capability of the models. Analysis using the database indicates that: (a) the power required to form ITBs decreases with increased negative magnetic shear of the target plasma, and: (b) the ExB flow shear rate is close to the linear growth rate of the ITG modes at the time of barrier formation when compared for several fusion devices. Tests of several transport models (JETTO, Weiland model) using the 2-D profile data indicate that there is only limited agreement between the model predictions and the experimental results for the range of plasma conditions examined for the different devices (DIII-D, JET, JT-GOU). Gyrokinetic stability analysis (using the GKS code) of the ITB discharges from these devices indicates that the ITG/TEM growth rates decrease with increased negative magnetic shear and that the ExB shear rate is comparable to the linear growth rates at the location of the ITB.

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Soft β limiting phenomena have been observed in T-10 in ECRH heated plasmas. Neoclassical tearing modes are supposed to be responsible for the β limitation. MHD onset was observed at high βp values but low βN values. The critical β has been found to be almost independent of the collisionality parameter νe*. Sawtooth stabilization by ECCD does not result in an increase of critical beta. A dependence of the critical β on the q(r) profile (modified by ECCD) has been observed.

Electron Cyclotron Current Drive (ECCD) on the 1st and 2nd harmonics of the Electron Cyclotron Resonance (ECR) is considered. Mainly the T-10 experimental raults are desctibed and comparison with the experimental data from various devices is performed. Features of ECCD are studied by comparison of Fokker-Planck (FP) calculations with measurements of X-ray spectra in discharges with ECCD. It is shown that ECCD efficiency is in a good agreement with FP calculations. Database obtained on various devices allows to assume that in ITER the ECCD efficiency can be achieved as high as l)CD=o.3X 102OAA"z This program has become one of the main experimental program on T-10. In this report the review is presented of the 1st stage of experimentsan investigation of ECCD on the 1st and 2nd harmonics. Comparison with the data obtained on the other devices is also done.

18,24 and for the International ITB Database Working Group and the responsible officers for the ITPA collaborative experiments on the 'hybrid' and 'steady-state' regimes:

High density experiments were carried out in T-10 with gas puffing and electron cyclotron resonance heating (with absorbed power value up to 1.4 MW) with oblique and perpendicular power launch. Densities exceeding the Greenwald limit (n Gw ) by up to a factor of 1.8 were achieved in a regime with a high value of the edge safety factor at the current flat-top, q(a) ∼ = 8.2. The decrease of q(a) to a value of 3 led to the reduction of the ratio ( ne ) lim /n Gw to 1. Confinement degradation with density increase was not significant up to the density limit. However, the typical T-10 linear increase of energy confinement time with density saturates at ne 0.6n Gw . This saturation is the result of the development of an additional transport in the electron heat channel. However, the saturated τ E values exceeded the ITER L-mode scaling predictions by up to a factor of 1.2 and were close to the value predicted by the ITER H-mode scaling. Effect of the strong gas puffing on the plasma confinement and experiments with neon seeding are also discussed in this paper.

Experiments on second harmonic electron cyclotron current drive were done on the T-10 tokamak using four gyrotrons. Total powers up to 1.2 MW at a frequency of 140 GHz were injected. Current generation by electron cyclotron (EC) waves was demonstrated in the experiments. The efficiency η of current generation and its dependence on plasma parameters were measured and it was shown that the efficiency is a nonlinear function of input power, more closely predicted by Fokker–Planck calculations than by linear theory. The interaction of EC waves with the tail of the electron distribution was shown to be important. It was also found that current density profile redistribution played an important role in the plasma behavior.