Experiments with plasma heating and current drive at the second harmonic of the electron cyclotron resonance in T-10

In this paper we show the efficiency of gyrotrons (together with their quasioptical lines) with high frequency (f = 140 and 157 GHz) and specific power ∼0.9 MW per tube. When the power input to the plasma was Phf = 0.45 MW the microwave pulse length reached 0.4 s. We show that at the second ECR harmonic at least 90% of the microwave power fed into the tokamak is absorbed for both oblique and perpendicular input. The behavior of the heating and energy containment in the plasma are similar to those obtained for heating at the first harmonic. For a microwave power Phf = 0.45 MW and temperature Te(0) = 3.8 keV current generation was not observed at the second ECR harmonic with an observation limit ICD = 10 kA. This means that the efficiency of EC current generation of the second harmonic is lower by at least a factor of 2.5 than at the first harmonic. In order to answer the question about the ratio of the current generation efficiency at the first and second harmonics it is necessary to perform experiments at a higher microwave power level. We also show that as expected most of the microwave power is absorbed near the center of the plasma column for central EC heating at the second harmonic, up to a density close to the maximum value [ne(0) ≅ 8·1019 m-3]. This permits us to heat the plasma efficiently at a high density, and hence for high values of βT(0)