Measurement of prompt loss of energetic electrons in a long LHCD discharge on TRIAM-1M

On TRIAM-1M, spontaneous enhancement of non-inductive current drive efficiency (ECD) has been observed in full lower hybrid current drive plasmas. It is predicted theoretically that the prompt loss of passing energetic electrons has a significant effect to current drive efficiency in small size tokamaks. As the orbit of the energetic electrons deviates from flux surface, the energetic electrons driving plasma current attack to the limiter in the low field side. Therefore the absolute value of the power due to the prompt loss of energetic electrons can be measured as the thermal input on the limiter located in the low field side of the plasma. The measured heat flux in both ECD and non ECD plasmas is less than 1 % of the injected microwave and most of the thermal input can be explained quantitatively by that from SOL plasma. This indicates that the loss of energetic electrons does not play a significant role in the enhancement of current drive efficiency in the ECD mode