Recent progress on TRIAM-1M

A steady state plasma with high performance and high current drive efficien cy is reported. In 2.45 GHz LHCD plasmas T-i is studied as a function of n( e) at the edge of the high ion temperature (HIT) window. Different characte ristic timescales are found for T-i and n(e) to enter the HIT regime and th e observed hysteresis behaviour of T-i with respect to n(e) is attributed t o this difference. The electromagnetic emission (<3.5 GHz) is studied in or der to understand ion heating mechanisms in the HIT regime. The spectrum sh ows several sidebands whose peak frequencies correspond to the ion plasma f requency. The spectral narrowing of the width of the sideband shows a clear correlation with ion heating. In 8.2 GHz LHCD plasmas an enhanced current drive (ECD) regime where both current drive efficiency eta(CD) (= (n) over bar(e)I(CD)R(o)/P-LH similar to 1 x 10(19) A m(-2)/W) and energy confinemen t time tau(E) (similar to 8-10 ms) are simultaneously improved is obtained at an (n) over bar(e) of 4.3 x 10(13) cm(-3) and B = 7 T under full current drive conditions. There exists a certain threshold power above which the E CD transition occurs. A hysteresis of eta(CD) is found around the threshold power, which is explained by the different characteristic time for the ECD transition in power rampup and rampdown schemes. Current profile control e xperiments are performed by using two opposite travelling LHWs. Current com pensation (Delta I-CD/I-CD < -10%) is clearly seen when the backward (BW) t ravelling LHW (8.2 GHz) is added to a target plasma whose current is driven by a forward travelling LHW (8.2 GHz). As the BW wave power is increased, however, the current tends to flow in the forward direction. The mechanisms of this non-linear behaviour of the driven current with respect to the BW wave power are discussed.