Year: 2000
Type: article
Abstract: A steady state plasma with high performance and high current drive efficiency 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 characteristic timescales are found for T i and n e to enter the HIT regime and the observed hysteresis behaviour of T i with respect to n e is attributed to this difference. The electromagnetic emission (<3.5 GHz) is studied in order to understand ion heating mechanisms in the HIT regime. The spectrum shows several sidebands whose peak frequencies correspond to the ion plasma frequency. 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 η CD ( = e I CD R 0 /P LH ∼1 × 10 19 A m -2 /W) and energy confinement time τ E (∼8-10 ms) are simultaneously improved is obtained at an e of 4.3 × 10 13 cm -3 and B = 7 T under full current drive conditions. There exists a certain threshold power above which the ECD transition occurs. A hysteresis of η 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 experiments are performed by using two opposite travelling LHWs. Current compensation (ΔI CD /I CD < -10%) is clearly seen when the backward (BW) travelling 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.
Source: Nuclear Fusion
Authors: H Zushi, S Itoh, K.N Sato, K Nakamura, M Sakamoto, K Hanada, E Jotaki, K Makino, Y.D Pan, S Kawasaki, H Nakashima
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1989697707