Recent progress on TRIAM-1M

Abstract

A steady state plasma with high performance and high current drive efficiency is reported. In 2.45 GHz LHCD plasmas Ti is studied as a function of ne at the edge of the high ion temperature (HIT) window. Different characteristic timescales are found for Ti and ne to enter the HIT regime and the observed hysteresis behaviour of Ti with respect to ne 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 ηCD( = n̄eICDR0/PLH ∼1 × 1019 A m-2/W) and energy confinement time τE (∼8-10 ms) are simultaneously improved is obtained at an n̄e of 4.3 × 1013 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 ηCD 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 (ΔICD/ICD < -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.

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

“…The latter holds the world record in pulse duration (2 h) using non-inductive current drive (see glossary) by lower hybrid waves, albeit in low-density, low-power discharges [125]. This clearly shows the potential for steady-state operation.…”

Key plasma wall interaction issues towards steady state operation

“…): they generally carry a small fraction of the coupled power, but impact very locally on the PFCs, giving rise to high localized heat loads (>1 MW/m 2 ). This effect is benign on short pulses, but not tolerable on long pulses [19]. In order to overcome this problem, ferritic inserts have been installed in HT7 and JT60U to reduce the ripple and the associated particle losses [7], and specific protection tiles were added in TS [20], decreasing the overall iron (Fe) level in the discharge [34].…”

Molecular Zeeman spectroscopy for H2 Fulcher-α band spectra as a local measurement of rovibrational structures

“…In this contact area, a so-called hot spot is observed. The heat flux from the plasma is highly localized to the point, and the local surface temperature becomes higher than 1000 K. 36 In the case of molybdenum, a surface temperature of above 1200 K dominates the desorption in the form of atoms. 37 We suspect, therefore, that the observed molecular emission originates in the region around the hot spot, where the surface temperature is low enough to desorb molecular hydrogens.…”