Initial results of electron cyclotron range of frequency (ECRF) operation and experiments in JT-60U

Physics basis for a tokamak fusion power plant

High power transmission and polarization measurement in 110 GHz transmission line

The author reviews the progress in the application of RF to heating and current drive for nuclear fusion made by the Japanese RF community.

https://iopscience.iop.org/article/10.1088/0741-3335/35/SA/011/pdf

Review of Japanese results on heating and current drive

Recent ion cyclotron range of frequencies experiments in JT-60U

Lower hybrid current drive and higher harmonic ICRF heating experiments on JT-60

Recently, the JT-60U has employed ECRF system in addition to LHCD and ICRF systems. Three types of RF experiments on JT-60U have been performed. A reversed magnetic shear (R/S) configuration with internal transport barrier (ITB) was successfully maintained for 4.7 s in a quasi-steady state by LHCD in addition to the bootstrap current, where all profiles of temperature and plasma current were almost stationary. On the normal operation without heating during plasma current ramp-up, high electron temperature (Te0∼10 keV) with a strongly peaked profile was produced by LHCD alone at the density of ∼0.5×1019 m−3. This peaked temperature profile was featured by a reduction in core density. The central electron temperature and density slowly changed in several seconds. The performances of ICRF (2ωCH) on the R/S configuration were also studied. Degradation of confinement of energetic particles was observed probably due to the large banana orbit loss. An 110 GHz ECRF system has been operated on JT-60U. Its gyrotron has successfully generated power at the level of up to 830 kW for 300 ms and is under conditioning. On the initial operation, the power of 620 kW was injected into plasmas. The central electron temperature increased from 3 keV to 5.5 keV at ne∼0.6×1019 m−3. A controllability of local heating was also demonstrated by the poloidally steerable mirror.

Recent RF activities on JT-60U

A plasma current of 2 MA is driven by lower hybrid current drive (LHCD) and the maximum CD efficiency of ηCD=25×1019 m−2 A/W is achieved, which agrees with the previously reported scaling: ηCD∼12<Te≳/(5+Zeff) The direct loss of launched wave power through energetic electrons is identified by measuring the x‐ray signal from the divertor plates The direct loss power is fairly low (typically <5%) and depends on the slowing down time of energetic electrons accelerated by launched LH waves This indicates that the slowing down process is dominant compared with loss mechanisms of fast electrons The radial diffusion coefficient of fast electrons is less than 1 m2/s from analyses on change in HX signal on pellet injection and direct lost power by fast electrons Good coupling characteristics are confirmed for a new large (48×4) multijunction launcher Significantly large loading resistances are obtained with a 2×2 phased ICRF antenna, especially ∼5 ohms with in‐phase current mode even at a big separatrix‐wall

Lower‐hybrid current drive and ICRF heating experiments on JT‐60U

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Lower hybrid current drive and higher harmonic ICRF heating experiments on JT-60

Recent RF activities on JT-60U

Lower‐hybrid current drive and ICRF heating experiments on JT‐60U