Radiation losses and global power balance of JT-60 plasmas

Abstract

The radiation losses and the global power balance for Ohmic and neutral beam heated plasmas have been investigated in different JT-60 configurations. Discharges with a TiC coated molybdenum wall and with a graphite wall, with limiter, outer and lower X-point configurations have been studied by bolometric measurements, thermocouples and an infrared TV camera. In neutral beam heated outer X-point discharges with a TiC coated molybdenum first wall, the radiation loss of the main plasma was very low (10% of the absorbed power). The radiation loss due to oxygen was dominant in this case. On the contrary, in discharges with TiC coated molybdenum limiters the radiation loss was very high (>60% of the absorbed power). In the discharges with a graphite wall the radiated power from the main plasma was 20-25% for both limiter and lower X-point configurations. In lower X-point discharges the main contributor to the radiation loss was oxygen, whereas in limiter discharges the loss due to carbon was equal to the loss due to oxygen. The radiation loss from the lower X-point divertor increased with increasing electron density of the main plasma.

Study of the density limit with pellet fuelling in JT-60

“…The small and the large pellets contain 0.96 x 10 21 atoms and 2.3 x 10 21 atoms, respectively [9]. The basic scenario of pellet injection, the plasma equilibrium and the diagnostics are presented in Refs [8] and [12]. The average efficiency of the particle inlet into the vacuum vessel for each pellet is about 70-80% of the particle inventory, determined by the ideal pellet dimensions, with the remaining particles lost in the formation and acceleration phases.…”

“…For measuring the effective charge Z eff in the outer region of the plasma column, we use the visible bremsstrahlung spectrometer which views along the same chord as the FIR interferometer. The radiation power P rad is measured by a 32-channel bolometer array with a time resolution of 20 ms [12].…”

“…This is especially important because the radiated power is a strong function of T e . The dominating light impurity species in JT-60 are carbon and oxygen [12]. For these impurities, the radiated power increases drastically with decreasing electron temperature for T e < 0.3-0.5 keV.…”

Bolometers for Fusion Plasma Diagnostics

“…The radiation profile gives an unambiguous picture of the Marfe location and the time profile gives its evolution. Marfes have been studied extensively in Alcator C (Lipschultz et al, 1984), JT-60 (Nishitani et al, 1990) and TFTR (Bush et al, 1988).…”

H-mode experiments with outer and lower divertors in JT-60

“…In the divertor discharge, the ratio of the total radiation from the main plasma to the absorbed power (=P£ d ain /P abs ) is 12% [36]. After the L-mode to H-mode transition, P^i n increases gradually.…”