Analysis of Exhaust Gas in JT-60U Tokamak Operation

Abstract

Abstract-In the operation of tokamak such as ITER, it is important to understand the behavior of hydrogen isotopes and other elements in vacuum vessel for tritium inventory control and design of the plasma exhaust process. Particularly removal of carbon-tritium codeposited layer is considered as a crucial issue for ITER, because of its suspected tritium inventory. In JT-60U, exhaust gas was analyzed in the operation of discharge cleaning and tokamak discharge experiments, and the behavior of hydrogen isotopes and carbon were investigated. In discharge cleaning experiments, the degassing rate of hydrogen isotopes in GDC (glow discharge cleaning) was much larger than that in TDC (Taylor discharge cleaning) and ECRDC (electron cyclotron resonance discharge cleaning). Exhausted hydrocarbons were far less than hydrogen. During tokamak discharge experiments, various carbon compounds such as CD 4 , C 2 D 2 , C 2 D 4 , C 2 D 6 and CO 2 were detected. The maximum amount of exhausted carbon was several mg for each shot. There was a strong correlation between exhausted hydrocarbon and tritium. The exhausted hydrocarbon increased with the wall temperature.

Development of helium electron cyclotron wall conditioning on TCV

“…In the presence of such a magnetic field, conventional DC-glow discharges are unstable and can therefore no longer be used between plasma pulses. Compatible with the magnetic field, Taylor discharge cleaning (TDC) has been developed and routinely used with B T on between plasmas in JT-60U to recover a satisfactory wall pumping capacity or low impurity levels, for instance after a disruption [3,4]. These short low current plasmas, typically with duration of 20-40 ms and a current of a few tens of kA, are created inductively in the vacuum vessel by rapidly changing the currents in the central solenoid coil, at a repetition rate of ~0.2-1 Hz.…”