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(EXP4/26) Recycling and Wall Pumping in Long Duration Discharges on TRIAM-1M

M. Sakamoto¹⁾, S. Itoh¹⁾, K. Nakamura¹⁾, H. Zushi¹⁾, K. Hanada¹⁾, E. Jotaki¹⁾, Y. D. Pan²⁾, S. Kawasaki¹⁾, H. Nakashima^1)
 
1) Advanced Fusion Research Center, Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan
²⁾ Southwestern Institute of Physics, China

Abstract.  Recycling and wall pumping have been studied comparing low ( $\sim$ 10¹⁸m^{- 3}) and high ( $\sim$ 10¹⁹m^{- 3}) density long duration plasmas in TRIAM-1M. The recycling coefficient of each plasma increases with time. There exist two time constants in the temporal evolution of the recycling coefficient. One is a few seconds and the other is about 30 s. They may relate with characteristic times during which the physical adsorption and absorption due to the CX neutrals reach the equilibrium state, respectively. The wall pumping rates of low and high density plasmas are evaluated to be $\sim$ 1.5×10¹⁶ atoms m^{- 2}s^{- 1} and $\sim$ 4×10¹⁷ atoms m^{- 2}s^{- 1}, respectively. The difference is caused by the difference of the total amount of the CX neutral flux with the energy of < 0.7keV. In the ultra-long discharge ($\sim$ 70 min), the recycling coefficient becomes unity or more and again decreases below unity, i.e. the wall repeats a process of being saturated and refreshed. This refreshment of the wall seems to be caused by the co-deposition of Mo, which is a material of the limiter and divertor plates. In the high power and high density experiments, the wall saturation phenomenon has been observed. The discharge duration limited by the wall saturation decreases with increase in the density.

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