Recycling and wall pumping have been studied comparinglow (≈1018 m-3) and high (≈1019 m-3) density long duration plasmas inTRIAM-1M. The recycling coefficient of each plasma increaseswith time. There exist two time constants in the temporalevolution of the recycling coefficient. One is a few seconds andthe other is about 30 s. The wall pumping rates of low and highdensity plasmas are evaluated to be ≈1.5×1016 atoms m-2 s-1 and ≈4×1017 atoms m-2 s-1, respectively. The differencemay be caused by the total number of diffused ions and thecharge exchange neutral flux with an energy of less than0.7 keV. In an ultra-long discharge (≈70 min), therecycling coefficient becomes 1 or more before again decreasingbelow 1, i.e. the wall repeats the process of being saturatedand refreshed. In high power and high density experiments, wallsaturation phenomena have been observed. The discharge durationlimited by wall saturation decreases with an increase indensity.
Wall pumping and saturation in divertor tokamaks