Toroidal structure of hydrogen recycling in ultra-long discharges on TRIAM-1M

The ultra-long discharge with the duration of 5 h 16 min has been achieved using the ML with good cooling capability in TRIAM-1M. The temperature increase in the plasma facing components could be successfully suppressed by the movable limiter (ML). The wall inventory continued to increase during the discharge and finally reached up to 8 x 1021 atoms at the end of the discharge. No Long time global balance between particle absorption and release of the wall was observed. The averaged wall pumping rate is evaluated to be ∼8.6 x 1016 atoms m-2 s-1, which is about 3.6 times higher than that evaluated in the previous ultra-long discharge without the ML. It seems to be attributed to suppression of the hydrogen release from the wall due to less temperature increase. The toroidal structure of hydrogen recycling changes only at the ML and its neighborhood, and the other part, i.e. main chamber recycling, still remain the same structure as that without the ML. Moreover, it is found that the structure of the main chamber recycling is the same in the low and high density cases. It suggests that the charge exchange neutral dominates the main chamber recycling. The contribution ratio of the main chamber to the wall recycling decreases by about half due to the ML. That of the section of the ML reaches about 45%. (author)