Global particle balance and wall recycling properties of long duration discharges on TRIAM-1M

The longest tokamak discharge, with a duration of 11406 s (3 It 10 min), has been achieved. The global particle balance has been investigated. In the longest discharge, the global balance between the particle absorption and release of the wall was achieved at t similar to 30 min. After that, the plasma density was maintained by the recycling flux alone until the end of the discharge. The maximum wall inventory is about 3.6 x 10(20) H at t similar to 30 min, but it is finally released from the wall at the end of the discharge. The hydrogen release seems to be caused by the temperature increase in the whole toroidal area of the main chamber. Moreover, it has been observed that there is a large difference between the properties of wall recycling in the continuous gas feed case (i.e. static condition) and in the additional gas puff case (i.e. dynamic condition). In the static condition, the effective particle confinement time increases to similar to 10 s during the I min discharge and it increases to similar to 100 s before the global balance in the longest discharge. In the dynamic condition, the decay time of the electron density just after the gas puff, i.e. the effective particle confinement time, is constant at 0.2-0.3 s during the discharge. The large difference in the effective particle confinement time between the static and dynamic conditions seems to be caused by the reduction in the recycling coefficient due to the enhanced wall pumping resulting from the additional gas puff.