Hydrogen Recycling and Wall Equilibration In Fusion Devices

The design of fusion devices for steady state operation requires the knowledge of relaxation processes and time constants affecting the stationary conditions. Among the more prominent candidates are the confinement times, current relaxation times, and the wall equilibration times. Typical confinement times of today’s midsize devices are in the order of 1 second, current relaxation times are, depending on the plasma parameters, in the range of 5 seconds, and wall equilibration times are commonly assumed to be in the range of hundreds of seconds. This wall equilibration time obviously determines the pulse length necessary to achieve stationary density conditions. On the other hand, it is not very well defined and depends to a large degree on the wall state and plasma conditions. In order to shed some light on the involved processes, this paper investigates wall equilibration processes which are controlled by hydrogen recycling.