Wall reflection and hydrogen recycling in tokamaks

A formal treatment of the particle recycling problem is given based on the boundary relation at the plasma-wall interface. This general theory is applied to the case of a steady-state, one-species system for which the basic equation of recycling can be formulated in convenient matrix forms. The problem is further specialized to that of hydrogen recycle in tokamaks using a slab model of plasma with a uniform cold neutral source at the wall and a SPUDNUT neutral transport code. Numerical results are obtained of the effect of wall reflection of neutrals on the neutral density profiles, the recycling fluxes and their energy distributions, etc., with parameters pertaining to the ST and TFTR tokamaks. Data are displayed comparing the results with reflection to those without reflection, the reflection amounting to 44% in ST and 29% in TFTR, respectively, from their stainless steel walls. (orig.)