Cit alpha extraction and measurement: Final report, September 1, 1988-November 30, 1993

Abstract

In the last year of active funding, progress in the investigation of the low-Z pellet-plasma interaction was made in two areas: 1) the calculations to determine a self-consistent solution to the region inside the sonic surface were extended to include boron and tritium tritide pellets as well as lithium and carbon, 2) a slab model for power losses due to line radiation has been included in the overall energy balance for lithium clouds. This has led to the identification of four candidate processes, which could account for the differences between the results from our calculations and the lengths of the Li{sup +1} clouds observed during pellet penetration experiments on TFTR: 1) line-radiation from the cloud holding down its temperature, 2) the charging up of the cloud reducing the incident hot electron flux from the plasma, 3) the cooling of the plasma in contact with the cloud, and 4) the reduction of the heat flux of the incident electrons to the cloud due to the backscatter of these electrons from the cloud (i.e., albedo). However, while each of these was explored individually, all could not be incorporated into a single computer code during active funding. Previously, self-consistent equilibrium and non-equilibrium charge-state models were formulated for the spherical expansion of low-Z pellet vapor as an inviscid perfect gas of constant ratio of specific heats being heated volumetrically by the incident electrons of a thermonuclear plasma. The models were found to agree where the ratio of the ionization length {zeta}{sub j} to pellet radius r{sub p} is less than one, but a single parameter was insufficient to determine whether an equilibrium model would be valid for all regions of the ablatant for carbon pellets. Thus a non-equilibrium model was necessary to model the outer regions of the ablatant cloud even for thermonuclear plasma conditions when the cloud is very dense. 16 refs., 2 tabs.