Neutral transport baffling studies for SST-1

Abstract

The Superconducting Steady-State Tokamak (SST-1) is being designed to have 1000 s shots. Scrape off layer (SOL) modelling of SST-1 shows a sheath limited flow regime in the SOL with low recycling of neutrals in the divertor chamber. This implies that there will be a high neutral backflow from the divertor plates to the core which can result in decreased density control or plasma disruption unless the neutrals recycling from the divertor plates are well baffled to prevent them from entering the core. This paper describes the various baffle plate designs considered for SST-1 and the procedure by which a suitable design was accepted. The Monte Carlo neutral transport code DEGAS was used to study the neutral transport and a steady state particle balance model was devised to interpret the DEGAS results. It is seen that fueling efficiency is an important parameter which should be considered when calculating the throughput at the pump opening and the particle backflow to the core. It is also seen that high recycling alone does not ensure a good density control, it is the ratio of the particle throughput at the pumps to the particle backflow which has to be optimised for good density control. The SST-1 baffle plates are designed to minimise the particle backflow to the core to achieve good density control, keeping the pumping requirements within bounds.