Plasma recombination and molecular effects in tokamak divertors and divertor simulators

TLDR

Molecular Activated Recombination (MAR) of vibrationally excited hydrogen is a key plasma process. The study examines various plasma recombination mechanisms in tokamak scrape‑off layers and divertor simulators. Experimental data show that plasma recombination, especially MAR, is essential for detachment, and electron–ion recombination can extinguish divertor plasma at about 0.15 eV.

Abstract

Analysis of the experimental data from tokamaks and linear divertor simulators leads to the conclusion that plasma recombination is a crucial element of plasma detachment. Different mechanisms of plasma recombination relevant to the experimental conditions of the tokamak scrape-off layer (SOL) and divertor simulators are considered. The physics of Molecular Activated Recombination (MAR) involving vibrationally excited molecular hydrogen are discussed. Although conventional Electron–Ion Recombination (EIR) alone can strongly alter the plasma parameters, MAR impact can be substantial for both tokamak SOL plasma and divertor simulators. Investigation of the effects of EIR on the plasma flow in divertor simulators shows that due to the balances of (a) energy transport and electron cooling, and (b) the plasma flow and recombination, that EIR extinguishes the simulator plasma at an electron temperature about 0.15 eV.