Hydronitrogen-enhanced MAR process in D₂-N₂ plasmas to induce plasma detachment

The Molecular Assisted Recombination (MAR) process is thought to be a main channel of volumetric recombination to induce the plasma detachment operation. Authors have suggested a new plasma recombination process supported by hydronitrogen molecules such as ammonia, which will be formed by impurity seeding of N2 for controlling divertor plasma temperature and heat loads in ITER. This hydronitrogen-enhanced MAR (HN-MAR) process would occur throughout two steps: 1) ion exchange reactions between hydrogen ions and ammonia molecules, 2) recombination reactions between NH3/4+ ions and electrons. In this study, the HN-MAR process is investigated in plasmas ne ~ 1016-1018 m-3 fueled by D2 and ND3 in the PISCES-E RF plasma device. Ion densities are calculated and directly measured by using a rate equation model and a calibrated Electrostatic Quadrupole Plasma (EQP). The EQP detected ND3/4+ ions (10-75% of whole ion densities) which is the production of the step 1 reaction according to the model estimation. When ne > 1017 m-3, the volumetric recombination process (step 2) cannot be ignored by comparing with the surface loss reaction. In the plasmas ne~ 1017-1018 m-3, the experimental result shows good agreement with the model including the step 2 recombination reactions.