Dissociative Recombination Process Of Ammonium For Hn-Mar In High Density D-N Plasmas

Ammonia molecules formed in a nitrogen-seeded D-fueled plasma are shown to catalyze volumetric recombination of hydrogen ions. This Hydronitrogen Molecular Assisted Recombination (HN-MAR) process occurs by charge and ion exchange reactions with ammonia (ND3), leading to subsequent volumetric recombination with ND3+ and ND4+ molecular ions. When the plasma density is raised to the point where volumetric recombination dominates plasma losses to the wall [n(e) > 10(18) m(-3)], a calibrated electrostatic quadrupole plasma analyzer shows that the ND4+ ammonium ion density fraction drops from 0.55 to 0.11. We show that this is consistent with a 0-d kinetics model that includes the HN-MAR process with rates that are proportional to the electron density. The results suggest that direct injection of ammonia would provide a more efficient pathway to achieve divertor detachment in future tokamak experiments. Published by AIP Publishing.