Neutralization processes of atomic/molecular deuterium ions assisted by ND3 in low density D2-N2 plasmas

Abstract

The formation mechanisms of ND3+ and ND4+ are investigated in weakly ionized nitrogen-hydrogen plasmas with electron densities ne ∼ 1016 m−3 and electron temperatures Te ∼ 3 eV. The plasmas are created by an inductively coupled RF (13.56 MHz) discharge of 500 W at the total pressure of 10 mTorr in the nitrogen partial pressure ranging from 0.02 to 2.9 mTorr. The ion density fractions are measured by an electrostatic quadrupole plasma analyzer, which is a combination of ion energy analyzer and mass spectrometer, after calibration with neutral gases. A zero-dimensional rate equation model, sometimes called a global model, is used to understand the source and loss processes of each ion and neutral species in the plasma. The ion density fractions calculated by the model show qualitatively good agreement with the experimental results. Model calculations suggest that ND3+ and ND4+ generation is dominated by electron or D+ exchange reactions of deuterium atomic/molecular ions with ND3. These processes are thought to play an important role in the recombination process of D plasma with ammonia formed in the N2 seeded divertor region.