Characterization of the hydrogen plasma in the RF negative ion source by optical emission spectroscopy

Optical emission spectroscopy (OES) is an important noninvasive diagnostic tool for providing insight into the plasmas of the negative ion sources. The plasma spectroscopic characterization of the RF driven negative ion source at Huazhong University of Science and Technology (HUST) is studied with the delivered power from 6 kW to 16 kW. The gas temperature, electron temperature, electron density and the density ratio of atomic hydrogen to molecular hydrogen are extracted from OES. The gas temperature is estimated from the Fulcher band of H-2. A global thermal model is developed to investigate the gas heating mechanisms in hydrogen plasmas. The gas temperature calculated by the model using the electron density and electron temperature from OES as input parameters is in good agreement with that from the experiment. The thermal model shows that the dissociation of molecular hydrogen by electron impact is the dominant source of gas heating and that approximately 11% similar to 12% of the delivered power is dissipated in gas heating at 0.3 Pa filling pressure. Moreover, the electron temperature, electron density and the ratio of atomic to molecular density are obtained from the absolute intensity of Balmer lines and Fulcher band by using collisional radiative (CR) models of H and H-2. The kinetics of the excited states of H are also discussed.