A Global Enhanced Vibrational Kinetic Model for Radio-Frequency Hydrogen Discharges and Application to the Simulation of a High Current Negative Hydrogen Ion Source

Averkin, Sergey Nikolaevich

Etd

A Global Enhanced Vibrational Kinetic Model for Radio-Frequency Hydrogen Discharges and Application to the Simulation of a High Current Negative Hydrogen Ion Source

Public

A Global Enhanced Vibrational Kinetic (GEVKM) model is presented and applied to the simulation of a new High Current Negative Hydrogen Ion Source (HCNHIS) developed by Busek Co. Inc. and Worcester Polytechnic Institute. The HCNHIS consists of a high-pressure radio-frequency discharge (RFD) chamber in which the main production of high-lying vibrational states of the hydrogen molecules occurs, a bypass system, and a low-pressure negative hydrogen ion production (NIP) region where negative ions are generated by the dissociative attachment of low energy electrons to rovibrationally excited hydrogen molecules. The GEVKM is developed from moment equations for multi-temperature chemically reacting plasmas and for a cylindrical geometry of an inductively coupled discharge chamber. The species included into the model are ground state hydrogen atoms H and molecules H2, 14 vibrationally excited hydrogen molecules H2(v), v=1-14, electronically excited hydrogen atoms H(2), H(3), ground state positive ions H+, H2+, H3+, ground state negative ions H-, and electrons e. The space-averaged steady-state continuity equations coupled with the electron energy equation, the total energy equation and heat transfer to the chamber walls, are solved simultaneously in order to obtain the space-averaged number densities of the plasma components, the electron and heavy particle temperatures as well as the wall temperature. The GEVKM is supplemented by a comprehensive set of surface and volumetric chemical processes governing vibrational and ionization kinetics of hydrogen plasmas. The GEVKM is verified and validated in the low pressure, in the intermediate to high-pressure (1-100 Torr) and high absorbed power density (8.26-22 W/cm3) regimes by comparisons with the numerical simulations and experimental measurements. The GEVKM is applied to the simulation of the RFD chamber of the HCNHIS. The GEVKM predictions of negative hydrogen ions number densities and electron temperatures in the RFD chamber of the HCNHIS are used to estimate the negative hydrogen ion current using the Bohm flux approximation. The estimated negative current compare well with the Faraday Cup measurements and provide additional validation of the model. The GEVKM is used in a parametric investigation of the RFD chamber of HCNHIS-2 with hydrogen inlet flow rates 5-1000 sccm and absorbed powers 200-1000 W.

Creator