Abstract:
Background Penning ion sources are widely employed in small-scale accelerators owing to their structural simplicity, compact geometry, and low power consumption, yet the quantitative dependence of their discharge characteristics and hydrogen ion species distribution on operating parameters remains insufficiently understood.
Purpose The present work systematically investigates the influence of operating parameters—working gas pressure, power, and magnetic field strength—on the plasma electron density and on the relative fractions of \textH^+ , \textH_2^+ , and \textH_3^+ ions.
Methods Taking the collisional ionization of \textH_2^ molecules as the object of investigation, a global physical model of the Penning ion source was established that incorporates the principal electron-impact ionization, dissociation, and ion–molecule reactions occurring in the discharge. The working gas pressure was scanned from 6×10−4 Pa to 8×10−2 Pa, the input power from 1 W to 10 W, and the magnetic field strength from 0.005 T to 1 T, and the predictive reliability of the model was further validated by comparison with PIC/MCC simulations and diagnostic measurements reported in the literature.
Results At a magnetic field of 0.5 T and an input power of 5 W, as the gas pressure increased from 6×10−4 Pa to 8×10−2 Pa, the \textH_2^+ fraction decreased from approximately 85% to below 5%, while the \textH_3^+ fraction rose from about 8% to over 90%, and the \textH^+ fraction remained below 7% throughout. At 5 W and 0.1 Pa, increasing the magnetic field from 0.005 T to 1 T raised the \textH^+ fraction from approximately 3.5% to about 10.7%, and the calculated trends agreed well with the reference simulations and measurements.
Conclusions These results indicate that the proposed global model reliably reproduces the variation of plasma electron density and hydrogen ion species fractions with pressure, power, and magnetic field, which providing a useful theoretical reference for the optimization and design of Penning ion sources.
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