Effects of magnesium on the negative hydrogen ion production in a magnetized sheet plasma source

Abstract

The effect of magnesium on the H⁻ ion production of a pure hydrogen discharge in a magnetized sheet plasma source is investigated with E x B and Langmuir probes at total initial gas filling pressures of 5 mTorr, 7 mTorr, and 9 mTorr and at discharge currents from 0.5 A to 2.5 A.
Magnesium disk placed at the anode of the source has significantly increased the H⁻ yield. The highest H⁻ enhancement was achieved at 6 cm probe distance from the sheet plasma core, 2.5 A discharge current and 9 mTorr total gas filling pressure. Here the H⁻ current density is enhanced by a factor of 5, from 5.51 x 10⁻⁸ A/m² to 1.32 x 10⁻² A/m² . The enhancement is associated with the significant increase in the electron density and decrease in the electron temperature at this position. Electrons incident on the Mg target are relatively hot at 11.98 eV, contributing to the vaporization of Mg atoms. The vaporized Mg atoms, interacting with plasma particles produce cold electrons. The dissociative attachment of cold electrons to the rovibrationally excited hydrogen molecule, contributes to the production of H⁻. The interactions of Mg atoms with electrons at the periphery also lead to the decrease in the electron temperature.