Effect of cesium seeding on the production of H− ions in a magnetized sheet plasma source

Abstract

The effect of the addition of cesium on the production of negative hydrogen ions (H⁻) in a magnetized sheet plasma source (SPNIS) is investigated. Plasma parameters and H⁻ yields were determined from Langmuir probe and E x B probe measurements, respectively. Significant increase on H⁻ yield is observed with the addition of a controlled flux of neutral Cs vapor. The maximum enhancement of 88 times compared to the uncesiated case is extracted at 5 cm away from the sheet plasma core at a discharge current of 0.5 A and initial gas filling pressure of 9 mTorr. The value is increased from 5.51 x 10⁻⁸ A/m² for the uncesiated case to 4.86 x 10⁻⁶ A/m² for the cesiated case. The largest negative hydrogen ion current density extracted is 0.0155 A/m² at 2.5 A discharge current, 9 mTorr initial gas filling pressure, and 1 cm probe distance from the plasma center. Here, enhancement is only 9.8 times compared to pure hydrogen discharge. The increase in H⁻ current density is attributed mainly to the cooling effect of Cs evidenced by the considerable decrease in electron temperature especially at the periphery of the plasma.