Two-Dimensional Simulations of H¯ Ions Extraction

The 2D particle-in-cell method based model of a negative ion source is presented. The spatial distributions of electrostatic potential and plasma component densities are presented. Changes of negative ion distribution and potential as well as the extracted H¯ current with the plasma grid bias voltage are investigated. The presence of the potential well near the plasma grid surface that traps the negative ions is shown. Increase of the H¯ ions density inside the chamber with the negative bias voltage is demonstrated. Influence of the H¯ ion flux outgoing from the plasma grid on the extracted current was checked: increase by factor 2 is observed when the flux rises 4 times. Current-voltage characteristics of the ion source are presented, saturation of the curve is observed above 50 kV.