Beam Potential Measurement of an Intense H- Beam by Use of the Emissive Probe Technique

An emissive probe has been developed to study the beam-plasma potential generated by a 20-keV, 30-mA/cm2 quiescent H- beam propagating in Xe background gas. An axial ion trap has been built, and its influence on the measured potentials is reported. The peak plasma potential at 1012 cm-3 Xe density increased from +5V to +10V when the ion-trap voltage was increased from zero to +80V. The quiescent H- beam rms emittance, measured 34 cm from the ion source, increased from 0.012 to 0.023 ¿·cm·mrad when the Xe density was decreased from 2.2 × 1012 cm-3 to zero.