High current electron source for beam neutralization experiments

To investigate the space charge neutralization effects in the extraction gap of a laser ion source (LIS) [1] a high current density electron beam with low energy spread is needed. The transient hollow-cathode discharge (THCD) source [2] has the required characteristics. The THCD is a pulsed hollow-cathode glow discharge that operates at low gas pressure (101 mbar) and high applied voltage. Characteristic for this type of discharge is that during the fast voltage breakdown, discharge currents of several kA are reached. At the beginning of the current increase a high current, well focused electron beam is emitted at the anode. The unique feature of the THCD produced beam is its self-focused, space charge neutralized propagation in the background gas. At the beginning of its propagation the beam charge is only partially neutralized. We use the channel spark geometry (Fig. 1) which consists of a hollow cathode and a capillary tube made of Al2O3.