Finding the Optimum Frequency and the H- Distribution in the HERA RF- Volume Ion Source

The HERA RF-Volume Source is the only source available that delivers routinely an H- current of 40 mA without Cs. The dependency of the quality of the H- beam on the frequency was investigated. A frequency range of 1.65 - 9 Mhz was scanned and the emittance was measured for several H- currents up to 40 mA. The production mechanism for H- ions in this type of source is still under discussion. Laser photodetachment measurements have been started at DESY in order to measure the H- distribution in the source. The measurements have also been done under extraction conditions at high voltage. The results of the measurements with and without extraction are a basis for the development of a theory for the transition between plasma and vacuum (sheath), a cornerstone for beam transport programs. Knowledge of the H- distribution and where they are produced makes further source improvements possible