Cold intense electron beams from -cooled GaAs-photocathodes

To study electron–ion interactions at the Heidelberg heavy-ion storage ring, electron beams with low-energy spreads and dc-currents of milliamperes are desired. Measurements of the photoelectron energy distribution showed that electron beams with energy spreads of 5–8 meV can be obtained from GaAs photocathodes, cooled to about LN 2 -temperature. However, in order to get milliamperes beam currents, the laser illumination has to be increased up to 1 W, causing substantial cathode heating. esented new electron gun design based on sapphire-substrate transmission-mode photocathodes, cooled by LN 2 , stabilizes the GaAs bulk temperature under 1 W laser illumination at about 95 K and thereby provides the prerequisites for an electron gun being operated at milliampere-currents with low-energy spreads.