THE TMX HEAVY-ION BEAM PROBE

A heavy ion beam probe has been used to measure the radial space poten tial distribution in the central cell of TMX. This was the first beam probe system to utilize computer control, CAMAC instrumentation, and f ast time response for broadband fluctuation capabilities. The fast tim e response was obtained using off-line processing of the energy analyz er detector signals and wideband transimpedance amplifiers. The on-axi s space potential was found to be 300-400 V, with phi(e)/T-ec similar to 8. The radial potential profile is parabolic when gas box fueling i s used. The frequency of observed fluctuations was found to agree with the E x B plasma rotation frequency during the discharge. The measure d Tl++ secondary ion current level is consistent with calculations, gi ven reasonable assumptions for beam attenuation.