Analysis of cesium distribution for negative ion sources: SID diagnosis and Monte-Carlo simulation

Cesium evaporation is commonly adopted in negative ion sources to form appropriate cesium coverage on the converter surface which lowers surface work function, thus improving negative ion production. The surface coverage of cesium is influenced by oven evaporation rate (controlled by the oven heating temperature) and wall sticking coefficient (influenced by the wall temperature). To investigate cesium transportation in chamber and to optimize cesium condition for future cesium injection in the HUST negative ion source, experiments are carried out in the cesium test stand with surface ionization detector (SID), including the oven SID and two movable SIDs along axis and radius direction, under adjusted oven temperatures and wall temperatures, to simulate the actual working conditions in negative ion sources. A Monte-Carlo model is established to carry out analysis, providing the relationship of cesium distribution and wall sticking coefficient under certain oven evaporation rates. With the oven evaporation rate obtained based on the oven SID, the wall sticking coefficient under various wall temperatures is acquired by comparing the experimental results of movable SIDs with simulation. The results show the relationship between cesium distribution under different oven evaporation rates and wall temperatures, along with wall sticking coefficients calculated.