Angular Distribution Measurement of Atoms Evaporated from a Resistive Oven Applied to Ion Beam Production
Résumé
A low temperature oven has been developed to produce calcium beam with Electron Cyclotron Resonance Ion Source. The atom flux from the oven has been studied experimentally as a function of the temperature and the angle of emission by means of a quartz microbalance. The absolute flux measurement permitted to derive Antoine’s coefficient for the calcium sample used : A=8.98± 0.07 and B=7787± 110 in standard unit. The angular FWHM of the atom flux distribution is found to be 53.7±7.3 °at 848K. The atom flux hysteresis observed experimentally in several laboratories is explained as follows: at first calcium heating, the evaporation comes from the sample only resulting in a small evaporation rate. once a full calcium layer has formed on the crucible refractory wall, the caclcium evaporation surface includes the crucible’s enhancing dramatically the evaporation rate for a givent temperature. A Monte-Carlo code, developed to reproduce and investigate the oven behaviour as a function of temperature is presented. A discussion on the gas regime in the oven is proposed as a function of its temperature. A fair agreement between experiment and simulation is found.
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