Radio-frequency ovens for ECR ion sources

Radio-frequency (rf) ovens have perspective advantages over their Ohmic equivalent in terms of uniformity of heating, separation (extending lifetime and use of reactive sample) and insulation; on the other side, rf losses in the coil must be minimized. Several geometries, crucibles, and coils were tested to optimize efficiency (power in the sample/total power); the final axial geometry with a copper coil is described, discussing the optimization of thermal contacts. A script to simulate the two-dimensional geometry of a rf oven (in particular, the wire separation and shape) was written; optimal working frequencies were found to be about or over 1 MHz, as confirmed by experiments, while the coil should be slightly longer than the sample. A temperature of 1680 K was reached with an iron crucible and 80 W of total rf power; silver and copper evaporations were tested; and carbon crucibles can reach higher temperatures (1750 K in a preliminary version).