The ion source design and test bench, BETSI, has been in use since 2006 to produce and analyze intense beams, in pulsed or continuous mode, up to several tens of mA and at energies up to 50 keV. The source on this facility, operating at up to 50 kV, is supplied with radiofrequency power via a high-voltage switch. A solenoid focuses the beam at the exit of the accelerator tube, and a dipole is used to separate the extracted species. The beam is characterized by various diagnostics already in place or under development.
A new magnetic configuration, composed of two, instead of three, permanent magnet rings, has been set up to obtain the electron cyclotron resonance – or ECR – to ionize the gas injected into the source. The new configuration was made possible by modifying the pure iron shielding. This improvement is the fruit of preliminary calculations performed using the Vector Field© Opera 2D and 3D codes and the Radia code. Thesis work on the interaction of the RF wave with the plasma, and on beam extraction in a strong magnetic field, has just begun.
Two development approaches to the extraction system are under study. A modified mechanical system to make it easier to optimize inter-electrode distances is being tested on BETSI. Backed up by numerical simulations, reducing the number of electrodes from five to four should minimize the emittance of very high-intensity beams on extraction (from a few mA to 150 mA). Compared with a simpler, three-electrode system, which is more effective in terms of transport, this solution, with its additional intermediate electrode, minimizes electrode loss.