AN ADVANCED HIGH-CURRENT LOW-EMITTANCE DC MICROWAVE PROTON SOURCE

The high-current low-emittance microwave proton source introduced two years ago act the Chalk River Laboratories has been extensively redesigned. The 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition. The layered microwave window has been replaced by a single plate of aluminum nitride. The solenoids were electrically isolated from the plasma chamber. Only the plasma chamber remains at the extraction potential. The total beam current and the proton beam current have been measured as a function of the microwave power, the hydrogen mass flow and the solenoid positions and currents. More than 95 mA dc of hydrogen ions with a proton fraction in excess of 85% were extracted from a single 2.5 mm radius aperture with only 500 W of microwave power and 2.0 sccm (3 mug/s) of hydrogen mass flow. The perveance at minimum divergence and the minimum emittance have been determined for various extraction geometries. The variation of the perveance with the aspect ratio of the extraction system was found to be virtually identical for microwave and arc discharge ion sources. The normalized rms emittance was less than 0.13 p mm mrad whatever the extraction geometry.