2-FREQUENCY PLASMA-HEATING IN A HIGH CHARGE-STATE ELECTRON-CYCLOTRON-RESONANCE ION SOURCE

The performance of the Lawrence Berkeley Laboratory (LBL) advanced ele ctron cyclotron resonance ion source, which is a single stage source d esigned to operate at 14 GHz alone (single-frequency heating), is enha nced by heating the plasma simultaneously with microwaves of 10 and 14 GHz (two-frequency heating). Production of high charge state ions was increased a factor of 2-5 or higher for the very heavy ions such as b ismuth and uranium, as compared to single-frequency heating. Plasma st ability was improved and the ion charge state distribution shifted to higher charge state. With two-frequency heating, the source can produc e more than 1X10(9) pps of fully stripped argon. High charge state ion beams of bismuth and uranium produced by the source were injected int o the 88-Inch Cyclotron at LBL. After acceleration to energies greater than 6 MeV/nucleon, the extracted beam intensities were 1X10(6) pps o r higher for Bi-50+,Bi-51+ and U-238(52+,53+). (C) 1995 American Insti tute of Physics.