PROTON-BEAM HEAVY-ION SOURCE

The feasibility of a very heavy ion source which utilizes ionization by intense proton beams is being investigated as a possible injector for cyclotrons and other heavy ion accelerators. Calculated cross sections for ionization to high charge states are ~10 times larger for protons at optimum energy (300–500 keV) than for electrons in working energy range of a few keV. Use of a superconducting solenoid to compress the proton beam and provide radial charge confinement is assumed in the feasibility model. Space charge repulsion produces magnetron motion of the heavy ions and a natural radial zoning with respect to charge state q which requires a correction for the magnetron period fraction spent in the ionizing flux. The radial zoning of different charge states also suggests a possible method of selective extraction. Preliminary calculations with no space charge compensation by electrons have been carried out for 400 keV protons with beam currents of 10, 25, and 100 mA, a solenoid length of 1 m and a magnetic field of B = 5T. Radial size parameters have been computed for yields of U+25 up to 1 pµA. Yields of 1 µA appear feasible without compensation of heavy ion space charge while compensation or other modification appear necessary for higher yields to avoid impractical radial dimensions. © 1979 IEEE.