Injectors for heavy ion fusion

A driver scale (2 MeV, 800 mA, K+) injector for the Heavy Ion Fusion Induction Linac Systems Experiments (ISLE) is under development at LBL. It consists of a 750 keV diode pre-injector followed by an electrostatic quadrupole accelerator (ESQ). One of the key issues for the ESQ centers on the control of beam aberrations due to the energy effect: in a strong electrostatic quadrupole field, ions at beam edge will have energies very different from those on the axis. The resulting kinematic distortions lead to S-shaped phase spaces, which, if not corrected, will lead eventually to emittance growth. These beam aberrations can be minimized by increasing the injection energy and/or strengthening the beam focusing. It may also be possible to compensate for the energy effect by proper shaping of the quadrupoles electrodes. We have chosen to control the energy effect by increasing the injection energy of the diode and strengthening the beam focusing of the ESQ within the voltage breakdown limits. To check the physics of the energy effect of the ESQ design a quarter-scale experiment was designed to accommodate the parameters of the source, as well as the voltage limitations, of the Single Beam Transport Experiment (SBTE) apparatus. The voltage breakdown limits were studied by running a cold test of a full scale ESQ quadrupole. Design of the experiments as well as the one-beam version of the ILSE ESQ Injector and corresponding 3D PIC simulations will be presented. copyright American Institute of Physics 1994