Multicusp Ion Source for Induction Linac Applications

At LBNL we are investigating the use of gaseous ion sources for induction linac applications such as heavy ion inertial fusion. Typical requirements for the ion source is to produce 20 μs pulses with a rise-time of 2 μs. The current density should be greater than 100 mA/cm2 at a duty cycle of 10 Hz [1]. Noble gases such as krypton, neon and xenon will be used. The source used for the measurements described in this paper was a standard 10 cm in diameter multicusp source with RF-discharge. Current densities of more than 400 mA/cm at RF-power levels of 20 kW using neon discharge were demonstrated. With heavier elements such as Ar, Kr and Ne, current densities of 200 300 mA/cm2 were obtained at the same extraction voltage of 20 kV. By using a starter filament, the rise-time has been reduced from 20 μs to 5 μs. Beam emittance was measured using a pepper-pot device. An argon beam showed that the normalized emittance is of the order of 0.1 πmm-mrad.