Gabor lens focusing of a proton beam

Abstract

Gabor or plasma lenses have previously been used to focus intense beams of positive ions at energies from 10 keV to 5 MeV. Such lenses are a possible candidate for matching an intense low-energy proton beam into a radio frequency quadrupole accelerator (RFQ). The conventional solution has been to match an intense beam with two solenoid lenses. This leads to a time-dependent emittance at the RFQ entrance due to neutralization effects. The neutralization time of a space-charge dominated 30–50 mA proton beam in the Gabor lens is <1 μs. A non-neutral electron plasma is contained in the Gabor lens by a 200 G solenoid magnet. The equivalent thin lens focal length of a Gabor lens operated at Fermilab has been determined to be 10 cm. This focusing strength is adequate for matching a proton beam into an RFQ.