Square and sine wave modulation of the beam from a 3 MeV Van de Graaff accelerator

Abstract

Methods of producing square and sine wave modulation of a 3 MeV Van de Graaff accelerator are described. Square pulses are produced at frequencies from 100kc/s to d.c. with up to a 100 per cent duty cycle and a minimum pulse length of 8 μs. The ratio of the off-current level to the on-current level is less than 5 x 10 -4 and can be further reduced by a post-acceleration deflection system to less than 10 -5. The unit, which is triggered from a command pulse external to the machine, is in the top terminal of the Van de Graaff and has shown itself to be highly reliable over some 1,000 hours of machine operation. The sine wave modulation unit described here operates in the range 80-1000 c/s with a modulation depth of up to 90 per cent and higher harmonic contamination of less than 1 per cent.