Square and Sine Wave Modulation of the Beam from a 3 MV Van de Graaff Accelerator

Abstract

Methods of producing square and sine wave beam modulation of a 3 MV Van de Graaff accelerator are described. Square pulses are produced at frequencies from 100 kc to zero with up to a 100% duty cycle and a minimum pulse length of 8 μsec. The ratio of the off-current level to the on-current level is less than 5×10−4 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 1000 h of machine operation. The sine wave modulation unit described here operates in the range 80–1000 cps with a modulation depth of up to 90% and higher harmonic contamination of less than 1%.