Twofold Pulsing of Van de Graaff Beams for Time-of-Flight Measurements

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Abstract
A system has been developed which combines pre‐ and post‐acceleration pulsing of the beam from a Van de Graaff accelerator. It has the advantages of low belt charge for a given target current, low background at the detector, and high time resolution. The internal pulser operates at a frequency of 5 Mc and produces bursts 5–10 mμsec long. The external pulser is driven sinusoidally by amplifying the pulses from a pickup loop with a tuned 5‐Mc amplifier containing a phase shifter. Synchronization can be accomplished with peak beam currents at the pickup loop as small as 10 μa. The sinusoidal signal at the external pulser is used as the timing reference signal to a Los Alamos time‐to‐pulse height converter. The burst duration at the target is determined by the amplitude of the sweep voltage applied to the external pulser.