Beam in gap measurements at the SNS front-end

The pulsed beam in the SNS accelerator has a fine time structure which consists of 695 ns long mini-pulses separated by 250 ns gaps in order to minimize transient beam losses in the accumulator ring which could arise during the ring extraction kicker rise time. This time structure is provided by a two stage Front End chopping system which must reduce the beam current in the gap to a level of 10^-4 of the nominal current in order to satisfy requirements on the ring extraction losses. A Beam-in-Gap measuring system based on H^- stripping using Nd-YAG laser was developed and tested during the SNS Front-End commissioning period. This paper describes the Beam-in-Gap measurement system design and measured performance.