Measurement Facility for New Acceleration Techniques

Interest in developing new, high gradient acceleration techniques is growing rapidly.1,2 Experimental investigation of new concepts, however, lags noticeably behind the ideas. To a large extent this situation arises simply because the very specialized beams and diagnostics required to make the necessary measurements are not available. A facility is being constructed at ANL which will permit the direct measurement of wake fields for a variety of experimental conditions. A single, short bunch of 22 MeV electrons from an existing linac is manipulated to form two separate pulses which can be set to specified time and space separations. Normally, the leading pulse will be an intense, full energy pulse of a few times 1010 electrons less than 10 psec in length. The trailing "witness" pulse will be at roughly 3/4 the energy of the leading pulse, will contain fewer electrons, and will have the same pulse length as the leading "driver" pulse. Energy gain/loss and deflections of each pulse will be measured after the bunch doublet has passed through the wake structure under test. Design specifications and project status are presented. The facility will provide a continuous 800 Hz sequence of two beams with adjustable intensity, pulse shape, and separation between pulses. Pulse widths can be selected from 100 picoseconds down to 6 picoseconds, and pulse separation from 0 to over 2000 picoseconds. A well-instrumented spectrometer situated downstream of the test section will permit accurate analysis of beam energies and trajectories.