A fast chopper for programmed population of the longitudinal phase space of the AGS

A fast beam chopper has been built that can produce an arbitrary pulse program of the 200-MeV H/sup -/ beam for synchronous injection into moving RF buckets in the Alternating Gradient Synchrotron (AGS). The chopper will eliminate RF capture losses and can be used to tailor the initial distribution in longitudinal phase space by varying the pulse parameters, width and phase, on a bunch-by-bunch time scale during multiturn injection. The chopper also serves as a studies tool, because it can provide controllable beam intensity with fixed longitudinal emittance (or conversely) and/or missing bunches. It is an electrostatic deflection device with 15 pairs of plates located above and below the 35-keV H/sup -/ beam between the ion source and the RFQ (radio-frequency quadrupole) preinjector. The plates are spaced 26-mm apart in the beam direction and connected as a slow-wave structure by coaxial cables. They are driven to +or-760 V by DC-coupled pulse generators. Beam current rise and fall times are less than 10 ns.<
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