Development of a longitudinal density monitor for storage rings

We report on development of a new storage ring operations tool for measurement of longitudinal beam density profile. The technique mixes synchrotron light with light from a mode locked solid-state laser oscillator in a nonlinear crystal and detects the up-converted radiation with a photomultiplier. The laser is phase locked to the storage ring RF system. The laser choices available for repetition frequency, pulse length and phase modulation give a very wide range of options for matching the bunch configuration of particular storage rings. Progress in the technology of solid-state lasers ensures this system can be made robust for routine use in storage ring operations. A very large number of important applications are possible including measurement of the fraction of untrapped particles prior to acceleration, the population of particles in the nominally unfilled RF buckets in a bunch train ("ghost bunches"), longitudinal tails, the diffusion of particles into the beam abort gap and the normal bunch parameters of longitudinal shape and intensity. We are currently investigating application to two devices: (1) the 1.9 GeV ALS electron storage ring at LBNL with 328 RF buckets, 2 ns bucket spacing, 276 nominally filled bunches, 15-30 ps rms bunch length and (2) the 7 TeV LHC proton collider under construction at CERN with 35,640 RF buckets, 2.5 ns bucket spacing, 2,808 nominally filled bunches, 280-620 ps rms bunch length. A proof of principle experiment is being conducted on ALS. The results of the ALS experiment and detailed analyses of the application to LHC and its requirements are described.