An integrating radiation monitor for intense beams

For the purposes of protecting downstream equipment in accelerator beam lines, radiation interlock systems generally trip when the particle flux reaches a certain level. In extracted beams, a spike in intensity will often cause a trip, even though the number of delivered particles at the time of the trip is below a desired level. This trip occurs because radiation monitors respond to flux, that is, they develop an output proportional to mR/hr (or R/hr). The addition of an integrating circuit to a commercially available radiation monitor permits it to interlock intense beams at a preset number of particles, rather than at a preset rate. The integrator works by inverting the transfer function of the radiation monitor/scintillator combination. The integration technique effectively prevents intensity spikes in the spill from causing beam trips, yet it properly limits the downstream exposure to some given level. We describe the circuit in detail, and give some data on calibration and testing in the Alternating Gradient Synchrotron