AN ULTRAHIGH-VACUUM BEAM PROFILE MONITOR

Ordinary gas ionization profile monitors, in common use at high-energy accelerators, are not useful in low density gases. Modern accelerators usually have high quality vacuum systems that maintain pressures below 10(-8) Torr. We will describe a beam profile monitor that not only operates in the range of 10(-11) Torr, but is noninvasive. Shaped electric fields sweep beam-generated ions out of a collection area onto the input face of a detector. The detector uses a dual microchannel plate to generate a gain of approximately 10(7) electrons per ion. An ultraviolet lamp provides a signal for monitoring the eventual degradation of the microchannel plate. The complete device contains a horizontal detector, a vertical detector, and a set of electrodes to nullify first-order electrostatic effects on the particle beam. Recent results from the initial use of the profile monitor are quite promising and demonstrate a new range of operation for this type of beam diagnostic device.