The Beam Loss Monitor

Beam Loss is the phenomena that a part of beam is lost when the beam hits various components on the beam line such as the beam duct, and magnet pole. When large unexpected loss of beam occurs on the beam line, the accelerator must be stopped immediately in order to prevent the equipments on the beam line from critical radiation damage. Especially, unexpected loss of the high power beam of 750 kW must be minimized in the J-PARC facility. Thus, beam loss monitors (BLMs) will be installed along the beam line, whose length could be a few hundred meter.

Currently, ionization chamber is considered as a preferable detector to monitor the beam loss. Especially, air-filled ionization chamber is suitable in the viewpoint of low cost and easy maintenance (no gas circulating system !). The following figure shows the first prototype of air-filled ionization chamber made of alluminum pipe with the coaxial structure. A SHV connector for high voltage and a BNC connector for signal readout are connected on each end. We are currently testing two prototypes of the BLM installed in the target station and the slope section of the neutrino beamline at KEK-PS.