Beam Loss and Beam Profile Monitoring with Optical Fibers

Beam losses and beam profiles at particle accelerators are determined by measuring the ionizing radiation outside the vacuum chamber. Four different radiation sensor systems using optical fiber will be presented. Two are based on the increase of radiation induced attenuation of Ge P doped multimode graded index fibers, whereas the other two systems detect the Cerenkov light generated by relativistic electrons penetrating radiation hard fibers. The used fiber is an undoped multimode step index fiber with 300 mm core diameter. Dosimetry at high dose levels uses the radiation induced Bragg wavelength shift of Fiber Bragg Gratings. The selection of a suitable fiber for the individual application is an important requirement and depends on the type, doping, used wavelength and annealing behavior. In addition, the dose range, dose rate and temperature must be considered. After an extensive selection procedure, two types of fibers for the particular application were chosen. One is used as a dosimetry sensor for the slow local and distributed beam loss position monitor BLPM and the other for fast beam loss monitor BLM as well as beam profile monitors BPM . At six accelerators, all systems are used for in situ particle loss control by measuring the ionization dose and or Cerenkov light. These monitors provide a technique to improve the beam performance. This paper summarizes the basics of these measurement technologies and the experience at linear accelerators and at storage ring