Performance of electrostatically-focussed image intensifier tubes in low magnetic fields

97-026 The particle identification system proposed for the LHC­B experiment is based on RICH counters with three different radiator materials and hybrid photon detectors (HPDs) as a possible readout. Within this framework, one approach to HPD design is based on standard image intensifier geometries with electrostatic cross­focussing. In order to study how these geometries are sensitive to the expected stray field of the LHC­B dipole magnet, tests have been carried out with a standard 18:7 mm image intensifier tube exposed to low magnetic fields. The use of thin mu­metal cylindrical foils for magnetic shielding was also investigated.