Performance of fine mesh photomultiplier tubes in magnetic fields up to 0.3 T

We have studied the performance of fine mesh photomultiplier tubes (R2490-05, R2021, H5756, R3423-01) in magnetic fields up to 0.3 T. The tube gain and the average number of photoelectrons have been measured as a function of the magnetic field, of the angle between the field direction and the phototube axis, and of the rotation of the phototube around its axis. The reduction of the photocathode effective area in a magnetic field has also been measured.