Cathode position response of large-area photomultipliers under a magnetic field

Abstract

With the increasingly common use of large area PMTs (photomultiplier tubes) for nuclear and particle physics experiments, information on the position dependent magnetic field effects across the PMT's photocathode is important to effectively analyze and understand data collected from PMTs. Using an automated twodimensional scanner, we have measured the PMT response to an external magnetic field as a function of the cathode position impinged by a collimated light source. This study shows a clear dependence on the cathode position in both collection efficiency and gain of the PMT in the presence of a magnetic field. In particular, a pronounced valley in the collection efficiency is observed for certain locations of the cathode when the magnetic field is transverse to the PMT axis. The pattern of the position dependence is presented for several different magnitudes and orientations of the magnetic field relative to the PMT.

Study of TTS for a 20-inch dynode PMT

“…Large diameter PMTs are sensitive to Earth's magnetic field. The performance of the PMT could be significantly worsened by the presence of magnetic field, because of divergent trajectories of photoelectrons from the photocathode to the first electrode and from there to the dynode chains and finally to the anode, which will cause a wide spread in transit time [5,11].…”

“…In this paper, we study TTS versus high voltage, light intensity, light spot size and different photocathode regions. Since the performance of PMTs, especially those with large area photocathodes, is sensitive to the magnetic field [5], the TTS in the presence of the Earth's magnetic field is also studied.…”

A model for the Global Quantum Efficiency for a TPB-based wavelength-shifting system used with photomultiplier tubes in liquid argon in MicroBooNE

“…The results of this study are shown in figure 3. The statistical contribution to the uncertainties is insignificant; the uncertainties displayed are purely systematic and arise from four sources: [1] corrections due to the changes in LED bias voltage (1% uncertainty); [2] corrections due to small gain shifts between different measurement periods (≈ 2% uncertainty); [3] corrections due to the measured fiber-to-fiber differences (≈ 10% uncertainty); and [4] uncertainty in transmission when changing from one fiber to the next (6.5% uncertainty). It is seen that the response varies by a factor of 3 over a distance of 13 cm in radius.…”

“…Based on measurements of the gain of large PMTs as a function of photocathode position [4,5], we do not expect a strong azimuthal angle dependence of the quantum efficiency arising from the PMT construction itself. In [4], a study of a nearly identical PMT (the Hamamatsu R5912), figure 4b suggests the azimuthal variation is not more than ±10% at a given radius from the center. Additionally, the magnetic shield removes the influence of the earth's magnetic field [6] which might have caused an azimuthal dependence in the efficiency.…”

Light-weight flexible magnetic shields for large-aperture photomultiplier tubes

“…We determined the response of a Hammamatsu R5912 PMT at each point of a grid on the photocathode by measuring the PE spectrum with a pulsing LED [8]. The orientation of the PMT is shown in Figure 17.…”