Andre, C.

Boutachkov, P.

Hoffmann, T.

Reiter, A.

GSI Repository

Bench tests of PMTs and voltage dividers for counting applications at FAIRP. Boutachkov, C. Andre, A. Reiter, and T. HoffmannGSI, Darmstadt, GermanyThis contribution presents selected results from tests ofPhotomultipliers (PMT) and active voltage dividers (AVD)with a laser diode.At FAIR, plastic scintillator counters will be used forbeam intensity and beam loss measurements [1]. Further-more, the Photonis company phased out the production ofthe XP2972 PMT, which is presently used in the beam diag-nostic counters at GSI [2,3]. Commercially available PMTsfrom Hamamatsu and ET Enterprises were selected, basedon photo-cathode area, gain, signal rise time and transittime spread. The gain variation and the maximum count-ing rate were determined for combinations of the selectedPMTs and AVDs at various luminances. These parametersdetermine the scintillator thickness necessary for detectionof an ion accelerated by SIS18/100, and the instantaneousbeam intensity which can be measured by the counters.Measurements and ResultsMeasurements were performed with the HamamatsuR6427, ET Enterprises 9442B and Photonis XP2972PMTs. They were biased by a Hamamatsu-H7415MOD,ET Enterprises E220BFN2-01 and an in-house developedactive voltage divider.The PMTs and AVDs were tested with a fast switchedlaser diode by PicoQuant (FSL500 with a LDH-S-C-405laser head). This light source emits at wavelength of405 nm, matching the 420 nm wavelength of maximumemission for a BC400 plastic scintillator.The full active area of the tested PMTs was illuminatedby light pulses of a fixed duration, of approximately 3 ns.Their intensity was varied by changing the FSL500 powersetting and by neutral glass filters. The laser was triggeredby a white noise generator. The trigger frequency was mea-sured by a rate meter, while the PMT minimum anode am-plitude and average anode charge were determined by a50 Ohm terminated broadband oscilloscope.The tested PMTs were illuminated by the same light in-tensity at different repetition rates. For each series of mea-surements the AVDs high voltages were adjusted in order toobserve signals with similar amplitude at 10-100 Hz triggerrate. Data from three measurements are shown in Fig. 1.Before reaching the maximum counting rate for a givenPMT-AVD combination the signal amplitude increases, dueto the higher voltage drop between the last dynodes.In the GSI AVD the last 6 dynode voltages are stabilized.The stabilization is done by a voltage follower based onthe BSS125 SIPMOS transistor. In comparison, the Hama-matsu divider has 3 stabilized dynodes, while in the ET En-terprises divider all dynodes are stabilized. The measure-ments showed that the ET Enterprises and the GSI AVDscan withstand counting rates above 10 MHz. Further in-beam tests [4] favored the GSI-AVD, due to better perfor-mance at higher counting rates.Measurements with different neutral glass filters showedmore than 10 times larger gain variation for the HamamatsuR6427 PMT, compared to the ET 9442B and XP2972PMTs. Based on the tests described in this contributionand in Ref. [4], one can conclude that the optimum PMT-AVD combination for the future counters at FAIR and GSIis a Hamamatsu R6427 PMT powered by the GSI AVD.Figure 1: The solid curves follow the evolution of the sig-nal amplitude of different PMT-AVD combinations as afunction of the trigger rate. Blue-squares: Plots for theHamamatsu R6427 PMT powered by GSI AVD. Orange-diamonds: ET 9442B PMT powered by E220BFN2-01. Green-circles: Hamamatsu R6427 PMT powered byHamamatsu AVD.References[1] FAIR Technical Design Report (TDR) – High Energy BeamTransport, GSI, December 2008[2] P. Forck, T. Hoffmann, DIPAC01, Grenoble, p. 129 (2001)[3] T. Hoffmann, D. A. Liakin, P. Forck, Proc. 10th Beam Instru-mentation Workshop, Upton, New York, p. 329 (2002)[4] P. Boutachkov, et al., “In-beam Tests of PMTs and VoltageDividers for Particle Detectors at FAIR”, GSI Scientific Rep.(2014)GSI SCIENTIFIC REPORT 2014 FG-GENERAL-47DOI:10.15120/GR-2015-1-FG-GENERAL-47 465

Bench tests of PMTs and voltage dividers for counting applications at FAIR

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Bench tests of PMTs and voltage dividers for counting applications at FAIR

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