Fine-mesh photodetectors for CMS endcap electromagnetic calorimeter

Abstract

The behaviour of fine-mesh vacuum phototetrodes and phototriodes (VPTs) in an axial magnetic field of (0 ÷ 4)T has been investigated. The measured VPT parameters are: fine-mesh cell dimensions, the photocathode sensitivity and its homogenity, the gain in zero and 4T magnetic field at tilt angles corresponding to the rapidity range of CMS ECAL Endcap 1.479 ÷ 3.0 and excess noise factor. Measurements have been performed on 21 and 30 mm diameter photodetectors with different fine-mesh structures: 30, 60 and 100 lines per mm under different types of photocathode illumination by green LED. Phototriodes with 30 or 60 lines per mm and an external diameter of 21 mm are found to be the best candidates for the CMS environment with the initial size of PWO crystals proposed to be used in the Endcap, by comparison with phototetrodes. They provide a gain of the order of 6 ÷ 8 in 4T magnetic field and an excess noise factor of 2 under full photocathode illumination.To be submitted to Nucl. Instr. and Meth.

Scintillation counters in modern high-energy physics experiments (Review)

“…The window is made of radiation hard ultraviolet glass, and the anode is a fine (10 μm) copper mesh (Fig. 44) [69]. They were developed and manufactured at the National Research Institute "Elektron" (St. Peters burg, Russia) and used in the CMS end cap ECAL.…”

Compact vacuum phototriodes for operation in strong magnetic field

“…Recently, the results of the RIE VPTs (diameter of 25 mm) tests in a magnetic field were presented in Ref. [11]. The output amplitude of the device making use of a fine mesh with 100 lines per mm decreases by about 40% at 4T and α = 0…”

“…In 1999 a new low cost VPT was developed for operation in strong magnetic field. In this paper the results of tests of the new devices in a magnetic fields up to 4.5 T are presented, and its performance compared with that of similar photodetectors described in [10,11].…”

Light-to-light readout system of the CMS electromagnetic calorimeter

“…The strong perpendicular magnetic field in the barrel precludes the use of vacuum detectors, whereas the high radiation levels in the very forward direction of the endcaps argue against solid state photodetectors. As a result, the ECAL will use large-area silicon avalanche photodiodes (APD) in the barrel [2] and vacuum phototriodes (VPT) in the endcaps [3]. Two APDs of 5 mm 5 mm area each are used per crystal, operating at a gain of 50.…”