Britting, A.

Eyrich, W.

Lehmann, A.

Uhlig, F.

GSI Repository

Lifetime of ALD-coated microchannel plate PMTs∗F. Uhlig1, A. Britting1, W. Eyrich1, A. Lehmann† 1, and PANDA Cherenkov subgroup1Physikalisches Institut IV, Universita¨t Erlangen-Nu¨rnberg, Erwin-Rommel-Str. 1, D-91058 ErlangenMicrochannel-plate photomultipliers (MCP-PMTs) arethe preferred photon sensors for the PANDA DIRC detec-tors for hadron identification. They reach a sub 50 ps timeresolution and can be used for single photon detection inmagnetic fields up to 2 Tesla [1]. MCP-PMTs are availableas multi-anode devices with a good gain uniformity and amoderate cross talk among the anodes [2]. The main draw-back until recently was a serious aging problem caused byfeedback ions from the rest gas hitting and damaging thephoto cathode (PC). This results in a fast diminishing quan-tum efficiency (QE) while the integrated anode charge in-creases [3].Approaches such as higher tube vacuum, electron scrub-bing of the MCP surfaces, protection films or modified PCswere tested by the manufacturers to increase the lifetimeof MCP-PMTs. The breakthough against the aging issuefinally came with the application of an atomic layer de-position (ALD) technique: in a sophisticated procedurethe MCPs are coated with an ultra-thin layer of usuallyAl2O3 or MgO which significantly reduces the desorptionof atoms from the MCP material. In 2011 PHOTONIS wasthe first manufacturer to supply us with a prototype of anALD-coated MCP-PMT (9001223) to measure its lifetime.In Fig. 1 the results of a comparative measurement ofseveral types of MCP-PMTs are shown which is ongoingsince 2011. By a simultaneous illumination within an en-vironment similar to PANDA conditions the systematic un-certainties are minimized and a fair comparison of the dif-ferent tubes is possible. For monitoring purposes the pulseheights are continuously recorded at a highly prescaled rateduring the illumination. Spectral and spacial QE scans areperformed every few days/weeks or months, respectively.From the plots it is obvious that the lifetime of the recentMCP-PMT models has tremendously increased in compar-ison to former tubes (open dots at the left side of the figure).In the ALD-coated PHOTONIS MCP-PMT (9001223)the degradation of the QE starts after 6 C/cm2. This is seenin Fig. 1 and in the QE chart of the whole PC surface in Fig.2 (upper right), where the left half shows a significantlyreduced QE. No sign of aging is observed yet at 5 C/cm2 inanother MCP-PMT (9001332) with the same specifications[4]. In both tubes the right half of the PC is not illuminated.In our comparative aging measurement (see Fig. 1) wehave meanwhile identified three MCP-PMTs (PHOTONISXP85112 9001223 and 9001332; Hamamatsu R10754X-07-M16M KT0001) which fulfill the PANDA requirement∗Work supported by GSI (contracts EREYRI1416 and ERANTO1419)and BMBF† Albert.Lehmann@physik.uni-erlangen.de]2integrated anode charge  [mC/cm0 1000 2000 3000 4000 5000 6000 7000 8000 9000quantum efficiency  [%]0510152025PANDA Barrel-DIRC time  [a]0 2 4 6 8 10 12 14 16 18BINP 82 BINP 1359 BINP 3548PHOTONIS XP85012 (9000296) PHOT. XP85112/A1 (9000897) PHOT. XP85112/A1-BSRD (9001394)PHOT. XP85112/A1-HGL (9001223) PHOT. XP85112/A1-D (9001332) PHOT. XP85112/A1-URD (9001393)Ham. R10754X-01-M16 (JT0117) Ham. R10754X-07-M16M (KT0001) Ham. R10754X-07-M16M (KT0002)Lifetime of various MCP-PMTs (400nm)                                             ALDnew PCno countermeasuresfilmFigure 1: QE at 400 nm for old (open) and recent, lifetime-enhanced (solid dots) MCP-PMTs versus the anode charge.x [mm]-20 -10 0 10 20y [mm]-20-10010201214161820222422915 mC/cmx [mm]-20 -10 0 10 20y [mm]-20-10010201214161820222424948 mC/cmx [mm]-20 -10 0 10 20y [mm]-20-100102010121416182025135 mC/cmx [mm]-20 -10 0 10 20y [mm]-20-100102010121416182027852 mC/cmFigure 2: QE at 372 nm as a function of the PC surfacefor two XP85112 MCP-PMTs: 9001223 [upper row] and9001332 [lower row]. In both tubes the right half (x > 0)of the PC was covered during the whole illumination.of an integrated anode charge of >5 C/cm2 without a sig-nificant QE degradation. This is an important result be-cause it implies that after several years of investigations wehave finally found photon sensors that survive the high rateenvironment at the DIRC focal planes for at least 10 years.References[1] A. Lehmann et al., Nucl. Instr. and Meth. A 595 (2008) 173[2] A. Lehmann et al., Nucl. Instr. and Meth. A 639 (2011) 144[3] A. Lehmann et al., GSI Scientific Report 2010, p. 106[4] F. Uhlig et al., doi:10.1016/j.nima.2014.11.046MU-HADRONS-05 GSI SCIENTIFIC REPORT 2014112 DOI:10.15120/GR-2015-1-MU-HADRONS-05

Lifetime of ALD-coated microchannel plate PMTs

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Lifetime of ALD-coated microchannel plate PMTs

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