1. page 1 www.photek.co.uk 1 The TORCH PMT: A close packing, multi-anode, long life MCP-PMT for Cherenkov applications James Milnes International Conference on New Photo-detectors, Moscow 7 July 2015

2. www.photek.co.uk 2 Photek MCP-PMTs Photek currently manufacture the fastest PMTs in the world in “analogue mode”: –Whole pulse is captured by an oscilloscope or digitiser –Applications often “single-shot, high intensity”, e.g. Fusion Research –We have several detectors on the diagnostics at the National Ignition Facility –Fast pulse response ~ 100 ps FWHM –Fast Gating Transition ~ 2 ns International Conference on New Photo-detectors, Moscow 7 July 2015

3. www.photek.co.uk 3 Photek MCP-PMTs MCP-PMTs are also the leading detector for time-resolved photon counting Jitter in photon arrival measurements ~ 30 ps FWHM –Significantly better for multi-photon events Excellent fit for Cherenkov-based particle detection Drawbacks: –Detector Lifetime –Most models are round, single anode and not close-packing International Conference on New Photo-detectors, Moscow 7 July 2015

4. www.photek.co.uk 4 The TORCH PMT In November 2012 Photek started the 3-year development of the TORCH (Timing Of internally Reflected CHerenkov photons) PMT A collaboration with CERN and the Universities of Oxford and Bristol for the LHCb upgrade Technical aims: –A lifetime of 5 C/cm 2 of accumulated anode charge or better –A multi-anode readout of 8 x 128 pixels Fine pitch resolution target 0.41 mm –Close packing on two apposing sides with a fill factor of 88% or better 53 mm working width within a 60 mm envelope International Conference on New Photo-detectors, Moscow 7 July 2015

5. www.photek.co.uk 5 TORCH - Motivation TORCH is an ERC funded R&D project Proposal to upgrade LHCb Particle ID capabilities in 2-10 GeV/c region International Conference on New Photo-detectors, Moscow 7 July 2015

6. www.photek.co.uk 6 The TORCH PMT Three main aims: 1.Lifetime 2.High granularity multi-anode 3.Square International Conference on New Photo-detectors, Moscow 7 July 2015

7. www.photek.co.uk 7 1. MCP-PMT Lifetime Standard MCP detectors suffer from sensitivity loss after prolonged exposure: –An MCP has a very large surface area –Prolonged electron bombardment of this surface releases material that is ionised –These ions are drawn back to the photocathode and reduce sensitivity Previous solutions have involved barrier films to prevent the ions reaching the photocathode –Limited success –Lowers MCP efficiency and overall sensitivity International Conference on New Photo-detectors, Moscow 7 July 2015

8. www.photek.co.uk 8 1. MCP-PMT Lifetime Recent technology of ALD (Atomic Layer Deposition) coating on MCP has significantly reduced out-gassing Two PMT samples produced in 2011: Double-MCP 10 mm diameter working area –One with coated MCPs, One control with standard MCPs Independently verified by Photek and others: Britting et al (PhotoDet 2012), Conneely et al (VCI 2013) International Conference on New Photo-detectors, Moscow 7 July 2015

9. www.photek.co.uk 9 1. MCP-PMT Lifetime ALD coating results in no detectable sensitivity loss after > 5 C/cm 2 Some gain reduction 6 test devices produced, 2 successfully life tested at Photek, 1 currently being tested at CERN International Conference on New Photo-detectors, Moscow 7 July 2015

10. www.photek.co.uk 10 1. MCP-PMT Lifetime ALD also gives major gain enhancement International Conference on New Photo-detectors, Moscow 7 July 2015

11. www.photek.co.uk 11 1. MCP-PMT Lifetime In other respects, coated MCPs behave as normal Jitter measurement made with 40 ps laser source International Conference on New Photo-detectors, Moscow 7 July 2015

12. www.photek.co.uk 12 Photek have licensed Arradiance ALD technology for in-house coating of MCP substrates We have started a KTP project in collaboration with the University of Liverpool ALD research group –Embed ALD process knowledge in Photek –Optimise process to improve MCP collection efficiency 1. MCP-PMT Lifetime International Conference on New Photo-detectors, Moscow 7 July 2015

13. www.photek.co.uk 13 2. High granularity multi-anode Traditional multi-anode manufacturing uses multiple pins brazed through a solid ceramic Prone to leaking, also unrealistic for a 128 x 8 array! Our aim is to use multilayer ceramic with filled vias Much smaller pad size allows for finer pitch The pads on this design are 0.75 mm wide on a 0.88 mm pitch Target resolution is 0.41 mm Vacuum side Air side International Conference on New Photo-detectors, Moscow 7 July 2015

14. www.photek.co.uk 14 2. High granularity multi-anode How do we obtain position resolution beyond the pitch of the pads? –Deliberately spread the charge footprint –Charge is shared over multiple pads –Charge is measured on each pad –Simple algorithm calculates the interpolated position Cannot share over too many pads without compromising the occupancy level –Important in a tube designed for high count rates International Conference on New Photo-detectors, Moscow 7 July 2015

15. www.photek.co.uk 15 Resistive layer collects the charge VACUUM SIDEAIR SIDE 2. High granularity multi-anode International Conference on New Photo-detectors, Moscow 7 July 2015 Charge cloud from MCP Image Charge technique is recognised way of spreading charge footprint However, charge would spread too much through 2 mm of ceramic Solution is to have buried pads: –UK Patent 1510859.0 By A.C. coupling the signal, the input window can be at 0 V The signal is A.C. coupled onto buried pads Thin insulator between resistive layer and pads

16. www.photek.co.uk 16 Seven 32×32 multi-anode prototypes built with charge sharing anode –In one direction 8 pads ganged together to create 32×8 layout (1/4 of square tube’s active area) –With charge sharing improve resolution to 64×8 pixel equivalent (or better) –Use Anisotropic Conductive film to connector detector output to readout PCB International Conference on New Photo-detectors, Moscow 7 July 2015 2. High granularity multi-anode

17. www.photek.co.uk 17 Test performed on University of Bristol laser scanning setup >15 µm laser spot size Use a 5 GHz, 40 GS/sec scope to sample output for four channels Digitised pulse integrated to measure charge per pad 17 Vertical motion stage Horizontal motion stage Pulsed 405nm laser MCP-PMT Readout International Conference on New Photo-detectors, Moscow 7 July 2015 2. High granularity multi-anode

18. www.photek.co.uk 18 International Conference on New Photo-detectors, Moscow 7 July 2015 2. High granularity multi-anode Charge footprint spread measured on oscilloscope FWHM ~ 1.7 mm Slightly larger than predicted –Modified prototype currently in production

19. www.photek.co.uk 19 2. High granularity multi-anode International Conference on New Photo-detectors, Moscow 7 July 2015 Applying imaging algorithm on event by event basis, with laser aligned in centre of 4 pixels 0.225 mm FWHM derived from pads on a 0.83 mm pitch Need to measure with NINO

20. www.photek.co.uk 20 2. High granularity multi-anode Contact made to anodes by Anisotropic Conductive Film (ACF) – Mechanically applied ACF used in circular prototypes –Thermally applied ACF aimed be used in square version –Promising early results with thermal application Detector ACF PCB x y z ACF is insulating in x and y but conducting in z International Conference on New Photo-detectors, Moscow 7 July 2015

21. www.photek.co.uk 21 2. High granularity multi-anode - readout NINO ASIC 32 channel differential amplifier /discriminator developed at CERN 10 ps RMS jitter on the leading edge >>10 MHz maximum rate The time-over-threshold technique uses the discriminator output pulse width to determine the event charge High Performance Time-to-Digital Convertor (HPTDC) A programmable TDC developed for ALICE time-of-flight RPCs at the LHC Two modes of 100 ps LSB resolution with 32 channels, or 24.4 ps LSB resolution with 8 channels Default maximum rate is 2.5 MHz per channel, can be increased beyond 10 MHz using higher logic clock International Conference on New Photo-detectors, Moscow 7 July 2015

22. www.photek.co.uk 22 3. Square Tube Development Square tube manufacturing was new to Photek So far, we have successfully developed methods of –Square body brazing –Square MCP locating –Square photocathode sealing –Square anode sealing Current status: –Producing leak-tight square test cells International Conference on New Photo-detectors, Moscow 7 July 2015

23. www.photek.co.uk 23 Summary TORCH PMT in development at Photek 3 year development aims to finish in November 2015 1 st year task complete: To produce long-life demonstrators 2 nd year task complete: To produce high-granularity multi-anode demonstrator Final year task: Fully functioning detector International Conference on New Photo-detectors, Moscow 7 July 2015

24. www.photek.co.uk 24 With thanks to… The members of the TORCH collaboration at the University of Bristol, CERN and the University of Oxford The TORCH project is funded by an ERC Advanced Grant under the Seventh Framework Programme (FP7), code ERC-2011-ADG proposal 299175. International Conference on New Photo-detectors, Moscow 7 July 2015

25. www.photek.co.uk 25 Thank you for listening International Conference on New Photo-detectors, Moscow 7 July 2015