Detector Technologies for WSO

1. Detector Technologiesfor WSO Jon Lapington Space Research Centre University of Leicester WSO Detector Workshop, Leicester

2. Outline Choice of detector: MCPs or CCDs? MCP detectors Photocathodes Microchannel plates Image readout devices The Vernier Anode Image Charge technique Readout developments WSO Detector Workshop, Leicester

3. CCD Option Detectors of choice in optical and X-ray applications High QE’s 80%+ achievable High performance down to 200nm e.g. WFC3 QE: 60% @ 250nm read noise: 3 e- Dark current: 1 e-/hr @ -80°C WSO Detector Workshop, Leicester

4. CCDs – a possibility? Cons Low QE 100-200nm Not photon counting Dark noise limits SNR Cooling Long integrations Accurate pointing Format limitations Radiation damage Pros • Ubiquitous • Monolithic • No HV required • Fixed pixel imaging • High Spatial resolution • High local/global count rate WSO Detector Workshop, Leicester

5. CCD Quantum Efficiency WFC-3 E2v CCD GOES E2V CCD64 device EVE - SDO WSO Detector Workshop, Leicester

6. MCPs –preferred Cons HV required Vacuum/hermetically sealed pre-launch Contamination sensitive Ageing – gain depression Over-bright shutdown Local count rate limitation Pros • True photon counting • Flexible format • Mature technology • High spatial resolution • High temporal resolution • QE 30 - 40% for LSS λ • Low background • No cooling • Radiation hard WSO Detector Workshop, Leicester

7. MCP detector overview Detection Bare MCP: ions, electrons & neutrons Photocathode: photons Window: 1200 to 120 nm Windowless: 200 nm to 10 keV Amplification 1/2/3 MCP stack Gain: up to 108 e- MCP pore ø: down to 2µm Pulse risetime: down to ~80 ps Image readout Electronic: Resistive anode Wedge and strip, TWA, Vernier anode CODACON, MAMA Delay line Parallel strip readout (cross strip, etc.) Hybrid: electronic EBCCD, MediPix2, Timepix Hybrid: optical Intensified CCD, CID, APS Microchannel Plate Cross-section Conductive coating Incident electron - HV + e- PHOTOCATHODE Output Electrons 104-108 e- WSO Detector Workshop, Leicester

8. Photocathodes Event detection via photoelectron released from a photocathode Windowed - above 120 nm Semi-transparent photocathode Alkali halide, bi-alkali, multi-alkali S20, GaAs (NEA) QE – up to 25-30 % Windowless - below 250 nm opaque photocathode deposited directly on MCP CsI, KBr, CsTe, (GaN), (Diamond) etc Alkali halides up to 50% in XUV GaN – 71 % reported Response up to 10 keV Poor energy resolution in X-rays WSO Detector Workshop, Leicester

9. FUV photocathodes • All window cut off below 120 nm • Windowless detector necessary • Typically 15000Å CsI, KBr deposited on MCP • Hermetic/vacuum enclosure pre-launch • Mechanical, on –orbit, one-shot door • Web photoelectrons - resolution/QE trade-off • Optimal QE not always achieved historically • MCP manufacturing variability WSO Detector Workshop, Leicester

10. MCP characteristics Spatial resolution Fundamentally limited by MCP pore geometry Pore diameters ≥ 2 µm LSS format: 6µm pore Ø Count rate Global rate limited by MCP strip current Point source rate < 1000 ct s-1 • Gain • Typically 1-5 pC for high resolution electronic readouts • Format • Chevron or Z stack • Double or triple thickness • Noise • Low noise <0.1 cm-2 s-1 • Lifetime • Gain plateau • 0.1C cm-2 to 1C cm-2 ≡ 1012ct cm-2 WSO Detector Workshop, Leicester

11. Advantages of MCPs for LSS Curved focal plane detector Slumped manufacture Ground and etched Large, flexible format Proven technology QE of 40%+ possible at FUV Curved image readouts possible WSO Detector Workshop, Leicester

12. Image readout design • Performance conflicts • Higher resolution requires higher gain • Higher count rate requires lower gain • Extended lifetime requires lower gain • Conflict resolution • Develop high resolution readouts requiring lower gain • Design choices • Improve existing readout techniques • Maximise dynamic range (WSA ► TWA) • Utilize dynamic range more efficiently (Vernier anode) • Increase electrode/channel number • Potential conflict with mass/vol./pwr resources • Resolve by use of miniaturization - multichannel ASICs WSO Detector Workshop, Leicester

13. Readout comparison WSO Detector Workshop, Leicester

14. Vernier Anodegeometric charge division Geometric charge division using 9 electrodes 3 groups of 3 sinusoidal electrodes 3 cyclic phase coordinates Cyclically varying electrodes allow Determination of a coarse position using a Vernier type technique Spatial resolution greater than charge measurement accuracy The full unique range of the pattern can be utilized JPEX: 3000 x 3000 FWHM pixel format Easy to reformat – e.g. 6000 x 1500, etc. Up to 200 kHz max. global count rate WSO Detector Workshop, Leicester

15. J-PEX MCP Detector WSO Detector Workshop, Leicester

16. J-PEX Detector Performance WSO Detector Workshop, Leicester

17. Imaging spectral lines Line width = s Line profile – top hat Assuming MCP pore delta response FWHM = s Extent = s + pore ø Convolve with noise gaussians: Centroid error from pore Readout noise Line width = s FWHM = s Extent = s + ø WSO Detector Workshop, Leicester

18. Image Charge Technique Pros Stable charge distribution No secondary e- effects No partition noise Readout Mechanically separate Electrically isolated <<100% electrode area ►Low capacitance Cons Infinite charge distribution WSO Detector Workshop, Leicester

19. Tetra Wedge Anode PCB Layer 1 PCB Layer 2 Y axis X axis WSO Detector Workshop, Leicester

20. Multilayer PCB TWA WSO Detector Workshop, Leicester

21. Image Charge Performance Position error Central 23 x 36: X - 13.2 µm rms Y - 12.4 µm rms WSO Detector Workshop, Leicester

22. Image Charge Optimizations • Image Charge uses capacitive coupling • No direct charge collection • Electrode area can be << 100% • Low inter-electrode capacitance • Beneficial for MCP gain/rate/lifetime trade-off • Vernier redesigned as 3 sets of parallel strips • Readout constructed as 3 layer flexi PCB • Improved peformance due to lowered capacitance • Can be simply curved to match curved focal plane/MCPs WSO Detector Workshop, Leicester

23. TWA detectorfor a UV spectrometer Detector Conservative performance requirements Low risk MCP detector One design for all spectrographs KBr and CsI photocathodes Redesigned Wedge and Strip (TWA) Readout using Image Charge technique Compact, low mass design 40 μm FWHM resolution Maximum event rate 10,000 ct/s Electronics One electronics board per spectrograph Hybrid analog electronics Digital processing using FPGA No processor or software Radiation hardened to suit HEO Standard control and data i/f Engineering unit already built WSO Detector Workshop, Leicester

24. Charge division readout limitations Requires accurate charge measurement longer shaping times for adequate SNR high MCP gain required ≥ 107 electrons High gain MCP suffers from: Lower local and global count rate Shorter lifetime Higher power requirements Serial event processing Readout electrodes have global scope Detector is paralysed while each event is processed WSO Detector Workshop, Leicester

25. Prototype detector for life science applications Window Photon Photocathode Photoelectron MCP stack MCP electron gain Resistive anode Charge localization Current induced on readout electrode Electrode array ASIC preamp and discriminator timesphoton event Readout electronics: PCB with ASIC electronics underside WSO Detector Workshop, Leicester LVDS logic out TDC + FPGA processing

26. The end goal is a 32 x 32 array, effectively 1024 PMTs WSO Detector Workshop, Leicester

27. NINO ASIC (CERN) WSO Detector Workshop, Leicester

28. 2D Parallel Strip Readout (Lapington - Leicester) 2D parallel strip readout – 128 electrodes 200 µm pitch (25mm x 25mm, scaleable) Charge spread over 3 strips per axis Capacitively coupled signal via Image Charge – Stable charge distribution, no degradations due to secondary electrons, no feed-throughs Threefold charge comparison  “fixed ”100 µm pixel Discriminator timing (amplitude walk)  sub-pixel centroiding (MCP limited resolution) Excellent counting statistics - comparison does not allow multiple event counting No explicit charge measurement, no ADCs required Matched to fast (6 ns dead-time) multi-channel preamp/discriminator ASIC (developed at CERN) X axis 25 mm Charge footprint Y axis 25 mm 128 sense strips at 200 μm pitch NINO ASICs NINO ASICs WSO Detector Workshop, Leicester