3-5 December, 2007WSO Detector Workshop, Leicester Detector Technologies for WSO Jon Lapington Space Research Centre University of Leicester

3-5 December, 2007WSO Detector Workshop, Leicester2 Outline Choice of detector: MCPs or CCDs? MCP detectors Photocathodes Microchannel plates Image readout devices The Vernier Anode Image Charge technique Readout developments

3-5 December, 2007WSO Detector Workshop, Leicester3 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: 250nm –read noise: 3 e - –Dark current: 1 e - -80°C

3-5 December, 2007WSO Detector Workshop, Leicester CCDs – a possibility? Pros Ubiquitous Monolithic No HV required Fixed pixel imaging High Spatial resolution High local/global count rate Cons Low QE nm Not photon counting Dark noise limits SNR –Cooling –Long integrations –Accurate pointing Format limitations Radiation damage 4

3-5 December, 2007WSO Detector Workshop, Leicester CCD Quantum Efficiency 5 WFC-3 E2v CCD GOES E2V CCD64 device EVE - SDO

3-5 December, 2007WSO Detector Workshop, Leicester MCPs –preferred Pros True photon counting Flexible format Mature technology High spatial resolution High temporal resolution QE % for LSS λ Low background No cooling Radiation hard Cons HV required Vacuum/hermetically sealed pre-launch Contamination sensitive Ageing – gain depression Over-bright shutdown Local count rate limitation 6

3-5 December, 2007WSO Detector Workshop, Leicester7 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 10 8 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 PHOTOCATHODE e-e e -

3-5 December, 2007WSO Detector Workshop, Leicester8 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 % 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

3-5 December, 2007WSO Detector Workshop, Leicester 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 9

3-5 December, 2007WSO Detector Workshop, Leicester MCP characteristics 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 ≡ ct cm -2 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 10

3-5 December, 2007WSO Detector Workshop, Leicester11 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

3-5 December, 2007WSO Detector Workshop, Leicester 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 12

3-5 December, 2007WSO Detector Workshop, Leicester13 Readout comparison

3-5 December, 2007WSO Detector Workshop, Leicester14 Vernier Anode geometric 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 x 1500, etc. Up to 200 kHz max. global count rate

3-5 December, 2007WSO Detector Workshop, Leicester15 J-PEX MCP Detector

3-5 December, 2007WSO Detector Workshop, Leicester16 J-PEX Detector Performance

3-5 December, 2007WSO Detector Workshop, Leicester17 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 FWHM = s Extent = s + ø Line width = s

3-5 December, 2007WSO Detector Workshop, Leicester 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 18

3-5 December, 2007WSO Detector Workshop, Leicester19 Tetra Wedge Anode X axis Y axis PCB Layer 1 PCB Layer 2

3-5 December, 2007WSO Detector Workshop, Leicester20 Multilayer PCB TWA

3-5 December, 2007WSO Detector Workshop, Leicester21 Image Charge Performance Position error Central 23 x 36: X µm rms Y µm rms

3-5 December, 2007WSO Detector Workshop, Leicester 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 22

3-5 December, 2007WSO Detector Workshop, Leicester23 TWA detector for 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

3-5 December, 2007WSO Detector Workshop, Leicester Charge division readout limitations Requires accurate charge measurement –longer shaping times for adequate SNR –high MCP gain required ≥ 10 7 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 24

3-5 December, 2007WSO Detector Workshop, Leicester25 Prototype detector for life science applications Window Photocathode MCP stack Resistive anode Electrode array Readout electronics: PCB with ASIC electronics underside Photon Photoelectron MCP electron gain Charge localization Current induced on readout electrode ASIC preamp and discriminator times photon event LVDS logic outTDC + FPGA processing

3-5 December, 2007WSO Detector Workshop, Leicester26 The end goal is a 32 x 32 array, effectively 1024 PMTs

3-5 December, 2007WSO Detector Workshop, Leicester27 NINO ASIC (CERN) ParameterValue Peaking time1ns Signal range100fC-2pC Noise (with detector)< 5000 e- rms Front edge time jitter< 25ps rms Power consumption30 mW/ch Discriminator threshold10fC to 100fC Differential Input impedance 40Ω< Zin < 75Ω Output interfaceLVDS

3-5 December, 2007WSO Detector Workshop, Leicester28 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) Y axis 25 mm X axis 25 mm NINO ASICs Charge footprint 128 sense strips at 200 μm pitch NINO ASICs

3-5 December, 2007WSO Detector Workshop, Leicester29 Conclusions Detector choice –CCDs would require substantial development programme MCP detector technology is mature –High spatial resolution, large format UV detectors available –UK has specific relevant & unique expertise –ROSAT WFC/HRI, Chandra HRC/HRCS, JPEX, SOHO, XMM-OM, TAUVEX, etc.

3-5 December, 2007WSO Detector Workshop, Leicester Single pores picked out with a 14 micron wide slit mask - resolution is 10 microns FWHM

3-5 December, 2007WSO Detector Workshop, Leicester Uniform illumination of JPEX detector showing filter support mesh

3-5 December, 2007WSO Detector Workshop, Leicester 2-D Vernier Schematic Pitch 1 Pitch 2 Pitch 3 Line of constant phase - triplet A

3-5 December, 2007WSO Detector Workshop, Leicester Variation of the 3 phases with position Phase APhase BPhase C

3-5 December, 2007WSO Detector Workshop, Leicester X = A + B Generation of fine and coarse x, y Y = B + CA + C - X/16 - Y/4