WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga UV detectors in Space John Vallerga Space Sciences Laboratory University of California, Berkeley

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga 200+ Detector Years in Orbit! Mission# of DetectorsYears EUVE78.3 ALEXIS612 SUMER (SOHO)24 UVCS (SOHO) FUSE27.9 IMAGE25.7 ALICE (Rosetta)13.7+ GALEX24.7+ ALICE (New Horizons to Pluto)11.8+ COS (Hubble)10 (Aug 08) + still operating

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Anode Types (at SSL) Cross Delayline (XDL) Cross Strip (XS) Medipix ASIC Intensified CCD

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Design/Performance Flexibility Input apertureWindow/door PhotocathodeKBr - CsI - CsTe - GaN (QE, bandpass)(xray to optical) MCPsd 7cm, (format, resolution) pore spacing > 3µm AnodeDelayline (4 amps) (resolution, gain, rate) Cross Strip (128 amps) Medipix ASIC (65k amps)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Case study of two UV spectrometer detectors Cosmic Origins Spectrograph “Hubble class” instrument Large, reliable, stable, well calibrated and tested. Extreme QA ALICE on New Horizons Pluto mission Low power, mass, telemetry “Moderate” resolution, calibration, testing, QA

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Case study of two UV spectrometer detectors (cont.) ParameterCOSALICE Size (mm)178 x 1038 x 20 Format (pxls)32768 x x 32 Resolution (µm)2580 Mass (kg) Power (W)371.1 Cost$$$$$$$$$$$ Both have: curved MCPs, vacuum doors, CsI photocathodes, 20 kHz ct rates (10% deadtime)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS resolution Resolution mask image (12 x 10 mm subsection )

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS spatial linearity Residual to linear fit Pixel size After correction

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS local gain sag

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS QE

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS flat field

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Improvements in MCP Detectors since COS MCP fixed pattern noise improved Electronics (Time to Digital Converters) –Faster (250 kHz at 10% deadtime) –FPGA logic –Lower power Readout technologies –Crossed Strip –Medipix and Timepix ASICs

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga MCP Fixed pattern noise COS flat field 16 x 10 mm Optical tube flat field 25 mm

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Cross Strip Anode Resolution mask, 5 µm pores Anode strips Y amps X amps (ASIC) Charge cloud from MCP Resolution < 8 µm FWHM at gain of Count rates > MHz 8µm8µm

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Medipix/Timepix ASIC readout 256 x 256 array of 55 µm pixels Integrates counts, not charge 100 kHz/pxl Frame rate: 1 kHz Low noise (100e - ) = low gain operation (10 ke - ) GHz global count rate ~1 W watt/chip, abuttable Developed at CERN

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Original Medipix mode readout Zoom 256 x 256 (14 mm)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Timepix version of Medipix Amplitude rather than counts using “time over threshold’ technique If charge clouds are large, can determine centroid to sub- pixel accuracy Tradeoff is count rate as event collisions in frame destroy centroid information Single UV photon events

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Factor of 8 improved resolution! 256 x 256 converted to 4096x4096 pixels (3.4µm pixels)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Factor of 8 improved resolution! 256 x 256 converted to 4096x4096 pixels (3.4µm pixels)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Zoomed 5-6 pattern resolved = 57 lp/mm Linewidth = 8.8 µm 5-6 The MCP pore spacing of 8µm limits further improvement

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Standard specifications Format size Spatial resolution Quantum Efficiency Linearity (integral and differential) Deadtime per event Maximum rate (global and local)

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Additional specifications Pixel size (bits per event, X,Y,T,P etc) Lifetime Thermal stability Fixed pattern distortions Response uniformity Livetime characteristics Calibration accuracy

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Lifetime (MCP gain loss) High-fluence missions concern Gain loss can affect response due to threshold Can also affect imaging performance Somewhat ameliorated by HV increase –Localized loss a problem

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga FUSE MCP gain loss (Sahnow, SPIE 5488, 2004) Total fluence map (through 2004) Gain vs. fluence

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Scrub to stabilize gain loss MCP gain initially decreases rapidly with extracted charge as adsorbed gasses are removed Rate of gain loss vs. extracted charge eventually decreases Scrub “end point” dependent upon expected fluence of misison Exposure to gas at atmospheric pressures resets gain to initial higher levels - hence the need for sealed tubes or closable doors

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS Test Scrub

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS Flight Scrub Initial ScrubPost Rework

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Detector walk due to channel bias Three different rear fields, fixed gain Bias Three different gains, fixed rear field

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga COS flat field

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Deadtime FUSECOS

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Detector “Oddities” in Space EUVE Filter pinholes Deadspot The “smudge” FUSE The “Worm” Current spikes and event bursts Y blooming Thermal drift Walk correction GALEX (sealed tube) Current transients FUV “Blob” Current “anomaly” FUV “flash”

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga EUVE Smudge Cosmic rays saturating charge amps Deadspot Best focus gain sag Pinholes in Al/B filter After launch, vibration?

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga FUSE (Sahnow, SPIE 4854, 610,2003) The “Worm” - focus near QE grid Current spikes and event bursts associated with Space Weather Y blooming function of input count rate - anode charging? Thermal drift poorly monitored Walk distortion in X set pre-launch for nominal gain correctable in list (X,Y,P) mode

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga GALEX (Morrissey, SPIE 6266, 2006) Current transients associated with space weather sealed tube concern FUV “Blob” window charging Current “anomaly” MCP short that was annealed FUV “flash” significant breakdown event that cured itself

WSO Detector Workshop Leicester University, Dec. 2007, John Vallerga Lessons Learned Start early Build Prototypes Stress Prototypes Build Flight Spares Include lots of “knobs” to adjust in orbit –Hardware –Firmware –Software