SNAP Collaboration meeting / Paris 10/20071 SPECTROMETER DETECTORS From science requirements to data storage

SNAP Collaboration meeting / Paris 10/20072 SUMMARY 1.Basic requirements for science 2.NIR Baseline 3.NIR Dark Current 4.NIR and SN : Cosmics, Readout, memory size and reduction 5.NIR and Galaxies : Readout, memory size and reduction 6.CCD : Science, Baseline, requirement and memory size 7.Summary 8.Addressed questions

SNAP Collaboration meeting / Paris 10/20073 SCIENCES GOALS Results shown during science talks concerning the SN and WL for the spectrometer have been obtained doing some assumptions on the detectors. CCDNIR array size (Mpxl²) 3,5x3,52x2 pxl size (µm) 10,518 number of detectors 2x ½ T (K) RN (e-) 25-7* DC (e/pxl/sec) 0,00030,002 * depend of the integration time. see later…

SNAP Collaboration meeting / Paris 10/20074 Spectro NIR Baseline NIR array size (Mpxl²)2x2 pxl size (µm)18 number of detectors 2x ½ T (K)110 RN (e-)5-7* DC (e/pxl/sec)0,002 Readout modes and memory size have to be thinked for each science Detector Area (2k x 2k pix) Minima requirements used for the science simulations spatial * depend of the integration time. see later…

SNAP Collaboration meeting / Paris 10/20075 Spectro NIR / Dark Current From dark current Imager requirement (0.02 e/pxl/sec.) to spectro requirement (0.002 e/pxl/sec.) Achievable down to 130K T requirement 110K Remarks/questions : have to be tested on more devices does the CCD work at this temperature  if not it means that two temperature are necessary on the spectro focal plane  2 structures  insulation  not the same thermal straping for CCD and NIR  heater? R.Smith & M.Bonati,

SNAP Collaboration meeting / Paris 10/20076 Spectro NIR and SuperNovae  how to manage such a long time with cosmics rays?  how to reach readout noises at the level of 7e- per exposure? Because of the readout noise limitation, science plots have shown clearly that you need long integration time and our baseline for the spectro have to be 3000sec.

SNAP Collaboration meeting / Paris 10/20077 Spectro NIR and SN / Cosmics With18µm pixels calculations show a rate1,3*10-3/s/pxl  1 cosmic/800s/pxl (TBC) The strategy to reject cosmics is to use an up-the-ramp readout : signal cosmic You have to know the previous slope good enough to reject the cosmic  choose the appropriate readout cadence (10-50 TBD) Some calculations have already shown that the loss of S/N using up-the-ramp and cosmic rejection is affected of only -1.6% for 3000sec exposure (TBC) (S/N no cosmic –S/N cosmic )/ S/N no cosmic

SNAP Collaboration meeting / Paris 10/20078 Spectro NIR and SN / Readout Noise Caltech, R.Smith measurements Actual measurements (our baseline) show that being read noise limited larger integration time are necessary but restriction on readout noise have to be under control With 3000 secondes of exposure time Fowler (TBC) are necessary to limit the readout noise

SNAP Collaboration meeting / Paris 10/20079 Spectro NIR and SN / Readout strategy Need of 3000 secondes exposures Need of a Up-the-Ramp (cadence sec.) Need of Fowler signal Reset N Fowler Samples stored Slow Up-The-Ramp stored + maximum clocking but not stored 3000sec This ideal readout mode HAVE TO BE TESTED WITH REAL DATA

SNAP Collaboration meeting / Paris 10/ Spectro NIR and SN / memory size hypothesys : 8h/day divided in 3000sec. exposure read with Fowler X ½ NIR = 2x2 (Mpxl²) x 2 bytes = 8 Mbytes  8 Mbytes/frame x 3 h/day / 3000 sec/expos x 600 frames ~ 17 Gbyt/day to be compared to the 63Gbyt/day NIR imager without data reduction

SNAP Collaboration meeting / Paris 10/ Spectro NIR and SN / memory size reduction 1650  /pxl/3000sec (TBC)  = 1 dynamic range = 1 e/ADCU 7 bit to get 1 extra bit for the sign of the difference do not store the frame (on 16bits) but only the differences between frames on 8 bits  if necessary adapt the dynamic range N e/ADCU Detector Area (2k x 2k pix) spatial Reduce the Region Of Interest stored to the SN and its host galaxy To conclude on that point : 1. check the hypothesys of that 17GByt/day 2. possibilities to reduce by a factor of 4 (at least) this volume Use lossy compression : reduction by a factor up to 5!!!

SNAP Collaboration meeting / Paris 10/ Spectro NIR and Galaxies science inputs : readout noise=7 e; DC=0.002 e/pxl/sec Integration time is drived by the imager : 4 x 300sec exposure with 3.5 pixels dithering 300sec. integration time : R.Smith curves show that a Fowler 30 reach the 7 e goal 14 electrons noise in 1200s 1200sec. integration time: R.Smith curves show that a Fowler 100 reach the 7 e goal 7 electrons noise in 1200s

SNAP Collaboration meeting / Paris 10/ Spectro NIR and WL / data storage with 300sec. integration time 220 exp/day x 60 frame/exp x 8 Mbyt/frame ~ 106 Gbyts/day with 1200sec. integration time 55 exp/day x 200 frame/exp x 8 Mbyt/frame ~ 88 Gbyts/day do we need this? probably NO (coadd.)  ~1.8Gbyt do we need this? probably YES REDUCTION Other possible reduction of volume : depending of the dynamic range of the galaxies one can code on 8bits instead of 16 check the dynamic range (e/ADCU) versus the number of  of galaxies (TBD) use lossy compression : factor 5 achievable?

SNAP Collaboration meeting / Paris 10/ Spectro CCD Baseline what is new for the spectro CCD? use of the same than the imager : LBNL 3.5x3.5 Mpxl²; 10.5µm each; same thickness Due to the thickness we have the same cosmic limitation on the integration time than for the imager : 300sec whatever the science! In terms of readout noise requirement we plan to have 2e- and this is achievable changing the readout frequency from 100kpxl/sec (imager) to 50kpxl/sec. In terms of Dark Current a requirement of e-/pxl/sec (1 e/pxl/hour) is needed  questions : is it feasable at 140K? does it work in space? Detector Area (2k x 2k pix)

SNAP Collaboration meeting / Paris 10/ Spectro CCD requirement summary and impact on data storage CCD array size (Mpxl²)3,5x3,5 pxl size (µm)10,5 number of detectors 2x ½ T (K)140 F (kHz)50 RN (e-)2 DC (e/pxl/sec)0,0003 DATA STORAGE : 3.5 x 3.5 (Mpxl²) x 2 (Byt) = 24.5 MByt/expos.  SN : 24.5 MByt /exposure x 36 exposures (3h/day) ~ 0.9 GByt /day without compression ~0.45% of the CCD imager  Galaxies : 24.5 MByt/exposure x 220 exposures (100%day) ~ 5.4 GByt /day without compression ~ 2.4 % of the CCD imager

SNAP Collaboration meeting / Paris 10/ Spectro CCD summary imagerspectro CCD array size (Mpxl²)3,5x3,5 pxl size (µm)10,5 number of detectors36 2x ½ T (K)140 F (kHz)10050 RN (e-)62 DC (e/pxl/sec)0,030,0003 Readout time (sec)30 SN integrated time300 exposures per day220 (100% day)36 (3h/day) memory size * (Gbyte) 1940,9 WL integrated time300 exposures per day220 (100% day) memory size * (Gbyte) 1945,4 *without compression

SNAP Collaboration meeting / Paris 10/ Spectro NIR summary imageurspectro NIR array size (Mpxl²)2x2 pxl size (µm)18 number of detectors36 2x ½ T (K) RN (e-)97 DC (e/pxl/sec)0,020,002 Readout time (sec)1,7 SN integrated time exposures per day220 (100% day)5 (3h/day) Read out mode fowler 16 coads on boards Fowler300+Up-the-Ramp50sec memory size * (Gbyte) 6317 WL integrated time exposure per day220 (100% day) 60 (100% day) Read out modeFowlerN coadsFowler30 coads Fowler100+Up- th-Ramp50 memory size * (Gbyte) 631,888 *without compression

SNAP Collaboration meeting / Paris 10/ Addressed questions stable assumptions inputs from science (TBC) CCD 140K TBC CCD DC OK in space? cosmic flux and inpact on NIR TBC Up-the-ramp readout cadence for cosmic rejetion have TBC Fowler N ( ) with 3000 sec. TBC with other devices FowlerN+Up-the-ramp+permanent clocking have to be really tested –with many devices different T ( K) NIR DC verify with different devices CCD works down to which T (is 110K OK?) dynamic range have to be confirmed : –for each science –for darks –for stars calibration dynamic range versus  flux have to be confirmed for galaxies distributions data storage size and reduction have to be studied for galaxies should we move from 300sec up to 1200sec ? does the CCD readout have effect on NIR integration/readout performance? hard tests. Could be done both in US and FR?

SNAP Collaboration meeting / Paris 10/ Spectro CCD and NIR summary CCDNIR array size (Mpxl²)3,5x3,52x2 pxl size (µm)10,518 number of detectors 2x ½ T (K) F (kHz)50TBD RN (e-)27 DC (e/pxl/sec)0,00030,002 Readout time (sec)301,7 SN integrated time exposures per day36 (3h/day)5 (3h/day) Read out mode Fowler300+Up-the-Ramp50sec memory size * (Gbyte) 0,917 WL integrated time exposure per day220 (100% day) 60 (100% day) Read out mode Fowler30 coads Fowler100+U p-th-Ramp50 memory size * (Gbyte) 5,41,888