May 4-5, 2006 T.Schweizer, CTA meeting Berlin Concept idea for a future telescope array observatory CTA meeting Berlin May 4-5, 2006 Thomas Schweizer

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Goals and constraints Specification of CTA observatory –Energy range 10 GeV to 100 TeV –Available budget: Mio Euro –Sensitivity ~ 5-10 times better than previous instruments It is impossible to span 7 orders of magnitude (10 GeV TeV) by one single detector and keep optimal performance (because of limited dynamic range and steep spectra)  One array 10 GeV to 1 TeV (LEA) -low energy threshold, ~10-20 large telescopes -75 % of budget (North and South)  One array 1 TeV up to 100 TeV (ULTRA II) -very large effective area, ~ small telescopes -25 % of budget (only South) -E. Lorentz talk

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Two arrays together – Overlap in energy between both arrays for cross-calibration - Simultanous observation with small and large array - Parallel observation of several sources with parts of array - Longterm monitoring of sources with single telescopes 1-2 km 2, large eff. area Lowest possible energy threshold and highest sensitivity

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Low energy array (LEA) What do we want for available budget (~70 Mio Euro) ?  As many telescopes as possible for high sensitivity and parallel observation of sources  As low energy threshold as possible Possibilities: –30 m telescopes (710 m 2 mirror) with classical PMTs –23 m telescope (415 m 2 mirror) with SiPM light sensors 23 m telescope –Increase in photon-detection efficiency rather than mirror area  high mirror reflectivity (90%), high QE (SiPM, 50%) –Smallertelescopes and lighter telescopes are cheaper, < 120 tons weight, 70 tons possible –Big question: is it possible to build telscopes for 70 Mio Euros ?

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Possible telescope parameters Active mirror control with improved optical quality (PSF) D= 23 m diameter parabolc mirror  430 m 2 FOV=5° F/D = 1.2:  acceptable aberation (5° FOV) F= 28 m Protection against wind lift-up  Lighter & cheaper telescope

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Possible parameters for camera design FOV 5°  D= 2.4 m  A=4.5 m 2 - Roundish camera, FOV 5° - Square pixels - Assume QE=50 % flat from nm

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Some numbers Case study: square pixels with 4 SiPM chips à 1 cm x 1 cm a)Light concentration 3.25 (with microlensing foil) b)Light concentration 5 Absolute maxim allowed dark rate for SiPM: 20% of NSB  Assume kHz/1mm 2 for future SiPM Pixel Case a)Pixel Case b) Pixel size in degrees0.075° x 0.075°0.94° x 0.94° Detector area4 cm 2 (4 chips) Light concentration3.255 Dark rate40-80 MHz (13%-26%)40-80 MHz (8%-16%) NSB rate~ 0.3 GHz~ 0.5 GHz Number of pixels Price 80 €/SiPM~ 1.1 Mio Euro~700 k€

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Data volume generated by telescope system Assume 2.5 GHz FADC (capacitor array) sampling Assume 50 samples per pixel à 16 Bits  100 Bytes Assume trigger rate of 2 kHz (at 10 GeV) Assume 3000 Pixels Assume 20 Telescopes Assume an average of 8h observation time  About 10.5 Petabytes per month !!  Even with modern computers in 10 years this amount will be a serious problem

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Data reduction  Necessity for online data reduction Online signal extraction from FADC slices  Amplitude, Arrival time, Pulse width of largest pulse 3 floats (can be reduced)  12 Bytes Zero suppression  Low level image cleaning assume reduction factor 20 (maybe more ?)  Reduced data rate: 65 Terrabytes per month (Still a lot ! ) Comment: Data reduction (signal processing) maybe already inside camera

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Readout ideas All the readout electronics inside the camera reduces the cost of the camera (maximum weight 2 tons) No heavy cabeling, simplified construction Data reduction (signal processing) already inside the camera Modules of 100 pixels 100 channel domino sampling Signal processor to extract signals and data reduction Collect data from all modules & ultrafast data transfer to DAQ Switch 1 Gbit Ethernet ?

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Cost estimates  The camera housing + mechanics + Cooling and temperature stabilization + Light concentrators: 400 k€  Price for 4 SiPM chips (one pixel): ~ 300 € (Hamamatsu)  Price for readout (Cap. array + signal processing) per channel: ~ 300  Sum price/channel: ~600 €  Sum all pixels (2250): ~1.4 Mio €  Total: 1.8 Mio €  Maxim price for camera + readout: 2 Mio €  Price for telescope frame 2-3 Mio €  Price for one telescope: 4-5 Mio €  70 Mio €/4-5 Mio €  telescopes

May 4-5, 2006 T.Schweizer, CTA meeting Berlin Timing First light within 5-6 years ? SiPM chips probably available within 2 years Use standard mechanics/electronics as much as possible Time plan –Camera development with SiPM: 4 years –Development time for mechanics 2-3 years –Production and installation of 16 telescopes: 2-3 years All together: 5 years until first telescope installed ?