May 4-5, 2006 T.Schweizer, CTA meeting Berlin

Concept idea for a future telescope array

observatory

CTA meeting BerlinMay 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: 100-150 Mio Euro– Sensitivity ~ 5-10 times better than previous instruments

• It is impossible to span 7 orders of magnitude (10 GeV - 100 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, ~100-150 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 km2, large eff. areaLowest possible energy thresholdand 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 m2 mirror) with classical PMTs– 23 m telescope (415 m2 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 16-20 telscopes

for 70 Mio Euros ?

May 4-5, 2006 T.Schweizer, CTA meeting Berlin

Possible telescope parameters

Active mirror control with improved opticalquality (PSF)

D= 23 m diameter parabolc mirror 430 m2

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 m2

- Roundish camera, FOV 5°- Square pixels - Assume QE=50 % flat from 300-600 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 100-200 kHz/1mm2 for future SiPM

Pixel Case a) Pixel Case b)

Pixel size in degrees

0.075° x 0.075° 0.94° x 0.94°

Detector area 4 cm2 (4 chips) 4 cm2 (4 chips)

Light concentration

3.25 5

Dark rate 40-80 MHz (13%-26%)

40-80 MHz (8%-16%)

NSB rate ~ 0.3 GHz ~ 0.5 GHz

Number of pixels 3460 2250

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 pulse3 floats (can be reduced) 12 Bytes

• Zero suppression Low level image cleaningassume 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 channeldomino sampling

Signal processorto extract signalsand 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 temperaturestabilization + 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 € 14-17 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 ?