A Possible  13 Electronics Architecture

1. A Possible 13Electronics Architecture A Strawman Proposal Kelby Anderson for Jim Pilcher 30-Apr-2004

2. The Objective • We should discuss and examine architecture • Do this before any detailed design • We need to get the high level features correct • More people can contribute ideas to high level planning • Once we agree on scope the detailed planning and design can begin • Lots of work for anyone interested • This talk is intended to provide a strawman plan for the architecture • Other options can be compared to it • Readout should take advantage of modern electronics developments • Can do more with given budget now compared to 10 years ago • This was when CHOOZ, SNO, KamLAND were designed J. Pilcher

3. Electronics Requirements • Digitize charge seen by each PMT • Energy reconstruction • Provide timing of signal from each PMT • one component of position info (also energy sharing of PMTs) • Provide trigger for DAQ • Physics triggers • Neutrinos (prompt EM energy, delayed neutron energy) • Backgrounds (to study and subtract) • Muons • Electronic calibration triggers (variable test pulses) • Source/laser/LED calibration triggers • Random triggers J. Pilcher

4. Electronics Requirements • Provide HV to PMTs • Provide LV for electronics • Provide ability to control and monitor detector and electronics • Temperatures • LV, HV • PLD firmware J. Pilcher

5. Electronics Requirements • Readout should not degrade intrinsic resolution • Energy resolution • eg. 7.5% / Sqrt[E(MeV)]  2%  5.7% at 2 MeV • This is KamLAND resolution. Perhaps we can do a bit better. • Timing • 1.0 ns (PMT jitter) •  for Hammamatsu 5912, 8” PMT • Energy readout must cover full dynamic range • Low end • Single photoelectron for individual PMTs • Assume 15 counts/pe • High end • Muon along diameter of detector • Emax of 10  <Emip> • ? pe for closest PMTs (to be determined) J. Pilcher

6. Attractive and Feasible Features • Trigger separately on positron energy and neutron energy • Link by recording time since last trigger • Gives better handle on background effects • Trigger should be able to impose loose time coincidence in case singles rate is too large • In this case prescale single energy triggers • Sample signals in time window around trigger event (  2.5 s ) • Earlier times provide input on possible backgrounds • Later times provide link to neutron triggers within the same event (cross check of event timing) J. Pilcher

7. Attractive and Feasible Features • Do zero suppression and data filtering off-detector • Take advantage of modern high-speed data links • More flexibility in PC than in front-end hardware • Provide independent electronic calibration for each channel over its full dynamic range (chg. injection) • Allows injection of simulated events • Allows easy tests for cross talk • Allows precise electronic calibration of each channel • In counts/pC • Sources give pe/MeV and pC/pe • Allows measurement of pulse shape by varying timing of injected signal for successive events J. Pilcher

8. Front-end • Convert PMT signals to “standard” analog shape • Amplitude reflects charge from PMT • Use low-noise passive shaper • Fully linear • Adapts PMT to speed of commercial sampling ADCs • eg. 12-bit, 40 megasamples/sec (every 25 ns) • TI’s ADS5130 (12-bits, 50 MSPS) or AD’s AD9042 (12-bits, 40 MSPS) J. Pilcher

9. Front-end • Sample signal every 25 ns • Synchronize all ADCs using optical timing system • Laser driven optical fiber modulated by clock • Control and trigger can be distributed with same system • LHC Timing Trigger and Control (TTC) system • Time resolution of clock at PMT ~100 ps • Each clock pulse is “numbered” • System is off the shelf with many utility modules and custom chips • Provides ability to set the clock timing independently at each PMT • Compensate for channel-to-channel delays • Synchronize all PMTs using LED at center of detector • Transit time variations between PMTs from variation in HVs • Save 200 samples in a pipeline (  2.5 s ) • Readout if trigger • Overwrite if no trigger • Use larger dual-port memory for dead-timeless operation J. Pilcher

10. Front-end • Digital pipeline systems built for LHC experiments • Fewer samples but similar delay to trigger • To obtain needed dynamic range use multiple gains • High gain gives 15 counts/pe and 4095 counts (270 pe) full scale • Low gain gives 128 counts (0.8%) at high gain maximum and 4095 counts (8,700 pe or 14,000 pC) full scale • PMT has 5% non-linearity at 1,200 pC • Readout will cover the useful range of PMT output • Dynamic range of readout 17 bits or 102 dB • These figures reduced a little by pedestal offsets • Useful full scale reduced by ~ 30 counts • Noise should be held to ~ 1 count to preserve dynamic range (waste of ADC resolution) J. Pilcher

11. Front-end • Standard pulse shape is fitted to extract amplitude and time offset with respect to sampling clock • Demonstrated time resolution of electronics is < 100ps • Feature extraction done off-detector • Can be done in PC • Digital signal processing modules used at LHC because of rate (100 KHz, Level 1 trigger rate) J. Pilcher

12. Data Collection • Attractive to use single optical or electrical data link to control room • to facilitate connection/disconnection • 500 Mbps is quite feasible with off-the-shelf components (doing this ourselves in ATLAS) • Data per PMT channel per event • 2x12 bits x 200 samples + 15% overhead (CRC, parity, identifiers) = 5.5 Kbits • Data per detector per trigger • 819 PMTs x 5.5 Kb = 4.5 Mbits • One data link could handle 100 ev/sec • Only needed for calibration • Could reduce width of time window when running calibrations • Derandomizing buffer needed at link input for normal data J. Pilcher

13. Detector Control System • Attractive to have single control bus from counting room to each detector • Facilitates connection/disconnection for moving detector • Functions • Set HV on PMTs • Control electronics calibration system • Monitor LV, HV, temperatures • Allows bi-directional communication • TTC system is uni-directional • Requirements • Must have high fanout capability (~ 800 PMT channels served by one bus) J. Pilcher

14. Detector Control System • Many commercial field bus systems • eg. CANbus • But fan-out capability could be a problem with this one J. Pilcher

15. HV System • Single HV cable per detector • Set HV to individual PMTs on detector • HVs adjusted so all tubes have same gain • Using laser ball or LED at center of detector • Needn’t have fine control of HV over full range • Just over range of PMT gain variation • For constant term in energy resolution of 2 % and 820 PMTs we need individual PMT gains settable to 2%/820 = 0.07% • For a PMT where  is ~ number of stages • For 10 stage tube • Need V to ~ 0.10 V out of 1500 V • Must be able to switch off individual PMTs • Non-trivial requirement J. Pilcher

16. Trigger System • Base trigger on number of photoelectrons seen in detector • Useful to have sums from segmented regions of detector • Protect against localized hot spots • Tile the detector into hexagonal patches • Generate pe sum from each patch (26 patches of 32 PMTs = 832) • How to do this? • Traditional option is to add analog trigger signals, but … • Beware of analog offsets and common mode noise • Trigger signals have separate timing and gain from DAQ branch • Must have own calibration • Better to use digital info from ADCs • Trigger signals then time-aligned with clock system • Need to use only coarse info from ADC (high order bits) • Add 32 digital signals for a patch to get local sum • Trigger signal assembled every 25 ns. (with latency) • May want running sum over several clock periods J. Pilcher

17. Cost Estimate Cost per channel Analog front-end $100 (ATLAS $88) Digitizer and pipeline $130 (ATLAS $94) Clock timing and distribution $50 Trigger $80 HV power and distribution $60 (ATLAS $46) Control system $40 Miscel. on-detector plumbing $40 (ATLAS $35) LV power $20 ______________ $520 3 detectors @ 812 channels each  $1.27M Add 30% for EDIA, 40% contingency $2.31M Overall constn. cost of experiment ~ $60M (readout is ~3.8%) J. Pilcher

18. Conclusions • These comments offer a possible architecture • Point of comparison for other options • Cost estimates rough but includes experience with LHC design (top down estimate OK at this point) • Much work needed for detailed planning, design, and implementation • Could add readout to Monte Carlo • Evaluate granularity and trigger • Important to agree on architecture before starting design • Divide detailed planning, design, and implementation among interested groups J. Pilcher

19. Conclusions • There will be PLENTY to do J. Pilcher