1. B.Satyanarayana Department of High Energy Physics Tata Institute of Fundamental Research Homi Bhabha Road, Colaba, Mumbai, 400 005 E-mail: bsn@tifr.res.inbsn@tifr.res.in Possible schemes for ICAL electronics

2. B.Satyanarayana TIFR, Mumbai September 21, 20072 Plan of the presentation Characterisation of RPC pulses ICAL detector requirements Front-ends currently in use RPC pulse profile studies Possible schemes for the ICAL detector Control and monitoring systems Summary

3. B.Satyanarayana TIFR, Mumbai September 21, 20073 Region recharges on scale of up to sec due to bulk resistivity (10 11  cm) Principle of operation of RPC Gas ++++++++++++++++ HV Resistive plate +++++  Streamer forms, depletes charge over (1-10mm 2 ). Field drop quenches streamer Charge depletion induces signal. Charge depletion fixed by geometry, resistivity, gas. +++++ + + +++++  HV Resistive plate HV Resistive plate Ionization leads to avalanche Dielectric

4. B.Satyanarayana TIFR, Mumbai September 21, 20074 RPC signal generation A passing ionising particle will liberate N 0 electrons, creating an initial current, i 0 =eN 0 v/g, that depends on the electron’s drift velocity v and on the width g of the gas gap. The gas avalanche process will immediately amplify the initial current in time as i=i 0 e st h(t), where s is a real positive parameter and h(t) the unit step function. The exponential multiplication factor may reach very large value, up to 10 8. The output voltage signal is given by v(t)=i 0 Z(s)e st

5. B.Satyanarayana TIFR, Mumbai September 21, 20075 RPC signal characteristics For a given threshold setting, time deference should be independent of i 0 (which fluctuates event by event) and independent of the circuit properties (represented by Z(s))

6. B.Satyanarayana TIFR, Mumbai September 21, 20076 Important conclusions The nature of the detector electrodes, coupling lines, amplifiers, etc, will affect only the magnitude of the output signal through the combined transimpedance Z(s), while leaving unaffected the time development of the signal. The signal shape (exponential) will be influenced only by the value of s, determined by the gas avalanche process in the detector.

7. B.Satyanarayana TIFR, Mumbai September 21, 20077 RPC mode definitions Let, n 0 = No. of electrons in a cluster  = Townsend coefficient (No. of ionisations per unit length  = Attachment coefficient (No. of electrons captured by the gas per unit length Then, the no. of electrons reaching the anode, n = n 0 e (  -  )x Where x = Distance between anode and the point where the cluster is produced Gain of the detector, M = n / n 0 M decides the mode of RPC operation M > 10 8  Streamer mode; M << 10 8  Avalanche (Proportional mode)

8. B.Satyanarayana TIFR, Mumbai September 21, 20078 RPC mode definitions Where, d = gap thickness V = Voltage applied to the electrodes  0 = Dielectric constant of the gas Lower the Q, Lower the area of the cell (that is ‘dead’ during a hit) and hence higher the rate handling capability of the RPC  A planar detector with resistive electrodes ≈ Set of independent discharge cells  Expression for the capacitance of a planar condenser  Area of such cells is proportional to the total average charge, Q that is produced in the gas gap. Q ~ 100pC = Streamer mode Q ~ 1pC = Proportional (Avalanche) mode Induced charge is only ~5% of the total charge collected by the anode

9. B.Satyanarayana TIFR, Mumbai September 21, 20079 RPC signal characteristics

10. B.Satyanarayana TIFR, Mumbai September 21, 200710 ICAL detector specifications No. of modules3 Module dimensions16 m X 16 m X 12 m Detector dimensions48 m X 16 m X 12 m No. of layers140 Iron plate thickness6 cm Gap for RPC trays2.5 cm Magnetic field1.3 Tesla RPC dimensions2 m X 2 m Readout strip width3 cm No. of RPCs/Road/Layer8 No. of Roads/Layer/Module8 No. of RPC units/Layer192 No. of RPC units26880 No. of readout channels3.6 X 10 6

11. B.Satyanarayana TIFR, Mumbai September 21, 200711 What is specific for ICAL DAQ? Large number of data channels to handle; large scale integration needed. But, fewer and simpler parameters to record Low rates; high degree of multiplexing possible Monolithic detector; unlike the case accelerator based detectors ASICs, pipelining, trigger farm,VME are the keywords ASICs for front-end, timing, even for trigger!

12. B.Satyanarayana TIFR, Mumbai September 21, 200712 Recordable parameters (Detectors) Event data –Strip hit information (Boolean, 1 bit per strip) –Strip signal timing with reference to event trigger –Strips ORed to reduce timing channels Monitor data –Strip single/noise counting rate –Chamber voltage and current

13. B.Satyanarayana TIFR, Mumbai September 21, 200713 Recordable parameters (DAQ) Preamplifier gain and input offset Discriminator threshold and pulse width Trigger logic parameters and tables DAQ system parameters Controllers and computers’ status

14. B.Satyanarayana TIFR, Mumbai September 21, 200714 Recordable parameters (Gas system) Open loop versus closed loop systems Gas flow via Mass Flow Controllers Exhaust gas flow monitor Residual gas analyser data Gas contaminants’ monitor data Gas leak detectors Safety bubblers’ status

15. B.Satyanarayana TIFR, Mumbai September 21, 200715 Recordable parameters (Ambient) Temperature –Gas –Front-end electronics Barometric pressure –Gas Relative humidity –Dark currents of the bias supplies –Electronics

16. B.Satyanarayana TIFR, Mumbai September 21, 200716 Pickup strip characteristics Characteristic impedance Capacitance Foam based pickup panel

17. B.Satyanarayana TIFR, Mumbai September 21, 200717 h Readout strips Ground plane w rr Transmission line impedance

18. B.Satyanarayana TIFR, Mumbai September 21, 200718 Impedance versus strip width

19. B.Satyanarayana TIFR, Mumbai September 21, 200719 G-10 based pickup plane

20. B.Satyanarayana TIFR, Mumbai September 21, 200720 Tests on signal pickup schemes Attenuation = 0.052 db/m  = Propagation constant = 5.6 ns/m The cross talk on the adjoining strips, after the signal propagation along the 15 m long FCS, is very small  tt 14.5 m Central strip Adjoining strip 

21. B.Satyanarayana TIFR, Mumbai September 21, 200721 Test on readout system  x (cm) = 2.  t.  = .  t (ns) The time performance of the X-system, of the order of 100 ps, shows that 15 m long FCS can be used without a worsening of the intrinsic time resolution of the Glass RPC (~1 ns). Even the Y-coordinate can be measured with a resolution of the order of 1 cm by a Δt measurement Raw data resolution = 2.4 cm. After subtracting quadratically the broadening due to the scintillator width σX (cm) = 1.23 cm

22. B.Satyanarayana TIFR, Mumbai September 21, 200722 Test on readout system Good linearity  t Vs position

23. B.Satyanarayana TIFR, Mumbai September 21, 200723 Preamps for prototype detector HMC based Opamp based

24. B.Satyanarayana TIFR, Mumbai September 21, 200724

25. B.Satyanarayana TIFR, Mumbai September 21, 200725 Preamplifier pulses on trigger

26. B.Satyanarayana TIFR, Mumbai September 21, 200726 Charge-pulse height plot

27. B.Satyanarayana TIFR, Mumbai September 21, 200727 Pulse height-pulse width plot

28. B.Satyanarayana TIFR, Mumbai September 21, 200728 Charge spectrum of the RPC  = 375fC

29. B.Satyanarayana TIFR, Mumbai September 21, 200729 Time spectrum of the RPC  t = 1.7nS

30. B.Satyanarayana TIFR, Mumbai September 21, 200730 Charge-timing scatter

31. B.Satyanarayana TIFR, Mumbai September 21, 200731 Decay constant of the preamp output

32. B.Satyanarayana TIFR, Mumbai September 21, 200732 Single/Noise monitoring Time profile Rate distribution

33. B.Satyanarayana TIFR, Mumbai September 21, 200733 Major sub-systems Analog and digital front-ends –Mounted on or very close to detectors –Programmable preamps and comparators –Latches, pre-trigger generators, pipelines and buffers –Data concentrators and high speed serial transmitters VME back-ends –Data collectors and frame transmitters –Time to digital converters (TDCs) Trigger system –Works on inputs from front-ends, back-ends or external –Place for high density FPGA devices

34. B.Satyanarayana TIFR, Mumbai September 21, 200734 A readout system concept

35. B.Satyanarayana TIFR, Mumbai September 21, 200735 Typical front-end circuit

36. B.Satyanarayana TIFR, Mumbai September 21, 200736 Various signal profiles

37. B.Satyanarayana TIFR, Mumbai September 21, 200737 Zero-crossing discriminator

38. B.Satyanarayana TIFR, Mumbai September 21, 200738 Discriminator response (Overdrive)

39. B.Satyanarayana TIFR, Mumbai September 21, 200739 Discriminator response

40. B.Satyanarayana TIFR, Mumbai September 21, 200740 Double pulse resolution

41. B.Satyanarayana TIFR, Mumbai September 21, 200741 Output driver

42. B.Satyanarayana TIFR, Mumbai September 21, 200742 Example for a front-end (NINO) Input stage Specifications Architecture

43. B.Satyanarayana TIFR, Mumbai September 21, 200743 24-channel NINO board Calibration

44. B.Satyanarayana TIFR, Mumbai September 21, 200744 Front-end ASIC concept

45. B.Satyanarayana TIFR, Mumbai September 21, 200745 HPTDC architecture

46. B.Satyanarayana TIFR, Mumbai September 21, 200746 HPTDC specifications

47. B.Satyanarayana TIFR, Mumbai September 21, 200747 Control and monitoring systems Front-end, DAQ and trigger system control and monitoring –Front-end gain, threshold, pulse width –Trigger tables etc High voltage control and monitoring Gas system control and monitoring Ambient parameter monitoring –Temperature, barometric pressure, relative humidity –Data can be used for even for off-line corrections

48. B.Satyanarayana TIFR, Mumbai September 21, 200748 High voltage system control and monitoring Number of independently controllable channels? –Worst case Combine all RPCs in a layer  140 channels –Best case One channel per RPC  26,880 channels! –We can settle for one channel/road/layer, for example Ramp rate, channel control, voltage and current monitoring are the bare minimum requirements Modular structure, Ethernet interface, local consoles, distributed displays, complete high voltage discharge etc are most desired features

49. B.Satyanarayana TIFR, Mumbai September 21, 200749 A scheme for dark current readout Dark current = Current drawn from negative supply – 3.5  A (Current drawn through 1G  )

50. B.Satyanarayana TIFR, Mumbai September 21, 200750 Gas system control and monitoring Channel control and flow monitoring On-line gas sample analysis (RGA) Gas leak monitoring Moister level monitoring

51. B.Satyanarayana TIFR, Mumbai September 21, 200751 On-line data browsers Web servers for operating parameter browsers –Java applets On-fly sample data quality checks –Interactive/configurable tools Remote access –Graded/filtered data, security issues

52. B.Satyanarayana TIFR, Mumbai September 21, 200752 Some technology standards Backend: VME OS platform: Linux Networking of processing nodes Front-end, gas system and HV control – Ethernet Ambient parameter monitoring – Embedded processors with Ethernet interfaces Data bases – Scientific versus commercial –Presets, event, monitor data

53. B.Satyanarayana TIFR, Mumbai September 21, 200753 Summary RPC’s pulse characteristics and ICAL’s requirements understood to a large extent; more will be known from the prototype detector Time to formulate competitive schemes for electronics, data acquisition, trigger, control, monitor, on-line software, databases and other systems A couple of best options could be selected for detailing. Feasibility R&D studies on front-ends, timing elements, trigger architectures, on-line data handling schemes should be concurrently taken up Power budgets, integration issues etc. must be addressed Procurement of design and simulation tools Design teams/centres and industry structure and coordination Preparation of Engineering Design Report (EDR) and Technical Design Report (TDR)