B.Satyanarayana Department of High Energy Physics Tata Institute of Fundamental Research Homi Bhabha Road, Colaba, Mumbai, Possible schemes for ICAL electronics

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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 The output voltage signal is given by v(t)=i 0 Z(s)e st

B.Satyanarayana TIFR, Mumbai September 21, 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))

B.Satyanarayana TIFR, Mumbai September 21, 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.

B.Satyanarayana TIFR, Mumbai September 21, 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)

B.Satyanarayana TIFR, Mumbai September 21, 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

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

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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!

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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

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

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

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

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

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

B.Satyanarayana TIFR, Mumbai September 21, Tests on signal pickup schemes Attenuation = 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 

B.Satyanarayana TIFR, Mumbai September 21, 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

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

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

B.Satyanarayana TIFR, Mumbai September 21,

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

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

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

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

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

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

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

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

B.Satyanarayana TIFR, Mumbai September 21, 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

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

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

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

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

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

B.Satyanarayana TIFR, Mumbai September 21, Discriminator response

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

B.Satyanarayana TIFR, Mumbai September 21, Output driver

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

B.Satyanarayana TIFR, Mumbai September 21, channel NINO board Calibration

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

B.Satyanarayana TIFR, Mumbai September 21, HPTDC architecture

B.Satyanarayana TIFR, Mumbai September 21, HPTDC specifications

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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

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

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

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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

B.Satyanarayana TIFR, Mumbai September 21, 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)