Current Mode Electronics for the Qweak Experiment Des Ramsay University of Manitoba/TRIUMF Qweak Collaboration Meeting TRIUMF, Vancouver October

Synthetic Quartz Scintillator Bars Shielding Wall Toroidal Magnet Liquid Hydrogen Target Electron Beam Layout of the Qweak Experiment Front-end electronics in extra shielding behind the wall

800 MHz 50 p.e. per event x ,000 e per event 6.4  A 6.4 V VME digital signal integrator 1 M  I-V to DAQ in shieldingoutside hall Nature of the Current Mode Signals shot noise:

I-V Preamplifier specs Gain: V out /I in = 1 M  with option of up to 10 M . Set by switches on board. Output: 0 to +10V. Adjustable  2V offset. Drives 130 m RG-213 Input: 10  A range. (e.g. +1  A to -9  A with +1 V offset.) Tolerates 5m of RG-62 on input. (Noise set primarily by length of input cable.) Bandwidth: f 3db = 30 kHz. (settles to <10 -4 in 50  s) Density: two amplifiers per module (one per detector bar). Uses 5 V DC Supply. Ground fully isolated by internal DC-DC converter. BNC connectors. Center conductor negative on input. Small size for ease of shielding.

MK1 Preamplifier at TRIUMF

Offset adjust Chan 1 Chan 2 Out IN Chan 1 gain Chan 2 gain +5 V DC MM MM MK2 Preamplifier Reduced power supply noise Switchable gains

Noise Measurements on Preamps Noise measured using x200, 50 kHz 5-pole amp, scope 500 kSPS Noise referred to preamp output. Used various lengths of RG-58C/U on input – measured capacitance. Compare to shot noise (for 1 M  ) :  70,000  V beam on  10,000  V LED test  300  V best-case battery test Noise in  V rms C in (pf) Measured Pspice open Gain (M  ) Noise (  V rms ) Channel Channel MK M  gain MK pf

four 1 ms integrals target bubbling not seen on few ms time scale T settle should be short to minimize dead time one spin state – (1/250) second 1 ms t next spin state  50  s settling time (not to scale) Q weak “1 kHz” Integration Scheme

Existing Gzero Ion Source Signals signals derived from 20 MHz crystal clock. Qweak integrator should use this clock as well Integration triggered by MPS (is present form OK?)

Integration time software selectable 1/300 s to 1/30 s To be set as a fixed number of samples. Integration triggered by external NIM signal (e.g. MPS) Triggers a selected time after leading edge and runs for pre-set number of samples. Clocked by 20 MHz NIM signal from ion source. Divided by pre-scale to get sample rate. Full differential high-impedance input provides common mode noise rejection. 50 kHz, 5-pole anti-aliasing filter. 18 bit ADC,  500 ksps. Four 32-bit sums per integral available to DAQ on VME. No dead time between the four periods. Buffered output permits reading previous integral during integration. Eight integrators per single width VME. TRIUMF Current Mode VME Integrator

VME registers Sample period multiplier, k. Sample period = k*(1/sys_clock) Number of samples per block, I Number of sample blocks, m. m = 1, 2, 4. Gate to Trigger Delay, n. Delay = n*(1/sys_clock). Gate source, EXT/INT. System Clock source, EXT/INT. Block integration time = k*l*(1/sys_clock). Total integration time = k*l*m*(1/sys_clock). (In the FPGA it may be simpler to do 4 sample blocks and a total at all times.) Data Readout Sequence number. Shows if a measurement has been lost or skipped. Block 1-4 sums. 32 bit. Total sum. 32 bit. Total number of samples actually taken -- Should equal k*l*m. Valid data flag or new data ready flag. Data buffer empty flag, if the data is buffered. VME section details

Outstanding Questions PREAMPS: What radiation dose will they take? (Dave Mack is testing one) What gain range should we use on the production amps? (MK2 has 1,2,5,10 and 0.5, 1, 2.5, 5 for evaluation.) Where, exactly, should we mount them? INTEGRATORS: Are we using 1/250 s spin states, and is 50  s settling time reasonable? Is ion source clock 20 MHz and can we get it as a NIM signal.? Is MPS good as a trigger and can we get it as a NIM signal?

approximate signal with samples Q = (average I)(T) band limit signal to small fraction of sampling frequency to eliminate the wiggles and kinks. we impose an analog cutoff at 1/10 the sampling frequency Integral From Samples (rectangular rule) 12 3 n … T = n  t t I tt

Averaging of Digitization Noise The 18 bit ADCs have ~0.5 LSB rms noise per sample. This is reduced by averaging ~500 samples per integration. This will only work if raw signal spreads over enough channels. Assuming equivalent noise bandwidth 47 kHz (f 3db = 30 kHz) and 18 bit ADC at mid range: condition Q rms noise before channels channels (e) integration (  ) (FWHM) beam ON 50, mV LED test 1, mV battery test mV  So this is OK even for very quiet signals.

rms noise on a 1 ms integral Condition noise (ppm) beam-ON shot noise 1120 shot noise during LED tests 160 shot noise during battery tests 5 preamplifier noise 2 digital integrator noise 1-2 Comparison of Different Noise Sources

chan 1 chan 2 Input side Output side megohms Channel 1 is shown set for 1 M  and channel 2 for 0.5 M  To change gain move the set switch back towards the input side and move the one you want towards the output side. Note the gains increase away from the center. The offset is set for 1.0 volts when shipped, but can be changed with the offset pot To open the preamp for adjustment, remove the hex nuts from the OUTPUT side and remove the black screws from the INPUT side. Changing gains and offset on the TRIUMF MK2 preamp

Qweak Collaboration Spokespersons Bowman, J. David - Los Alamos National Laboratory Carlini, Roger (Principal Investigator) - Thomas Jefferson National Accelerator Facility Finn, J. Michael - College of William and Mary Kowalski, Stanley - Massachusetts Institute of Technology Page, Shelley - University of Manitoba Qweak Collaboration Members Armstrong, David - College of William and Mary Averett, Todd - College of William and Mary Birchall, James - University of Manitoba Botto, Tancredi - Massachusetts Institute of Technology Bruell, Antje - Thomas Jefferson National Accelerator Facility Chattopadhyay, Swapan - Thomas Jefferson National Accelerator Facility Davis, Charles - TRIUMF Doornbos, J. - TRIUMF Dow, Karen - Massachusetts Institute of Technology Dunne, James - Mississippi State University Ent, Rolf - Thomas Jefferson National Accelerator Facility Erler, Jens - University of Mexico Falk, Willie - University of Manitoba Farkhondeh, Manouchehr - Massachusetts Institute of Technology Forest, Tony - Louisiana Tech University Franklin, Wilbur - Massachusetts Institute of Technology Gaskell, David - Thomas Jefferson National Accelerator Facility Grimm, Klaus - College of William and Mary Hagner, Caren - Virginia Polytechnic Inst. & State Univ. Hersman, F. W. - University of New Hampshire Holtrop, Maurik - University of New Hampshire Johnston, Kathleen - Louisiana Tech University Jones, Richard - University of Connecticut Joo, Kyungseon - University of Connecticut Keppel, Cynthia - Hampton University Khol, Michael - Massachusetts Institute of Technology Korkmaz, Elie - University of Northern British Columbia Lee, Lawrence - TRIUMF Liang, Yongguang - Ohio University Lung, Allison - Thomas Jefferson National Accelerator Facility Mack, David - Thomas Jefferson National Accelerator Facility Majewski, Stanislaw - Thomas Jefferson National Accelerator Mammei, Juliette - Virginia Polytechnic Inst. & State Univ. Mammei, Russell - Virginia Polytechnic Inst. & State Univ. Mitchell, Gregory - Los Alamos National Laboratory Mkrtchyan, Hamlet - Yerevan Physics Institute Morgan, Norman - Virginia Polytechnic Inst. & State Univ. Opper, Allena - Ohio University Penttila, Seppo - Los Alamos National Laboratory Pitt, Mark - Virginia Polytechnic Inst. & State Univ. Poelker, B. (Matt) - Thomas Jefferson National Accelerator Facility Porcelli, Tracy - University of Northern British Columbia Ramsay, William - University of Manitoba Ramsey-Musolf, Michael - California Institute of Technology Roche, Julie - Thomas Jefferson National Accelerator Facility Simicevic, Neven - Louisiana Tech University Smith, Gregory - Thomas Jefferson National Accelerator Facility Smith, Timothy - Dartmouth College Suleiman, Riad - Massachusetts Institute of Technology Taylor, Simon - Massachusetts Institute of Technology Tsentalovich, Evgeni - Massachusetts Institute of Technology van Oers, W.T.H. - University of Manitoba Wells, Steven - Louisiana Tech University Wilburn, W.S. - Los Alamos National Laboratory Wood, Stephen Thomas - Jefferson National Accelerator Facility Zhu, Hongguo - University of New Hampshire Zorn, Carl - Thomas Jefferson National Accelerator Facility Zwart, Townsend - Massachusetts Institute of Technology

Shot Noise one-sided shot noise, [A 2 ] equivalent noise bandwidth [Hz] or charge quantum [C] current [A] Example, 1 ms integration with beam on, assuming 800 MHz: Q = 50,000 e I = 6.4  A (800 MHz x 50,000 e) B = 500 Hz i n = 7.2 nA rms (7.2 mV with a 1 M  preamp) Note that in 1 ms, N = 8 x 10 5 counts. = 1120 ppm, same as 7.2 nA/6.4  A

Q weak Front End Electronics

four 1/120 second integrals multiples of 60 Hz cancel in sum individual integrals show if 60 Hz (or odd harmonics) was present one spin state – (1/30) second (1/120) t next spin state  200  s settling time (not to scale) Old “120 Hz” Q weak Integration Scheme

Block Diagram of Current Mode Electronics

Prototype Dual Preamplifier

time current 3.6 pA (0.6 ppm p-p) ( ppm) 6  A helicity Size of Q weak Signal figure shows regular spin flip; in practice use or for 50 kHz noise bandwidth, rms shot noise is 70 nA on a scope the noise band would be  100,000 x the signal !

charge counts Q0Q0 - helicity+ helicity charge ADC error +s -s ADC reads S channels low below Q 0 and jumps to S channels high above Q 0 This causes the measured asymmetry to depart from the real asymmetry, A 0, by an amount, where  is in channels. The DNL won’t introduce an asymmetry when none is there, it only changes an existing one. Differential Nonlinearity (DNL) Example

Summary of Electronics Needs

DSP eprom external trigger serial port (diagnostic) channel 1 channel 2 TRIUMF E761 VME Module

Number of samples Offset Sample rate Calibration

-16-bit ADC - DSP summing - calibration mode - channel offset and gain - takes N samples when triggered - adjustable delay from trigger - delivers gate during integration - features can be programmed TRIUMF Parity 2 module