1 / 28

Hamamatsu R2046PT vacuum photodiode

Hamamatsu R2046PT vacuum photodiode. Outer diameter: 76 mm Length : 55 mm Effective dia. : 67 mm min. Window : Borosilicate Photocathode : S-20 multialkali Wavelength : 300 nm – 700 nm (peak at 420 nm)

christmas
Download Presentation

Hamamatsu R2046PT vacuum photodiode

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Hamamatsu R2046PT vacuum photodiode Outer diameter: 76 mm Length : 55 mm Effective dia. : 67 mm min. Window : Borosilicate Photocathode : S-20 multialkali Wavelength : 300 nm – 700 nm (peak at 420 nm) Sensitivity : 60 mA/Lm min, 80 mA/Lm typ Dark Current : 100 pA max at 90 V Standard Voltage: 90 V • TRIUMF ran these at around 50 nA, as did npdgamma. • At 35 GHz, 10 p.e. per event would be 56 nA

  2. current helicity - + - + - + - 6 A 3.6 pA (0.6 ppm p-p) ( ppm) time Size of Qweak 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 !

  3. Shot Noise equivalent noise bandwidth [Hz] or [A2] one-sided shot noise, charge quantum [C] current [A]

  4. Aliasing

  5. Integral From Samples (we want the analog bandwidth low) • sample at the center of each interval (n samples) • Q = (sum of samples) x (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

  6. Averaging of Digitization Noise (we don’t want the analog bandwidth too low) • 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 (f3db= 30 kHz) and 18 bit ADC at mid range: • condition Q rms noise before channels channels • (e) integration () (FWHM) • beam ON 50,000 69 mV 1420 3339 • best possible 1 0.31 mV 6.3 15 • So this is OK even for very quiet signals. • Averaging makes integral equivalent to about 21 bits

  7. “noise” = Asymmetry width with 16 ms quartets [4 x (1/250)s] Noise sourceCharge Quantumnoise (ppm) beam-ON shot noise 50,000 e 280 shot noise during LED tests 2,500 e 63 Lowest possible 6.4 mA noise 1 e 1.2 Current source + 1 MW preamp + TRIUMF integrator 2.3 Only cable + 1 MW preamp + integrator 1.4 Comparison of Different Noise Sources for Qweak • Assuming: • 800 MHz event rate • 20 p.e. per event • 2500 PMT gain • 6.4 mA to preamp electronic noise is small compared to counting statistics even the current source test would reach 10-9 (one ppb) in a day

  8. next spin state one spin state – (1/250) second 200 s settling time (not to scale) t 1 ms NIM gate NIM gate Possible DAQ pattern • integrates for 4 ms • stored as four 1 ms integrals • Tsettle as short as 50 s allowed Rapid spin flip reduces noise from target boiling.

  9. Existing Ion Source Signals • Integration triggered by MPS • signals derived from 20 MHz crystal clock • Qweak integrator uses this clock as well

  10. Signals from the current mode scanning polarimeter Peak photodiode current about 50 nA into a 150 MW transimpedance preamplifier

  11. equivalent noise bandwidth [Hz] or [A2] one-sided shot noise, charge quantum [C] current [A] Shot Noise Recap 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 • in = 7.2 nA rms (7.2 mV with a 1 M preamp) Note that in 1 ms, N = 8 x 105 counts. = 1120 ppm, same as 7.2 nA/6.4 A

  12. “noise” = Asymmetry width with 16 ms quartets [4 x (1/250)s] • Assuming: • 35 GHz event rate for one octant • 10 p.e. per event from vacuum photodiode • 56 nA to preamp • preamp noise 2 ( referred to input). • note that at 20 C and 150 MW, Noise sourceCharge Quantumnoise (ppm)† beam-ON shot noise 10 e 42 lowest possible 56 nA noise 1 e 13 cable +150 MW preamp + integrator ~2 † (divide by ~2 for 1/15 second integral) Comparison of Different Noise Sources for Møller (Note that the beam-on shot noise is the same as counting statistics and can only be reduced by increasing the count rate.)

  13. TRIUMF VME integrator component side: solder side:

  14. Other Noise Thoughts for the Møller Measurement • For the whole detector the counting statistics noise is divided by 8 , but I expect the electronic noise is divided by 16. • Dave Mack points out that, for the current monitors, the relevant noise is for whole detector (42 ppm / 8 = 15 ppm for 16 ms quartets). We should be OK from an electronics standpoint. • We might need ~4 ppm normalization from the Lumis to remove target density fluctuations. Assuming several detectors, we are probably still OK here from an electronics standpoint. • For low noise and high speed the detector-to-preamp distance must be kept small. This will be particularly important if we need high-gain preamps.

  15. Main VME registers • Sample Frequency = system clock / (PERIOD_MULT + 40) • 0 ≤ PERIOD_MULT ≤ 255 • Number of Blocks per integral (1,2,3, or 4) • Samples per Block : 1 ≤ SAMPLE_PER_BLOCK ≤ 16383 • Gate to Trigger Delay = 2.5 ms + (sample period x GATE_DELAY) 0 ≤ GATE_DELAY ≤ 255 • Gate Source: 0=internal, 1=external • System Clock Source: 0=internal, 1=external • Internal Gate Frequency = (100 kHz) / (INT_GATE_FREQ) 1 ≤ INT_GATE_FREQ ≤ 65535 • Individual block sums and total sum for each channel • Firmware Revision Date: REV_DATE always shows the release date of the current firmware revision running in the module August, 2008

  16. Short description of VME Integrator • Quasi-differential isolated BNC connectors – 100 kW from BNC outer conductor to ground. • Input range -10 V to +10 V. Input impedance 12 KW. • Eight integrators per single width VME module. • Module clocked by 20 MHz signal from ion source. Sampling rate set as a fraction of the clock. Range 68 ksps to 500 ksps with 20 MHz clock. • Integration time software selectable – set as a fixed number of samples. (e.g. 2000 samples = 4 ms at 500 ksps) • Module gated by external NIM signal (e.g. MPS). Integration starts a selected time (gate-to-trigger delay) after the leading edge of the gate and runs for preset number of samples. • 32 bit overall sum available to the DAQ via VME bus. This sum can be divided into 1,2,3, or 4 sub- blocks (time intervals) as selected through VME. At full scale, the sum fills up in 1/30 s at 500 ksps. • Internal gate and internal 20 MHz clock provided for testing. • 50 kHz, 5-pole anti-aliasing filter • 18 bit ADC, sample rate up to 500 ksps • Buffered output permits reading previous integral during integration. • Crate power 0.5 A at +12 V and 1.0 A at +5 V August, 2008

  17. + + - - Signal loss at start of spin states • If polarization has not settled by start of integration, some signal is lost • In the case of the above (+ - - +) quartet, more (+) is lost than (-) • For the parity signal itself, this is only a small part of an already small signal and is likely OK • In the case of helicity correlated current or position it may be a problem

  18. Changing gains and offset on the TRIUMF SNS preamp increasegain increasegain • To open the preamp for adjustment, remove the hex nuts from the OUTPUT side and remove the black screws from the INPUT side. • The rotary gain switches are used to select gain of 10k, 100k, 1M, or 10M. Turn the switch counter-clockwise to increase the gain. • The offset is set for 1.0 volts when shipped, but can be changed with the offset adjust pot.

  19. Integral From Samples (trapezoidal rule) • sample at the sides of each interval (n+1 samples) • Q = (average of first and last samples plus sum of others) x (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

  20. VME Integrator Front End Quasi-differential Full-differential

  21. Location of adjustments on TRIUMF MK2 “lumi”-style preamp: M Chan 1 gain Offset adjust 50 25 1 0.5 Chan 1 IN Out Chan 2 0.5 1 25 50 +5 V DC Chan 2 gain M

  22. Location of adjustments on TRIUMF MK2 “main”-style preamp: M Chan 1 gain Offset adjust 4 2 1 0.5 Chan 1 IN Out Chan 2 0.5 1 2 4 +5 V DC Chan 2 gain M

  23. Input Cables Large input capacitance increases the noise gain of the first stage. For Qweak we should limit the input cable capacitance to ~200 pf, for example 5m of RG-62. Some typical cables: TYPE Z0(ohm) C(pF/M) diameter(mm) RG-58 53 94.4 5.0 RG-62 93 44.3 6.2 RG-63 125 32.8 10.3

  24. Firmware Running Modes • Integration starts at the preset time (set via VME) after the gate. • We have tried three modes: • No conversion until gate received. • Continuous conversion – integration starts at next sample period. • Continuous conversion, but timing is re-synched on each gate. • We noticed, for 4 ms integrals, 500 ksps, and 4 x 1 ms blocks: • Mode 1 – first block in four block integral was low (~25 mV). • Mode 2 – no difference in blocks, but phase of two modules coulddiffer by half a sample period (1 ms at our 500 ksps). • Mode 3 – initially seemed to solve both problems, but with long runs,detected small residual block difference (1.5 mV with500-sample blocks). Neither the block offset or small time offset can affect the asymmetry Nevertheless, it looks like we can eliminate both by using scheme 3with sufficient gate-to-trigger delay.

  25. E497 DAQ Sequence for One Spin State

  26. 150 MW I to V Amplifier

  27. shot noise: A Possible Møller Configuration 10 p.e. per event 150 M I-V 35 GHz VME digital signal integrator to DAQ 8.4 V 56 nA vacuum photodiode in shielding outside hall

More Related