qweak main detector status
DESCRIPTION
Qweak Main Detector Status. Des Ramsay, Dave Mack, Michael Gericke. Main Detector Project Overview. The Main Detector WBS has spent 85% of our $468.5K budget. $$ All custom PMT’s are at JLab and tested. $ All magnetic shields are at JLab (and actually fit!) - PowerPoint PPT PresentationTRANSCRIPT
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Qweak Main Detector Status
Des Ramsay, Dave Mack, Michael Gericke
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Main Detector Project Overview
The Main Detector WBS has spent 85% of our $468.5K budget.
$$ All custom PMT’s are at JLab and tested.
$ All magnetic shields are at JLab (and actually fit!)
$ All TRIUMF low-noise preamplifiers are at JLab and tested.
$$$ Quartz bar shipments are complete. (some QA remaining)
$$ Quartz lightguide shipments are complete. (lots of QA remaining)
Remaining funds are for digital integrators, voltage dividers (bases), detector housing, and support structure.
Several person-years of design, testing, and assembly remain.
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Irradiation Tests
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Glue Joints in the Optical Assembly
There will be 5 glue joints per optical assembly which all need to be strong and UV transparent down to 250 nm.
The central joint also has to be rad-hard: 100kRad nominal, (1 MRad for plan B)
Glue joints
e-Two glue candidates.
Elastomer Adherence to Quartz
Working Viscosity
Strength
SES 403No
(peels off easily)
Low (veg. oil)
poor (like
tough gelatin)
SES 406 Yes
High (cold
engine oil)
excellent
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Optical Transmission Apparatus
Spectrophotometer and software by Carl Zorn of JLab Detector Group.
Monochromator
Integrating sphere with PMT
Sample on
translation stage
out in
monochromator
Integrating sphere + PMT
Due to lamp instabilities, we squat at one λ, normalize the beam with sample out, then measure with sample in, and repeat to estimate the random error.
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Samples
Two glued samples and experimental controls.
One of our original
100 cm x 2.5 cm x 12 cm
prototype bars of Spectrosil 2000 was cut lengthwise into 15 slides of about
6 cm x 2.5 cm x 12 cm.
Except for a few avoidable new scratches, the 6cm x 12 cm faces remained in excellent condition.
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Analysis
The correction for Fresnel reflection is typically 8%.
Using precision n(λ) from Melles-Griot and a next higher order expression, the error on this correction is below 0.1%.
Random errors are dominated by short-term lamp instability of about 0.2%.
T(λ) = Corr(λ) x
(Iin(λ) – Idark)/(Iout(λ) – Idark)
Corr(λ)
Corr(λ) = 1/(T(2) + T(4))where
T(2) =TF2
T(4) = TF2(1-TF)2
TF = 4n1n2/(n1+n2)2
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Pre-irradiation Baselines2.5 cm Spectrosil 2000
(non-glued control)5.0 cm Spectrosil 2000+ glue joint
Below 300 nm, • SES403 glue joint reduces transmission 0.25%.• SES406 glue joint reduces transmission 0.75%. • With SES406, total light losses from all glue joints
will be less than 3%.
The control data are almost consistent with 100% transmission as expected for undamaged Spectrosil 2000.
(The small dip near 275 nm is repeatable but not understood.)
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Irradiation
Irradiations with a 60Co source were done by Nuclear Services at North Carolina State University.
Initial 100 KRad irradiation
(nominal Qweak dose):
controls SQ2, Air-Gap, and
glued samples SES403, SES406.
Final additional 1 MRad irradiation
(plan B dose):
control SQ2, and
glued sample SES406
from Nuclear Services website:
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Before and After 100 KRad
Our central glue joint will not suffer any significant rad damage during the Qweak experiment.
The 1 MRad data are still under analysis by Katie Kinsley (Ohio U.), but the preliminary results suggest no detectable damage.
2.5 cm Spectrosil 2000
(non-glued control)
5.0 cm Spectrosil 2000
with glue joint
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PMT Nonlinearity
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PMT Nonlinearity Measurements
Our goal is to keep the detector chain nonlinearity below 0.1%. (See D. Mack at http://qweak.jlab.org/doc-public/ShowDocument?docid=172)
Measuring linearity to better than 1% requires special techniques:
1. We previously developed a 2-LED method with sensitivity at the few times 10-4 level.
(See M. Geicke at http://qweak.jlab.org/doc-public/ShowDocument?docid=575)
But Riad Suleiman wasn’t happy. If the nonlinearity is frequency dependent, this method may measure it only in the DC limit. So …
2. In the last few weeks, summer student M. Andersen (U. Manitoba) has
demonstrated a new 3-LED technique which measures nonlinearity near the reversal frequency with sensitivity at the 10-6 level.
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cathode current
anod
e si
gnal
IAC
VAC
IDC
quadratic nonlinearity
linear
Testing PMT linearity
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Definitions
The PMT transfer function from cathode to anode can be written
Vanode = G Ik (1 + βIk)
Vanode is the effective voltage at the anodeG is the gain x 50 Ohmsβ is a small nonlinearity parameterIk is the cathode current or signal
Differentiating,
ΔVanode = GΔIk (1 + 2βIk)
The result depends on the load, so β alone isn’t very useful. We will call the dimensionless quantity 2βIk “the nonlinearity”: the relative error made when making a measurement with a bent ruler.
It may help to think of nonlinearity as a load-dependent gain:
G’ = G(1+βIk)
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New 3-LED Technique
• Measures nonlinearity away from DC limit.• Self-normalizing: insensitive to drifts • Great sensitivityWe have only demonstrated proof of principle. No reliable numbers yet.
• Nonlinearity is equivalent to self-multiplication. Multiplying two frequencies yields sum and differences. The appearance of mixing peaks at f1+-f2 therefore gives access to the nonlinearity.
Technique requires:
1. one DC LED to provide the load
2. one AC LED at f1 to mimic a small signal
3. one AC LED at f2 (near f1) to induce the mixing.
Inserting
Ik(f) = IDC + I1 + I2
into
Vanode = GIk(1 +βIk)
the nonlinearity in terms of easily measurable quantities is
2 IDC 50Ω |V(f1+-f2)| / (|V(f1)|| V(f2)| )
f1 f2 f1+f2f2-f1
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Low Gain Base Tests
Michael Gericke
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PMT Low Gain Base Testing StatusWe went through several generations of low gain dividers since summer 2006
We need a nominal gain of 2000.
We want to be able to go up to a “contingency” gain of 16000.
Last year we had 3 base generations with 4 and 5 active stages respectively:
Voltage required to get to a gain of 16000 was still too high for 5 stages.
Go to more stages :
7 active stages with 6 141 kOhm Resistors and 2 Zeners
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Small setup at University of Manitoba:
As before: Used reference PMT 128 and 2 280 nm UV LEDs
Assembly and measurements done bysummer student Charles Koop
Currently at JLab
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Dark current increased too much withvoltage with 5 stage. 7 stage is good.
Several tests indicate the dark currentis mostly coming from the PMT (not leakage in the base)
The dark current is now only a 0.05% dilution for a 6 A nominal signal.
Measured gain vs voltage for 5 and 7stage
Contingency gain range can be obtainedwith 1000 to 1250 Volts of bias.
Everything looks good so far, but morestages means less stability and linearity measurements are in progress
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MiscellaneousDave Mack
High gain divider tests
Panel stiffness measurement
Magnetic field sensitivity
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High Gain Divider Tests• Mitchell Andersen also built our first high gain divider to look at pulses. (gain = few x 106)• Large pulses OK, but found unacceptable baseline noise for spe at 1-2 mV.• Problem tracked down, with great difficulty, to noisy zeners. • For now, we are using all-resistive dividers which give acceptable pulses and quiet baselines for
upcoming cosmic tests. • Lower noise zeners and external amplifiers were ordered and have arrived. • Tests continuing.
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Panel Stiffness Measurement
• The glued quartz bars will be supported in front by a low radiation length (1.7%) composite panel.• The prototype panel from Composiflex has a core of IG-71 Rohacell (0.075 g/cm3) wrapped in 7 layers of
epoxy-impregnated Carbon fiber.
The deflection was measured with a Mitutoyo Dial Caliper BS-74 under a load representing the 10 kG weight of a 200 cm long quartz bar.
Measurements by Mkrtchyan et al.
Maximum deflection is 0.5 mm. We’re pretty happy with this, but still need to check that the glue joint won’t pop during transport.
Blue = more realistic loading
Application of weights
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Magnetic Field SensitivityStray fields from QTOR will be < 0.1 Gauss. (W. Falk) Earth’s field dominates.
10% variation < 1% variation
Mkrtchyan et al.
Sensitivity of our 5” PMT’s with Vk-d1 = 280 V is negligible with shields.
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Current Mode Electronics Update
Des Ramsay
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Overall Tally of Current Mode Electronics
14Octal
integrators
14 main
14 Lumi28
Dual preamps
TOTAL MODULES
610SPARE MODULES
818MINIMUM MODULES
63362736TOTALS
2020Essential Beamline Monitors
44Target BPM (in scattering chamber)
22“Fake BPM” isolation monitor
11“Fake BCM” isolation monitor
2Lumi1 + 122Soft background detector
2main1 + 122Real-time isolation detector
16Lumi8 + 41616Lumi Monitors: 2 monitors x 8 tubes
16main8 + 41616Main Detectors: 8 bars x 2 tubes
VME
integrator
channels
type
I-V
modules +
spares
I-V
channels
voltage
signals
current
signalsITEM
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Current Mode Electronics Summary
10 dual preamplifiers (20 channels) with transimpedance selection 0.5, 1, 2, 4 M are already at JLab for the main detectors.
4 More main detector style preamps are finished at TRIUMF. 14 Lumi-style preamps with gain selection 0.5, 1, 25, 50 M are also complete.
The testing is almost finished at TRIUMF.
Paul king is testing the prototype VME octal integrator. We have made a couple of firmware upgrades and the module appears to be working properly. We now need more detailed tests.
Preliminary designs are ready for a TRIUMF test source that will give us a realistic current of ~5 A, upon which a small simulated parity violating signal can be superimposed.
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Modulated Current source
Reference current of 5 A DC
Choice of 16 modulations from ~10-6 to ~10-9
Unmodulated reference channel available
Responds to external spin state signals, or can run in stand-alone mode.
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Modulated Current Source
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Modulated Current Source Block Diagram
Voltage ramp on small capacitor
~10-15 A
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Some Comments on Our Frequency Acceptance
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switching function -- 18 ms quartet
4 ms
4 ms 4 ms
4 ms
0.5 ms0.5 ms
0.5 ms 0.5 ms
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Switching function in time domain = ten regular 18 ms quartets.
Fast Fourier Transform (FFT)
Odd multiples of 55.5 Hz Hzms
5.5518
1
FFT essentially assumes waveform goes on forever
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Simulation for finite run times
The FFT does not properly account for finite run times
For this I took a test sinusoid, multiplied by the switching function and integrated over the run time
I stepped the frequency and integrated each frequency for the run time
The simulation shows the same “acceptance” frequencies as the FFT,but shows a sensitivity to “off resonance” frequencies for finite run times.
For very long run times, only signals coherent with the switching function remain
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100 random 18 ms quartets = 1.8 s run
1000750500250
222.2 444.4 666.6 888.8
111.1
333.3 555.5 777.7
Exactly equal + and – rejects DC The 4 ms spin state rejects multiples of 250 Hz The quartet structure rejects multiples of 111.1 Hz
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200 random or 9 ms doublets = 1.8 s run
1000 Hz750 Hz500 Hz250 Hz
222.2 Hz 444.4 Hz 666.6 Hz 888.8
Exactly equal + and – rejects DC The 4 ms spin state rejects multiples of 250 Hz The doublet structure rejects multiples of 222.2 Hz
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400 random or 4.5 ms singlets = 1.8 s run
250 Hz 500 Hz 750 Hz
1000 Hz
Each spin state is integrated for 4 ms
1/(4ms) = 250 Hz, so multiples of 250 Hz are rejected
States are randomly chosen, so in general there will notbe exactly the same number of + and -, and there will besome sensitivity to DC.
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A-B (Lumi-BCM), 25 A, LH2, 2mm square raster, normal target cooling and pump speed
60
120
180
240
300
360
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(A-B)/(A+B), 10 A, LH2, 2mm square raster, normal target cooling and pump speed
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Next 6 Months
• Delivery of last preamplifiers to JLab (D. Ramsay)
• Continue testing prototype sampling ADCs (P. King)
• Support structure design
• Full-scale glue-up (Yerevan, Mack)
• Complete scintillation measurements (K. Kinsley)
• Complete low gain divider design (Gericke)
• Complete high gain divider design (Mack)
• Procure dividers (Mack, Gericke)
• Full-scale prototype (Yerevan, Mack)
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Main Detector Summary
• We’re making adequate progress. Need more designer help.
• Full-scale optical assembly and cosmic tests by end of summer ’07.
• Full-scale prototype module fall ’07.
• Procurement of production module parts in early ’08.
• Complete gluing and module assembly in summer ’08.
• Production modules complete by Sept. 1, ’08.
… followed by more QA and detailing until installation
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END
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Supplementary Slides Follow
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Expected Performance (updated 7/12/07)
Isolates the elastic e+p e+p channel good elastic focus with few hard inelastics.
Operates close to counting statistics 3.5% excess noise from sum of: showering,
pe-statistics, and nonuniformity of light collection at a tilt angle of 0 degrees
(where main faces of 12 o’clock bar are vertical)
Insensitive to backgrounds
(weighted by f(1-Abkg/Ael) )
Elastic channel bkg: O(1%) electrons + photons
photons from primary channel unknown
photons from neutron capture unknown
Insensitive to 100 kRad radiation damage (assuming 250nm cutoff)
Fused silica, brand name “Spectrosil 2000”,
Glue joint tested to 1 MRad
Modest Q2 bias 2.5%
Might worsen with radiation damage
Nonlinearity less than 1% < 1x10-4 with gain = 2000 base
Switchable between
current-mode (PV production) and
pulsed-mode (background studies)
PV production – 2x103 gain
Bkg studies – 2x106 gain
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Our 2-LED Technique
Issue: Measures nonlinearity in the DC limit O(min-1)Annoyance: Precision is limited by the stability of the AC LED during the
measurement, so serious measurements require 24 hours of burn-in.
It works! Here, 2βIk= few x 10-4
Using early 5-stage prototype:Changes in small AC signal due to shifts in DC load give
access to the nonlinearity. Technique calls for:
•one DC LED to provide the load
•one AC LED to mimic a small signal
Doing the math:
Vanode = GIk(1 +βIk)
Ik(f) = IDC + IAC
Then to non-mixing order,
Vanode(f) = G(1+βIDC)IDC + G(1+2βIDC)IAC
The non-linearity is
(ΔVAC/VAC) / (ΔIDC/IDC)
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Bias on <Q2> Due to Detector Response
The PV asymmetry is proportional to Q2, so we need to understand <Q2> with an error << 2%.
Our earlier estimates of <Q2> included the acceptance, cross section, and radiation, but neglected the detector bias.
Simulations indicate that our current
mode experiment will give events far from the
center of the bar about 5% higher weight.
Because our higher Q2 events have a wider distribution, the weak correlation with yield increases the detected <Q2>.
The new <Q2> = 0.02754.
5% bias
pe
Y
X
The estimated detector bias on Q2 is +2.5%.
This could worsen with radiation damage, and will be measured with wire chambers.
Y
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Use of a Pre-radiator: Trade-offs A shower-max preradiator could increase Signal/Background.
But at what cost?
Potential for increasing S/B > 30 Excess noise increases to 12%.
A 2 cm Lead sheet in front of our quartz bars would increase S/B by > 30, but would require 390 additional hours, and increase the radiation dose to 3 MRad. Won’t need this if backgrounds are only 1%.
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Photo-electron Count
PDG formula predict ~900 photons
above 250 nm cutoff:
Simulation gives ~ 1000 photons
on average for arbitrary path lengths.
~250 photons get to the cathode the rest is lost
The photon is counted only if it makes a volume
transition from the PMT window to the cathode.
The mean number of photoelectrons per event:
No Wrapping: ~40 Pes Millipore : ~50 Pes
Original design criteria: > 10 PEs
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Target
QTORMini-torus
R-3 Chambers & Rotation System
R-2 HDCsPb Shielding
Beam
Experiment Component Details
GEMs
R-3 VDC Main Detectors
Lumis
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Detector Design
Elastic envelope on bar of Spectrosil 2000.
Dimensions are 200 cm x 18 cm x 1.25 cm.
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Modulated Current Source -- I/O
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integrates for 4 ms stored as four 1 ms integrals Tsettle as short as 50 s allowed
Anticipated DAQ pattern
one spin state – (1/250) second
1 ms
t
next spin state
200 s settling time(not to scale)
NIM gate NIM gate
Rapid spin flip reduces noise from target boiling
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switching function -- 18 ms quartet
4 ms
4 ms 4 ms
4 ms
0.5 ms0.5 ms
0.5 ms 0.5 ms
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switching function -- 18 ms quartettest signal -- 9 ms period sinusoid
9 msf =111.1 Hz
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(18 ms quartet) x (9 ms period test sinusoid)
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product
integral
any multiple of
will integrate to zero regardless
of phase
Hzms
1.1119
1
The 18 ms quartet rejects multiples of 111.1 Hz
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switching function test signal
product
integral of product
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time
current
3.6 pA(0.6 ppm p-p)( ppm)
6 A
helicity- + - + - + -
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 !
3.0zA
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• sample at the center of each interval (500 samples)• first sample 1 s after gate• Q = (sum of samples) x (t)• band limit signal to small fraction of sampling frequency to eliminate the wiggles and kinks.
Integral From Samples (rectangular rule)
= 1 ms
2 s
1 s
NIM gate
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• 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
Integral From Samples (trapezoidal rule)
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Prototype TRIUMF VME integrator details
FPGA
FPGA Prog/Debug Ports
VME Module SelectSwitches
Status LEDsVME AccessExt Clock EnbExt Gate Enb
Ext NIM Gate
Ext NIM Clock
DC-DCConverter
ADC
8 inputs
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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?)
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charge
counts
Q0
- helicity+ helicity
charge
ADCerror
+s
-s
• ADC reads S channels low below Q0 and jumps to S channels high above Q0
• This causes the measured asymmetry to depart from the real asymmetry, A0, by an amount , where is in channels.
• The DNL won’t introduce an asymmetry when none is there, it only changes an existing one.
)(0 sAA
Differential Nonlinearity (DNL) Example
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Switching function in time domain = one 18 ms quartet.
Fast Fourier Transform (FFT)
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B (BCM only), 10 A, LH2, 2mm square raster,normal target cooling and pump speed
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A (Lumi sum only), 10 A, LH2, 2mm square raster, normal target cooling and pump speed
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5 inch S20 Cathodes have a specified thermionic dark current of ≤ 0.1 pA at room temperature = 0.2 nA (Gain 2000 Low-Gain Base)
Several tests indicate the dark currentis mostly coming from the PMT (not the base)
The dark current is a 0.05% dilution for a 6 A nominal signal.
Contingency gain range can be obtained in the range of 1000 to 1250 Volts of bias.
The cathode currents were measured with the diode base.
LED intensity was monitored andremained constant over the measurements.
Everything looks good so far, but morestages means less stability and linearity measurements are in progress