Triplet polarimeter - Arizona State Universitydugger/polToGo.pdf · Comparison of GEANT4 study of...
Transcript of Triplet polarimeter - Arizona State Universitydugger/polToGo.pdf · Comparison of GEANT4 study of...
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Triplet polarimeter
M. Dugger, March 2015
M. Dugger, February 2012 2
Triplet production
• Pair production off a nucleon: γ nucleon → nucleon e+ e-.
• For polarized photons σ = σ0[1 + PΣ cos(2φ)], where σ0 is the
unpolarized cross section, P is the photon beam polarization
and Σ is the beam asymmetry
• Triplet production off an electron: γ e- → eR- e+ e-, where eR
represents the recoil electron
• Any residual momentum in the azimuthal direction of the e- e+
pair is compensated for by the slow moving recoil electron.
This means that the recoil electron is moving perpendicular to
the plane containing the produced pair and can attain large polar
angles.
3
Event generator
• Diagrams used
• Screening correction
• Most important diagrams
4
Triplet production (pair like)
• Here we have two electrons in final state and must include
diagrams that have 4 ↔ 5 interchange
1
2
3 4 5
q
Q 1
2
4 3 5
q
Q
1
2
3 5 4
q
Q 1
2
5 3 4
q
Q
time
5
Triplet production (Compton like)
• Includes 4 ↔ 5 exchange
1 2
4 Q
q
5 3
1 2
4 Q
5 3
1 2
5 Q
q
4 3
1 2
5 Q
4 3
time
M. Dugger, February 2014 6
Screening correction
7
Screening correction
• Leonard Maximon informed me that the screening correction for
triplet production should not be important for the beam asymmetry
but was very important for the cross section
• Used the screening correction provided in the paper by Maximon
and Gimm [1] to compare cross section results of the event
generator to values from the NIST
[1] L. C. Maximon, H. A. Gimm Phys. Rev. A. 23, 1, (1981).
8
Comparison plot of total cross section for
triplet production • Black line: Total cross
section from NIST
• Blue points: Total cross
section from event
generator without
screening correction
• Red points: Total cross
section from event
generator with screening
corrections included
• Very nice agreement once screening is included
9
Most important diagrams
• The Mork paper [2] says that the Compton-like diagrams and the
switched electron leg diagrams should be negligible at high
photon energy
[2] K. J. Mork Phys. Rev. 160, 5, (1967).
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Calculations
• Ran 100,000 events at Eγ = 9.0 GeV using:
• Full calculation: σ = 10.856 mb
• Reduced calculation: σ = 10.855 mb
• Reduced calculation neglects Compton-like and crossed electron-
line diagrams
• Reduced calculations are well within 0.1% of full calculations
1
2
3 4 5
q
Q 1
2
4 3 5
q
Q
time
M. Dugger, February 2012 11
Comparison of GEANT4 study of triplet
polarimeter to previous study
• The SAL detector
• δ-rays
• Pair to triplet ratio
• ASU simulation of SAL
• Could SAL have been modified to work in the Hall-D environment?
M. Dugger, February 2012 12
The GW SAL detector • Eγ = 220 to 330 MeV
• 2 mm scintillator converter
• Polarimeter located ~39 cm downstream of converter
• Recoil θ = 15 to 35 degrees
• Recoil φ = 0, 90, 180, 270 degrees with Δφ = 44 degrees
• Analyzing power at the event generator level = 12%
• Analyzing power from simulation 3-4% (post experiment)
• Measured analyzing power = 2.7%
• Quick check - Can ASU reproduce the GW results?
M. Dugger, February 2012 13
δ-ray comparison with Iwata 1993 simulation
• Eδ is δ-ray kinetic energy
after traveling through 1 mm of
scintillator using Iwata’s polar
geometry and scintillator
widths
• BLUE: Current ASU
GEANT4 results
• RED: Iwata GEANT3 (scaled
to GEANT4 results by ratio of
signal integration)
• Shapes of the distributions
look similar
Eδ (MeV) • ASU simulation Eγ = 300 MeV
• Iwata simulation Eγ = 250, 365, 450 MeV
Note: ASU simulation did not wrap scintillators
M. Dugger, February 2012 14
NIST cross sections for triplet and pair
production off carbon
• σpair/σtriplet:
5.75 @ 300 MeV
5.16 @ 9.0 GeV
• Ratio does not vary much over large energy range
M. Dugger, February 2012 15
Comparison of ASU MC of SAL detector to GW results Note: ASU results are for Eγ = 300 MeV and GW is of Eγ = 220 to 330 MeV
Analyzing power:
• At event generator level: 12.6 ± 0.1 % ASU; ~12% GW (no error reported)
• ASU simulation: 2.65 ± 0.05%
• ASU simulation (30 μm Al wrapped scintillators): 2.8 ± 0.1 %
• GW experiment: 2.7% (no error reported)
• GW simulation: 3-4% (range given with no error reported)
• ASU results are in agreement with the GW results for the SAL detector ☺
M. Dugger, February 2012 16
How could the SAL detector be modified to
work in Hall-D environment?
Air → Vacuum Converter rad length → 10-4
E → 9 GeV ΔE pair < 1.5 GeV Analyzing power
2.8(1) %
X 6.9(1) %
X X 12.5(2) %
X X X 10.6(2) %
X X X X 17.5(3) %
M. Dugger, February 2012 17
Dependence of analyzing power on
ΔEpair for 16 sector detector
• Same parameters as previous best configuration but now with 16
sectors instead of 4 paddle SAL design
• Analyzing power fairly constant
for ΔEpair < 1750 MeV
• The 16 sector design increases
the analyzing power to 19.1 ± 0.7 %
from 17.5 ± 0.3 % of the 4 paddle
design (ΔEpair < 1500 MeV) ΔEpair (MeV)
An
alyzi
ng
po
wer
(%
)
M. Dugger, February 2012 18
Recap of modifications that would make
SAL type detector work in Hall-D
Air → Vacuum Converter rad length → 10-4
E → 9 GeV ΔE pair < 1.5 GeV 16 Sector Analyzing power
2.8(1) %
X 6.9(1) %
X X 12.5(2) %
X X X 10.6(2) %
X X X X 17.5(3) %
X X X X X 19.1(7) %
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Detector • Decided to use
Micron S3 design
instead of the S2
• The S3 has 32
azimuthal sectors
instead of 16 for the
S2
22 mm
70
mm
1 mm thick
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Preliminary design (slide 1)
• Micron S3
• Converter
• 200 events thrown
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• Micron S3
• Converter
• Mounting plate and brackets
• Having a removable plate will allow for
easy modification of how the detector is
mounted without having to modify the
chamber
Preliminary design (slide 2)
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• Micron S3
• Converter
• Mounting plate and
brackets
• Chamber with
electrical feed-
through flange, and
blank flange
• Inner dimensions:
11in by 9in by 9in
Preliminary design (slide 3)
Actual design: 12 in by 12 in by 12 in
23
• Includes ribbon cable from
detector to electrical feed-
through
Preliminary design (slide 4)
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• With front door in
see through mode
• 200 events thrown
Preliminary design (slide 5)
25
Simulation
φ (degrees)
En
erg
y d
epo
site
d (
MeV
)
• Generated pairs and
triplets with Eγ= 9 GeV
• Required energy of e+
e- pair to be within 1.75
GeV of each other
• Required energy
deposition in detector
to be greater than 200
keV
• Converter: 35 μm beryllium
• Used full calculation (all diagrams included)
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Simulation results
cro
ss s
ecti
on
wei
gh
ted
co
un
ts
φ (degrees)
• Assumed collimated photon
rate in coherent peak : 99 MHz
• Δt = 4 hours
• Analyzing power: 0.186
• Polarization uncertainty: 0.01
Rates:
• Total rate on device = 955 Hz
• Rate surviving software and trigger cuts = 64 Hz
121
22
PNP
P
where N ≡ Rate surviving cuts * 4 hour,
P ≡ Polarization = 0.4, and
α ≡ analyzing power
Assumed
Polarimeter location (red box)
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Future home
• Sources of magnetic fields in red circles
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B-field study
• Study performed in April 2012
• Applied magnetic field in vertical direction
M. Dugger, April 2012 29
Effect of B-field on δ-rays
x (cm)
x (cm)
y (
cm)
y (
cm)
No field →
350 gauss field →
30
Azimuthal distribution with applied B-field
φ
• 350 gauss field applied A[1+Bcos(2φ)]
A[1+Bcos(2φ)+Ccos(φ)]
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Analyzing power vs. B-field
Anal
yzi
ng p
ow
er (
B)
Field strength (gauss)
Small field → Small systematic effect
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Polarimeter stand in collimator cave
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Upstream of polarimeter stand
• Secondary
collimator
• Secondary
sweep magnet
• Polarimeter
stand
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Further upstream of polarimeter stand
• Primary sweep
magnet
• Secondary
collimator
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Construction
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Vacuum system
• When the polarimeter is installed in the collimator cave, the
vacuum will come from the beam line
• In the test bench, the vacuum has to be provided by a
temporary system
• Using a rotary vane pump for the vacuum system of the test
bench
• Rotary vane pumps will back-stream oil and this issue must be
addressed
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VisiTrap
• VisiTrap will
catch any back-
streaming before
it hits the
vacuum hose
38
Molecular Sieve and Stinger
• Molecular sieve
will catch stray
contaminates
• Loaded sieve
with zeolite and
heated for two
hours
39
Vacuum system attached to chamber (view 1)
• Cleaned chamber
with:
• Acetone
• Methonal
• DI water
• Attached the
vacuum system
40
Leakage and outgassing tests
Procedure:
• Pump down chamber
• Close butterfly valve between vacuum system and chamber
• Record the pressure as a function of time
cycle 1
Slope = 0.0266 mTorr/min
41
Vacuum leakage test results (empty chamber)
• For area and volume calculations of the chamber I included all of
the flanges
• Volume ~ 29.5 liters. Surface area ~ 6500 cm2
• Outgassing rate = (Volume/Area)*dP/dt
• Tim Whitlatch said steel will outgas at a rate of
2E-09 Torr*l/(cc*s)
• It looks like the test is consistent with the dP/dt of the chamber
being from the outgassing of steel: No big obvious leaks
Cycle dP/dt (mTorr/min) dP/dt (Torr/s) V/A*dP/dt (Torr*l/cc*s)
1 0.0266 4.4 * 10^-7 2.00E-09
2 0.0216 3.6 * 10^-7 1.60E-09
3 0.0169 2.8 * 10^-7 1.30E-09
4 0.0091 1.5 * 10^-7 6.90E-10
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• Five hour pump down to ~20 mTorr
• Ql = V*dp/dt found to be 1.80x10-4 Torr*liter/s
• A turbo pump on the chamber with a flow rate of 100 liters/s with
a working pressure of 2x10-5 Torr will have a Qw = 2x10-3
Torr*liter/s
• Pfeiffer vacuum says that a system is adequately tight if Qw >
10*Ql
• Putting a turbo pump with flow rate 100 liters/s on the base of the
chamber should be sufficient to maintain a vacuum of 2x10-5 Torr
Vacuum test results (detector in chamber)
43
Detector upstream view with source stand and
Po210 source
• Teflon fasteners
connect detector
to supports
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Detector downstream view
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Preamps
• Decided to have a parallel development of the preamps:
• Glasgow is building a pre-amplification system based off
of the Rutherford Appleton Laboratory RAL-108 pramps
and custom motherboards
• ASU is using a pre-amplification system from Swan
research (“Box16 preamps”)
46
Swan preamps The STARS detector uses Micron S2
with swan research preamps
Input view Output view
16 channel box
Preamp hybrid Stars detector
47
Preamp to feedthrough cable assembly
• The Micron S3 detector
uses special ribbon
cable connectors
• Could not find suitable
ribbon cables. Instead
used Kapton wires that
were individually
placed in the cable
connector
• 40 Wires attached to
connector in picture
shown
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Detector, cable and source
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Ring side cable
• Only enough
preamps to
instrument the
sectors but
made the ring
side cables
first
50
Preamps wired up and ground connections
• Sector side
cables
• Ring side set
to ground
51
Distribution box connected to preamp
enclosure
• Original
distribution
box
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New distribution box (view 1)
• While Kei was at
ASU getting trained
to be a polarimeter
expert he was able to
help assemble to new
distribution box
Signal plate
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New distribution box (view 2)
Power plate
54
Copper preamp-box grounding (slide 1)
• Preamp supports made
out of anodized
aluminum
• Decided to help ground
the preamp boxes by
using copper foil on the
preamp supports
55
Copper preamp-box grounding (slide 2)
• Lined three sides of the
preamp enclosure with
the copper foil
• View: looking into the
preamp enclosure
through the opening for
the vacuum chamber
feedthrough flange
• Ground connector to ring side of detector
56
Copper preamp-box grounding (slide 3)
• View: looking into the
preamp enclosure from
the top
• Can see the EM-
shielding copper mesh
for the fan inlet/outlet
grounded to the copper
foil
57
Signal plate grounding
• Cutting copper foil
for the signal plate
grounding
• Also grounded to
the input voltages
(power plate)
58
Signal plate and power plate grounding
59
Fan leads
• Routed the fan leads
through the preamp
enclosure towards the
distribution box
60
View of polarimeter with original distribution
box completely removed
61
• Wrapping signal wire around
toroidal core reduces noise
• Putting AC Power Entry Module
(with inline filter and earth-line
choke) into LV supply also helped
with the noise
Noise reduction
62
The silicon detector
• The detector is very much like a diode operated in reverse bias
mode
• As the voltage is increased across the detector, the depletion
region gets larger
• The larger the depletion region, the smaller the capacitance of
the detector
• For each 3.6 eV of energy deposited in the depletion region there
is one electron-hole pair that is created and then swept out of the
detector
63
Noise of preamps versus input capacitance
• Preamp noise has a linear
relationship with the
detector capacitance
Typical noise versus
detector capacitance plot
64
High voltage
Tennelec TC 952 • For the test bench we are using a
temporary power supply that is
rather old
• The permanent power supply will
be provided by JLab and will be of
higher quality
• The temporary power supply has a
ripple of about +/- 5 mV at 60 Hz
65
Ripple and other noise as function of HV (slide 1)
HV = 0V HV = 20V
HV = 40V HV = 60V
10 mV/div
10 ms/div
Using
Po210
source
66
Ripple and other noise as function of HV (slide 2)
HV = 80V HV = 100V
HV = 120V HV = 140V
10 mV/div
10 ms/div
67
Ripple and other noise as function of HV (slide 3)
HV = 160V HV = 180V
HV = 200V HV = 200V
200 mV/div & 1 µs/div
10 mV/div
10 ms/div
α
68
Alpha o-scope picture
• Polonium 210
source
• Alpha energy =
5.3 MeV
• Signal about 500
mV
69
Electron o-scope picture
• Cesium 137
source
• Signal about 25
mV for this shot
• Finer time scale
for this shot (50
ns/div)
70
Data acquisition system at ASU
• Using a Tektronix logging
oscilloscope as a slow ADC
• Acquisition rate ~ 1 Hz
LabView signal express GUI
71
Fit to signal
• Assume voltage has same form
V = [Γr Vm/(Γr - Γf)][exp(Γrt) – exp(Γrt)]
Volt
age
time (μs)
Po210 signal
72
Calibration (sector 3)
Counts
mV
Center = 505.5 mV
• Po210 alpha source
• Ek = 5304.33 keV
• One hour of data
• Calculated sensitivity = 95mV/MeV
73
Alpha-test widths
• Looked at all 32 sectors
• Looks good except for a
single channel (sector 32,
lower preamp-box channel
10)
74
Typical fit to signal for Ba133 source
Volt
age
time (μs)
75
MC Data
• MC
• Generated photon energies: 223, 276, 302, 356, 383 keV
• Smeared energy deposited by standard deviation of 12 keV
• Fit:
• Centers locked to same photon energies that were generated in MC
• Standard deviation was the same for each Gaussian and allowed to vary
• Standard deviation from fit found to be 11+/- 1 keV
• Therefore, resolution of detector plus electronics is about 12 keV for this sector
Ba133 MC compared to data (sector 3)
76
Pile-up study
2.1% of total
• Threw 10 million photon events
• Only 469 events seen on detector
• Assume
• 108 Hz in photon range
between 8.4 and 9 GeV
• Timing window of preamp
pulse to be 18 μs
• For a single sector we expect 0.7%
of events to have more than one
signal in the timing window
• Pile-up should not be much of an
issue
77
Work still to be done at ASU
• Need to complete the positioning system (should be able to finish
this week)
78
Convertor tray
Bottom of converter tray
Top of converter tray
79
Positioning system
• Still need to clean
parts and install
limit switches
• I expect the
positioning system
to be ready to ship
by the end of this
week
80
Chamber crated up
81
Initial work to be done at JLab
• Set up the chamber with vacuum system attached and do leakage
and outgassing tests
• Attach the preamps and make sure that the signals look as they did
at ASU
• Send the signals through the fADC and take data
• Attach the position control system and test
New stuff
82
Chamber
Chamber at JLab
• JLab started
receiving the
polarimeter parts
last week
• Initial test bench
in the
Experimental
Equipment
Laboratory (EEL)
at Jefferson Lab