comet pmt

Extinction Monitor R&D
Masa Aoki
AC-dipole BL
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Puled proton beam for COMET
(COherent Muon Electron Transition)
1.17μsec
108 protons
Radiative pion capture
π − + ( A,Z ) → (A,Z −1)* → γ + (A,Z −1),
Muon decay in flight
γ → e +e−
µ− → e − + ν µ + ν e
Pion decay in flight
π − → e− + ν e
€
100nsec
COMET time window 400nsec
Proton Extinction
leaked proton
108 protons
Proton Extinction :
COMET time window 400nsec
RExtinction
N extra Nextra−9:No. of leaked protons
=
< 10
N pulse Npulse:No. of main protons
In order to achieve 10-16: Proton Extinction<10-9
How to measure the Proton Extinction?：Extinction Monitor
€
Extinction Monitor (Idea No. 1)
Direct measurement of the protons in-between
pulses, pulse-by-pulse base to reject the bad pulse
＜Extinction Monitor Requitement＞
①Radiation hardness
②Fast response
③Good S/N
④Must withstand beam flash
PiP counter
Gas Cherenkov counter
①→Gas IS radiation-hard.
②→Cherenkov light is fast .
③→Choose low-scintillation gas
Gating PMT
④→Off the PMT during main
pulses
Extinction Monitor
Gas
Proton Beam
Cherenkov light
Cherenkov light
Cherenkov light from
leaked proton
Mirror
108 protons
Gating PMT
COMET time window
PMT
Off
On
Off
Gas Selection
Gas Candidates
Gas
N 2O
CO2
C 2H 2
C 2H 4
C 2H 6
SF6
n
1.024
1.038
1.048
1.060
1.046
1.018
50
43.3
50
38.5
16.6
flambl
flambl
flambl
nonflambl
Pressure 50
(atm)
Note
flamma nonble
flambl
scintillation light
・Requirements for gas
1.Refractive index n>1.02 (5GeV/c p)
2.small delayed-scintillation yield
1 proton:signal
108 protons : background
Measurement of Gas Scintillation
α source
(Am241)
E=5486keV
300kBq
after collimation:600Hz
Hamamatsu
R585S
area：5x8mm2
PIN diode
Hamamatsu
S5390-19
area：1x1cm2
α trigger
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Setup
DAQ
PMT
PMT amp.
FADC
pre-amp
shaping amp
DAQ timing
PHADC
dE/dx by α rays.
Trigger DAQ by α on PIN diode.
photon-count scintillation light by PMT.
Tag dE on gas by PIN diode.
Result
Number of photons (/MeV/10nsec)
Gas Scintillation Yields
102
N2
SF6
CO2
C2H6
10
1
10-1
10-2
10
-3
10-4
10
-5
10-6
-800
-600
-400
-200
0
200
400
600
800
1000
(nsec)
* Constant Background Subtracted
Ethane：(1.11 0.09)x10-6 photons/MeV/nsec
Some crude calculations
active area
Cherenkov light
scintillation light
effective area
Gas : C2H6 30 atm(n=1.035)
Effective Area L : 20cm
PMT : 200nm 500nm Q.E.:12%
Solid angle for scintillation light
Ω : 1/100
Detector Model for photon yield estimation
Nch=74 photons/cm
– Frank-Tamm
– 200nm 500nm
photo-electrons on PMT = Nch x L x Q.E. = 178
Nsc=0.11 photon/cm/nsec
– Bethe-Bloch (8-GeV protons, 30 atm C2H6, dE/dx =0.10MeV/cm)
– 108 protons
photo-electrons on PMT (50 nsec window) = 13
S/N = 178/13 = 14 -> Ethane is promissing
C2H6
104
C2H6 Gas Scintillation Yields
103
Number of p.e.
Number of photoelectrons (/10nsec)
Long-life Scintillation
102
10
5
10
104
3
10
1
-800
-600
-400
-200
0
200
400
600
800
1000
(nsec)
102
Long-life Component?
10
wide-time meas.
( 1µsec→ 20µsec)
1
-5000 -4000 -3000 -2000 -1000
•Difference between [-20µs
0
1000 2000 3000 4000 5000
time(nsec)
-2µs] and [+2µs +20µs] is:
(after) - (before) = -107 76
•Not Significant
•We eventually need a beam test with pulsed beam.
Gating PMT
Cherenkov
Cherenkov from offtiming protons
108 Protons
PMT
Detector Active
Off
On
Off
Cherenkov from main pulse : 10A of anode current if the PMT gain = 106
Raise (a) dynode(s) high voltage to stop electrons -> gating-off
-HV
Photocathode
Focus
Electrode
off state
Light
on state
K
1
2
3
...
Dynode
Photoelectron
1-7: Dynodes
8: Anode
Requirements
• Anode current: < 100μA
• on/off ratio = 10
• After Pulse Suppression:
• off gain < 10
• Switching Speed < 100 ns
• Repetition Frequency*: 1 MHz
• Photocathode Coverage*: 100%
• to maximize Cherenkov detection ε
-6
-1
*: Unique feature for this particular application
compare to the LIF (Laser-Induced Fluorescence).
Static Switching Test
HV divider
PMT
Electron Tubes
9954B
Result of Static Test
100 V
400 V
200 V
on gain: 106
on/off ratio by focus electrode: 10-4
on/off ratio by Dy3: 5x10-3
overall on/off ratio: 5 x 10-7
overall off gain: 0.5
Dynamic Switching Development
•Plan
•1st step：Switch only focus electrode at 20 kHz
•2nd step：Switch both focus and dy3 at 20 kHz
•3rd step：Switch both at 1MHz
Block Diagram of
single switching circuit
Electron Tubes 9954B
Anode
Dy12
Dy11
…
Dy10
Dy2
Dy1
Focus
K
CONTROL
Buffer FET
NIM入力
HV
Switching Circuit
Test of the Circuit Alone
HV:1200V
10kHz
Focus Electrode HV
280V
100nsec
On
Gate Input
Off
On
Note: HV was slightly reduced down to 1200 V from 1500 V
just by the limitation coming from a probe of oscilloscope.
on/off ratio
HV:1200V
10kHz
LED light during on state
LED light during off state
LED Output Gain：1
LED Output Gain：70
LED trigger
PMT output
Gate Input
On
Off
On
Off
Note: on/off switching noise is visible but within
100 nsec : no problem
On
on/off ratio
Log Scale
Linear Scale
Off
Off
On/Off ratio
On/Off ratio
On/Off ratio
On/Off ratio
1
10-1
1
0.8
10-2
0.6
-3
10
0.4
LED:6.5V
LED:18V
10-4
-1000 -500
•
•
0
500
1000
1500
2000
2500 3000
time(nsec)
LED:6.5V
0.2
LED:18V
-1000 -500
0
500
1000
1500
2000
2500 3000
time(nsec)
Achieved an on/off ratio of 10-4 for focus electrode switching.
Gain recovery to 80% within 300 nsec
1st step completed -> move to the 2nd step
2nd circuit
Switch both Focus Electrode and 3rd Dynode
PMT output
Focus Electrode HV
Gate Input
w/o PMT
w/ PMT
Fall Time 14nsec
Fall Time 28nsec
Rise Time 14nsec
Rise Time 122nsec
576µA
766µA
The difference is caused by the on resistance of n-FET: still fast enough
HV.1200V
10kHz
On/Off ratio
On/Off ratio
On/Off ratio
On/Off ratio
on/off ratio
1
10-1
1.4
1.2
10-2
1
10-3
0.8
10-4
0.6
LED:5.6V
10-5
LED:18V
10
-6
-1000
-500
•
0
500
1000
1500
2000
2500 3000
time(nsec)
0.4
LED:5.6V
LED:18V
0.2
0
-1000
-500
0
500
1000
1500
2000
no visible signal in the off state:
only upper limit at a single point is shown.
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on/off ratio: < 2x10-6
Rise Time 200 nsec: Still fast enough
Gain Stability after off->on: need improvement
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•
Isolate a power supply for the switching circuit
this isolation is needed for 1 MHz operation anyway.
-> 3rd stage
2500 3000
time(nsec)
Thing To-Do
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•
Increase LED light gain to measure the off gain of the
tandem-gating PMT.
After pulse is visible at a level of 1%: very strange
Rate of after pulse should be decreased as on/off gain
increase (electron tubes: technical reprint R/P061).
This after pulse could be the after pulse of LED.
Laser pulser will be used.
PMT structure dependent?
R329-02 (Hamamatsu) will be tested.
Move to 3rd stage
Independent power supply for the switching circuit.
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To-Do (2)
• Fix a concept of the monitor.
• Design of Gas chamber:
• high-pressure window
• heat load from proton beam
• Beam Optics
• Multiple scattering by pressurized gas:
should be OK (only 0.5 mm @ target)
Note
• What shall we do if the gating-PMT does
not work.
PLZT light shutter.
We can always back to an average
measurement with this device.
Better to have a backup device.
Muon-counter embedded in a beam
dump.
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•
PLZT light switch
• Kerr effect
• off/on = 1/100
• ε=90% (>400 nm)
• for switching
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<ε> 30%
switching speed:
200-300 nsec
Better w/ good PS
50 mm□ 2mm :OK
•