measurement of ge detector by new cooling system 2 @ kek
DESCRIPTION
Measurement of Ge detector by New cooling system 2 @ KEK. May 30 th K.Shirotori. Problems of previous experiment. The heat leak around the connection between Ge detector and the cooling machine. → improvement on this connection . The oscillation of cooling system . - PowerPoint PPT PresentationTRANSCRIPT
Measurement of Ge detector by New cooling system 2 @ KEK
May 30th K.Shirotori
Problems of previous experiment The heat leak around the connection
between Ge detector and the cooling machine.
→ improvement on this connection.
The oscillation of cooling system. Noise from environments.
We can’t test it.
Energy Resolution @ KEK Side room.HV +2500 (P-type semi-con)60Co 1.33MeV6μs shaping time @ 671 AmpDAQ Amptek MCA8000A (maru-chan)
Set up of measurement
60Co 1.72[keV]Test pulse 0.79[keV](3.2ch for ADC)Consistent with the measurement
in Tohoku Univ.
Eγ[keV]
Counts
Set up - LN2 @ KEK
Ge detectorLN2 Dewar
60Co source
Set up – Refrigerator @ KEK
Vacuum pumpPower supply
Ge detector
Cooling machine
Thermo couple
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Noise from environmentsLarge noises are …. Power supply of cooling machine→Prepare two types of power supply(Previous one and “clean” one) Vacuum pump, Thermo couple→Separable
We checked themby Test Pulsar.
Noise and resolution by test pulsarResolution
[keV]Power supply
Vacuum pump
Thermo couple ※
19.0 ○ ○ ○
13.6 ○ ○ ×
4.79 ○ × ×
0.79 × × ×
Contribution
[keV]4.7 13 13
σ2energy resolution=(σ2
crystal+)σ2elec+σ2
power+σ2pump+σ2
thermo
Noise from thermo couple by Ge detector coverOpen
↓Noisy
・ Unstable ground connection・ Electric wave from environment
Noise of Previous power supply Too bad …
↓We didn’t measure this condition.(Same as previous measurement)
・ 20kHzchopping noise form power supply
Output from PreAmp
Noise of Clean power supplyIt looks good, but energy resolution is bad.→~ 4[keV]
Output from PreAmp
Noise check of power supply
Power supply : OFFVacuum pump : ON→13[keV]
Power supply : ONVacuum pump : ON→19[keV] by test pulse
Power supply : ONVacuum pump : OFF→5[keV]
50[mV]
10[μs]
671 AmpOutput
Noise check of power supply
Bad Power supply : ONVacuum pump : OFF→Impossible…
Power supply : OFFVacuum pump : OFF→0.8[keV] same as LN2Ideal condition
Everything connected with Ge detector contribute its noise.→No solution without insulation.
671 AmpOutput
Energy resolution of 60Co 1.33MeVγ-rayWe only checked the important part, the contribution of noise from Power supply.
[ch]
WithPowersupply
WithoutPowersupply
Test pulse[keV]
Ge
ResolutionWith Power Supply
60Co 1.7 5.0
Test
Pulse0.85 4.7
We can know each contribution.
Contribution for Energy resolutionEnergy resolutionσ2
energy resolution=σ2crystal+σ2
elec+σ2power+σ2
vibration Test pulseσ2
test=σ2elec+σ2
power
σcrystal = 1.5[keV] σelec = 0.85[keV] σpower = 4.6[keV] σvibration = 0.82[keV]
The effect of vibration is small.
→Microphonics is small.
σ2resolution =σ2
crystal+σ2elec+σ2
vibration
→1.9[keV]
Temperature @ Cooling machine 2 The final (steady states)
temperature is 97[K]. The contact between Ge
and the cold head is worse than previous measurement.
The heat conducting grease is not enough.
Resistance
0100200300400500600
0 5 10 15 20[hour]
[Ω]
Resistance[Ω ]
ResistanceKEK[Ω ] 4/ 20
ResistanceKEK[Ω ] 5/ 22
Temperature
0
100
200
300
400
0 5 10 15 20[hour]
[K]
Temperature[K]TemperatureKEK[K] 4/ 20
TemperatureKEK[K] 5/ 22
Problems and things to do The heat leak around the connection betwee
n Ge detector and the cooling machine. → Improvement on this connection. The oscillation of cooling system.→Relatively small. Noise (electric).→We need electric insulation between Ge and
cooling machine. Next test.
Next step The first thing is to construct new connection
parts between Ge detector and the cooling machine. This improvement will reduce the heat leak and noise.
The second is to test the long time stability.
Summary It is clear which contribution of noises makes
energy resolution worse. It is most important to insulate Ge detector from cooling machine.
Cooling Mechanism The cooling mechanism
is simply a heat cycle. 1
2
3
4
1→2 : Isothermal absorption (等温吸熱 )2→3 :Adiabatic compression (断熱圧縮 )3→4 :Isothermal heat rejection (等温放熱 )4→1 :Adiabatic expansion (断熱膨張 )
TCTH TH
TH
TC
The harmonic wave for heat cycle The heat cycle is made by “LC circuit of fluidity”.
Commpressors move symmetrically.→To reduce vibrationElectricity ⇔ Fluid