Measurement of Ge detector by New cooling system 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. Noise from environments. We can’t test it.

Energy KEK Side room. HV (P-type semi-con) 60Co 1.33MeV 6μs shaping 671 Amp DAQ Amptek MCA8000A (maru-chan) Set up of measurement 60 Co 1.72[keV] Test pulse 0.79[keV] (3.2ch for ADC) Consistent with the measurement in Tohoku Univ. E γ [keV] Counts

Set up - KEK Ge detector LN2 Dewar 60 Co source

Set up – KEK Vacuum pump Power supply Ge detector Cooling machine Thermo couple

Noise from environments Large 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 them by Test Pulsar.

Noise and resolution by test pulsar Resolution [keV] Power supply Vacuum pump Thermo couple ※ 19.0○○○ 13.6○○× 4.79○×× 0.79××× Contribution [keV] σ 2 energy resolution =(σ 2 crystal +)σ 2 elec +σ 2 power +σ 2 pump +σ 2 thermo

Noise from thermo couple by Ge detector cover Open ↓ 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) ・ 20kHz chopping noise form power supply Output from PreAmp

Noise of Clean power supply It looks good, but energy resolution is bad. → ～ 4[keV] Output from PreAmp

Noise check of power supply Power supply : OFF Vacuum pump : ON →13[keV] Power supply : ON Vacuum pump : ON →19[keV] by test pulse Power supply : ON Vacuum pump : OFF →5[keV] 50[mV] 10[μs] 671 Amp Output

Noise check of power supply Bad Power supply : ON Vacuum pump : OFF →Impossible… Power supply : OFF Vacuum pump : OFF →0.8[keV] same as LN2 Ideal condition Everything connected with Ge detector contribute its noise. →No solution without insulation. 671 Amp Output

Energy resolution of 60 Co 1.33MeV γ-ray We only checked the important part, the contribution of noise from Power supply. [ch] With Power supply Without Power supply Test pulse [keV] Ge Resolution With Power Supply 60 Co Test Pulse We can know each contribution.

Contribution for Energy resolution Energy resolution σ 2 energy resolution =σ 2 crystal +σ 2 elec +σ 2 power +σ 2 vibration Test pulse σ 2 test =σ 2 elec +σ 2 power σ crystal = 1.5[keV] σ elec = 0.85[keV] σ power = 4.6[keV] σ vibration = 0.82[keV] The effect of vibration is small. →Microphonics is small. σ 2 resolution = σ 2 crystal +σ 2 elec +σ 2 vibration →1.9[keV]

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.

Problems and things to do The heat leak around the connection between 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 →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 ) TCTC THTH THTH THTH TCTC

The harmonic wave for heat cycle The heat cycle is made by “LC circuit of fluidity”. Commpressors move symmetrically. →To reduce vibration Electricity ⇔ Fluid