Measurement of Ge detector by New cooling system

Measurement of Ge detector by New cooling system 2 @ KEK May 30 th K. Shirotori

Problems of previous experiment n The heat leak around the connection between Ge detector and the cooling machine. → improvement on this connection. We can’t test it. The oscillation of cooling system. n Noise from environments. n

Energy Resolution @ KEK Side room. Set up of measurement n. HV +2500 (P-type semi-con) n 60 Co 1. 33 Me. V n 6μs shaping time @ 671 Amp n. DAQ Amptek MCA 8000 A (maru-chan) 1. 72[ke. V] Test pulse 0. 79[ke. V] (3. 2 ch for ADC) Counts 60 Co Consistent with the measurement in Tohoku Univ. Eγ[ke. V]

Set up - LN 2 @ KEK Ge detector 60 Co source LN 2 Dewar

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

Noise from environments Large noises are …. n Power supply of cooling machine →Prepare two types of power supply (Previous one and “clean” one) n Vacuum pump, Thermo couple →Separable We checked them by Test Pulsar.

Noise and resolution by test pulsar Resolution [ke. V] 19. 0 13. 6 4. 79 0. 79 Contribution [ke. V] Power supply Vacuum pump Thermo couple ※ ○ ○ ○ × × × 4. 7 13 13 σ2 energy resolution=(σ2 crystal+)σ2 elec+σ2 power+σ2 pump+σ2 thermo

Noise from thermo couple by Ge detector Open cover ↓ 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) ・ 20 k. Hz chopping noise form power supply Output from Pre. Amp

Noise of Clean power supply It looks good, but energy resolution is bad. →～ 4[ke. V] Output from Pre. Amp

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

Amp Noise check of power supply 671 Output Power supply : OFF Vacuum pump : OFF → 0. 8[ke. V] same as LN 2 Ideal condition Bad Power supply : ON Vacuum pump : OFF →Impossible… Everything connected with Ge detector contribute its noise. →No solution without insulation.

Energy resolution of 60 Co 1. 33 Me. VγWe rayonly checked the important part, the contribution of noise from Power supply. [ke. V] Ge Resolution With Power Supply 60 Co 1. 7 5. 0 Test Pulse 0. 85 4. 7 Test pulse Without Power supply With Power supply We can know each contribution. [ch]

Contribution for Energy resolution σ2 energy resolution=σ2 crystal+σ2 elec+σ2 power+σ2 vibration Test pulse σ2 test=σ2 elec+σ2 power n n σcrystal = 1. 5[ke. V] σelec = 0. 85[ke. V] σpower = 4. 6[ke. V] σvibration = 0. 82[ke. V] The effect of vibration is small. σ2 resolution =σ2 crystal+σ2 elec+σ2 vibration → 1. 9[ke. V] →Microphonics is small.

Temperature @ Cooling machine 2 n n n 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. n The oscillation of cooling system. →Relatively small. n Noise (electric). →We need electric insulation between Ge and cooling machine. Next test. n

Next step n 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. n The second is to test the long time stability.

Summary n It is clear which contribution of noises makes energy resolution worse. It is most important to insulate Ge detector from cooling machine.

Cooling Mechanism TH TC TH 1 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) n The cooling mechanism 2 3 4 TH is simply a heat cycle. TC

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