Measurement of Ge detector by New cooling system 2 @ KEK

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

2. 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.

3. Energy Resolution @ KEK Side room. Set up of measurement Counts • HV +2500 (P-type semi-con) • 60Co 1.33MeV • 6μs shaping time @ 671 Amp • DAQ Amptek MCA8000A (maru-chan) 60Co 1.72[keV] Test pulse 0.79[keV] (3.2ch for ADC) Consistent with the measurement in Tohoku Univ. Eγ[keV]

4. Set up - LN2 @ KEK LN2 Dewar Ge detector 60Co source

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

6. 日本語です 大きさ

7. 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.

8. Noise and resolution by test pulsar σ2energy resolution=(σ2crystal+)σ2elec+σ2power+σ2pump+σ2thermo

9. Noise from thermo couple by Ge detector cover Open ↓ Noisy ・Unstable ground connection ・Electric wave from environment

10. 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

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

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

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

14. Energy resolution of 60Co 1.33MeVγ-ray We only checked the important part, the contribution of noise from Power supply. Test pulse Without Power supply With Power supply We can know each contribution. [ch]

15. Contribution for Energy resolution Energy resolution σ2energy resolution=σ2crystal+σ2elec+σ2power+σ2vibration Test pulse σ2test=σ2elec+σ2power • 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 =σ2crystal+σ2elec+σ2vibration →1.9[keV]

16. 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.

17. 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.

18. 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.

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

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

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