1. Low Temperature Detector Design for the particle search Kim Seung Cheon (DMRC,SNU)

2. Contents The motivation of the low temperature detector The principle of the low temperature detector The scheme of our detector design The initiation of the low temperature detector

3. Motivation Improved energy threshold and sensitivity than the usually used particle detector. In the interaction of the particle with the detector, about 30% of the deposited energy produces charged particles, e-h pairs. 70 % of the deposited energy goes as the thermal energy. To make the e-h pair, ~ eV of energy needed To make the quasiparticle in the superconductor, ~ meV of energy needed.

4. Motivation Strong background rejection by the hybrid detection. Charged particles make more charged secondary particles than the neutral ones. Low temperature detector is very powerful tool for the experiment which requires low energy Threshold >1 keV, good energy sensitivity, and strong background rejection.

5. The principle of the low temperature detector The phonon induced by the particle becomes ballistic, which means the mean free path is ~ mm, in microseconds. -> athermal phonon The whole detector is thermalized in milliseconds. -> thermal phonon

6. The principle of the low temperature detector The energy of the athermal phonon is higher than the thermal phonon. The number of the athermal phonon is less than the thermal phonon. If we detect the athermal phonon, the data taking speed is faster than the thermal case. But the coverage area have to be larger.

7. The principle of the low temperature detector At sub-Kelvin Temperature, the heat capacity of the lattice vibration is very small (Debye T 3 law) and the thermal fluctuation is very small. The change of the resistance (NTD Ge, Superconducting TES) The excess quasiparticle (Superconducting tunnel junction) cryostat Temperature sensor substrate

8. The description of Our detector design Electrothermal Feedback Transition Edge Sensor (ETF TES) R Bias point TTcTc cryostat substrate R s ~m  ~V ~k  TES~  Squid

9. The description of Our detector design The composition of the detector Substrate : diamond ( C ) Electrically insulator Thermally good conductor (fast response) Heat capacity is very small. TES meandering : Mo/Cu bilayer operating at 100mK. Sputtered at ~10 -7 torr. This is patterned by photolithography. Etched chemically. Electrode : Nb At the operating temperature, this is the superconductor. Poor thermal conductivity, best electrical conductivity

10. TES ~  Rs ~m  squid 4.277mm  5.122mm 200  12 =2400 segments I bias = 100  A ~ mA Electrothermal Feedback Transition edge sensor (ETF TES) Diamond (1cmx1cmx1mm)

11. Nb(20  m ) Mo/Cu (5  m  300  m 33  m pitch)

12. The description of Our detector design cryostat substrate R s ~m  ~V~V ~k~k TES ~  Squid Adiabatic Demagnetization Refrigerator AC Resistance Bridge Low temperature facility For the pilot test -> ADR ( the limit ~ 50mK)

13. The initiation of the low temperature detector The work to do Uniform, reproducible TES meanderig fabrication Refrigerator test and the temperature calibration I co-work with Dr. M K Lee at KRISS.