1. Xiangyi Cui Shanghai Jiao Tong U. On Behalf of the Collaboration
Distillation tower and Krypton measurement system of PandaX experiment
Xiangyi Cui
Shanghai Jiao Tong U.
On Behalf of the Collaboration
2018/5/25

2. Direct detection with Xenon
Accessible cryogenic temperature (178.5K, 1.8Bar)
No long-lived radioisotopes (Except Xe136 with T1/2=2.2·1021year)
High light yield and fast time response
High stopping power (high mass number A~131 and density 2.9kg/L)
High rate for Spin Independent Interactions
2018/5/25

3. Krypton background 85Kr dominat βdecay with T1/2=10.756y
85Kr/Kr ~ in air
Uniform distribution in liquid xenon
Need Kr/Xe~10- 12mol/mol for events/keV/day/kg
2018/5/25

4. PandaX-xT: multi-ton DM
PandaX experiment
PandaX = Particle and Astrophysical Xenon Experiments
PandaX-III:
200 kg to 1 ton 136Xe 0vDBD
2016
Phase I:
120 kg DM
Phase II:
500 kg DM
PandaX-xT: multi-ton DM
2016
2018/5/25

5. Target of distillation
204kPa
Dew-point line
Bubble-point line
Production Krypton level below 3ppt.
Process speed to 5kg per hour.
Collection efficiency is 0.99.
Original xenon fed into tower in gas phase.
Kr Tboiling = 120K.
Xe Tboiling = 165K.
2018/5/25

6. McCabe-Thiele(M-T) method
Krypton level in orignal xenon is 3·10-9mol/mol.
Process temperature is 178K with 2barg.
Reflux ratio is 191 with Rmin=109.
6 stages of theoretical cells are needed.
Vapor liquid equilibrium in each plate.
Raoult's Law.
2018/5/25

7. Packing and column size
mesh count
100
wire diameter
(mm)
0.085
cloth thickness
0.4
peak height
2.5
waves pitch 4
porosity
(%) 77
specific surface area (m2/m3)
1135
Bain-Hougen model:
Gas velocity in empty tower μ~ 0.225m/s.
Gas loading F ~ pa1/2.
HETP ~ 35cm.
Tower diameter D = 80mm.
Tower height H = 4m with double theoretical plate number.
2018/5/25

8. Distillation tower 1 original xeon input 2 Getter 3
Precooling heater exchanger 4
Precooling cryocooler 5
offgas xenon 6
GM cryocooler 7
condenser 8
Inner vessel 9
Liquid level meter 10
Reboiler 11
Heating rod 12
Outer vessel 13
Production xenon 14
Pump connector
offgas
fed gas
production
2018/5/25

9. Process of the distillation
1. Temperature drop during precooling
2. Pressure variation during filling xenon
3. Kr content variation during full-flux
4. Stable pressure during distillation
2018/5/25

10. Summary of distillation tower
Install the system from 2012 and first distillation in 2013.
Purify about 2ton original xenon.
Stable running more than 4 months.
Move the tower to Jinping underground laboratory.
2018/5/25

11. Krypton measurement by RGA
Trap xenon by liquid nitrogen (77K).
Test the krypton counts by Residual Gas Analyzer.
2018/5/25

12. Structure Small volume Purification system Gas supply
Calibration system
Small volume
Purification system
Big volume
Gas supply
2018/5/25

13. Setup and process Pump system with heater band.
Fill 5bar xenon into 1L big volumn.
Fill LN2 into dewar and start RGA.
Open leak valve, save the RGA spectrum.
2018/5/25

14. Calibration and counting
Purify Xenon by pumping system after LN2 cooling.
Mixture Kr and purified Xenon get the sample with known Kr level.
Linear relation between Krypton level and RGA Krypton counts.
Kr/Xe = 1.2±0.3ppt
2018/5/25

15. PandaX-xT: multi-ton DM
PandaX experiment
PandaX = Particle and Astrophysical Xenon Experiments
PandaX-III:
200 kg to 1 ton 136Xe 0vDBD
2016
Phase I:
120 kg DM
Phase II:
500 kg DM
PandaX-xT: multi-ton DM
2016
2018/5/25

16. Distillation tower of sub-ppt Kr
Production Krypton vs. Filling rate
Production Krypton vs. Process pressure
Production Krypton vs. Reboiler power
Optimize parameters by Hysys simulation.
Further test about the HETP and the theorem.
Flow field simulation try new packing with high HETP.
2018/5/25

17. Theoretical plate number
10kg/h production speed.
10-14 Kr/Xe content.
Same recovery (0.99) and reflux ratio (191).
Same process temperature.
2018/5/25

18. Krypton measurement of sub-ppt Kr
New pump lower the system air background.
Lower xenon partial pressure study by micro-leak valve.
More sensitive RGA improve the precision.
New calibration for new system with more accurate kr/xe content mixture.
Two system in CJPL and SJTU!!!
2018/5/25

19. Thank you !
2018/5/25

20. Open questions
M-T method and Raoult's Law still working for that low concentration?
HETP relationship with the gas loading? (could lower than 35cm?)
Empirical formula like Bain-Hougen model working for our system?
2018/5/25

21. Back up
2018/5/25