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

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

Krypton background 85Kr dominat βdecay with T1/2=10.756y 85Kr/Kr ~ 10-11 in air Uniform distribution in liquid xenon Need Kr/Xe~10- 12mol/mol for 10-4 events/keV/day/kg 2018/5/25

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 2009-2014 Phase II: 500 kg DM 2014-2017 PandaX-xT: multi-ton DM 2016 2018/5/25

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

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

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 ~ 0.957 pa1/2. HETP ~ 35cm. Tower diameter D = 80mm. Tower height H = 4m with double theoretical plate number. 2018/5/25

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

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

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

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

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

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

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

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 2009-2014 Phase II: 500 kg DM 2014-2017 PandaX-xT: multi-ton DM 2016 2018/5/25

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

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

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

Thank you ! 2018/5/25

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

Back up 2018/5/25