China Jinping Underground Laboratory

The China Jinping Underground Laboratory (Chinese: 中国锦屏地下实验室; pinyin: Zhōngguó jǐn píng dìxià shíyàn shì) is a deep underground laboratory in the Jinping Mountains of Sichuan, China. The cosmic ray rate in the laboratory is under 0.2 muons/m2/day,[5] placing the lab at a depth of 6720 m.w.e.[6]: 2  and making it the best-shielded underground laboratory in the world.[7]: 17  The actual depth of the laboratory is 2,400 m (7,900 ft), yet there is horizontal access so equipment may be brought in by truck.

"CJPL" redirects here. For the community radio station, see CJPL-FM.
China Jinping Underground Laboratory
中国锦屏地下实验室
EstablishedDecember 12, 2010 (2010-12-12)
Field of research
Dark matter physics
DirectorCheng Jianping[1]
FacultyZeng Zhi
Ma Hao
Li Jianming
Wu Qifan[1]
LocationMianning County[2]: 3 , Sichuan, China
28.15323°N 101.7114°E / 28.15323; 101.7114[3]
Owner
Yalong River Hydropower Development Company[4]
Operating agency
Tsinghua University
Websitejinping.hep.tsinghua.edu.cn

Although the marble through which the tunnels are dug is considered "hard rock", at the great depth it presents greater geotechnical engineering challenges[8][9]: 16–27 [10]: 16–19  than the even harder igneous rocks in which other deep laboratories are constructed.[11]: 13–14  The 10 MPa (1500 psi; 99 atm) water pressure in the rock is also inconvenient. But marble has the advantage for radiation shielding of being low in radionuclides,[12][13] such as 40K, 226Ra, 232Th,[7]: 17  and 238U.[14]: 16  This in turn leads to low levels of radon (222Rn) in the atmosphere.[15]: 5 

The laboratory is in Liangshan in southern Sichuan, about 500 km (310 mi) southwest of Chengdu.[7]: 3  The closest major airport is Xichang Qingshan Airport, 120 km (75 mi) away by road.[9]: 5 

History

The Jinping-II Dam hydroelectric power project involved excavating a number of large tunnels under the Jinping Mountains: four large 16.7 km (10.4 mi) headrace tunnels carrying water east,[8]: 30  two 17.5 km (10.9 mi) vehicular access tunnels,[9]: 1  and one water drainage tunnel. Hearing of the excavation in August 2008,[16][17] physicists at Tsinghua University determined that it would be an excellent location for a deep underground laboratory,[18] and negotiated with the hydropower company to excavate laboratory space in the middle of the tunnels.

A formal agreement was signed on 8 May 2009,[16] and excavation was promptly started.[9]: 29  The first phase CJPL-I, consisting of a 6.5 × 6.5 × 42 m (21 × 21 × 138 ft) main hall,[19]: 8  plus 55 m (180 ft) of access tunnel (4,000 m3 total excavation)[9]: 15  was excavated by May 2010,[20]: 7  and construction completed 12 June 2010.[20]: 7  A formal laboratory inauguration was held 12 December 2010.[9]: 37 

The laboratory is to the south of the southernmost of the seven parallel tunnels, traffic tunnel A.

The air ventilation in CJPL-I was initially inadequate, resulting in the accumulation of dust on the equipment and radon gas in the air until additional ventilation was installed.[21]: 239 

A more difficult problem is that the walls of CJPL-I were lined with ordinary concrete taken from the hydroelectric project's supply. This has a natural radioactivity higher than desirable for a low-background laboratory.[21]: 238  The second phase of construction uses materials selected for low radioactivity.[22]: 30–37 

CJPL-II expansion

The laboratory is currently undergoing a major (50-fold) expansion. The first phase was rapidly filled, and plans for a second were made quickly, before the excavation workers and equipment departed following completion of the hydroelectric project in 2014.[23]: 20 

Slightly west of CJPL-I, two bypass tunnels totalling roughly 1 km (3,300 ft) long[23]: 20  are left over from constructing the seven tunnels of the hydropower project. They are sloped criss-crossing tunnels which connect the midpoints of the five water tunnels (four headrace and one drainage) to the road tunnels beside and slightly above them. Totalling 210,000 m3 (7.4×10^6 cu ft),[24]: 4  and originally intended to be blocked off after construction,[23]: 20  they have been donated to the laboratory and will be used for support facilities.[25]: 5 

The expansion has added 151,000 m3 (5.3×10^6 cu ft),[26]: 4  of additional excavation: some interconnecting access tunnels, four large experimental halls, each 14×14×130 m (46×46×427 ft),[24]: 6 [10]: 12 [15]: 15 [23]: 22 [21]: 239–240  and two pits for shielding tanks below the halls' floors.[27]: 20–21 [23]: 24,27  The China Dark Matter Experiment has a cylindrical pit, 18 m (59 ft) deep and in diameter,[lower-alpha 1] which will be filled with a liquid nitrogen tank, and PandaX has an elliptical pit[lower-alpha 2] for a water shielding tank, 27×16 m (89×52 ft) and 14 m (46 ft) deep.[21]: 239–240,245  The halls were complete by the end of 2015,[27]: 17 , the pits by May 2016,[23]: 24  and as of May 2017 are being fitted with ventilation systems[23]: 24–25  and other necessities. (This is somewhat behind expectations that they would be ready for occupation in January 2017.[15]: 20 )

When complete, it will be the world's largest underground laboratory, surpassing the current record-holder the Laboratori Nazionali del Gran Sasso (LNGS). Although greater depth and weaker rock force the halls to be narrower than the 20 m (66 ft) wide main halls of LNGS, their combined length of 520 m (1,710 ft) provides more floor space (7,280 vs. 6,000 m2) than LNGS's three halls totalling 300 metres (980 ft).

CJPL's halls also enclose more volume than those of LNGS. CJPL has 93,300 m3[6][lower-alpha 3] in the halls proper, and an additional 9,300 m3 in the shielding pits making a total of 102,600 m3, slightly more than LNGS's 95,100 m3.[lower-alpha 4]

Including the service areas outside the main halls, the result is 200,000–300,000 m3 of usable space,[27]: 18 [23]: 22 [21]: 239  more than LNGS's grand total of 180,000 m3. CJPL's total volume of 361,000 m3 would suggest that CJPL is twice the size, but that would be misleading; all of LNGS's excavation was designed to be a laboratory, and thus can be used more efficiently than CJPL's repurposed tunnels.

CJPL facility resources[19][25][24][27]
CJPL-ICJPL-II
Overall volume[27]: 21  4,000 m3
140,000 cu ft		210,000 + 151,000 m3
7.4×10^6 + 5.3×10^6 cu ft
Laboratory area 273 m2
2,940 sq ft		7,280 m2
78,400 sq ft
Laboratory volume 1,800 m3
64,000 cu ft		102,600 m3
3.62×10^6 cu ft
Electrical power 70 kVA[24]: 4  1250 (10000) kVA[24]: 15 
Fresh air 2,400 m3/h[24]: 4 85,000 cu ft/h24,000 m3/h[24]: 10 [21]: 239 0.85×10^6 cu ft/h

Thanks to the laboratory's location within a major hydroelectric facility, additional electrical power is readily available. CJPL-II is supplied by two redundant 10 kV, 10 MVA power cables;[24]: 15 [27]: 21  available power is temporarily limited by the 5×250 kVA step-down transformers in the laboratory (one per experiment hall, and a fifth for facilities).[24]: 15  There is likewise no shortage of water[24]: 14  for cooling high-powered equipment.

The muon flux in (and thus water equivalent depth of) CJPL-II is currently being measured,[23]: 25  and may differ slightly from CJPL-I, but it will certainly remain lower than SNOLAB in Canada and thus retain the record for the world's deepest laboratory as well.

Experiments

Experiments currently operating in CJPL are:

Also operating in the laboratory is a low background facility using a high purity germanium detector, for measuring very low levels of radioactivity.[1]: 7 [19] This is not a physics experiment itself, but tests materials intended for use in the experiments. It also tests materials used to construct CJPL-II.[24]: 27–32 

Experiments currently planned for CJPL-II are:[15]: 24–29 [27]: 23 

Proposals also exist for:

  • CUPID (CUORE Upgrade with Particle Identification), a neutrinoless double beta decay experiment,[23]: 26  and
  • a directional dark matter detector by the MIMAC (MIcro-tpc MAtrix of Chambers) collaboration,[27]: 23  as a follow-on to their detector currently operating at the Modane Underground Laboratory.[33]

Notes
  1. Earlier plans were for 16 m wide and deep, but this was enlarged to 18 m.
  2. It's not totally clear if the pit is elliptical (with an area of 27×16×π/4 = 339.3 m2) or a stadium-shaped oval (with an area of 11×16 + 162×π/4 = 377.1 m2). The difference is a volume of 4750 m3 vs. 5279 m3.
  3. The cross-section drawings of CJPL's halls are inconsistent.[19]: 13  A vaulted roof 14 m wide with 4.08 m sagitta spans an angle of 121°; the smaller 114° angle shown would imply a larger radius and smaller sagitta of 3.8 m. These lead to cross-sectional areas of 179.434 and 180.275 m2, respectively, and lab volumes of 93,306 and 93,743 m2, respectively.
  4. LNGS's main halls are assumed to be 20 m wide, with a hemispherical roof peaking at 18 m. Thus, the cross-sectional area is 20×(8+10×π/4) = 317.08 m2.

References
  1. Zeng, Zhi (2011-03-26). Low Background Facility Setup in CJPL: A Brief Introduction (PDF). Symposium on Future Applications of Germanium Detectors in Fundamental Research. Beijing. Retrieved 2014-11-19.
  2. Neutrino opportunities at Jinping (PDF). May 28, 2015. Retrieved 2015-12-24.
  3. "Data Acquisition Project for CJPL". GitHub. 21 August 2010. Retrieved 2015-09-16. CJPL position in Google Maps – http://goo.gl/xwcA (You may use the coordinates directly in google maps: 28.153227,101.711369). This is CJPL-I; CJPL-II is about 500 m farther west.
  4. Lin, S.T.; YuJainmin, Q. (12 September 2013). Status and prospects of CJPL and the CDEX experiment. 13th International Conference on Topics in Astroparticle and Underground Physics. Physics Procedia. Vol. 61. pp. 201–204. Bibcode:2015PhPro..61..201L. doi:10.1016/j.phpro.2014.12.032. The laboratory is owned by the YaLong River Hydropower Development Company, and managed by Tsinghua University, China.
  5. Wu, Yu-Cheng; Hao, Xi-Qing; Yue, Qian; Li, Yuan-Jing; Cheng, Jian-Ping; Kang, Ke-Jun; Chen, Yun-Hua; Li, Jin; Li, Jian-Min; Li, Yu-Lan; Liu, Shu-Kui; Ma, Hao; Ren, Jin-Bao; Shen, Man-Bin; Wang, Ji-Min; Wu, Shi-Yong; Xue, Tao; Yi, Nan; Zeng, Xiong-Hui; Zeng, Zhi; Zhu, Zhong-Hua (August 2013). "Measurement of cosmic ray flux in the China JinPing underground laboratory" (PDF). Chinese Physics C. 37 (8): 086001. arXiv:1305.0899. Bibcode:2013ChPhC..37h6001W. doi:10.1088/1674-1137/37/8/086001. Archived from the original (PDF) on 2017-01-01.
  6. Li, Jainmin; Ji, Xiangdong; Haxton, Wick; Wang, Joseph S.Y. (9 April 2014). "The second-phase development of the China JinPing underground Laboratory". Physics Procedia. 61: 576–585. arXiv:1404.2651. Bibcode:2015PhPro..61..576L. doi:10.1016/j.phpro.2014.12.055.
  7. PandaX Collaboration (August 2014). "PandaX: A Liquid Xenon Dark Matter Experiment at CJPL". Science China Physics, Mechanics & Astronomy. 57 (8): 1476–1494. arXiv:1405.2882. Bibcode:2014SCPMA..57.1476C. doi:10.1007/s11433-014-5521-2. S2CID 255200277.
  8. Zhang, Chunsheng; Chu, Weijiang; Liu, Ning; Zhu, Yongsheng; Hou, Jing (2011), "Laboratory tests and numerical simulations of brittle marble and squeezing schist at Jinping II hydropower station, China" (PDF), Journal of Rock Mechanics and Geotechnical Engineering, 3 (1): 30–38, Bibcode:2011JRMGE...3...30Z, doi:10.3724/SP.J.1235.2011.00030
  9. Li, Jianmin (6 September 2013). The Status and Plan of China JinPing underground Laboratory (CJPL) (PDF). 13th International Conference on Topics in Astroparticle and Underground Physics: A Town Meeting for the 2nd-phase Development of the China Jinping Underground Laboratory. Asilomar, California. Retrieved 2014-11-19.
  10. Li, Jianmin (9 September 2015). The recent status and prospect of CJPL (PDF). XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP2015). Retrieved 2015-11-28.
  11. Zhao, Zhihong (2015-06-05). Geological conditions and geotechnical feasibility. 2015 Workshop of Jinping Neutrino Program. Tsinghua University. Archived from the original on 2015-12-08. Retrieved 2015-08-15.
  12. Chui, Glennda (February 2010), "World's deepest lab proposed in China", Symmetry, 7 (1): 5, ISSN 1931-8367
  13. Strickland, Eliza (January 29, 2014), "Deepest Underground Dark-Matter Detector to Start Up in China", IEEE Spectrum, 51 (2): 20, doi:10.1109/MSPEC.2014.6729364, China's new underground lab is the deepest in the world, meaning it's well protected from cosmic radiation; in addition, the rock around it is marble, which is particularly devoid of radioactive materials that could produce false signals. "The big advantage is that PandaX is much cheaper and doesn't need as much shielding material," Lorenzon says.
  14. Pocar, Andrea (8 September 2014). Searching for neutrino-less double beta decay with EXO-200 and nEXO (PDF). Neutrino Oscillation Workshop. Otranto. Retrieved 2015-01-10.
  15. Yang, Li-Tao (21 July 2016). Recent status of the China Jinping Underground Laboratory (CJPL). Identification of Dark Matter 2016. Sheffield. Archived from the original on 19 August 2016.
  16. Normile, Dennis (5 June 2009), "Chinese Scientists Hope to Make Deepest, Darkest Dreams Come True", Science, 324 (5932): 1246–1247, doi:10.1126/science.324_1246, PMID 19498133
  17. Feder, Toni (September 2010), "China, others dig more and deeper underground labs", Physics Today, 63 (9): 25–27, Bibcode:2010PhT....63i..25F, doi:10.1063/1.3490493
  18. Kang, K.J.; Cheng, J.P.; Chen, Y. H.; Li, Y.J.; Shen, M. B.; Wu, S. Y.; Yue, Q. (1 July 2009). Status and Prospects of a Deep Underground Laboratory in China. Topics in Astroparticle and Underground Physics (TAUP 2009). Journal of Physics: Conference Series. Vol. 203, no. 12028. Rome. doi:10.1088/1742-6596/203/1/012028.
  19. Yue, Qian (Feb 28, 2014). The status and prospect of CJPL (PDF). Dark Matter 2014. Westwood, California. Archived from the original (PDF) on 2014-11-29. Retrieved 2014-11-19. The figure on p. 13 shows the shape of the halls, although the dimensions have evolved.
  20. Wong, Henry (2011-09-06). Construction and commissioning of the China Jinping underground laboratory and the CDEX-TEXONO experiment. 12th International Conference on Topics in Astroparticle and Underground Physics. Munich. Retrieved 2014-11-19.
  21. Cheng, Jian-Ping; Kang, Ke-Jun; Li, Jian-Min; et al. (October 2017). "The China Jinping Underground Laboratory and Its Early Science". Annual Review of Nuclear and Particle Science. 67: 231–251. arXiv:1801.00587. Bibcode:2017ARNPS..67..231C. doi:10.1146/annurev-nucl-102115-044842.
  22. Zeng, Zhi (23 October 2015). Status of CJPL-II (PDF). Final Symposium of the Sino-German GDT Cooperation. Schloss Ringberg, Germany. Retrieved 2018-03-01.
  23. Ma, Hao (24 May 2017). China Jinping Underground Laboratory (CJPL): Status and prospects (PDF). Low Radioactivity Techniques 2017. Seoul.
  24. Li, Jianmin (2015-06-05). Introduction of Jinping underground laboratory II. 2015 Workshop of Jinping Neutrino Program. Tsinghua University. Retrieved 2015-08-15. A description of CJPL-II construction progress through the beginning of May 2015. Note that some pages in this presentation say the halls are 12×12 m; those appear to be figures copied from older presentations, and 14×14 is the new decision.
  25. Li, Jainmin; Ji, Xiangdong; Haxton, Wick; Wang, Joseph S.Y. (12 September 2013). The Second-Phase Development of the China JinPing Underground Laboratory for Physics Rare Event Detectors and Multi-Disciplinary Sensors. 13th International Conference on Topics in Astroparticle and Underground Physics. Asilomar, California. Retrieved 2014-11-21.
  26. Wang, Zhe (5 November 2016). China Jinping Underground Laboratory and Jinping neutrino experiment (PDF). International Workshop on Next Generation Nucleon Decay and Neutrino Detectors (NNN16). Shanghai.
  27. Lin, Shin-Ted (29 December 2016). Status and Results from CDEX Collaboration at the Jinping Underground Laboratory (PDF). 4th International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Asymmetry. Hsinchu, Taiwan.
  28. Qian Yue (March 24, 2011). China JinPing underground Laboratory (CJPL) and China Darkmatter Experiment (CDEX) (PDF). Symposium on Future Applications of Germanium Detectors in Fundamental Research. Beijing. Retrieved 2014-11-19.
  29. Xu, Benda (9–13 September 2019). Jinping Neutrino Experiment: a Status Report. XVI International Conference on Topics in Astroparticle and Underground Physics (TAUP 2019). Toyama, Japan. doi:10.1088/1742-6596/1468/1/012212.
  30. Beacom, John F.; et al. (21 June 2015). "Letter of Intent: Jinping Neutrino Experiment". Chinese Physics C. 41 (2): 023002. arXiv:1602.01733. Bibcode:2017ChPhC..41b3002B. doi:10.1088/1674-1137/41/2/023002. S2CID 197514524.
  31. Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A.; Xi, Yufei; McDonough, William F. (9 September 2016). "Revealing the Earth's mantle from the tallest mountains using the Jinping Neutrino Experiment" (PDF). Scientific Reports. 6: 33034. Bibcode:2016NatSR...633034S. doi:10.1038/srep33034. PMC 5017162. PMID 27611737.
  32. Liu, WeiPing; et al. (12 February 2016). "Progress of Jinping Underground laboratory for Nuclear Astrophysics (JUNA)". EPJ Web of Conferences. 109 (9001): 09001. Bibcode:2016EPJWC.10909001L. doi:10.1051/epjconf/201610909001.
  33. Santos, D.; Billard, J.; Bosson, G.; et al. (8 April 2013). "MIMAC: A micro-tpc matrix for dark matter directional detection". Journal of Physics: Conference Series. 460 (1): 012007. arXiv:1304.2255. Bibcode:2013JPhCS.460a2007S. doi:10.1088/1742-6596/460/1/012007. S2CID 73723876.
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