China Jinping Underground Laboratory

China Jinping Underground Laboratory
中国锦屏地下实验室

Established	December 12, 2010 (2010-12-12)
Field of research	Dark matter physics
Director	Cheng Jianping
Faculty	Zeng Zhi Ma Hao Li Jianming Wu Qifan
Location	Mianning County, Sichuan, China
Owner	Yalong River Hydropower Development Company
Operating agency	Tsinghua University
Website	hep.tsinghua.edu.cn/CJPLNE/

"CJPL" redirects here. For the community radio station, see CJPL-FM.

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 Sichuan, China. The cosmic ray rate in the laboratory is under 0.2 muons/m²/day, placing the lab at a depth of 6720 m.w.e. and making it the best-shielded underground laboratory in the world. 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.

Although the marble through which the tunnels are dug is considered "hard rock", at the great depth it presents greater geotechnical engineering challenges than the even harder igneous rocks in which other deep laboratories are constructed. 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, such as ⁴⁰K, ²²⁶Ra, ²³²Th, and ²³⁸U.

The laboratory is in western China, near Tibet, about 500 km (310 mi) southeast of Chengdu. The closest major airport is Xichang Qingshan Airport, 120 km (75 mi) away by road.

History

The Jinping-II Dam hydroelectric power project involved excavating a number of large tunnels under Jinping mountain: four large 16.7 km (10.4 mi) headrace tunnels carrying water southeast, two 17.5 km (10.9 mi) vehicular access tunnels, and one water drainage tunnel. Hearing of the excavation in August 2008, physicists at Tsinghua University determined that it would be an excellent location for a deep underground laboratory, 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, and excavation was promptly started. The first phase CJPL-I, consisting of a 6.5×6.5×42 m (21×21×138 ft) main hall, plus 55 m (180 ft) of access tunnel (4,000 m³ total excavation) was excavated by May 2010, and construction completed 12 June 2010. A formal laboratory inauguration was held 12 December 2010.

The laboratory is to the southwest of the southwesternmost of the seven parallel tunnels, traffic tunnel A.

CJPL-II expansion

The laboratory is current undergoing a major (50-fold) expansion, which is expected to be complete at the end of 2015. This will make it the world's largest underground laboratory, larger by many measures than the current record-holder the Laboratori Nazionali del Gran Sasso.

Slightly northwest of CJPL-I, two bypass tunnels are left over from constructing the seven tunnels of the hydropower project. They are sloped criss-crossing tunnels which connect 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), they have been donated to the laboratory and will be used for support facilities.

The expansion is adding 131,000 m³ (4.6×10^⁶ cu ft), of additional excavation: a short connection between the bypass tunnels, and four large experimental halls, each 14×14×130 m (46×46×427 ft). 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) will provide almost as much volume (93,300 vs. 95,100 m³) as, and more floor space (7,280 vs. 6,000 m²) than, LNGS's three halls totalling 300 metres (980 ft).

Comparing CJPL's total volume of 341,000 m³ with LNGS's 180,000 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

	CJPL-I	CJPL-II
Overall volume	4,000 m3 140,000 cu ft	210,000 + 131,000 m3 7.4×10^6 + 4.6×10^6 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	93,300 m3 3.29×10^6 cu ft
Electrical power	70 kVA	1250 kVA
Fresh air	2,400 m3/h 85,000 cu ft/h	30,000 m3/h 1.1×10^6 cu ft/h

Due 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; the temporary limit is the 5×250 kVA step-down transformers in the laboratory (one per experiment hall, and a fifth for facilities). There is likewise no shortage of water for cooling high-powered equipment.

The muon flux (and thus water equivalent depth) in CJPL-II has not yet meed measured, 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:

• China Dark Matter Experiment (CDEX), a germanium dark matter detector, and
• PandaX, the Particle and Astrophysical Xenon Detector for dark matter (and neutrinoless double beta decay)

Also operating in the laboratory is a low background facility using a high purity germanium detector, for measuring very low levels of radioactivity. 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.

Both CDEX and PandaX have plans for larger (tonne-scale) versions in the CJPL-II space.

External links

• CJPL home page (Tsinghua University)
• CJPL GitHub page
• Symposium on Future Applications of Germanium Detectors in Fundamental Research in Beijing, with multiple CJPL presentations
• A Town Meeting for the 2nd-phase Development of the China Jinping Underground Laboratory (Sept. 8, 2013) at the 13th International Conference on Topics in Astroparticle and Underground Physics
• CJPL 2015 conference presentations