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McKinsey JinPing workshop Author Daniel McKinsey Created Date 6/9/2014 5:51:25 PM ...
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LargeScale Cryogenic Detectors, and Sensi5vity to Solar Physics Dan McKinsey Yale University Future Solar Neutrino Detector at JinPing Workshop Lawrence Berkeley Na5onal Laboratory June 9, 2014
Transcript of McKinsey JinPing workshop Author Daniel McKinsey Created Date 6/9/2014 5:51:25 PM ...
Large-‐Scale Cryogenic Detectors, and Sensi5vity to Solar Physics
Dan McKinsey Yale University
Future Solar Neutrino Detector at JinPing Workshop
Lawrence Berkeley Na5onal Laboratory June 9, 2014
References for noble liquid solar neutrino experiments
CLEAN: D. N. McKinsey and J. M. Doyle, astro-‐ph/9907314, Journal of Low Temperature Physics 118, 153 (2000). K. J. Coakley and D. N. McKinsey, arXiv:physics/0309033, Nuclear Instruments and Methods A 522, 504 (2003).
D. N. McKinsey and K. J. Coakley, arXiv:astro-‐ph/0402007, Astropar5cle Physics 22, 355 (2005).
M. G. Boulay, A. Hime, and J. Lidgard, arXiv:0410025, Nucl. Phys. B, Proc. Suppl. 143 , 486 (2005). M. K. Harrison et al, Nuclear Instruments and Methods A 570 (2007) pp. 556-‐560 W. H. Lippincoa, Ph. D. thesis, Yale University (2010); hap://mckinseygroup.yale.edu/publica5ons
XMASS: Y. Suzuki, arXiv:hep-‐ph/0008296. XAX: K. Arisaka et al, arXiv:0808.3968, Astropar5cle Physics 31, 63 (2009). DARWIN: L. Baudis et al, arXiv: 1309.7024, JCAP 01, 044 (2014). 6/9/14 2
pp and 7Be Solar Neutrino Measurements in LXe
• Proposed experiments: XMASS (single-‐phase), XAX, DARWIN, XENON10T (two-‐phase)
• Main background is two-‐neutrino double beta decay from 136Xe (T1/2=2.1e21 years)
• Requires subtrac5on of this background. Can also consider using 136Xe-‐depleted LXe (expensive, though could be paired with a dedicated, separate
136Xe-‐enriched double beta decay experiment?)
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Solar Neutrino and Background Es5mates in DARWIN 21.4 ton LXe (14 ton fiducial). Kr/Xe at 0.1 ppt.
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Predicted signal and background rates in the 2-‐30 keV energy region as a func5on of fiducial liquid xenon mass, for a proposed 21.4 ton (14 ton fiducial) DARWIN experiment. In 5 years, have 5900 pp neutrino events, 3925 136Xe double beta decay events, and 2825 85Kr events in this energy window. If background rates perfectly known, have a pp-‐solar neutrino precision of sqrt(5900+3925+2823)/5900 = 2.0%. Use 136Xe-‐depleted LXe instead?
Solar Neutrino and Background Es5mates in DARWIN (2-‐30 keV)
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CLEAN (Cryogenic Low Energy Astrophysics with Noble Liquids)
Photomultipliers
Water tank
Outer vessel
Inner vessel
Liquid Neon
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Why Liquid Neon for low-‐energy solar neutrinos?
• Unlike Ar, Kr, and Xe, Neon is completely free of long-‐lived radioac5ve isotopes.
• Neon is a bright scin5llator • Liquid Neon has high density (1.2 g/cm3), allowing excellent
self-‐shielding against gamma ray and neutron backgrounds. • In fact, CLEAN was the first proposed self-‐shielding noble
liquid detector for low-‐energy rare events, an approach that in recent years has proven very effec5ve in direct searches for WIMP dark maaer interac5ons.
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• The CLEAN detector will be a spherical vessel filled with ~40 tons of purified LNe at a temperature of 27 K.
• The center of the vessel will be viewed by 2000 PMTs immersed in the liquid. In the center of the spherical vessel will be mounted a soccer-‐ballshaped array of acrylic plates, with light guides connected to the PMTs.
• Tetraphenyl butadiene (TPB), a wavelength shining fluor, will be evaporated onto the inward-‐poin5ng surface of each plate. Light from each wavelength shiner plate will be transported to the nearest PMT via an acrylic light guide.
• Ionizing radia5on events within the wavelength shiner plate array will cause scin5lla5on in the vacuum ultraviolet (80 nm), which is shined to 440 nm by the wavelength shiner. The photon-‐to-‐photon conversion efficiency of TPB is about 130% for LNe scin5lla5on. The blue light will then be detected by the PMTs.
• We have calculated the signal yield in CLEAN from detailed Monte Carlo studies of scin5lla5on photon propaga5on and detec5on, and es5mate a signal strength about 5.6 photoelectrons/keV in CLEAN.
The CLEAN Technical Approach
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Projected pp neutrino flux uncertainty for a 200 cm radius (40 ton) CLEAN experiment
With a pp neutrino flux of ~6e10 cm-‐2s-‐1, you get about 1 event/tonne/day. So you don’t need a huge detector to build up adequate sta5s5cs. Above analysis assumes a radial systema5c uncertainty of 0.5% (2 5mes beaer than in SNO), leading to a volume uncertainty of 1.5%. Analysis threshold: 35 keV 6/9/14 9
Solar neutrino signal in 10-‐ton fiducial mass
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pp-‐solar neutrino flux measurement with a 300-‐cm radius CLEAN detector
(140 tonnes LNe)
M. G. Boulay, A. Hime, and J. Lidgard, arXiv:0410025, Nucl. Phys. B, Proc. Suppl. 143 , 486 (2005)
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Space Requirements
• A 40 (140)-‐tonne CLEAN experiment would have a liquid neon volume about 4 (6) meters in diameter.
• With PMTs immersed in the LNe, this might be a cryostat 5 (7) meters tall.
• About 2 meters of water shielding is needed to bring the gamma ray and neutron flux down to PMT levels.
• So a 40-‐140 tonne CLEAN experiment would need a ceiling height of 9-‐11 meters.
• Space needed for purifica5on and cryogenic systems, control room (200 square meters, three-‐level structure next to the experiment).
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Neon purifica5on • Neon has lower binding energy to ac5vated charcoal than all other contaminants
other than Helium. Binding 5me (adsorp5on coefficient) is exponen5ally dependent on the ra5o of this binding energy over temperature.
• This results in highly effec5ve purifica5on using charcoal columns. • The charcoal will remove impuri5es that can absorb scin5lla5on signal, as well as
muon spalla5on products like 7Be, 3H, and 14C. • With proper calibra5on, the charcoal may be periodically warmed and sampled, to
determine the level of impuri5es. • Studies completed on gaseous neon purifica5on (see M. K. Harrison et al, Nuclear
Instruments and Methods A 570, 556 (2007).) • Studies needed on liquid-‐phase purifica5on, which would allow lower heat load on
the detector, faster circula5on.
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Charcoal column adsorp5on
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Adsorp5on coefficients in gaseous neon M. K. Harrison et al, Nuclear Instruments and Methods A 570, 556 (2007).
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Cryogenics • Though the CLEAN approach requires a cryogenic apparatus (the boiling
temperature of neon is 27 K), this would not make the experiment overly complex or costly. For example, a commercial Gifford-‐McMahon cooler opera5ng at 27 K with a cooling power of 75 W costs only $34,000. With a total es5mated heat load of 200 W in the full-‐sized CLEAN, the apparatus described above would derive liale of its cost from its cooling requirements.
• A custom-‐designed refrigerator, with gaseous neon used as its refrigerant, should also be considered for higher efficiency.
• The tank could be supported from below with stainless steel or 5tanium tubes, as is done commonly with large liquid helium-‐cooled accelerator magnets.
• Such a large cryogenic detector would not cons5tute a substan5ally new technical challenge; for example, the ICARUS collabora5on has successfully built and tested a 5me projec5on chamber filled with 600 metric tons of liquid argon at 90 K. Also, ICARUS now uses photomul5plier tubes immersed in liquid argon, the same basic technology to be used in CLEAN.
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Neon purchase and transport The cost of neon was last determined to be $90,000/ton in large quan55es, more than an order of magnitude less expensive than xenon. Given the total cost of neon (~$4M) the neon purchase itself would require substan5al management oversight. Note, however, that the neon could be sold back to the market at the end of the experiment. Three methods may be considered for transpor5ng the neon underground:
1. Neon could be brought underground as a liquid, in standard storage dewars. This would allow efficient use of lin, but result in a rela5vely high neon cost. 2. Neon could be transported in high-‐pressure gas cylinders. This would result in a somewhat lower neon cost, but require more extensive use of the lin. 3. Neon could be carried to the underground laboratory through a 1-‐inch gas line connec5ng the surface to the CLEAN gas-‐handling system. This would allow the neon to be brought to the lab by tanker truck and would avoid the use of the lin, but would require the gas line to be installed.
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Safety • The ac5ve media in CLEAN are liquid neon and water. • Neon is inert and poses no environmental hazard. However, like all inert gases, it is
an asphyxiant and can be dangerous if released in large quan55es. The possibility of unintended cryogen release would have to be be studied very carefully prior to approval and construc5on of CLEAN.
• Below are listed two neon release scenarios and the resul5ng boiloff rates: – 1. Failure of vacuum insula5on in the CLEAN cryostat. Assuming a cryostat area of 140 m2, a gap
between 77 K and 27 K of 2 cm, and a gaseous neon conduc5vity of 2 x 104 W cm−1 K−1, the heat load at 27 K is 7 kW. This corresponds to a gaseous neon boiloff rate of 5.4 m3 per minute. The gas would start off at 27 K, warming as it rises in the cavity. This boiloff, unless stopped, would con5nue for 460 hours.
– 2. Severing of the line pumping liquid neon to the CLEAN purifica5on system, as well as failure of the system that would shut off flow. For a liquid neon flow rate of 1 kg/s, a boiloff rate of 67 m3 per minute would result.
• The dangers posed by large quan55es of cryogenic liquids have been well studied, notably at CERN and other accelerators in which large numbers of superconduc5ng magnets are connected by liquid helium jumpers. In the CERN safety risk analysis, the most disastrous event that could release helium from the LHC is a ”jumper connec5on break”, severing the connec5on between two adjacent superconduc5ng magnets. This would spill 28 kg/s of liquid helium, giving a helium boiloff rate of 9400 m3 per minute. This is considerably higher than the volume displacement rate associated with either neon release scenario considered above.
• Also note that CLEAN is small in comparison to the ICARUS and LBNE experiments, which use extremely large liquid argon detectors underground. 6/9/14 18
Power requirements
• Electronics: 5 kW. • Power for refrigerators: 50 kW once cold, 300 kW while neon is
being liquefied during the cooldown. • The experiment will require 10 kW of emergency power to
maintain the neon temperature in the case of a power interrupt. (The main heat load on the liquid neon will come from liquid neon circula5on, which would cease in this event.)
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Summary • For pp-‐neutrino detec5on via electron scaaering, LNe is s5ll the
way to go. • No show-‐stoppers; LNe scin5lla5on is a robust signal, and Ne has
the crucial advantages of no long-‐lived isotopes and easy purifica5on, while being dense enough to provide good self-‐shielding.
• CLEAN could certainly be built at JinPing; detector size matches the hall size, and there is plenty of depth.
• This is a unique experiment, and an excellent opportunity.
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