From Sanford Underground Research Facility: “LZ begins new phase: testing the xenon circulation system”

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From Sanford Underground Research Facility

February 25, 2019
Constance Walter

Test will ensure critical element of the next-generation dark matter experiment will operate as needed.

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David Woodward, a researcher on the LZ experiment, works on the test cryostat. Photo by Claudio Pascoal da Silva

In preparation to test the xenon circulation system for the LUX-ZEPLIN (LZ) dark matter experiment, David Woodward carefully positioned a tower holding a stainless-steel test cryostat. The LZ collaboration will circulate liquid xenon through the test cryostat to ensure the system will work properly when the experiment begins operations next year.

LBNL LZ project at SURF, Lead, SD, USA

“We aren’t looking for dark matter with this test. But we do want to make sure all of our systems work the way they are supposed to,” said Woodward, a post doc at Penn State University.

The circulation system is, perhaps, the most critical component of the LUX-ZEPLIN dark matter experiment. LZ will use 10 tons of liquid xenon to look for WIMPs—weakly interacting massive particles—and that xenon must meet very high radio-purity standards to eliminate background noise. To achieve and maintain this level of radiopurity, the xenon must be continuously removed, purified and reintroduced to the LZ detector, or circulated, during operation.

The circulation system sits outside the water tank, which will house LZ. It’s a complicated system comprised of thousands of components: circulation compressors, tubing, wiring, sensors, all of which will connect to the actual experiment. The inner cryostat will hold the xenon, which will be fed into the experiment through an opening at the bottom of the water tank then continuously circulated.

The test cryostat is designed very much like the real inner cryostat. It is the same height and has many of the same components; however, it is not as big around.

“One of the goals of the test is to make sure we can circulate the xenon at the correct rate,” Woodward said. “That’s definitely possible even with a test device that isn’t exactly the same size as the actual device. It helps us understand whether the flow will work correctly—to make sure we can get the xenon to circulate all the way to the top of the actual cryostat,” Woodward added.

The tower holding the test cryostat was positioned precisely to ensure the xenon transfer lines, which have a fixed length, will reach the real LZ cryostat once the experiment is actually running. The collaboration will monitor the system; however, there are some things they won’t be able to know, unless they can physically look inside the test cryostat. To do that, they added a glass view port on the top of the device.

Why do they need a viewport?

“The xenon has to stay at a certain temperature to remain liquid (minus 169.2 degrees F),” Woodward said. “If it doesn’t stay cold enough, it can revert back to gas. Gas creates bubbles, so if that happened, we could see the bubbles. But, really, we don’t want to see anything—we want this test to be boring and just see a nice flow of the liquid xenon. But if something did happen, we could see it.”

The team will test the circulation system for several months, or as long as possible, Woodward said, to ensure it is working correctly. Then the test cryostat will be unhooked and removed. By end of summer this year, the actual cryostat will be installed, with operation of the experiment expected to begin in early 2020.

“This test is very important to our experiment, a very important check for the next phase,” Woodward added.

Facts and figures

The test cryostat is made of stainless steel, whereas the one that will be used in the experiment is made of titanium. Although it is as tall as the actual cryostat, it is much smaller in diameter. “We are not looking to collect physics data with the test vessel, so we don’t need the volume,” said Woodward.

In building the test vessel, the team followed fairly closely the cleanliness protocols for the actual vessel that will be used. It’s important that we have the purest materials possible to minimize radioactive backgrounds in the actual experiment. “We don’t want this test to dirty the real circulation system, so we had to construct it inside the surface clean room then seal it up before bringing it underground,” Woodward said.

The test cryostat arrived from Penn State where it was initially assembled inside a cleanroom. At Sanford Lab, the test cryostat was cleaned and prepared for use underground. Now, it is underground where it is being used to test the circulation system. “That’s how we’ll know if the system is working.”

By the numbers:

100 inches: The height of the inner cryostat
10 feet: The height of the outer cryostat
10 tons: The amount of liquid xenon that will be used inside the inner cryostat
70 kg: The amount of liquid xenon used to test the circulation system

See the full article here .


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About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

LBNL LZ project will replace LUX at SURF [see below]

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
“LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

Fermilab LBNE
LBNE

U Washington Majorana Demonstrator Experiment at SURF

The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

LBNL LZ project at SURF, Lead, SD, USA

CASPAR at SURF


CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”