Voyaging Into a Sea of Liquid Argon

Argonaut is a robotic system designed to monitor the interior of a liquid argon particle detector kept at minus 193 degrees Celsius. CERN’s ProtoDUNE neutrino detector uses a fixed internal camera to look for problems such as air bubbles and sparks when filled with 800 tonnes of liquid argon. Credit: CERN

Greek mythological Argonauts bravely roamed sharp rocks, rough seas, magic and monsters to find the legendary golden fleece. The new robotics project at the Fermi National Accelerator Laboratory of the Department of Energy shares the same name and spirit of adventure.

Argonaut’s mission is to sail into a sea of ​​liquid argon kept at minus 193 degrees Celsius and monitor the condition inside the ultra-low temperature particle detector. Celsius — Cold like some months Saturn And JupiterFunded in March, the project aims to create one of the coldest robots ever made, not only for particle physics, but also for deep space exploration. May also be applicable.

Argon, an element commonly found in the air around us, has become an important component in the quest of scientists to better understand our universe. In its liquid form, argon is used to study particles called. Neutrino In several Fermilab experiments, including MicroBooNE, ICARUS, SBND, and next-generation international deep underground neutrino experiments. Liquid argon is also used in the following applications: Dark matter Detectors such as DEAP 3600, ARDM, MiniCLEAN, DarkSide-50.

Liquid argon has many advantages. Due to its high density, the more notorious it is, the more distant neutrinos are likely to interact. Because it is inert, it can record the electrons released by the interaction of neutrinos to create a 3D image of the orbit of the particle. Being transparent, researchers can also collect light and “timestamp” interactions. It’s also relatively cheap — DUNE uses 70,000 tonnes of material, which is a big plus.

However, liquid argon detectors are not without their challenges. Liquid argon must be kept extremely cold and extremely pure to produce high quality data. This means that the detector must be isolated from the outside world so that argon does not evaporate or become contaminated. Due to restricted access, problems within the detector are difficult to diagnose or address.Some liquid argon detectors such as the ProtoDUNE detector CERN, Mount the camera inside and look for problems such as air bubbles and sparks.

Argonaut truck

To keep power requirements low and avoid liquid argon turbulence, Argonaut moves slowly along the track on the side of the detector. Its main function is a movable camera, but engineers working on it want to add features such as an expandable arm for minor repairs of electronics. Credits: Bill Pellico, Fermilab

Jen Raaf, a Fermilab physicist studying liquid argon detectors in several projects such as MicroBooNE, LArIAT, and DUNE, said:

The idea for Argonaut came when Fermilab engineer Bill Pellico wondered if he could make the indoor camera movable. Robot cameras may sound simple, but designing a camera for a liquid argon environment presents unique challenges.

All electronic devices must be able to operate in extremely cold, high voltage environments. All materials must withstand cooling from room temperature to cryogenic temperatures without excessive shrinkage, brittleness or disintegration. All moving parts need to move smoothly without the grease that contaminates the detector.

“There can be nothing that falls, breaks and falls, shorting something, contaminating liquid argon, or making noise in the system,” Perico said.

Pellico received Argonaut funding through the Laboratory Directed Research and Development program. This program is an initiative established at the Ministry of Energy’s National Laboratory to promote innovative scientific and engineering research. In this early stage of the project, the team — Perico, mechanical engineers Noah Calfman and Mailing Wong Squires, and neutrino scientist Flabio Cabanna — focuses on assessing aspects of components and basic design. The first goal is to demonstrate that the robot can communicate, power, and move in a cryogenic environment.

“We want to at least prove that we can use a camera that can move, pan and tilt in liquid argon without contaminating it or creating bubbles. It’s the life of the detector. “Mr. Calfman said.

The plan is to power Argonaut through a fiber optic cable so that it does not interfere with the detector’s electronics. Fist-sized robots can only get about 5-10 watts of power to move and communicate with the outside world.

The motor that moves the Argonaut along the track on the detector side is located outside the cold environment. The camera is in a cold liquid and moves very slowly. But that’s not a bad thing — too fast can cause unwanted disturbances in argon.

“As we progress further, we will start adding more degrees of freedom and more rails,” Curfman said.

Other future upgrades to Argonaut may include a temperature probe or voltage monitor, a movable mirror and laser to calibrate the photodetector, or an expandable arm with tools for minor electronics repairs. there is.

Many of Argonaut’s technologies are widely applicable to other cryogenic environments, including space exploration. This project has already attracted interest from several universities and NASA Engineer.

Deep space robots “will go to remote areas with little power, have a lifespan of at least 20 years, similar to our detectors, and must operate at very low temperatures,” Pellico said. Stated. The Argonaut team can build on existing robotics know-how and Fermilab’s expertise in cryogenic systems to push the boundaries of cryogenic robotics.

Even the outer surfaces of active interstellar probes such as Voyager 1 and Voyager 2 are not as cold as liquid argon. Use thermoelectric heaters to keep the thrusters and scientific instruments at a temperature sufficient to operate.

“No robot system has ever operated at these temperatures,” says Pellico. “NASA has never done it. We have never done it. As far as I know, no one has done it.”

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