Argonaut is a robotic system designed to monitor the inside of liquid argon particle detectors, which are maintained at minus-193 degrees Celsius.
The ProtoDUNE neutrino detector at CERN uses fixed internal cameras to look for problems such as bubbles and sparks when filled with 800 tons of liquid argon. Credit: CERN
The Argonauts of Greek mythology braved sharp rocks, rough seas, magic and monsters to find the legendary Golden Fleece.
A new robotics project at the Department of Energy’s Fermi National Accelerator Laboratory will share the same name and spirit of adventure.
Argonaut’s mission will be to monitor conditions in ultra-cold particle detectors by traveling in a sea of liquid argon maintained at minus-193 degrees Celsius — as cold as some of the moons of Saturn and Jupiter.
Funded in March, the project aims to create one of the most cold-tolerant robots ever, with potential applications not only in particle physics, but also in deep space exploration.
Argon, an element commonly found in the air around us, has become a key ingredient in scientists’ quest to better understand our universe.
In liquid form, argon is used to study particles called neutrinos in several Fermilab experiments, including MicroBooNE, ICARUS, SBND and the international Deep Underground next-generation Neutrino experiment.
Liquid argon is also used in dark matter detectors such as DEAP 3600, ARDM, MiniCLEAN and DarkSide-50. Liquid argon has many advantages. It’s dense, increasing the chances of notoriously distant neutrinos interacting.
It’s inert, so electrons released by a neutrino interaction can be captured to create a 3-D image of the particle’s trajectory. It’s transparent, so researchers can also collect light to “time stamp” the interaction.
It’s also relatively cheap – a huge plus, considering DUNE will use 70,000 tons of the stuff. But liquid argon detectors are not without their challenges.
To produce quality data, the liquid argon must be kept extremely cold and extremely pure.
That means the detectors must be isolated from the outside world to prevent the argon from evaporating or becoming contaminated.
With limited access, it can be difficult to diagnose or address problems in a detector. Some liquid argon detectors, such as the ProtoDUNE detectors at CERN, have cameras inside to look for problems such as bubbles or sparks.
To keep the power requirement low and avoid disturbances in the liquid argon, Argonaut will move slowly along tracks on the side of the detector. Its main feature is a movable camera, but the engineers working on it hope to add other features, such as extendable arms for minor electronics repairs. Credit: Bill Pellico, Fermilab
“Seeing things with our own eyes is sometimes much easier than interpreting data from a sensor,” said Jen Raaf, a Fermilab physicist who works on liquid argon detectors for several projects, including MicroBooNE, LArIAT and DUNE.
The idea for Argonaut came about when Fermilab engineer Bill Pellico wondered if it would be possible to make the indoor cameras movable.
A robotic camera may sound simple, but designing it for a liquid argon environment presents unique challenges.All electronics must be able to operate in an extremely cold, high voltage environment.
All materials must withstand room cooling to cryogenic temperatures without contracting too much or becoming brittle and disintegrating.
All moving parts should move smoothly without grease, which would contaminate the detector.
“You can’t have something that goes down and breaks and falls off and shorts out something or contaminates the liquid argon, or puts noise into the system,” Pellico said.
Pellico received funding for Argonaut through the Laboratory Directed Research and Development program, an initiative designed to advance innovative scientific and technical research in the Department of Energy’s national labs.
At this early stage of the project, the team — Pellico, mechanical engineers Noah Curfman and Mayling Wong-Squires, and neutrino scientist Flavio Cavanna — is focused on evaluating components and basic design aspects.
The first goal is to demonstrate that it is possible to communicate with, power and move a robot in a cryogenic environment.
“We want to prove that we can at least have a camera that can move, pan and tilt in liquid argon, without contaminating the liquid argon or creating air bubbles, with reliability that shows it can last for the life of the detector Curfman says.
The plan is to power Argonaut through a fiber optic cable so as not to interfere with the detector electronics.
The fist-sized robot only gets about 5 to 10 watts of power to move and communicate with the outside world. The motor that will move Argonaut along a track on the side of the detector will be outside the cold environment.
The camera is in the cold liquid and moves very slowly; but that’s not a bad thing – going too fast would cause unwanted disturbances in the argon.
“As we get more advanced, we’re going to add more degrees of freedom and more rails,” Curfman said.
Other future Argonaut upgrades include a temperature probe or voltage monitor, movable mirrors and lasers to calibrate the light detectors, or even extendable arms with tools for minor electronics repairs.
Much of the technology Argonaut is developing will be widely applicable to other cryogenic environments – including space exploration.The project has already sparked some interest from universities and NASA engineers.
Deep space robots “will go to remote locations where they have very little power, and the lifespan should be more than 20 years, just like in our detectors, and they have to operate at cryogenic temperatures,” Pellico said.
The Argonaut team can build on existing robotics know-how along with Fermilab’s expertise in cryogenic systems to push the boundaries of cold robotics.
Even the exteriors of active interstellar space probes like Voyagers 1 and 2 don’t reach temperatures as low as liquid argon — they use thermoelectric heaters to keep their thrusters and scientific instruments warm enough to work.
“There has never been a robotic system that has worked at these temperatures,” Pellico says. “NASA never did it; we’ve never done it; no one has ever done it, as far as I can see.”