At only 20 degrees warmer than Neptune, liquid argon is not the easiest gas to work with. On top of needing to be kept extremely cold, it also needs to be pure when it is being used to study particles, neutrinos and dark matter.
So pure, in fact, that the ProtoDUNE neutrino detector at CERN—the European Organization for Nuclear Research—is kept isolated from the outside world to ensure the 800 tons of liquid argon stored inside does not evaporate or become contaminated. With restricted access and a -193˚C climate, diagnosing or addressing issues inside a detector can be difficult.
Fixed cameras mounted inside ProtoDUNE give researchers a look inside, allowing them to eye any issues like bubbles or sparks. But, sometimes, there is no eye like your own.
“Seeing stuff with our own eyes sometimes is 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.
Fermilab engineer Bill Pellico shared Raaf’s frustration, leading him to wonder if it would be possible to make the interior cameras movable. The challenge is—literally—unprecedented.
“There’s never been a robotic system that operated at these temperatures,” said Pellico. “NASA’s never done it; we’ve never done it; nobody’s ever done it.
But that doesn’t mean Pellico is not going to try. Backed by funding from the Department of Energy, Pellico and mechanical engineer colleagues Noah Curfman and Mayling Wong-Squires are in the early stage of the Argonaut project. The first goal is to demonstrate that it’s possible to communicate with, power and move a robot in a cryogenic environment.
The plan is to power Argonaut through a fiber-optic cable so as not to interfere with the detector electronics. The fist-sized robot will only get 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 situated outside of the cold environment.
“We want to prove that we can have, at a bare minimum, a camera that can move around and pan and tilt in liquid argon, without contaminating the liquid argon or causing any bubbles, with a reliability that shows that it can last for the life of the detector,” said Curfman.
At first, the camera inside the detector will move very slowly to avoid disturbances in the liquid argon; but, the engineers hope to add additional features as their technology advances and succeeds. The team said future upgrades could include extendable arms for minor electronics repair, temperature probes or voltage monitors and even movable mirrors and lasers for calibrating the detectors.
Pellico’s and team say the technology behind their super-cold robots is applicable for similar environments, including space. Some of the moons of Saturn and Jupiter are roughly -190˚C, while Neptune—the coldest planet in the solar system—averages a temperature of -214˚C.
Photo: The ProtoDUNE neutrino detector at CERN uses fixed internal cameras to look for issues like bubbles and sparks when filled with 800 tons of liquid argon. Argonaut is being designed to monitor the interior, which is kept at -193˚C. Credit: CERN