In the search for dark matter particles, a desktop experiment in the heart of a Canadian mining area may play a role. The sensei collaboration uses skier charge-coupled devices (ccd), the most sensitive sensors of its kind, a dream decades ago, only recently.
The collaborative project recently demonstrated that the experiment has a sensitive dark matter detector and that it can reduce the background rate in an underground experimental area of the Department of Energy's Fermilab. Now, the collaborative project is running a larger, quieter, and more sensitive experimental version of snolab more than a mile underground in Canada.
With the COVID-19 pandemic and the closure of the U.S.-Canada border, the experiment could easily fall behind schedule in 2020. Instead, it's in the commissioning phase – testing with about 20 percent of the target material that the experiment will use after the outer shield is in place. Extraordinary teamwork between physicists on both sides of the boundary ensured it moved forward as planned.
Stay safe while advancing science
As the COVID-19 pandemic enters its third or fourth month, Javier Tiffenberg, associate scientist at FermiLab and collaborator at Sensei, suddenly realized that the experimental installations that the Fermi lab team planned to begin in 2020 needed to be reconsidered.
With no way to get to the site, the sensei team contacted Snolab to see if the staff would be willing to install the ultra-sensitive experiment themselves under the remote guidance of FermiLab. Snolab's staff has become familiar with the unique challenges of installing experiments in a clean laboratory located in a working mine. This time, they'll be installing an experiment for weeks that they didn't otherwise intend to participate in.
Snolab used to be a game.
Silvia Scorza, a research scientist at Snolab, said of the perspective adopted by the project: "Since they can't be here, we will be their hands." Scorza is one of Snolab's employees, which took on the task of remotely helping with the installation project during the pandemic.
"When the people at Snolab say they're interested in contributing to this, and then the engineers and technicians from our side say, 'Yeah, we can do this,' I'm super excited because I really think it's together," Tiffenberg said.
Greg derylo, an engineer in particle physics at Fermilab, designed the layout of sensei, worked with the drawing team to draw all the mechanical parts, and procured parts from the machine shops inside and outside the site. Due to the impact of the COVID-19 pandemic lockdown on the campus of Fermilab, he also completed most of the physical assembly of the experiment.
Derylo said disassembling at Fermilab and reassembling it has always been part of the plan, but remote installation raises a new problem.
"The real trick is who assembles it underground," he says. The main problem is dealing with fragile (and expensive) captain CCDs, who are "very vulnerable to static electricity damage.") Smaller than a person can feel on their hands after rubbing their feet on the carpet and touching the doorknobs, it destroys the sensor. To that end, snolab's physicists and technicians took a special class on electronics processing.
Testing, testing, and a very pandemic-style gathering
Before an experiment can be put into the hands of snolab, it must be tested and documented.
"We tested everything at Fermi's labs. We assemble everything in the same way they did there," Derylo said.
The first test is a mechanical test — assembling the shell of the experiment to confirm that it maintains vacuum — and thermal performance testing. Sensei relies on cryogenic technology for "cold runs". To do this, the Fermilabs team installed additional instruments to monitor the temperature and run diagnostic procedures. Both performed in line with expectations.
In the early autumn of 2020, the FermiLabel team installed a set of test modules in the experiment and opened, cooled, cold-run and operated the modules. The reading result was completed successfully. The team celebrates with champagne through zoom.
Documentation and manual simulations
Often, documents are more of a series of reminders than detailed instructions, and team members can intuitively judge the process or rely primarily on memory.
Creating instructions for a team unfamiliar with the experiment requires a higher level of communication. This mainly means creating documents that are more detailed.
Because the team knew the installation would be remote, they leveraged their own assembly during testing.
"We took pictures of everything," Tiffenberg says, "and it's crucial to have these files." ”
But the presentation of these documents is not without its challenges. Due to the pandemic, multiple people are taking notes at different times, and communication within groups has become more important than usual. Different technologists have different perspectives – literally.
Derylo said: "It turns out that we actually have the opposite definition of what is in the previous setting. "What can be done to remedy that? One of sensei's newest and most important components: adhesive labels.
The team also established stops in the file. Once the snolab pair reaches one of these points, they can determine if they have time to proceed with the next shift or whether they need clarification from the Fermi Labs team.
The first document will be ready around the beginning of 2021. Derylo said the document was divided into different sections and ended up with about 70 pages. The file resembles a compendium and makes extensive use of photographs. Schematics of vacuum systems, cooler systems and electrical wiring are also provided, but are not part of the brochure.
"Then we take it apart, but try to keep as many parts together as possible, and then we ship it to snolab in January," Tiffenberg says. ”
An ultra-clean clean room in a working mine
Pandemic issues aside, the process of installing experiments at snolab's underground facilities is always complicated. After all, it's a clean laboratory more than a mile underground —inside a working mine.
Scorza said: "Careful planning and preparations start from the ground. ”
There, at the beginning of the day, physicists, engineers and technicians wait for the "cage" in miner-like clothes, and a mining elevator takes them deep underground.
The process of going down takes less than five minutes. But then there's a long way to go, through a mine tunnel with a railroad track along the way, almost a mile away.
"So, pay attention to your footsteps," Scorza said.
At the end of this trek, is a clean laboratory. Before entering, the boots are washed at a special site. Clothes and boots were set aside. People entering the cleaning lab undress, bathe and put on new cleaning clothing on the other side of the shower to avoid contamination. A laboratory coordinator is responsible for checking whether the laboratory can work – checking oxygen levels and other parameters. It takes about an hour from the ground to the start of work, and the same is true on the way back – the shower is removed. During the 10-hour work day, about 8 hours were set aside for each shift to assemble the experiment.
A four-person team of snolab scientists and a technician worked in turns, with teams of two for the installation. No one can be alone underground, and physical distance is maintained, and there are also restrictions on the maximum number of people.
Scorza said every item received had to go through an "underground car wash." Each item is packed in three layers, with two trays, simplifying the complex process of unpacking and wiping material before entering the cleanroom laboratory. On the other side is the clean laboratory. For sensei, components include pipes, cables, vessels, copper on the inside, cryogenic equipment, lead and copper shields and bell housings.
"When these things are designed, of course, shipping everything that's assembled isn't on the requirements list," Tiffenberg says, "and for the vast majority of things we ship, everything is very good." ”
There are only a few small plastic pieces – easy to replace – that loosen and crack.
Tiffenberg said that once everything was opened and looked good, it was a big, big consolation.
Installation began on April 19 and was completed in late summer.
While Snolab's clean rooms are equipped with phones and Wi-Fi, communication outside of the documents takes place mostly at weekly meetings. The plan shifts from one week to another, depending on whether the team can go underground due to availability and COVID-19 restrictions.
Scorza said the mix of work that SNOLAB allows scientists to do — including hands-on and analytical — gives them a more complete experience in experimental physics.
"I believe that a team, a team of scientists who had little to do with the experiment, but was able to make progress in installing it underground, shows that, first of all, physicists are very flexible," Scorza said, "and [it] proves how powerful the plan for this experiment is." Hats off to the FermiLab team. ”
Tiffenberg said he was grateful that there were no small episodes or surprises during the installation. "It took a long time to reach this situation without surprises. In the beginning, everything felt like, 'Okay, we spent a lot of time adjusting, coordinating, reviewing things'. And that took a long time. But now things are going on and we're grateful for the time we spend there because now everything is no surprise. ”
While experiments are now acquiring data, surprises in the form of scientific discoveries would be a nice bonus.