With the participation of Polish scientists, a prototype of the cryogenic units of a powerful “neutrino factory” was created

Fermi National Accelerator Laboratory technicians have completed a prototype of a special superconducting cryogenic unit, the only instrument of its kind in the world. The PIP-II project, in which Polish scientists also participate, aims to Build the most powerful neutrino source in the world. Poland has also invested in it.

The HB650 will be the tallest and largest freeze unit in the new Linear Accelerator (LINAC). Together with three others, it will accelerate protons to 80% of the speed of light. From Linac, the protons will pass to other accelerators, where they will be accelerated and converted into a stream of neutrinos. These neutrinos will be sent on a 1,300-kilometer journey through the Earth’s crust until they reach the Deep Underground Neutrino Experiment and Long Lead Neutrino Facility in South Dakota.

Work on the innovative freezing unit began in 2018, and in 2020 its design was finally approved and component production began. In January 2022, technicians began assembling the Fermilab cryogenics unit. HB650 is a 10 meter long cylinder weighing about 12.5 tons. Inside are a series of recesses that look like soda cans connected together. The cavities are made of superconducting niobium, which will remain at a temperature of 2 K during operation. At such a low temperature, niobium becomes a superconductor that can accelerate protons effectively.

To achieve such a low temperature, the cavities will be immersed in liquid helium, in which there will be many dielectric layers, including MLI, aluminum and a vacuum layer. The whole is placed in a steel vacuum chamber, which protects the cavities from the influence of the Earth’s magnetic field.

Linac will accelerate protons using an electric field with a frequency of 650MHz. The inside of the cavities must be kept extremely clean, because after assembling the device it is impossible to clean them, and even the slightest contamination would disrupt the operation of the metronome. The cleanliness must be so high that it is not enough for all the work to be done in the cleanroom. All items in the cleanroom and the procedures used are designed to maintain the highest possible level of cleanliness. For example, workers cannot move very quickly so as not to cause any pollutants to be released into the air.

Currently, the cryogenic unit is cooled to a temperature of 2 K. Scientists are checking if the whole thing will hold up. It’s a prototype for a reason. Thanks to him, we want to identify any problems, find out what does not fit together, and what does not worksays Saravan Chandrasekaran of Fermilab. After cooling is completed, the device will undergo a … transfer test. The cryo unit will go to the UK and when it’s back at Fermilab tests will be done to make sure everything is still working.

When the HB650 passes all the tests, it will start building the actual freezer unit. It will be attended by PIP-II (Photon Improvement Plan II) project partners from Poland, India, France, Italy, Great Britain and the USA.

Fermilab’s PIP-II neutrino