SCIENTISTS AT CERN EVALUATING HFOs FOR PARTICLE DETECTORS

The planned 3-year shutdown at the CERN Large Hadron Collider (LHC) will enable repairs and upgrade the accelerator to be able collect more detailed data about fundamental particles in the universe. Some of the LHC’s detectors are filled with gas, including fluorocarbons to help particle detection. When particles collide, they ionize gas molecules, creating ions and electrons measurable as an electrical current.

Most detectors use a three-gas mixture. One of these is an ionizing gas, and R-134a is commonly used for this purpose. The detector gases are selected because of their stability, but particle detection depends on cracking some gas molecules in the detector to generate ions but at a controlled level to minimise the impurities created in the chamber. Detector gases are typically selected from refrigerants, however many low-GWP gases are less stable breaking down much more quickly in the atmosphere and the same conditions of that degrade these molecules in the atmosphere are found in the LHC’s detectors. Currently a leading candidate is 1,3,3,3-tetrafluoropropene, HFO-1234ze. Tests are ongoing to make sure a detector could operate with that molecule for 20 years without repair.

Photo: © Shutterstock - Cefic

To detect these fundamental particles, much of the LHC’s equipment operates at low temperatures maintained with refrigeration. One of the objectives is to reduce emissions of or replace where possible high GWP fluorocarbons used as refrigerants or in detectors. A new detector is being added to the LHC’s experiment (the LHCb), which tracks particles to better understand matter and antimatter. To achieve the cold temperatures required, CERN intends to use a hydrofluoroolefin (HFO) refrigerant.

Source: C&EN Chemical & Engineering News