Half of the CARME system being commissioned at Daresbury Laboratory (Credit: University of Edinburgh/STFC)
The CRYRING Array for Reaction Measurements (CARME) vacuum chamber has left STFC’s Daresbury Laboratory for its new home in Germany.
STFC and the Nuclear Physics Group of the Universities of Edinburgh and Liverpool have worked closely together on this project which is heading for CRYRING – a heavy ion storage ring at the Facility for Antiproton Research (FAIR) in Germany.
CARME particle detector array is unique in that it can work in extremely high vacuum (XHV) conditions. To put in perspective, this is similar to the atmosphere on the surface of the moon.
XHV is the level of vacuum needed to store and recirculate an ion beam in CRYRING. A higher level of vacuum means fewer gas molecules to scatter the beam ions from their path and lost to the experiment as they circulate in the ring at over 100,000 times per second.
Very few places have experience of working with such high vacuum levels, but the teams at Daresbury Laboratory are well versed in working in the ultra-high vacuum (UHV) and XHV regimes, making them an excellent fit for the CARME project.
The chamber was designed by a joint effort between the STFC Nuclear Physics cross-community mechanical design engineers and the Universities of Edinburgh and Liverpool. It was up to Keith Middleman, Senior Vacuum Engineer at STFC, to calculate how many pumps would be required to reach XHV given the particle detector arrays are to be mounted inside CARME.
STFC’s Mechanical Engineering teams and Vacuum Solutions Group worked together to find the necessary space inside the chamber to make it pump at the required speed. They then created a complete set of construction specifications, from mechanical requirements to what material to weld CARME.
When it came to building CARME’s vessels, they were manufactured in the UK and delivered back to the lab. Each element had to be dismounted, cleaned, fired to high temperatures, rebuilt and then checked for leaks, a very detailed job which took the time and patience of the mechanical and vacuum technicians.
Finally, before being carefully packaged for delivery, CARME was re-assembled and tested. This was very successful, with the empty CARME chamber achieving some of the lowest pressures ever measured at Daresbury Laboratory and proving that the required level of vacuum can be achieved in the complex chamber in which the detector array will be mounted.
CARME is a detection array for nuclear and atomic physics experiments and experiments are due to begin in 2021. The initial focus will be on detecting charged particles for nuclear astrophysics experiments. Elements heavier than helium are created by nuclear reactions taking place in stars. Nuclear astrophysics aims to study these key nuclear reactions to understand the origin of the elements.
In stellar explosions such as novae and supernovae, nuclear reactions involving short-lived radioactive isotopes play a key role in the synthesis of new elements. Producing these radioisotopes in Earth-based laboratories is a major challenge. CRYRING at FAIR offers the unique possibility to recreate the conditions in which nuclear reactions occur in stellar explosions, such as novae and supernovae, using pure beams of radioisotopes inaccessible elsewhere in the world. In particular, the first experiment approved for CARME (led by Dr Carlo Bruno, University of Edinburgh) will aim at improving our understanding of the expected composition of cosmic dust formed in nova explosions.
Whilst the initial focus will be on detecting charged particles, CARME is special in that it will also be able to detect gamma rays and X-rays, making it very flexible. In the longer term this will be advantageous because to mount/unmount a system like this is very time consuming, not least because when you break the vacuum it can take weeks or months to recover those specific conditions.
This project is part of the UK’s contribution of scientific equipment to FAIR.
Last updated: 13 January 2021