Increasing our reliability
Installation of new radiofrequency cavities
Here at Diamond we have been busy improving the reliability of the synchrotron by installing two normal conducting radiofrequency (RF) cavities in the storage ring. This massive operation has been ongoing for over a year and the first cavity will be operational by the autumn with the second cavity following shortly afterwards.
To understand why the new RF cavities are being installed it is important to consider the inner workings of the synchrotron. The huge set-up fires electrons around a large storage ring for periods of up to several hours. During this orbit the electrons produce synchrotron light for our users to apply at the various beamlines. However, to maintain their energy as they fly around the ring, the electrons pass through cavities containing electromagnetic fields that oscillate at radiofrequencies.
Figure 1: One of the new NC cavities preparing to be installed.
The current 300 mA electron beam at Diamond is maintained by two 500 MHz superconducting (SC) cavities. In recent years, these SC cavities have sadly failed, resulting in machine down-time and reduced experimental time while the cavities were being fixed. Repair of the cavities is a prolonged and costly process, so the team at Diamond sought to safeguard against future failures by installing additional cavities of a simpler, normal-conducting (NC) design that can be repaired in-house.
Two NC cavities are currently being installed in the storage ring to support the operation of the SC cavities and to act as a back-up should any failures occur again. This immense undertaking requires RF amplifiers, transmission lines, low-level RF as well as storage ring engineering, vacuum, and controls.
The new NC cavities are positioned outside the RF straight to preserve the purity of the superconducting cavities and to reduce the risk of contamination of all cavities by a vacuum leak in the RF straight. The first cavity was vacuum tested and baked at 120°C for two weeks back in March to clear contamination and then powered up to full field in July in the RF test bunker, proving that it was ready for installation. The second cavity is not far behind and will be added to the ring shortly after.
The wheels are in motion to further improve the reliability and performance of the synchrotron, with an additional booster cavity installation planned for 2018. This will provide RF redundancy in the booster ring and will be powered by a 60 kW solid state amplifier. This is just a small snapshot of the fantastic upgrades Diamond has planned for the future to ensure its users continue to get robust results at the beamlines.
Figure 2: A view of the storage ring during the installation process, where the new cavity can be seen on the left wrapped in aluminium foil.