Vulcan has two large vacuum chambers in Target Area Petawatt (TAP). The largest, with an inner volume of 100m3, contains the pulse compression optics and needs to be kept under a high vacuum at all times for alignment purposes. The smaller chamber is the interaction chamber, where the laser beam is focused down to a few microns in diameter and the intense light intensity that this achieves is used to super-heat a solid target during plasma physics experiments. This has an inner volume of about 20m3 and is covered with lead and white plastic and sits behind concrete walls for radiation shielding purposes. During a laser shot both chambers must be at a high vacuum of about 1x10-4 mbar or better.
Plasma physicist Ceri Brenner aligns a target inside the interaction chamber, wearing a full body clean suit
However, to provide the user community with a flexible working environment during experimental or pre-shot setup, the inside of TAP’s relatively large interaction chamber can be accessed by up to three qualified users at a time. To permit this there is a special 630mm diameter vacuum valve fitted which can be closed to enable just the interaction chamber to reach atmospheric pressure, but opened when both chambers are at high vacuum.
To work inside the chamber a full cleanroom body suit must be worn with gloves and a mask. Even with all these precautions hair and other contamination can be found around the inside of the interaction chamber, as well as debris from ablation during the laser-solid interaction. This build-up eventually compromises the vacuum seal between the two chambers which necessitates a full strip and clean of the valve to be carried out by the suppliers, VAT Vacuum Products Ltd.
The time lapse sequence shows the crane first lifting the actuator and bonnet assembly and then the valve from inside the VAT gate valve body. The parts are lifted to a clear space in the target area where they are all completely stripped and re-built with new components by a VAT service engineer. Each of the windows, leaf springs, locking mechanism etc. can be seen being stripped, cleaned and re-assembled. The crane is then used to return the valve gate to the valve body, followed by the bonnet assembly, where it is re-assembled, tested and commissioned. CLF staff also worked in parallel to clean the valve body in order to minimise downtime.
The full report on this maintenance is provided by Steve Blake, CLF lead mechanical engineer, and can be found in our forthcoming facility annual report.
Read more on how CLF engineering supports high power laser experiments.
