One of the primary functions of Diamond Light Source is to provide an electron beam that can be controlled to emit synchrotron light for investigations on the molecular scale. With beamtime a valuable commodity for academic and industrial users, the reliability and availability of the beam can be the key to a successful visit.
Success for users is therefore closely linked to the success of those who provide the beam. Diamond’s Technical Division has ten different technical groups that all play a part in keeping the beam running. Collectively, these groups have all contributed to the latest record in beam reliability at Diamond. Over the course of the second run in 2015, Diamond recorded the longest 'mean time between failures' (MTBF) in its history, clocking 264 hours without tripping off – more than doubling its previous best.
A view inside a vacuum vessel that makes up the storage ring.
In synchrotron circles however, it is widely considered that you are only as good as your last run. Whilst the latest MTBF was indeed record-breaking, MTBF figures and beam uptime are vulnerable to fluctuations. This difficulty comes from the fact that the machine is a complex set of interconnected sub systems within the accelerator complex that rely on one another to keep the operation running. It is therefore essential that the interaction between these systems is managed very closely.
Vince Kempson, Head of the Accelerator Operations Group, coordinates all of the efforts to make the machine as reliable as possible, within a continuous improvement programme: "The MTBF is used in all accelerators of Diamond’s type around the world and each facility has their own set of targets depending on their size and focus. We each have our own unique set of problems with improving or sustaining reliability, but there is a consensus that forward planning and close monitoring mean we can react quickly in a failure situation. Sharing of experiences is also important when it comes to planning for the future, so we as light sources get together annually to share what problems we’ve been having and discuss potential solutions."
Senior Operations Technician John Fox (right) and Storage Ring Manager Chris Bailey (left) monitoring the beam systems in the control room.
Responsibility for the machine’s individual components and operating systems is carried out by the different technical groups. The Accelerator Operations Group, based in the control room at the entrance to the synchrotron building, work in shifts 24/7 to keep an eye on the balance of all these systems when the beam is on. The operators are senior technicians, often with a background in computing, interfacing hardware, or electronics, and with a graphical view of all systems and performance parameters on their control consoles, they can identify and respond to any developing issues or beam trips. Dealing with a beam trip means diagnosing what’s occurred, discussing with the technical groups, applying a solution and then refilling the accelerator with electrons. The overall aim is to continue operation in as short a time as is practical. Beam trip faults are then analysed with a view to eliminate them in the future as part of the continuous improvement programme.
Even with the best planning and monitoring in place, there are some incidents that cannot be predicted. Last September Diamond had an unscheduled period of downtime after one of the radiofrequency (RF) cavities failed without warning. The helium-cooled RF cavities restore the energy to the beam as it goes round, and it was discovered that one of these components developed a leak in its cooling system. It was the rapid response to this helium leak by the Operations Group and RF Group that meant the disruption to beamtime was kept to a minimum as the back-up cavity was installed. Speaking at a recent staff talk, Diamond’s CEO Andrew Harrison said: "What [the cavity failure] brought home to me was just how effectively we can respond to events like this, and the importance of foresight. Foresight that extended back a number of years that led to people saying 'this is a critical component and we must have another one of these'."
This foresight is now being applied again, with the plan to install additional normal conducting cavities to augment the current superconducting ones. The new cavities will be installed in the machine adjacent to the current cavities with the aim of giving Diamond a greater operating margin, which will be especially useful in minimising the impact of any planned – or unplanned – work on the RF system. Reliability can never be guaranteed, but rest assured that the groups looking after the machine are continually working behind the scenes to monitor and improve their systems, and be on hand at a moment’s notice should a rapid response be required in the future.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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