In memoriam: Alan Letchford

This was an ideal combination for a designer of reliable high-performance accelerators, with particular expertise in linear accelerators (linacs). At a recent international conference, Alan was amused to learn that some younger members of the community referred to him as ‘Lord Linac’ — no doubt with tongue firmly in cheek, but nonetheless fittingly.

Alan’s work on the ISIS radio frequency quadrupole (RFQ) that replaced the old Cockcroft-Walton high-voltage pre-injector, and his close supervision of its installation and commissioning in 2004, has successfully underpinned ISIS operations ever since.  His design of a new, improved, replacement for the fourth section of the ISIS linac ‘tank IV’, his management of its construction, and his leadership of its pre-installation testing programme, enabled the ~50-year-old tank IV with its chronic and irreparable vacuum leaks to be replaced in 2022 with confidence. Once the old tank had been removed and the new tank installed, there would have been no possibility of reverting to the old equipment.

After completing a 4-year apprenticeship on radar and communications systems for the Thames Navigation Service, Alan joined ISIS in 1987 as a Shift Technician on the ISIS machine Crew.  This was at a time when, not long after first beam, the machine was far from reliable, and so Alan had an excellent opportunity to learn all about the machine through fixing faults.  In 1989 he transferred from the Crew to work on power supplies and RF systems, particularly those for the injector linac. In 1990 he began a 3-year B.Eng. course at the Royal Military College of Science, Shrivenham, achieving 1st class honours.  After returning to ISIS in 1993 and working on control and software engineering in the Injector RF Group, he spent most of 1996 and 1997 in Germany at the Forschungzentrum Jülich and University of Frankfurt, working on RFQ design with Alwin Schempp and as the linear accelerator task group leader within the European Spallation Source (ESS) design study ongoing at the time.

During 1998–2003, Alan’s extensive and comprehensive work on the ISIS RFQ ensured that when it was installed as the pre-injector in 2004 it had been fully characterised and soak-tested. The high quality of Alan’s work has been amply demonstrated by the remarkably good performance of the RFQ over two decades: the duplicate RFQ built at the time as a spare has never been needed.

In 2003, Alan became the ISIS Injector Group Leader with overall responsibility for the 70 MeV injector linac, including making provision for replacing key items of plant and equipment that were becoming obsolete.  At the same time, Alan led a multi-disciplinary team from RAL, Imperial College London, Warwick University, University College London, Huddersfield University and the University of the Basque Country, Spain, to design, construct, characterise and operate a ‘Front End Test Stand’ (FETS) to demonstrate key technologies for the low-energy end of next generation high power proton accelerators. This programme of work is contributing significantly to the establishment of accelerator technology as a discipline in UK universities, and also providing training opportunities for new, young accelerator physicists and engineers from outside STFC. Alan was delighted to see first beam successfully through the FETS RFQ in 2022.

In 2010 Alan became an STFC Individual Merit (IM) Fellow. The fellowship was the first ever to be awarded within the ISIS Accelerator Division and enabled him to carry out research for the development of the next generation of accelerator technology in the context of a future ISIS-II. At the same time, Alan took on the exacting time-limited task of replacing the 50-year-old linac tank IV by a new higher performance tank, taking advantage of design and construction possibilities that had been unavailable 50 years previously, but also having to accommodate the loss of manufacturing facilities in the UK over the past 50 years. The new tank has worked perfectly since its installation in 2022.

In addition to his far-ranging and important work leading projects for ISIS, Alan was the go-to person in the UK for novel linear accelerator design. Throughout his career he was in high demand for consultancy work with the MoD, AWE, Culham, Siemens and the medical linac community. He was also frequently invited to participate in or advise on international accelerator projects, notably at the ESS, J-PARC in Japan and the Spallation Neutron Source in the USA.

Alan’s international standing was recognised by being selected to give the invited plenary talk at the 31st International Linear Accelerator Conference, and more recently he gave a very well received public lecture on the history of particle accelerators on the Harwell site. An ISIS case study in 2024 showcased Alan’s career and contribution to his field and this also provides some insight into his personality and sense of humour.

Alan was never content to rest on his laurels and continued to work on novel and challenging projects in the run up to his anticipated partial retirement this year. His death represents a great loss to ISIS, and he will be very much missed by all his colleagues. Alan is survived by his wife, Linda.

 Dean Adams, David Findlay, Ian Gardner and John Thomason.