Posted on: 6th December 2005

portrait of John D Lawson

John D Lawson, 4 April 1923; Educated Wolverhampton Grammar School; St John’s College, Cambridge; BA 1943 Mechanical Sciences Tripos, including special wartime “radio” course; ScD Physics 1959; Fellow of Institute of Physics 1970; Fellow of Royal Society 1983 “for his contributions to the field of applied electromagnetism, in particular the physics of charged particle beams and high temperature plasmas”.

John D Lawson, well known for his derivation of the Lawson criterion – a fundamental criterion (or principle) in fusion research – originally trained as an engineer. Through a series of coincidences he became involved in fusion research from its early days, and made important contributions that continue to influence the design of proposed fusion reactors.

“I started during the Second World War,” he recalls. “I was one of the lucky people who were just about to take Higher Certificate and try for a scholarship for university; in 1941 the government suddenly realised that they needed a lot more scientists, so everybody who was doing science was given a free one or two year university course. Although encouraged to study Classics at school, I had wanted to read physics at university, but they wouldn’t take me because I hadn’t done chemistry in grammar school, so I took mechanical sciences, which is an engineering degree. For that reason I was somewhat different from most people who had taken a conventional physics degree. And as an engineer my method of thinking is slightly different.”

His first scientific job was during the war. He was based at TRE (Telecommunications Research Establishment) Malvern where he worked on microwaves and microwave aerials. In 1951 Lawson moved to AERE Harwell General Physics Division. With the outbreak of the Korean War in 1950 researchers who had worked on defence projects were encouraged to return to defence work. Lawson, because of his experience with microwaves, was assigned to lead a section designing a klystron, a valve for producing high power at very short wavelengths, or microwaves, within a group led by Peter Thonemann. Thonemann, having completed a Masters degree at Sydney University, came to the Clarendon Laboratory Oxford in October 1946 to carry out research into controlled fusion for his PhD. By 1952 Thonemann was working at Harwell, where he took charge of the development of the ZETA fusion experiment, which was first operated on 12 August 1952.

It was through sharing an office with Thonemann that Lawson heard about fusion for the first time. The emphasis at Harwell at that time was on mechanisms for producing fusion. Lawson (the engineer) insisted that it was important to check that more energy was produced than consumed in a complete system – hence the criterion, which, according to him, was “very simple to deduce”. This now plays an important role in assessing the efficacy of fusion reactor design.

“Being an engineer I wondered what different parameter ranges there could be for a practical device. People were describing all sorts of things such as colliding beams which have come back in a different form in inertial confinement fusion now, but what I did was to put some parameters on a sheet of paper and then worked out a whole lot of actual numbers that would make sense in that they lay within a practical range.”

At the suggestion of the Harwell Director John Cockcroft, Lawson was chosen to present a paper on fusion power in Dublin in September 1957 at the British Association for the Advancement of Science Meeting. The paper created great excitement and was widely reported in the media. “ZETA and other experiments were classified because of the fact that they could be neutron sources to produce fissile material,” he notes, “but my criterion was not, so it was allowed to be talked about.”

But in spite of the stir his worked caused, Lawson says, “I never was really in fusion. I spent most of my working life working on particle accelerators. My main original achievement here was to show that the parameters suggested for a strong focusing machine were not realistic, although it’s still a very strong and powerful principle. Sharing an office with Peter Thonemann I saw what the fusion problem was. I produced the criterion, produced the report, and then I got involved with lots of other discussions and wrote the other report, a survey of different methods. And that was it. Then I was back to accelerators.

“I wrote one or two other papers surveying the other ideas that had been suggested and showing that most of them wouldn’t work. I also knew that I wouldn’t see fusion power in my own lifetime, although most people were talking about it coming in 20 years or so. They still are. My work was always negative and was tending to be showing things that wouldn’t work, or surveying an area to see whether it might possibly be feasible.”

After Lawson transferred to the Rutherford Laboratory in 1961 to continue his work on accelerators he did have one more foray into fusion research with a two year sabbatical at Culham in 1975-76 working on a design study of a conceptual fusion power reactor based on the reversed field pinch principle with Hugh Bodin and Roger Hancox.

He retired in 1987. During his long, productive and ultimately satisfying career he published numerous papers and reports. He also wrote The Physics of Charged-Particle Beams, now in its second edition and still considered to be a classic textbook on particle accelerators.

“I’ve been lucky – very lucky – in always being in the right place at the right time,” he says. “Finishing my education just when they wanted scientists during the war got me straight into a very elite group that had already been recruited from universities and so at the age of twenty I was able to get started without needing a PhD. I was later awarded a Cambridge Doctorate of Science in engineering based on my published papers. I was able to do interesting work and had the chance to visit very interesting places, including Russia and China, at a time when they were generally inaccessible to western travellers. All in all, I’ve had a good career.”