Bas Pease

Director of Britain's fusion research for 20 years at UKAEA Culham

Rendel Sebastian Pease, physicist: born Cambridge 2 November 1922; research scientist, Atomic Energy Research Establishment, Harwell 1947-61; Division Head, Culham Laboratory for Plasma Physics and Nuclear Fusion, United Kingdom Atomic Energy Authority 1961-67, Assistant Director, UKAEA Research Group 1967, Director, Culham Lab 1968-81, Programme Director for Fusion, UKAEA 1981-87; FRS 1977; President, Institute of Physics 1978-80; Vice-President, Royal Society 1986-87; Chairman, British Pugwash Group 1988-2002; Visitor, Blackett Laboratory, Imperial College London 1992-97; married 1952 Susan Spickernell (died 1996; two sons, three daughters), 1998 Jean White (died 2000), 2004 Eleanor Barnes (née Spray); died Oxford 17 October 2004.

Bas Pease had a long and brilliant career as a physicist with the United Kingdom Atomic Energy Authority. He retired in 1987 as Director of Fusion Research at the Culham Laboratory.

Elected a Fellow of the Royal Society in 1977, he did major work in radiation damage in solids, and on the location of hydrogen atoms in crystals. He set Culham on the scientific map of leading research establishments, and hosted there the Joint European Torus (Jet) project, Europe's flagship fusion experiment. A good Fabian and a founder member of the Pugwash Association (devoted to world peace and nuclear disarmament), he combined infectious charm with rebelliousness and fixity of purpose. He was quite a man.

Rendel Sebastian Pease was born in 1922 into an intellectual and cultural socialist-oriented family who contributed greatly to the Fabian Society. He was educated at Bedales School, and Trinity College, Cambridge, where he read read Physics for the wartime degree course.

In 1942 he was assigned to the Ministry of Defence as a Scientific Officer in the Operational Research Service of RAF Bomber Command. He was released in 1946 and able to complete his Cambridge degree, which qualified him to take up a post as Scientific Officer at the Atomic Energy Research Establishment at Harwell in 1947.

His scientific work at Harwell started in the X-ray analysis section of General Physics Division and was directed towards understanding the structure of solids so that their behaviour under the intense and damaging radiation in the core of a nuclear reactor could be explained. Among the key substances were graphite, uranium and the structural metals holding the assembly together.

It was known from the American atomic project that many peculiar phenomena occurred inside the reactor. But decision by the US to forbid the transfer of such information to their allies - who had contributed crucially in the first place - meant that it all had to be rediscovered (or memories confirmed) when the UK decided to develop nuclear weapons of its own.

Harwell was set up to secure the science base, Aldermaston to study the weapon technology and Risley/Windscale to develop the reactor engineering needed. The science base needed was perceived by Harwell's Director Sir John Cockcroft as very broad indeed and recruitment of able, young scientists the key to success. Bas Pease fitted the model in an ideal way and, over the next 10 years, he produced much seminal work.

One key paper, on the mechanism of the damage to solids by the energetic sub-atomic particles and other radiation in a reactor core, was published by Pease and George Kinchin in 1955. It described in mathematical detail how a heavy, fast particle could pass through a solid, knocking its atoms out of place whilst continuing on its way; how light particles would bounce this way and that in such collisions, causing minor displacements but not following a specific track; or how the passages of particles or gamma rays could electrically disturb the equilibrium of charged atoms in the crystal structure. This paper remained the key to damage mechanism analysis for decades.

With the availability of research reactors at Harwell, it became possible to use beams of neutrons to study solids in a way analogous to their study by X-rays. A big advantage of using neutrons is that they are scattered by hydrogen atoms, which are invisible to X-rays. By 1952, Pease had, in collaboration with George Bacon, completed another seminal study elucidating the role of hydrogen atoms in potassium di- hydrogen phosphate as the origin of its piezoelectric power.

Though Pease did not himself do much more work with neutron beams, this paper led to much interest and, by the late 1950s, the Science Research Council had negotiated formal access to the neutron beams at Harwell for university researchers.

It was in 1957 that Pease was offered the chance to work in the field of fusion where atoms of hydrogen isotopes are forced together to form helium and release energy - the process at the heart of the hydrogen bomb and the source of the power of the sun.

The possibility of making a device to release this energy on a usable scale had engaged the interest of several groups of researchers since the Second World War, mostly in universities at first. Then, it was realised that the physics involved overlapped to some extent the science of weapon development and all the work was pooled into two groups, where it was classified as secret. Finally, it was recognised that this connection was very tenuous and fusion work was declassified in 1958 and the major powers all presented papers on their work at the "atoms for peace" conference in Geneva.

The problem with fusion, or, to mention its original and more descriptive name, Controlled Thermonuclear Reactions, is that the gas must be so hot (millions of degrees), so dense that atoms frequently collide and held for so long that the energy released keeps it hot. The main thrust has been to create a magnetic bottle within which the hot gas can be held well away from the cold walls of the physical container. Then, the gas could be heated by passing an electric current through it.

Experiments up to 1958 had shown that to reach all of these conditions simultaneously was unlikely with equipment in a size and cost appropriate to countries such as the UK, France and Germany, though projects like the famous Zeta (Zero Energy Thermonuclear Assembly) experiment at Harwell, which Pease had led, showed that the toroidal configuration known as the Tokamak could produce discharges lasting many milliseconds and with particles energetic enough to produce nuclear reactions. These nuclear reactions were, however, the product of stray atoms not seated in the main bulk.

In 1957 Euratom (the European Atomic Energy Community) formed a fusion research committee in Brussels which gave financial support for specific major projects at the national fusion laboratories. The UK's newly formed lab at Culham was not included in this formal arrangement, since Britain was admitted to the community only in 1973. However, the UK participated in the fusion research committee discussions as a guest, and Pease was our main spokesperson and played an important part in establishing collaboration as a theme.

At Culham, Pease had produced, in 1972, with his colleagues, a 20-year plan, the final stage of which would be the construction of a prototype fusion reactor generating electricity. This plan was ambitious and the first stage would have needed exceptional investment from the Atomic Energy Authority. Fortunately, the discussions within the Euratom fusion community were also leading to the view that a larger machine was needed but no one country was ready to go it alone. Then, in 1973, the UK was admitted to the community and so joined the fusion committee formally.

Pease enthusiastically supported the notion of constructing a big machine as a joint venture involving all of the member countries. It was partly due to his efforts that agreement was reached to set up a design team to design the Joint European Torus and, under Paul-Henry Rebut, a team was formed. With typical flair, Pease offered accommodation and full general support to site the team at Culham.

This was accepted by the Euratom committee and the design group arrived at Culham in October 1973. A satisfactory designed was tabled by 1976 but the selection of a site for its construction was difficult and led to a lot of political infighting. After much discussion, the choice was narrowed to Germany or Britain. Then, in October 1977, the UK helped Lufthansa to rescue the plane and passengers that had been hijacked at Mogadishu and, in a moment of gratitude, the Germans conceded Jet should be constructed at Culham.

The construction went ahead on a site adjacent to Culham, with many support services provided from Culham to serve until Jet would build its own infrastructure. Pease had to balance this support with his own duty as director of the fusion programme within the UKAEA, still a substantial research effort involving lines of work not necessarily allied to Jet. He accomplished this with his usual flair and charm.

Pease married his first wife, Susan, mother of his five children, in 1952. They lived a full and happy life, sharing their passions for music until, sadly, after some 46 years, Susan died. He later married Jean, who brought him happiness for a short time but, by a cruel fate, died herself less than two years later. His last years were comforted by Eleanor, who survives him as widow. Throughout the last, sad, 10 years, he had the loving and unstinting support of his children.

Mick Lomer