Chris Lashmore-Davies, a theoretical plasma physicist, worked for more than 40 years on nuclear fusion, and the principles behind the generation of electricity from such reactors.

He spent most of his career at the United Kingdom Atomic Energy Agency’s Culham Science Centre near Abingdon, Oxfordshire. Culham is one of the world’s leading centres for fusion research, where scientists reproduce conditions akin to those in the sun and the stars in the hope of harnessing an energy source that is safe and environmentally benign.

Nuclear fusion, which provides the energy in the cores of the sun and stars, occurs when the nuclei of light atoms come together at very high temperatures and “fuse”, producing enormous amounts of energy. Two nuclei of hydrogen can fuse together to become a nucleus of helium. The huge gravitational pressures and temperatures of about 10 million degrees celsius in celestial bodies are sufficient to produce fusion. At the much lower pressures that it is possible to produce on Earth, temperatures need to be much higher — above 100 million degrees celsius. To achieve these temperatures there must first be powerful heating, and thermal losses must be minimised by keeping the hot fuel particles, usually hydrogen particles, away from the walls of the container. This is achieved by creating a magnetic “cage” made by strong magnetic fields, which prevent the particles from escaping.

In a typical nuclear-fusion reactor, the hydrogen fuel is in the form of a plasma, a very hot (millions of degrees) partially ionised gas in which some of the electrons are free instead of being bound to hydrogen atoms. The plasma is in a toroidal, or doughnut-shaped, chamber, called a tokamak, surrounded by electromagnets which exert powerful magnetic fields, designed to keep the plasma away from the chamber’s walls.

Lashmore-Davies made important contributions to Culham’s development of experimental tokomak devices such as JET (Joint European Torus), Europe’s flagship fusion device, and MAST (Mega Amp Spherical Tokamak). Information obtained from both JET and MAST is aiding the development of the International Thermonuclear Experimental Reactor (ITER), the international fusion project based on a tokamak reactor.

Under construction at Cadarache, France, ITER is being designed to prove the scientific and technological feasibility of nuclear fusion as an practically energy source. ITER is being funded by seven international partners (from China, the EU, India, Japan, Russia, South Korea and the US).

Chris Lashmore-Davies was born in Sale, Greater Manchester, in 1937 and later moved to Evesham, Worcestershire, where his father had been appointed town clerk. He attended Prince Henry’s Grammar School, Evesham, and later studied physics at University College London, receiving his PhD in 1965. After working briefly for Standard Telecommunications he joined Culham Laboratory as a research associate in 1966.

He was an honorary professor at the University of St Andrews, Scotland, and a generation of PhD students are grateful to him for his conscientious support and guidance over many years. He continued his interest in educating young physicists into his retirement and was giving a lecture course at University of Bristol until his death.

Lashmore-Davies wrote more than 150 research papers and conference papers and co-authored a monograph on plasma instabilities. His work was often innovative and always meticulous and his voluminous notebooks were legendary. His warm personality and flair for building collaborative links were well known.

The arts and sport played a large role in his life. He was a keen footballer and tennis player and continued playing these as he grew older, adding golf in later years. He always cycled to work and encouraged others to lead an equally active and healthy lifestyle.

Lashmore-Davies is survived by his wife, Mary, and four sons.

Chris Lashmore-Davies was born on August 28, 1937. He died after a heart attack on April 5, 2009, aged 71