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ITER will demonstrate feasibility of nuclear fusion: P.I. John

Plasma physicist P.I. John on India's contribution to the nuclear fusion experiment – and the passion that drives scientists.

Professor P.I. John, 82, is among a small group of scientists who built up India's plasma physics programme, a crucial field of study on the road to building nuclear fusion reactors. After a stint in academia, he joined the Physical Research Laboratory (PRL), Ahmedabad, in 1972. In 1982, he was one of a handful of scientists who prevailed upon the Indian government to start a plasma physics programme. That led to the founding of the Institute for Plasma Research (IPR) in 1986. ADITYA, the first Indian tokamak – an experimental machine designed to study the physics of fusion plasmas – was built under this programme. John also participated in the discussions that led to India becoming a partner in the International Thermonuclear Experimental Reactor (ITER) nuclear fusion experiment in southern France. Now in retirement, he continues to serve as a consultant to the IPR. In 2022, IPR celebrated the 25th anniversary of the establishment of the Facilitation Centre for Industrial Plasma Technologies, which he had set up to harness plasma physics for industrial use. Excerpts from an interview:

How is building a fusion reactor related to plasma physics?

For fusion to happen, the nuclei have to overcome the Coulomb repulsion between like charges. If you want to fuse nuclei of tritium with nuclei of deuterium, for example, you have to overcome this repulsion. You can shoot the nuclei towards each other at high velocity, but you need a large number of nuclei to make the energy gain viable. The best way to do it is to assemble a large number of nuclei and heat them so that as per the Maxwellian distribution of these particles, there are always some particles at the tail end of the distribution that can fuse. This assembly of nuclei with their electron cloud is the plasma. In moving from single-particle interactions to an assembly of particles, you enter a state of matter known as plasma. This is a state where fusion reactions can take place in an energetically meaningful way.

What is a tokamak? How does it contribute to a nuclear reactor?

If you heat the assemblage of electrons and ions to millions of degrees, what keeps it from flying apart? At that temperature, the thermal velocities are of the order of thousands of kilometres per second. To prevent it from dispersing, you have to trap it in some way. In the early days of fusion, many types of traps were invented. One of the most successful is the tokamak. Tokamaks were conceptualised in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov. Physicist Lev Artsimovich was associated with its development.

What is the role of Indian scientists in ITER's development?

At first, only the Soviet Union, the U.S., Japan and Europe were associated with ITER. Later, Korea and China became members; India was the last to join, in 2007. In 2002, I was heading the physics division of the International Atomic Energy Agency (IAEA), from where the ITER programme was being co-ordinated. India was at that time far less developed in building tokamaks. The European Union was keen that India join the ITER programme, partly to share the expense; we were invited to join in 2007. Each partner contributes 10% of the cost; Europe has a larger share because ITER is located there. India has promised to supply the liquid helium cryoline system, very high radio frequency microwave generators, and other such high-tech components. These were assigned to us and we have been successfully delivering them.


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