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Most matter you can see in the night sky is not solid, liquid or gas. It is plasma: gas so hot or so energised that electrons have been pulled off their atoms. The Sun, the solar wind and the upper layer of our atmosphere are all plasmas. Bimla Buti spent her working life on how waves travel through plasmas, and how those waves can turn wild. This post sets out what the records say about her career and what a student can learn from it.
Who was Bimla Buti?
According to her Indian National Science Academy (INSA) fellow profile, Buti earned a BSc (Hons) and an MSc from Delhi University, then went to the Department of Physics at the University of Chicago. There she worked with S. Chandrasekhar and obtained her PhD in plasma physics in 1962. Chandrasekhar later shared the 1983 Nobel Prize in Physics "for his theoretical studies of the physical processes of importance to the structure and evolution of the stars", and Chicago was still his university when he won it. You can read about his most famous result in our post on the Chandrasekhar limit.
Her early papers show the questions she started with. In 1962 she published Plasma Oscillations and Landau Damping in a Relativistic Gas in The Physics of Fluids, with the University of Chicago as her affiliation. The next year she published a two-part study of relativistic effects on plasma oscillations and the two-stream instability in the same journal.
What is a plasma oscillation?
Picture a plasma as a sea of light electrons moving among heavy positive ions. Push a group of electrons slightly to one side and you leave a patch of positive charge behind. That charge pulls the electrons back, they overshoot, and the whole cloud swings back and forth. This is a plasma oscillation. Its natural angular frequency is ω = √(ne²/ε₀m), where n is the number of electrons per cubic metre, e and m are the electron's charge and mass, and ε₀ is the permittivity of free space.
Two features of the formula are worth noticing. A denser plasma oscillates faster, because n sits on top. And the light particle, the electron, sets the pace, because m sits underneath. "Landau damping", in the title of Buti's first paper, is the way such a wave can die away even without collisions, as it trades energy with particles moving at about the wave's own speed. "Relativistic" means some particles move fast enough that Einstein's corrections matter.
Where did she work after her PhD?
Her INSA profile traces the route. She returned to Delhi University as a postdoctoral researcher, then went back to the USA to work at NASA's Goddard Space Flight Center. She worked at IIT Delhi from 1968 to 1970. Vikram Sarabhai, then Director of the Physical Research Laboratory (PRL) in Ahmedabad, invited her to join PRL, where she worked from 1970 to 1993 as Associate Professor, Professor, Senior Professor and Dean of Faculty.
At PRL she started the experimental plasma physics programme. The same profile records that this group grew, moved out of PRL and became a new institute, now the Institute for Plasma Research under the Department of Atomic Energy. She was also Director of Plasma Physics at the International Centre for Theoretical Physics in Trieste from 1985 to 2003, and after retiring she spent four years at NASA's Jet Propulsion Laboratory (JPL).
What did she find about waves and chaos?
Much of her later work was about nonlinear waves: waves big enough that the simple, straight-line rules stop working. In a 1991 paper written at PRL, Nonlinear Alfvén waves in inhomogeneous plasmas, she showed that these magnetic waves in an uneven plasma follow a modified derivative nonlinear Schrödinger equation. Depending on the plasma's pressure ratio and density gradients, solitary waves called solitons could speed up or slow down as they travelled, with possible uses in space and astrophysical plasmas.
By 1999, writing from JPL, she was asking when such waves become chaotic. Her paper Chaos in Magnetoplasmas starts from the idea that a nonlinear wave is equivalent to a nonlinear dynamical system, which can show chaos. Using the tools of dynamical systems, she studied when Alfvén waves and lower-hybrid waves turn chaotic, and how heavy ions can help control that chaos.
How was her work recognised?
Her INSA profile lists the Vikram Sarabhai Award for Planetary Sciences (1977), the Jawaharlal Nehru Birth Centenary Lectureship Award (1993), the INSA Vainu Bappu Medal for Astronomy and Astrophysics (1994) and a Professional Achievement Citation from the University of Chicago (1996). INSA elected her a Fellow in 1981.
She also built up her field. The same record says she founded the Plasma Science Society of India and was its President in 1992 and 1993, was an Associate Editor of IEEE Transactions on Plasma Science from 1977 to 1983, and was President of Commission 49 of the International Astronomical Union from 1991 to 1994. She set up awards for young scientists and a scholarship and gold medal for women scientists at IIT Delhi.
What can a student take from how she worked?
Start with the simplest version of a wave. Her first papers took a familiar idea, the plasma oscillation, and added one complication at a time: relativity, then streams of particles. When a topic feels hard, write the simplest case first and add one effect at a time.
Borrow tools from another field. Her work on chaos used methods from nonlinear dynamics to understand waves in space. Maths you learn for one chapter often solves problems in another.
Build the place, not just the paper. She started a programme that became an institute, founded a society and set up awards. Science is also people and labs.
If an idea like a wave in a plasma is hard to picture from equations alone, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than to read.
Try it now: write the plasma frequency formula from memory and explain in one sentence why a denser plasma oscillates faster.
