Discovering a fourth state
In 1879 the British chemist William Crookes described the glowing gas in discharge tubes as "radiant matter", a fourth state of matter. In 1928 the American chemist Irving Langmuir, watching ionised gas carry charged particles and oscillate collectively, named it "plasma", borrowing the word for blood plasma, which carries cells. In 1920 the Indian astrophysicist Meghnad Saha derived an equation for how strongly a gas ionises at a given temperature and pressure, opening the way to reading stellar spectra. Debye shielding, introduced by Peter Debye and Erich Hückel in 1923, explains how a plasma screens out charges and stays neutral overall.
Plasma in space and on Earth
More than 99% of the visible matter in the universe — stars, the Sun, interstellar gas — is plasma. In the early 1900s the Norwegian physicist Kristian Birkeland argued from expeditions and lab experiments that auroras form when charged particles from the Sun pour down Earth's magnetic field into the polar regions, an idea later confirmed by satellites. In 1942 Hannes Alfvén predicted waves in which plasma and magnetic field ripple together, winning the 1970 Nobel Prize, and in 1958 Eugene Parker predicted the solar wind, a constant outflow of plasma from the Sun. The Parker Solar Probe, launched in 2018, now flies through that wind to sample the plasma filling the solar system. On Earth, lightning, parts of flames and the ionosphere are plasmas.
Plasma technology and fusion
Fluorescent lamps, neon signs, plasma cutters, and the etching and deposition steps that carve semiconductor chips all rely on plasma. The biggest goal is fusion power. The doughnut-shaped magnetic bottle called the tokamak, devised by Igor Tamm and Andrei Sakharov in the Soviet Union in the 1950s, is the leading design, and in 1957 John Lawson set out the density, temperature and confinement-time conditions a fusion reactor must reach. South Korea's KSTAR has held plasma above 100 million °C for tens of seconds, and the international ITER device is under construction in France. In 2022 the US National Ignition Facility compressed a fuel pellet with lasers and for the first time released more fusion energy than the laser energy delivered to the target, though commercial power that beats the whole facility's electricity use remains far off. Unlike fission, fusion produces little long-lived high-level waste.
FAQ
- How is plasma different from gas?
- A gas is made of neutral atoms or molecules, while in a plasma charged ions and electrons move freely, so it conducts electricity, responds strongly to magnetic fields and often glows.
- Is it the same as blood plasma?
- Both are called plasma in English — Langmuir borrowed the name from blood plasma — but the physics state of matter and the liquid part of blood are entirely different things.
Sources reviewed: 2026-10-26
References
- Birkeland, K. (1908). The Norwegian Aurora Polaris Expedition 1902–1903 (Vol. 1). Christiania: H. Aschehoug.
- Saha, M. N. (1920). Ionization in the solar chromosphere. Philosophical Magazine, 40(238), 472–488.
- Debye, P., & Hückel, E. (1923). Zur Theorie der Elektrolyte. Physikalische Zeitschrift, 24, 185–206.
- Langmuir, I. (1928). Oscillations in ionized gases. PNAS, 14(8), 627–637.
- Alfvén, H. (1942). Existence of electromagnetic-hydrodynamic waves. Nature, 150(3805), 405–406.
- Lawson, J. D. (1957). Some criteria for a power producing thermonuclear reactor. Proceedings of the Physical Society B, 70(1), 6–10.
- Parker, E. N. (1958). Dynamics of the interplanetary gas and magnetic fields. Astrophysical Journal, 128, 664–676.
- Chen, F. F. (2016). Introduction to Plasma Physics and Controlled Fusion (3rd ed.). Cham: Springer.
- Abu-Shawareb, H., et al. (Indirect Drive ICF Collaboration). (2024). Achievement of target gain larger than unity in an inertial fusion experiment. Physical Review Letters, 132(6), 065102.