Plasma Physics physics.plasm-ph

Shine a flashlight through a narrow slit, and the beam doesn't stay a thin stripe; it spreads out sideways. Light has a habit of bending around obstacles, and because of that, the smallest spot you can get with an ordinary lens is no smaller than half a wavelength.

Deep inside stars, light nuclei fuse, giving birth to helium and streams of neutrons. On Earth, we recreate this process by combining deuterium and tritium — special isotopes of hydrogen.

A fusion reactor resembles a giant boiler where hydrogen is 'cooked' into helium. The plasma inside is heated to 150 million degrees — ten times hotter than the Sun's core. But like any boiler, scale forms: harmful impurities that settle on the walls and quench the plasma.

A magnetar is a neutron star with a magnetic field a quadrillion times stronger than Earth's. Sometimes it ejects a blob of plasma, like a tiny balloon with thousands of invisible springs bouncing around inside.

Everyone has a kettle in their kitchen, but few brew herbs in water that has just had an electric discharge passed through it. That's exactly what researchers did with neem and tulsi leaves — plants used for centuries in India as natural remedies. First, they 'activated' the water with plasma: they sent a glowing electric discharge through it, like a miniature lightning bolt.

A heavy ion beam in an accelerator is like a crowd of people shoving each other with elbows: the more people, the wider the crowd. Charged particles repel each other, and at currents above a few microamps the beam spreads and loses its shape.

A new study confirms: shock waves in plasma around supermassive black holes at the cores of galaxies act like ocean swells, shoving protons to near-light speeds. Even a weak wave passes on a tenth of its energy, like a gentle surf launching a surfer into space.

In a hot gas of charged particles — plasma — chaotic electric fields work like a sieve. A slow particle gets surrounded by a cloud of opposite charges, which cancels the external field. A fast one sheds this armor and gets accelerated.

The Sun constantly produces brief plasma ejections — nanojets. They are about the size of a small city, travel at hundreds of kilometers per second, and vanish in less than half a minute. Each such flare is like a tiny explosion that hurls hot gas upward.

Water in a glass settles down once you stop stirring it. Oil in an engine dampens vibrations. It seems viscosity is always about damping. But in some flows, it's the opposite: add friction, and waves start to grow as if from nowhere. Physicists have found a simple explanation.

The scorching gas streaming from the Sun is not a continuous flow but rather a soup of charged particles. In this soup, waves constantly boil up: electric fields flare and fade like ripples on water from a tossed stone. One such wave is the ion-ion acoustic wave.

Igniting a miniature sun is a long-held dream of humanity. Typically, scientists try to confine scorching plasma (a gas of charged particles) at temperatures of hundreds of millions of degrees. But plasma tends to escape magnetic traps, and confinement comes at enormous cost.

A wheat seed is like a traveler sleeping in cold soil: to wake up, it needs a warm rain. Scientists from India have found a way to wake it without chemicals — using cold plasma, the same stuff that glows in neon lamps. Plasma is a gas in which some atoms have lost electrons. It slightly scratches the seed coat, letting water penetrate faster.

Inside a tokamak, a giant magnetic donut, plasma is heated to hundreds of millions of degrees. It doesn't touch the walls; it floats in a vacuum, held by invisible magnetic fields. But plasma is finicky: a slight change in current or pressure and its shape starts to wobble like jelly on a plate.

A fusion reactor is like an orchestra, where the plasma is the melody and the magnetic coils are the musicians. If one instrument plays out of tune, the whole symphony falls apart.

The Sun constantly emits a stream of charged particles, mostly hydrogen — the solar wind. Sometimes the Sun ejects dense blobs of magnetized gas, inside which calm usually reigns. But in 2000, scientists noticed two regions inside one such cloud where the gas was churning.

Plasma in a fusion reactor is like a swarm of fireflies that you need to keep inside an invisible jar. It used to be thought that the jar's walls had to be perfectly smooth, or the fireflies would find a crack and escape. New work shows that the jar can be glued together from pieces with noticeable seams, and the swarm will still stay inside.

A fusion reactor is an attempt to hold a miniature sun in a magnetic cage. To get more energy out of it, you need to squeeze the plasma denser. But tokamaks have an invisible fence: once the density crosses a certain line, the plasma shudders and falls apart. This disruption is one of the main mysteries on the road to clean energy.

A short laser pulse strikes the air, and a tiny lightning bolt flashes at the point of impact. It lives longer than you'd think: the bright glow is visible for half a millisecond, and a faint one for nearly twenty milliseconds.

In a pot of boiling soup, small bubbles churn, but gradually large-scale flows come to dominate. Something similar happens in cosmic plasma, where magnetic fields behave like tangled threads.

In the stream of charged particles that constantly blows from the Sun, radio bursts sometimes occur — short, powerful signals at frequencies you can pick up on an ordinary radio. Until now, it was unclear how exactly these signals are born in that stream.

Hot plasma is like a swarm of frantic fireflies darting around in a jar. Keeping it confined in an open magnetic trap is like trying to keep those fireflies from touching the glass. A new computer model shows how to do it more precisely. Ions and electrons in plasma constantly collide, exchanging energy.

Hot plasma in a future fusion reactor is like a packed dance floor: billions of particles whirl in a complex rhythm, colliding and changing speed. Figuring out how tangled this dance is — no easy task. Scientists have found a way to measure its complexity without watching every move.

Plasma is a gas heated so intensely that electrons are stripped from atoms. Waves run through it, akin to sound in air, but they are governed by the magnetic field. When the magnetic field becomes periodic rather than uniform, like a fence with alternating slats, waves behave differently. Some frequencies simply vanish: the wave cannot propagate and is reflected back.

A laser strikes a target, and a cloud of plasma, accelerated to hundreds of kilometers per second, shoots into the chamber. The chamber isn't empty: it's filled with a tenuous gas that plays the role of the cosmic medium. The plasma slams into this gas like a speedboat hitting still water, shoving it aside.

A solar flare is like thunder on a clear day: a short but powerful burst of energy. The MeerKAT radio telescope in South Africa caught one such M1.3-class flare and examined it with unprecedented clarity. Ordinary instruments see either bright details or faint ones, but not both at once.

In a tokamak, plasma is like a crowd on a narrow street: once someone starts running, everyone takes off at once. In a stellarator with a non-circular cross-section, the street is winding, with dead ends and pockets. The crowd can't gather into a single wave — people get stuck in different corners.

A laser pulse racing through plasma is like a runner carving a path through a crowd. It shoves electrons aside, leaving behind a rarefied channel, just as the crowd parts for a sprinter. In this channel, the crest of the light wave moves slightly faster than light in a vacuum, and it is this speed that determines how efficiently the pulse transfers energy to particles.

October 10, 2024. The Sun hurled a cloud of magnetized plasma toward Earth, and four spacecraft, stationed at a single point between the Sun and Earth, simultaneously recorded how that cloud churned. The distance between the outermost probes was just 80 Earth radii, about half a million kilometers.

Plasma is a gas in which electrons are stripped from atoms, and it conducts electricity. In space, such gas is often so rarefied that particles rarely collide, and its behavior is described by the equations of motion for each particle. The computer method Particle-in-Cell (PIC) does exactly that: it tracks millions of particles and the electric fields they create.

The Sun constantly emits a stream of charged particles — the solar wind. Among them are many electrons, some of which fly back toward the Sun. But observations show that fewer electrons return than expected.

A radio telescope picks up a signal from the Crab Nebula, and instead of a smooth line, the screen shows bright and dark bands, like on a zebra's hide. This is the emission from the pulsar, a rapidly spinning neutron star left over from a supernova explosion.

Plasma isn't just hot gas; it's a mix of charged particles that constantly move and generate magnetic fields. When plasma churns, these fields intertwine like spaghetti in a boiling pot. Scientists simulated what happens when the churning subsides and turbulence decays.

Modern X-ray light sources are like an orchestra without a conductor: electrons in the beam fly every which way, and the radiation comes out blurry. The new idea is to make electrons line up in neat rows with a spacing of a few nanometers. Then the light they emit becomes coherent, like a laser beam.

Before every tokamak startup, a device where superheated gas is held by magnetic fields, operators spend hours calculating how the plasma will behave. Mistakes are too costly: one wrong parameter can ruin the experiment.

Inside a future fusion reactor, a magnet weighing as much as a small car will float. It holds the superheated plasma like an invisible hand holding a cloud. Previously, such a magnet was considered unsuitable for deuterium-tritium fuel: neutron fluxes would quickly destroy it.

A blast wave slams into a surface, and the surface starts to wrinkle like a carpet when you drag your foot across it. These wrinkles grow, curl into vortices, and stir everything around. In fusion, such mixing is a big problem: the fuel doesn't compress evenly, and the reaction fizzles out. Physicists have found a way to stop this process without touching the wave itself.

A calm river suddenly starts churning in the middle of a flat stretch: that's the puzzle the authors of a new study set out to solve. They took a thin layer of charged gas with a very weak magnetic field and tracked on a computer what would happen to it. At first, everything flows smoothly, like water from a tap.

In plasma where some atoms remain neutral, magnetic field lines can rearrange at different speeds. This is like two rubber bands that are initially stuck together, then suddenly snap apart and contract, releasing energy.

Every time deuterium and tritium fuse in a fusion reactor, a fast neutron flies out. It can turn one substance into another — for example, create valuable isotopes for medicine. Today such neutrons cost a fortune, because there are few experimental facilities and they rarely operate.