In physics, each State of aggregation is a different form in which the matter. There are many possible states for ordinary matter, some well studied and others only theoretical, but there are four that are usually considered as the four fundamental states: solid, liquid, gas and plasma.
The plasma was first identified by William Crookes in 1879, who called plasma "radiant matter", but as a state of matter it is a concept introduced by the chemist Irving Langmuir during the 1920s.
It is usually understood as a gaseous mixture of negatively charged electrons and positively charged ionsthough the net charge of a plasma medium is neutral. In this state, matter has properties and triggers phenomena that do not occur in solids, liquids or gases, hence it is considered as another state of matter.
General characteristics
The plasmatic state is achieved by heating a gas until the electrons have enough energy to separate from the atomic nuclei, thus forming ions and electrons that can move through the plasma and generating electrical currents in the presence of a magnetic field. Although electrons and atoms are unbound, they cannot be considered as completely free particles, since they continue to maintain interaction forces between them within the mass of the plasma.
Each state of matter is differentiated by unique properties. The solid state has a definite volume and shape. The liquid state, on the other hand, has a definite volume but not a shape; the liquid can adapt to the shape of its container, but not its volume. Gas, on the other hand, has neither a defined volume nor a shape and can be adapted to both the shape and the volume of its container.
Plasma shares certain properties with gases, since it is a fluid state without definite shape or volume, but it has properties that do not occur in gases. Specifically, plasmas, by containing charged particles, conduct electricity and react to magnetic fields creating electrical currents, while most gases are electrical insulators.
Unlike the other three fundamental states, plasma does not exist in a free form in the surface conditions. our planetonly occurs temporarily in some atmospheric phenomena such as lightning, but they can be produced artificially by heating a gas or by subjecting a gas to a strong electromagnetic field to cause the separation of electrons from atomic nuclei. The formation of ions and the release of electrons can also occur by breaking molecular bonds.
In the Universenevertheless, plasma is the most common state of ordinary matternot counting dark matter, and is the predominant form of matter in stars, intracluster gases, and intergalactic regions.
plasma types
Plasma is formed as a result of the ionization of atoms that form a gas. The degree of ionization depends fundamentally on the temperature; the higher the temperature, the higher the degree of ionization.
Depending on the degree of ionization, two types of plasma are distinguished:
- Fully ionized plasmas: also called hot plasmas. They are plasmas that have all or almost all of their particles ionized.
- Partially ionized plasmas: also called cold plasmas if the degree of ionization is very low, but not to be confused with the temperature of the plasma, the temperature of a cold plasma can be very high. There are gases that with a degree of ionization of only 1% can present plasma characteristics.
Partially ionized plasmas are those that can be seen in lightning storms and artificial plasmas such as neon lights or plasma televisions. Hot plasmas need conditions that can hardly be found on Earth, but are very abundant in stars, for example the interior of the Sun and the solar corona are in a completely ionized state of hot plasma.
Another classification distinguishes thermal plasmas Y non-thermal plasmas. In thermal plasmas, all the particles that form it are in thermal equilibrium, while in non-thermal plasmas the electrons are at a much higher temperature than the rest of the particles (ions and neutral particles of the plasma can even be at room temperature) .
Plasma associated phenomena
The response of plasmas to electromagnetic fields gives rise to various phenomena, such as filamentation or stratification, which often present complex characteristics such as fractal shapes. Some of the most common phenomena are:
- filamentation: formation of structures in the form of filaments known as birkeland currents. They are due to the displacement of charged particles along the lines of a magnetic field. They can be easily observed in plasma lamps or lightning.
- non-neutral plasmas: the good conductivity of plasmas causes the density of positive and negative particles to be distributed homogeneously, hence plasmas are neutral or almost neutral in any region. But there are plasmas with excess positive or negative charge that are not neutral. The most extreme case are plasmas formed by a single chemical species; for example, jets of charged particles, electron clouds, or positron plasmas.
- powder plasmas: dust plasmas are plasmas that contain suspended charged particles with sizes of millimeter (10-3 m) to nanometer (10-9 m). Due to their behavioral complexity, dust plasmas are also known as complex plasmas.
- waterproof plasmas: are thermal plasmas that are impermeable to other gases and other cold or partially ionized plasmas.
Application Examples
Artificial plasmas are created by applying electric and magnetic fields to a gas. In this way, partially ionized plasmas can be created that are used in numerous applications, both industrial and domestic.
Plasmas are as common as neon lights, fluorescent lamps, plasma displays, gas lasers, or plasma lamps used for decoration. Other less everyday applications include controlled thermonuclear fusion wave ion propulsion.
Plasma in the Universe
It is estimated that 99% of ordinary matter in the observable Universe is in the plasma statealthough it is estimated that 90% of the matter that makes up the Universe is dark matter, a type of matter whose properties and states are still unknown.
Stars, stellar jets, extragalactic jets and the interstellar medium itself are examples of plasmas in the Universe. In the Solar System, the Sun and interplanetary space consist of plasma, as well as the Earth's magnetosphere or the ionosphere of comets and some planetary satellites.
However, many of these plasmas are extremely tenuous and have densities even lower than those achieved in the "vacuum conditions" of terrestrial laboratories. For example, the highest density in the magnetosphere is approximately 1000 particles per cubic centimeter, and can reach as low as 1 particle per cm3 in the less dense parts. Other plasmas, for example in stars, can have a much higher density and reach temperatures of millions of degrees Celsius.