Plasma is an ionized gas that consists out of a mixture of ions, electrons and neutral particles. These particles are in constant interaction with each other and with photons with different energy or stimulation states. The plasma, also called the plasma state, is often referred to as solid, liquid and gaseous as the fourth state of matter, because it possesses some specific properties that substances in the three aggregate states do not have.Plasma can be produced in different ways and also exists in nature. It is widely used and plays an important role in controlled nuclear fusion studies.
The field of physics that deals with the production and properties of plasmas is called plasma physics.
Properties and classification of plasma
Although a plasma contains ions and electrons, it is quasi-neutral in its entirety. This means that on average it has the same number of positive and negative charges. It has a high electrical conductivity and behaves diamagnetically from a magnetic point of view. Due to the electrically charged particles, it is influenced by electric and magnetic fields. The specific heat capacity of a plasma is strongly temperature-dependent and shows a series of maxima that result from single, double or triple ionization.
Plasma can be classified in different ways. By the pressure in a plasma, one divides into high-pressure plasma and low-pressure plasma, whereby the normal pressure is taken as reference pressure. According to the electron concentration, a distinction is made between thin plasma and dense plasma. Thin plasma are those with less than 100 electrons per cubic meter, dense plasma those with more than electrons per cubic meter. Regarding the plasma temperature it is differentiated between cold plasma and hot plasma.
Important plasma states are a stationary plasma, ie a plasma that is in the same state over a longer period of time. A homogeneous plasma is characterized in that there is a nearly constant charge carrier concentration in a volume range. A completely ionized plasma only consists out of charged particles. The neutral particles are largely absent.
Occurrence or production of plasmas
Plasma occurs in nature in various places, u. a. in lightning, electric sparks or in flames. It can also be found in higher atmospheric layers, in space in the form of the interstellar gas, in the stellar atmospheres and in the interior of the stars.
The positive column used in fluorescent tubes, the glow discharge and arcs occurring in glow lamps are also plasmatic states.
In the laboratory, plasma is usually generated by strong gas discharges in cylindrical or tubular tubes. At the occurring high temperatures of several million degrees Celsius evaporate all substances and from the neutral atoms or molecules produced by ionization free electrons and ions.
For the preparation of very hot plasma, as they are e.g. In nuclear fusion studies, heating of the plasma can be induced by current flow. As a result of the resistance, the plasma counteracts the current flow, it comes to a heating. The process is referred to as ohmic heating. Heating with high-frequency methods is also possible.
Use of plasma
Plasma plays a significant role in lighting technology. In fluorescent tubes and fluorescent tubes, plasma is stimulated and the resulting light is used for lighting.
In the technical field, fine plasma jets are e.g. used for cutting (plasma cutting), welding (plasma welding) and drilling (plasma drilling). As special rocket engines of low power, plasma thrusters (magnetohydrodynamic thrusters) can be used. In doing so, a high-temperature plasma is accelerated by the LORENTZ force.
Of particular importance is plasma for controlled nuclear fusion studies. For this purpose, plasma is enclosed by magnetic fields in such a way that it does not come into contact with the walls. It can then be heated to very high temperatures.