In this article, you will find detailed information on the question “What is plasma?” in physics and how the fourth state of matter is used in low-pressure plasma systems.
Definition of Plasma – What Is It?
Plasma is (in physics) a high-energy, ionized gas and the fourth state of matter, of which it consists of over 99% (visibly). It forms when a gas is supplied with so much energy, e.g., heat or electrical voltage, that the electrons are separated from the atoms (ionization).
Plasma is therefore an ionized gas in which molecules and atoms have released their electrons and are electrically conductive. Since it reacts to electromagnetic fields, it is often luminous. Plasma effects can be observed in nature, for example as the aurora borealis or lightning, but especially as the sun and stars.
This diagram provides a simplified illustration of the composition of plasma.
Hot Plasma and Cold Plasma
The difference explained simply: Hot plasma is hot—that is, in thermal equilibrium—while cold plasma is cold—that is, not in thermal equilibrium—which is why the difference lies in their temperatures.
In hot plasma, charged ions, free electrons, and some neutral atoms are in an extremely hot state (often millions of °C) and are in thermal equilibrium.
In cold plasma, only the electrons are excited or hot, while ions or atoms are at room temperature (ambient temperature) and are not in thermal equilibrium.
Low-pressure plasma explained simply
Low-pressure plasma is a technically generated plasma that is non-thermal (or cold) and has a pressure significantly lower than Earth’s atmospheric pressure. It is produced by ionizing a gas in an evacuated vacuum chamber using an energy source. For this reason, it is often referred to as vacuum plasma.
Technical production in a low-pressure plasma system
A low-pressure plasma system essentially consists of a vacuum chamber, a vacuum pump, a gas supply system, a medium- or high-frequency generator, and an electrode. It is operated using electricity. In the first step, a workpiece is placed in the vacuum chamber and the vacuum pump extracts the air, creating a vacuum or low pressure.
An electric field is generated using electricity. A gas or process gas (e.g., O₂) is introduced into the electric field at a pressure of approximately 0.1 mbar. The pressure range is between 0.1 and 1.0 mbar. The gas is ionized by the application of energy (usually electricity), and a plasma is formed.
At low pressures of < 100 Pa (1 mbar), a cold plasma is generated in a vacuum chamber. By applying electromagnetic fields, the gases or gas mixtures contained in the chamber are ionized and thus converted into the highly reactive plasma state.
Atmospheric Pressure Plasma Explained Simply
Atmospheric pressure plasma (APP) is generated using compressed air or ambient pressure, without the need for a vacuum chamber. It differs from low-pressure plasma (LPP) primarily in terms of operating pressure.
Key technical differences
Atmospheric pressure plasma processes are well-suited for inline processes and offer time advantages over low-pressure plasma processes.
In contrast, LPP processes are significantly more flexible in terms of process gas selection, making them ideal for uniform and ultra-fine plasma treatments, as well as for processing materials with complex 3D geometries.
You can learn more about plasma effects and the applications of low-pressure plasma systems in our informational article on our plasma technology.
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