Vacuum

A technical vacuum is not at all a matter-free space, but a gas volume at low pressure, characterized by large free paths of the matter particles before collisions with other particles occur. While the mean free path until collision with other particles is still under 1 µm at atmospheric pressure, it is more than 10 cm in a medium vacuum of under 10^-3 mbar, which means that many particles within the dimensions of a vacuum chamber do not suffer any collision. In this way, active species of a low-pressure plasma can fill out the total volume of a vacuum chamber without neutralisation or recombination triggered by collisions.