During the transport of both metal neutrals and ions,there is a certain probability that these particles will collide with the neutral gas background. These collisions lead to
heating of the gas followed by expansion (decrease in gas density in front of the target) in a process that is called gas rarefaction. It has extensively been investigated in magnetron discharges both experimentally and theoretically during the last three decades. The loss of process gas results in a reduction of ions available for sputtering (often Ar ions) leading to a reduced deposition rate as well as
a reduction of plasma density, which means that the desired IPVD properties will be lost.