Plasma is defined as mass per unit volume. The technique used to measure the density of a fluid is a determination of mass and volume. The plasma density is a way of deferring to the degree of ionization of plasma. The plasma density is a measure of what percentage of gas particles have ionized, more primarily it is the standard of how many free electrons there are per unit of volume. It is the percentage of ionized gas in relation to the total of ions and gas in the plasma.
Higher energy and higher frequency of the HF generation and lower pressure of the process gas increased plasma density. Any changes in density are due to plasma expansion and not recombination. Density is a straightforward and highly sensitive solution for neutral gas and plasma density measurement.
