In the resonator mode, the plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 density does not exceed the
critical density.
A standing electromagnetic wave, which is confined by a
resonator cavity, penetrates the plasma and sustains it in the regions of highest field
intensity. The geometry of this region determines the spatial distribution of the plasma. Plasmas excited in resonator mode are less resistant against detuning, for instance by the insertion of electric probes (Langmuir probe

Langmuir probe

A Langmuir probe is a device named after Nobel Prize winning physicist Irving Langmuir, used to determine the electron temperature, electron density, and electric potential of a plasma. It works by inserting one or more electrodes into a plasma, with a constant or time-varying electric potential...

s) or electrically conducting samples compared
to surface-wave

Surface-wave-sustained mode

Plasmas that are excited by propagation of electromagnetic surface waves are called surface-wave-sustained. Surface wave plasma sources can be divided into two groups depending upon whether the plasma generates part of its own waveguide by ionisation or not. The former is called a self-guided plasma...

plasmas. There, the high plasma density better shields disturbing potentials.