Investigation of a plasma source sustained by an electromagnetic surface wave at 2.45 GHz under free-fall regime

The plasma column sustained by an electromagnetic surface wave under the free-fall regime, a still unexplored pressure domain for such a plasma, has been experimentally investigated. Because of the relatively large values of the frequency (2.45 GHz) and plasma diameter (56 mm), the wave propagates either in the dipolar (m=1) or quadrupolar (m=2) mode rather than in the azimuthally symmetric mode (m=0). The radial distributions of the electron density and temperature, obtained by means of electrostatic probes, show the existence of a resonant absorption mechanism of the wave electric field by the electrons. The measured value of the power loss per electron, theta , is found to be four to ten times larger than the value extrapolated from a diffusion model for the m=0 mode. Such a discharge is intended to supply plasma in a reactor operating with a multipolar magnetic confinement used for surface processing.