The characteristics of plasma-sheath resonances in a non-uniform radio-frequency plasma

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:213010

Ku, V P.T.; Annaratone, B M; Allen, J E ^[1]

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1. Univ. of Oxford (United Kingdom)

Plasma-sheath resonances in the resonance-probe were first reported by Takayama et al. in 1960. At that time the resonance was thought to occur at the plasma frequency; later work, however, showed that a plasma-sheath resonance was taking place. In this paper the authors plotted the ratio of RF field in the probe sheath to the RF probe voltage versus {omega}/{omega}{sub ep}, and found that the ratio passed through a maximum when the probe was at resonance. The maximum corresponded to a ratio {omega}/{omega}{sub ep} less than 1, the resonance frequency was confirmed to be below the plasma frequency and the {open_quotes}series resonance model{close_quotes} was verified. After this definitive paper on the subject the interest of resonance probe moved into more practical applications. These include: determining the collision frequency between the electrons and neutrals in a low density plasma; measuring the electron density in the ionosphere; measuring the averaged densities of the charged particles as well as their temperature in a bounded plasma with an external magnetic field; studying antenna signals in space plasmas, etc. It is apparent that the harmonics developing in the plasma may weaken the conventional {open_quotes}driven{close_quotes} Langmuir probe technique which is widely used in plasma research. There have been many attempts to resolve this problem, for example, driving, actively, the first two RF harmonics that appear across the probe sheath to achieve more precise plasma parameters. Nevertheless, it has been recently found that the natural frequency of the plasma-sheath system can be much more influential than the contributions from the external circuitry at certain fairly low pressures. This in particular when the plasma-sheath resonance coincides with one of the harmonics of the fundamental frequency. In this contribution we present some theoretical and experimental aspects of the plasma-sheath resonance in a parallel-plate RF plasma reactor.

• OSTI ID: 213010
• Report Number(s): CONF-950749--
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
IMPEDANCE
INHOMOGENEOUS PLASMA
MATHEMATICAL MODELS
PLASMA POTENTIAL
PLASMA SHEATH
PROBES
RF SYSTEMS