High-frequency instability of the sheath-plasma resonance

Technical Report · Sun Jan 01 04:00:00 EST 1989

OSTI ID:7225181

Stenzel, R L

Coherent high frequency oscillations near the electron plasma frequency (omega approx. less than omega sub p) are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath-plasma resonance and is driven by a negative RF sheath resistance associated with the electron inertia in the diode-like electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening and copious harmonics. The fundamental instability is a bounded oscillation due to wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres) which excludes other radiation mechanisms such as orbitrons or beam-plasma instabilities. The line broadening mechanism was identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burst-like RF emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.

• Research Organization: California Univ., Los Angeles, CA (USA)
• OSTI ID: 7225181
• Report Number(s): N-90-14910; NASA-CR--186127; NAS--1.26:186127
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700107* -- Fusion Energy-- Plasma Research-- Instabilities
DATA
ELECTRODES
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
FLUID MECHANICS
HYDRODYNAMICS
INFORMATION
INSTABILITY
MAGNETOHYDRODYNAMICS
MECHANICS
NUMERICAL DATA
OSCILLATIONS
PLASMA INSTABILITY
PLASMA SHEATH
RADIATIONS
RESONANCE