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New low-frequency waves and negative mass instability in dusty plasmas

Published online by Cambridge University Press:  09 September 2003

D. P. RESENDES
Affiliation:
Instituto Superior Técnico, 1096 Lisboa Codex, Portugal
R. BINGHAM
Affiliation:
Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK (r.bingham@rl.ac.uk)
A. GUERREIO
Affiliation:
Departamento de Física, Faculdade de Ciências, Universidade do Porto Rua do Campo Alegre 687, 4169-007 Porto, Portugal
V. N. TSYTOVICH
Affiliation:
General Physics Institute, Vavilova Str 38, 117942, Moscow, Russia

Abstract

Low-frequency dusty plasma waves with frequencies much smaller than the frequency of charging collisions of plasma particles with dust particles are considered, taking into account elastic and charging collisions of plasma particles with dust and with neutrals. The usual dust sound waves with an upper frequency equal to the dust plasma frequency are found to be present only for wavelengths much smaller than the plasma particle effective mean free path due to the effective collision frequency. The effective collision frequency is found to be inversely proportional to the square root of the product of the charging frequency and the frequency of particle momentum losses, involving processes due to elastic plasma particle–dust collisions, and collisions with neutrals. It is shown that when the wavelength of the wave is much larger than the mean free path for effective collisions the properties of the waves are different from those previously considered. A negative mass instability is found in this domain of frequencies when the effective mean free path of ions is larger than the effective mean free path of electrons. In the absence of neutrals this appears to be possible only if the temperature of ions exceeds the electron temperature. This can occur in laboratory experiments and space plasmas but not in plasma-etching experiments. In the absence of instability a new dust oscillation, a dust charging mode, is found the frequency of which is almost constant over a certain range of wavenumbers. It is inversely proportional to the dust mass and charging frequency of the dust. A new dust electron sound wave is found for frequencies less than the frequency of the dust charging mode. The velocity of the dust electron sound wave is determined by the electron temperature but not the ion temperatures, as for the usual dust sound waves, with the electron temperature exceeding the ion temperature substantially.

Type
Papers
Copyright
© 2003 Cambridge University Press

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