THE EFFECT OF A DUST-SIZE DISTRIBUTION ON DUST ACOUSTIC-WAVES

Using a kinetic model for low-frequency dust acoustic waves (DAW) in a dusty plasma, we hare examined the effects of a dust-size distributio n on their propagation and damping. Both Landau damping and damping du e to dust charge variation are included. We consider Gaussian and powe r-law dust-size distributions. In accordance with earlier results of M elandso et al., we find that the dust Landau damping dominates at shor t wavelengths. At wavelengths longer than the Debye length lambda(D0), the dust-charge variation is generally dominant. It is always dominan t for the power-law size distributions that we have studied. We also f ind that if the upper and lower size limits of the dust are chosen so that the average dust size remains constant, regardless of the power-l aw exponent gamma, the wave properties are practically identical to th ose of a monosize distribution of the average dust size. For a Gaussia n dust-size distribution. Landau damping may be the dominant damping m echanism if the dust plasma is tenuous (P much less than 1) and the wi dth of the distribution is large.