N. D’Angelo

Laboratory observation of the dust‐acoustic wave mode

A laboratory observation of the dust‐acoustic instability is reported. The results are compared with available theories.

Laboratory studies of waves and instabilities in dusty plasmas

Theoretical and experimental studies of low-frequency electrostatic waves in plasmas containing negatively charged dust grains are described. The presence of charged dust is shown to modify the properties of ion-acoustic waves and electrostatic ion-cyclotron waves through the quasineutrality condition even though the dust grains do not participate in the wave dynamics. If the dust dynamics is included in the analysis, new “dust modes” appear—dust acoustic and dust cyclotron modes. The results of laboratory experiments dealing with dust ion acoustic (DIA) waves and electrostatic dust ion cyclotron (EDIC) waves are shown. These modes are more easily excited in a plasma containing negatively charged dust. Finally, observations of dust acoustic (DA) waves are presented and measurements of the dispersion relation are compared with one obtained from fluid theory.

Dust acoustic waves in a direct current glow discharge

An experimental investigation of dust acoustic (DA) waves in a dc glow discharge plasma is described. The glow discharge is formed between a 3 cm anode disk and the grounded walls of a 60 cm diameter vacuum chamber which is filled with nitrogen gas at a pressure of about 100 mTorr. Dust located on a tray in the chamber is attracted into the plasma where it is trapped electrostatically. The dust acoustic waves were produced by applying a modulation signal (5–40 Hz) to the anode. The wavelength of the DA waves was measured from single frame video images of scattered light from the dust grains. The measured dispersion relation is compared with theoretical predictions.

Experimental study of shock formation in a dusty plasma

An experimental investigation of the effect of negatively charged dust on ion acoustic shock formation in a Q machine is described. Ion acoustic compressional pulses were observed to steepen as they traveled through a dusty plasma if the percentage of the negative charge in the plasma on the dust grains was ≳75%.

Dusty plasma ionization instability with ion drag

The effect of ion drag on negatively charged dust grains is considered as a possible mechanism of excitation of the dust-acoustic (DA) ionization instability. It is found that DA waves are more and more damped as the coefficient for ion drag, μ, increases from zero to a critical value, μcrit. For μ>μcrit a zero-frequency (nonpropagating) perturbation grows when the drag of the ions on the dust grains overcomes the effect of the perturbation electric field.

Electrostatic ion‐cyclotron waves in a plasma with negative ions

The dispersion relation for electrostatic ion-cyclotron (EIC) waves in a plasma containing a fraction of negative ions is derived from the fluid picture. Two wave modes are generally possible. Some of their features are investigated.

Shock formation in a negative ion plasma

An experimental investigation of the effect of negative ions on shock formation in a (collisional) Q machine plasma is described. Shock formation was observed only when the ratio of the negative ion to positive ion density, e, exceeded about 0.9.

Ionization instability in dusty plasmas

The ionization instability in a dusty plasma in which the neutral gas is ionized by a constant flux of energetic electrons with energy slightly above the ionization energy is examined by using fluid equations for the three charged components, namely positive ions, electrons, and negatively charged dust grains. The presence of negatively charged dust increases both the frequency and the growth rate of the IA (ion-acoustic) wave excited through the ionization instability. The DA (dust-acoustic) mode, even in the absence of ion–neutral collisions, ion viscosity, and neutral gas drag on the dust grains, is always damped within the parameter ranges explored here and relevant to laboratory plasmas. The present results on the DA wave excitation are at variance with results obtained by Shukla and Morfill [Phys. Lett. A 216, 153 (1996)].

A dusty plasma device for producing extended, steady state, magnetized, dusty plasma columns

We describe a rotating‐drum dust‐dispersal device, which we have used, in conjunction with an existing Q machine, to produce extended, steady state, magnetized plasma columns. The dusty plasma device (DPD) is to be used for the investigation of waves in dusty plasmas and of other plasma/dust aspects. The device is capable of generating dusty plasmas in which as much as ∼90% of the negative charge is attached to dust grains of 1–10 μm size.

Electron and ion inertia effects on current-driven collisional dust acoustic, dust ion acoustic, and ion acoustic instabilities

Ion acoustic waves can be excited by electrons drifting relative to the ions in a plasma. This relative drift can be produced, in a collisional plasma, by a static electric field. In the analysis of this instability, which occurs for frequencies well below the ion plasma frequency, the electron inertia term in the momentum equation is typically neglected. A similar assumption has been employed in the investigation of the dust ion acoustic instability in a collisional dusty plasma. In the study of the collisional current driven dust acoustic instability, both the electron and ion inertial terms were neglected. It is shown here that the inclusion of the appropriate inertia terms can result in significant differences in the growth rates for these instabilities. The cases studied, including the inertia terms, led to a decrease in the critical electric fields necessary to excite the current driven dust acoustic, dust ion acoustic, and ion acoustic instabilities.