Suppression of dust density wave in nanodusty plasma

Research in the field of dusty plasma medium containing nanometer size dust particles has grown immensely in the last few decades because of its wide application in the field of plasma nanotechnology and space plasma. Study of waves and instabilities in nanodusty plasma has grown into a new domain of research interest in recent past. The challenges in the detection technique of these nano particles and the negligible effects of gravity have given momentum in the nanodusty plasma research. Here we have performed an experiment with 50 nm diameter carbon particles in a glass chamber of 15 cm in length and 3 cm in diameter. The experimental chamber is evacuated to a base pressure of 10^-3 mbar with the help of a rotary pump. Argon gas is inserted at the rate of 0.5 sccm to maintain the chamber pressure at 0.015 mbar. Plasma is produced by capacitive coupled rf discharge (power = 10 – 15 W and frequency = 13.56 MHz). Plasma is characterized by IV characteristics curve measured by cylindrical Langmuir probe of diameter 0.2 mm and length 4 mm. Plasma potential profile along the axis of the chamber is drawn from these curves. Laser light of 532 nm and 50 mW is used for illuminating the dust cloud. The dynamics of the dust particles are recorded by a high resolution camera at a high frame rate of 240 – 420 fps. A dust void is observed at the center, just above the rf live electrode by the balance of electric field force and ion drag force on the dust particles. Dust density wave of characteristics frequency ~ 78 Hz is observed propagating from the void boundary due to the ion streaming instability. This wave is used as a diagnostics tool for the measurement of dusty plasma parameters such as dust density, coupling parameter etc. An external sinusoidal signal is applied to the DDW by a circular exciter from a function generator. The ion streaming is modulated by the external signal. At a modulation frequency closer to the natural frequency, the suppression of the DDW is observed. This phenomenon of suppression is studied in details. (author)