Ultrasonic frequency driven long plasma column

Abstract

A study of argon gas stimulated at ultrasonic frequencies reveals different characteristic aspects. The plasma is created in a 50 cm tube with an effective work length of 25 cm. In order to initialize and maintain the process, plasma discharge parameters, namely, current, voltage, power, pressure, and frequency are studied and optimized. The data obtained show that in order to maintain a plasma discharge specific current, it would be sufficient to apply a higher frequency and lower voltage, whereas the current, at higher frequency and higher voltage, would be higher. Moreover the increase of the discharge voltage, frequency, and pressure increases the discharge current and consequently the discharge power. On the other hand along the half length of the tube, the plasma parameters; temperature, density, mean electron energy, and Debye length are studied and evaluated by means of a floating double Langmuir probe system. Moving from the hot electrode towards the grounded one, the electron temperature increases while the electron density decreases. The plasma temperature measured is 3–20 eV and the average plasma density is on the order 1011 cm−3, according to the pressure, the frequency, and the discharge voltage applied. The plasma source has low power consumption where, for normal operation of 25 W, the discharge voltage VD is 300 V, and the discharge current Ip is 80 mA. Away from gas breakdown, the maximum power absorbed is found to be 60 W, where VD=500 V and Ip=120 mA. A plasma phenomenon of alternatively dark and bright regions appear in the vessel, and are easily seen along the plasma tube, denoting the response of both the electron temperature and the electron density to an oscillatory behavior. The range of the applied pressure, discharge voltage, frequency, current, and power consumed inside the vessel are, respectively, 0.01–0.25 Torr, 50–500 V, 10–100 kHz, 1.5–160 mA, and 5–60 W. The formed plasma is durable, until it would be discarded. Physically it has a pale pink color that becomes brighter by increasing the discharge voltage.