Effect of ultrasound waves on a hollow needle to plate electrical discharge in air or mixture of air with VOCs S. Pek´ arek, R. B´ alek, J. Khun Czech Technical University, Faculty of Electrical Engineering, Department of Physics, Technick´a 2, 166 27 Prague, Czech Republic e-mail: {pekarek, balek}@fel.cvut.cz M. Posp´ ıˇ sil Institute of Chemical Technology, Technick´a 5, 166 28 Prague, Czech Republic Received 4 May 2006 The plasma technologies based on corona discharge in a stationary medium are not suitable for applications such as efficient ozone generation, VOC decomposition etc. The reason is that corona discharge is relatively low power electrical discharge. The increase of the discharge power leads to the transition of the corona discharge to the spark. Discharge stabilization and at the same time the discharge power enhancement can be achieved by different ways. One of these is the application of the airflow with respect to the active electrode [1, 2]. Still further increase of the discharge current–voltage range can be achieved by the application of ultrasound waves. In this paper we demonstrate that the proper application of the ultrasound waves can increase the current–voltage range of the discharge beyond the limits, which are reached by simple application of the airflow. In this way it is possible to obtain higher density of electrons which are the starting particles for wide range of plasmachemical reactions leading to ozone generation, VOC decomposition etc. The discharge used in our experiment was the hollow needle to plate electrical discharge enhanced by the flow of air or mixture of air with VOC. PACS : 52.80.Hc, 52.35.Dm Key words : non–thermal plasma, ultrasound waves, volatile organic compounds 1 Introduction The non–thermal plasma based technologies are becoming more and more im- portant for wide range of applications such as ozone production or destruction of volatile organic compounds (VOC) in air streams. There are several types of non–thermal plasma electrical discharges, which have been tested for these pur- poses [3, 4]. Among them are corona discharge (DC, AC or pulsed) and barrier discharge in a confined space. The second category includes packed–bed plasma re- actors (discharge takes place among the pellets in the granulated bed) and surface and silent discharges. The corona discharge reactors involve different configurations of electrodes. The most frequent one is wire to cylinder configuration. The other configurations such as corona torch, point to plate and multi–point to plate are also used. The corona discharge is relatively low power electrical discharge. The in- crease of the discharge power leads to the transition of the corona discharge to the B982 Czechoslovak Journal of Physics, Vol. 56 (2006), Suppl. B