Cold Plasma Jets Made of a Syringe Needle Covered With a Glass Tube

A syringe needle assembled with a glass tube has been used as a plasma jet device for biomedical applications. According to the various types of ground electrode installed at the glass tube, argon plasma from an atmospheric pressure discharge has been investigated with a dc-ac inverter of several tens of kilohertz. When the ground electrode is absent or floated, the length of the plasma jet is about 10 mm at an ignition voltage of about 3 kV, and it extends further to a few tens of millimeters as the voltage increases to 5 kV. If the ground electrode is inserted inside the end of the glass tube, all plasma current is sunk directly to the ground electrode so that the plasma plume cannot emit out of the glass tube. For the case of an external ground electrode which is similar to a dielectric barrier discharge, the ignition voltage is as low as 1 kV, and the plume length is easily adjustable to be 1-10 mm in the voltage range of 1-3 kV.