Abstract
We have investigated the V-I characteristic of plasma in the glow-to-arc transition at atmospheric pressure in argon. Plasma is generated between the electrodes with the gap spacing of 1 mm. Both of the electrodes are the ThO2-W rods, which are 1 mm in a diameter and needle-shape. The rods are located in a quartz tube coaxially. A DC power source is supplying constant voltage of 600 V during the discharge. The voltage between the electrode and the current into plasma are measured at the sampling rate of 2.5 kHz. As a result of the measurements, the V-I characteristic of plasma in the current range from the arc to the glow discharge is obtained. Plasma in a transition changes some metastable states cyclically. The cathode spot has been observed on the tip of the cathode in a metastable state and it has not been done in another metastable state. Our observation suggests that the metastable state of the plasma in the glow-to-arc transition will be affected on the boundary condition at the cathode.
