E–H mode transition of a high-power inductively coupled plasma torch at atmospheric pressure with a metallic confinement tube

Abstract

Inductively coupled plasma torches need high ignition voltages for the E–H mode transition and are therefore difficult to operate. In order to reduce the ignition voltage of an RF plasma torch with a metallic confinement tube the E–H mode transition was studied. A Tesla coil was used to create a spark discharge and the E–H mode transition of the plasma was then filmed using a high-speed camera. The electrical potential of the metallic confinement tube was measured using a high-voltage probe. It was found that an arc between the grounded injector and the metallic confinement tube is maintained by the electric field (E-mode). The transition to H-mode occurred at high magnetic fields when the arc formed a loop. The ignition voltage could be reduced by connecting the metallic confinement tube with a capacitor to the RF generator.