Influence of electrode size on the generation of low-pressure coaxial ECR microplasmas

Electrode structure and size are the most important factors, as much as the operating pressure is, in the generation of low-pressure coaxial electron cyclotron resonance (ECR) microplasmas. The experimental results will be presented showing the influence of these on the generation of low-pressure coaxial ECR microplasmas. The discharge conditions for various magnetic field were investigated in three types of coaxial electrodes when the gap length was fixed to 3.5 mm. With increasing magnetic field, a breakdown occurred at the “breakdown magnetic field” and vanished at the “maximum trapping magnetic field”. Comparing the plasma discharge region of the three types of coaxial electrodes, it was found that microplasma generation is easier for an electrode with a longer axial length of plasma generation point and a shorter inner electrode radius because initial electrons can be confined axially. Furthermore, the surface electric field strength of the inner electrode with shorter radius is stronger.