An ECR ion source directly excited in a selected microwave mode cavity resonator for material processing

Abstract

An electron cyclotron resonance (ECR) ion source using a selected circular mode microwave is studied for material processing. It is expected to enhance efficiency of ECR. A cavity resonator of large diameter (280mm) is constructed for simulated experiments, and excitation of several modes in the resonator is studied. A microwave of 2.45-GHz frequency is launched from an L-shaped antenna and selected modes are directly excited. The electric field of standing waves in the resonator is measured with an electric probe. According to the experiments, the intensity of electric field becomes periodically very high as a metal plate for tuning is moved. This finding is considered to be evidence for excitation of several TE modes. It is possible to selectively excite a single mode, i.e. TE21 or TE01 in the large diameter resonator.An ion source in form of the cavity resonator is designed and constructed on the basis of the above results. As a preliminary experiment, the ECR plasma is generated in a race-track magnetic field formed by permanent magnets. It is found that ion saturation current density increases stepwise as the metal plate is moved. This increase is considered to be caused by enhancing the intensity of electric field at the ECR zone in the resonator.