Electron cyclotron resonance applicator of the Wilkinson microwave power divider type for large diameter ion sources

Abstract

We have designed and tested a new model of coaxial 2.45 GHz electron cyclotron resonance (ECR) ion source based on the splitting of the microwave power traveling along a coaxial line into a set of periodically distributed antennas. Our motivation was the study of the scaling-up feasibility of a coaxially fed ion source in which it is desirable to circumvent the transverse electric and magnetic (TEM) mode conversion into azimuthally unsymmetrical higher-order modes. Another important characteristic of this source is the possible incorporation of permanent magnets into the individual antennas in order to create the ECR zones around the latter. The validity of these concepts was tested on a 5 cm in external diameter coaxial ECR ion source in which the single thick coaxial antenna was replaced by a set of quarter wavelength magnetized rod antennas in order to enhance the magnetic field created by the external splitted ring magnets. For an incident power of 100 W and an argon pressure of 1.2×10−4 mbar, a 500 eV singly charged ion beam with a current density of 1 mA/cm2 was delivered through an accel-decel set of grids. Implementation of a scaled-up 20 cm in diameter ion source is in progress.