ELECTRON-CYCLOTRON-RESONANCE APPLICATOR OF THE WILKINSON MICROWAVE-POWER DIVIDER TYPE FOR LARGE-DIAMETER ION SOURCES

We have designed and tested a new model of coaxial 2.45 GHz electron c yclotron resonance (ECR) ion source based on the splitting of the micr owave power traveling along a coaxial Line into a set of periodically distributed antennas. Our motivation was the study of the scaling-up f easibility of a coaxially fed ion source in which it is desirable to c ircumvent the transverse electric and magnetic (TEM) mode conversion i nto azimuthally unsymmetrical higher-order modes. Another important ch aracteristic 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 c m in external diameter coaxial ECR ion source in which the single thic k coaxial antenna was replaced by a set of quarter wavelength magnetiz ed 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 x 10(-4) mbar, a 500 eV singly charged ion beam with a current density of 1 mA/cm(2) was delivered through an accel-de cel set of grids. Implementation of a scaled-up 20 cm in diameter ion source is in progress. (C) 1998 American Institute of Physics.