Uniform excitation of a cylindrical plasma column by a microwave ring resonator

Abstract

To overcome the problem of insufficient absorption of microwave power by a plasma column a new concept for the microwave excitation of cylindrical gas discharges on the basis of a microwave ring resonator is presented. A theoretical description of this resonator loaded by a gas discharge is developed using the S parameters of its elements by which is determined the dependence of the two ring waves on the tuning of the resonator. It is predicted from theory and confirmed by measurements that one ring wave can be suppressed to a high degree by a proper tuning of the resonator. With the ring resonator a high power absorption at a frequency of 2.45 GHz is achieved over a wide pressure range. A uniform cylindrical plasma column with a length of more than 30 cm suitable for laser operation can be realized.