Compact electron cyclotron resonance ion source with high density plasma

Abstract

A compact electron cyclotron resonance (ECR) ion source has been developed that has an outer diameter of 11 cm and generates a high-density plasma (1×1013 cm−3, O2 gas) at low microwave power (200 W). The source incorporates a plasma chamber with a 5-cm diam., which is smaller than the cutoff size (7.2 cm) as determined by the microwave frequency (2.45 GHz). To accommodate this chamber size, the waveguide for coupling microwaves into the chamber through a vacuum window was miniaturized by filling it with dielectric material. A plasma density of 4×1011 cm−3 was obtained by using a BN plate as the microwave window. Moreover, the coupling efficiency of the microwaves to high-density plasma was enhanced by choosing alumina with a high dielectric constant as the window. With this window, a much higher plasma density of 1×1013 cm−3 was achieved at a low microwave power of 200 W. A coaxial cable can be utilized at this power for easily adapting this compact ECR source to vacuum systems.