Plasma production in large volume plasma system by compact electron cyclotron resonance sources

There are several applications which require plasma to be produced over large volumes (~few cubic meters) and where it is desirable to have high radial/axial uniformity and high plasma density. Although electron cyclotron resonance (ECR) plasma sources are efficient and yield high plasma densities, these do not scale well with the volume. This paper presents a scheme for large volume plasma production that retains the advantages of ECR plasma sources without sacrificing on uniformity or high plasma density. It uses multiple, compact ECR plasma sources (CEPS) that are highly portable and easily mountable on any chamber. The large volume plasma system (LVPS) described in the paper is a scalable, circular cylindrical vessel of diameter ≈ 1m, consisting of source sections (SS) and spacer sections (SPS). The CEPS were mounted in azimuthally symmetric manner on matching ports along the periphery of the source sections, and the system was configured for 4/6 CEPS (one SS, two SPS, height ≈ 1.1 m) and 12 CEPS (two SS and three SPS, height ≈ 1.55 m). Since plasma filling in this scheme is radially inwards, the decrease in the volume to be filled as the plasma flows inwards, partially offsets the depletion of plasma as it flows away from the sources. This results in a more uniform plasma density over the system volume. The scheme also takes advantage of the magnetic field of the CEPS (produced by ring magnets) to produce a cusp magnetic field inside the chamber aiding confinement and uniformity. The paper discusses the development of the LVPS and presents plasma production results for two different configurations of the LVPS. The mechanism of plasma production is discussed in the light of results obtained for single CEPS.