The effect of external magnetic field on the collisional power absorption in helicon plasma sources

Abstract

The paper reports on the effects of uniform and non-uniform external magnetic field on the power absorption in a helicon plasma source, which are computationally investigated by the CST Microwave Studio code. RF (13.56 MHz) power deposition was studied using one designs of antennas, namely, the Nagoya type-III. Argon was used as the plasma working gas at the operating pressure of 15 mTorr. We have focused on the collisional power absorption utilizing WKB approximation to describe the plasma inhomogeneity. We put discrete plasma density layers in CST. The obtained results show that the radial inhomogeneity has different effects on the power absorption at the uniform and the non-uniform external magnetic fields. It is found that at uniform external magnetic fields (i.e., B₀ = 200 G), there is a specific density (n_c) ranging from 1 × 10¹⁸ m⁻³ to 5 × 10¹⁸ m⁻³, before and after which the radial inhomogeneity decreases and increases the absorbed power, respectively. On the other hand, at uniform external magnetic fields (i.e., B₀ = 900 G), the inhomogeneity has no regular effect on the power absorption in various plasma densities. In addition, for a given plasma density (e.g., n = 10¹⁸ m⁻³), as the magnetic field increases, the radial inhomogeneity effect on the power absorption would decrease for the Nagoya type-III.

Graphical abstract