# Effect of Inhomogeneous magnetic field on Plasma generation in a low magnetic field helicon discharge

## TL;DR

This study investigates how inhomogeneous magnetic fields influence plasma generation in low magnetic field helicon discharges, revealing that diverging fields near the antenna enhance plasma density through wave resonance effects.

## Contribution

It demonstrates that diverging magnetic fields near the antenna improve plasma density by facilitating multiple wave resonances and oblique wave propagation in low magnetic field helicon discharges.

## Key findings

- Maximum plasma density occurs with diverging magnetic fields near the antenna.
- Oblique helicon wave propagation is observed along the resonance cone boundary.
- Enhanced ionization efficiency is due to multiple resonances and broad magnetic field range.

## Abstract

The ionization efficiency of helicon plasma discharge is explored by changing the low axial magnetic field gradients near the helicon antenna. The highest plasma density is found for a most possible diverging field near the antenna by keeping the other operating condition constant. Measurement of axial wave number together with estimated radial wavenumber suggests the oblique mode propagation of helicon wave along the resonance cone boundary. Propagation of helicon wave near the resonance cone angle boundary can excite electrostatic fluctuations which subsequently can deposit energy in the plasma. This process has been shown to be responsible for peaking in density in low field helicon discharges, where the helicon wave propagates at an angle with respect to the applied uniform magnetic field. The increased efficiency can be explained on the basis of multiple resonances for multimode excitation by the helicon antenna due to the availability of a broad range of magnetic field values in the near field of the antenna when a diverging magnetic field is applied in the source.