Tuning of Radio-Frequency (RF) Plasmas by a Perpendicular Magnetic Field

Recently, there has been a surge of interest in exploring the tunability of plasma for high-frequency applications. This interest stems from the wide range of tunability of plasma permittivity and electrical conductivity offered by plasma and the unique characteristic of being the only natural material capable of providing negative permittivity. Traditionally, plasma has been tuned by adjusting parameters such as pressure, input power, and excitation frequency. However, an alternative and promising approach involves manipulating plasma properties using an external magnetic field. Currently, there is a lack of readily available information regarding the electrical properties of a capacitively coupled plasma sustained by radiofrequency (RF) power under the influence of a perpendicular magnetic field. Past research has proposed manipulating plasma properties, such as electron number density, to facilitate communication during spacecraft reentry blackout. However, these models relied on bulky electromagnets, which can be impractical in specific scenarios.

This study investigates RF plasma under the influence of a magnetic field generated by a permanent magnet positioned at a specific location along the electrode gap. The pressure within the system is varied within the range of tens to hundreds of millitorr, and the impact of plasma excitation frequency on properties such as plasma conductivity, permittivity, reflection, and transmission is examined—the probing frequencies used in the study span from 100s of MHz. The primary objective of this research is to minimize plasma loss by reducing plasma conductivity while maintaining the necessary negative permittivity. To pursue this objective, the results are compared across three scenarios: no plasma, plasma operating without a magnetic field, and plasma subjected to a perpendicular magnetic field.