Variable dual-frequency electrostatic wave launcher for plasma applications

Abstract

A variable tuning system is presented for launching two electrostatic waves concurrently in a magnetized plasma. The purpose of this system is to satisfy the wave launching requirements for plasma applications where maximal power must be coupled into two carefully tuned electrostatic waves while minimizing erosion to the launching antenna. Two parallel LC traps with fixed inductors and variable capacitors are used to provide an impedance match between a two-wave source and a loop antenna placed outside the plasma. Equivalent circuit analysis is then employed to derive an analytical expression for the normalized, average magnetic flux density produced by the antenna in this system as a function of capacitance and frequency. It is found with this metric that the wave launcher can couple to electrostatic modes at two variable frequencies concurrently while attenuating noise from the source signal at undesired frequencies. An example based on an experiment for plasma heating with two electrostatic waves is used to demonstrate a procedure for tailoring the wave launcher to accommodate the frequency range and flux densities of a specific two-wave application. This example is also used to illustrate a method based on averaging over wave frequencies for evaluating the overall efficacy of the system. The wave launcher is shown to be particularly effective for the illustrative example--generating magnetic flux densities in excess of 50% of the ideal case at two variable frequencies concurrently--with a high adaptability to a number of plasma dynamics and heating applications.

Experimental Characterization of Plasma Heating with Beating Electrostatic Waves

“…28 This provides near optimized matching over the frequency range of interest in this investigation, f = f ci − 5f ci = 20 − 100 kHz. The maximum current excited in each mode is 22 A -the point where excessive heating of the matching network by resistive losses significantly changes the matching characteristics.…”

Stochastic Threshold for Ion Heating with Beating Electrostatic Waves

“…Maximal power was coupled into each excited mode by means of the variable dual-frequency matching network described in Ref. [16]. In order to determine the properties of the propagating waves, we measured the dielectric response of the ion population by means of a laser induced fluorescence system tuned to the Ar II ion transition at 668.614 nm [17].…”