Exploring hairpin resonator configurations for electron densitymeasurements in magnetized plasmas

When immersed in a plasma, a hairpin probe can measure electron densities from the shift of

the resonant frequency of the hairpin structure relative to the electron plasma frequency.

Previous efforts have developed hairpin probe hardware and theory that enable measurements

of electron densities up to approximately 10¹² cm^-3, with the use of both quarter-wavelength

and three-quarter-wavelength hairpin probes in a transmission mode together with the

associated microwave electronics. More recent theories for interpreting hairpin

measurements use a transmission line model to accurately relate the resonant frequency of the

probe and the electron density, including the resistive effects of a hairpin partially immersed

with epoxy. These models have been used to accurately extract density measurements in

inductively coupled plasmas; however, the models do not reliably account for measurements in

magnetized plasmas. We present a novel hairpin design and model that minimizes the resistive

effects of the epoxy and potentially provides measurements of electron plasma densities up to

10¹³ cm^-3, while also allowing the probes to be reliably used in magnetized plasmas, like those

created in the Large Plasma Device (LAPD) at UCLA.