Experimental antenna impedance measurements in a magnetized plasma

Abstract

Summary form only given. The characteristic impedance of two antennas immersed in a magnetized plasma have been measured by monitoring the reflection coefficient using a network analyzer. The first antenna is spherical, the second a short (1 Lt) monopole. There have been numerous theoretical studies done on antenna impedance in magnetized plasmas, but experimental measurements are more rare, primarily because of difficulties involving eliminating effects of the antenna circuitry and/or mounting hardware. Previously impedance measurements were made using a spherical antenna in a unmagnetized plasma, in which it was found that the impedance could be modeled as a capacitive sheath in series with a RLC tank circuit resonant at the plasma frequency. The introduction of a magnetic field would complicate the interpretation of these results by providing a preferred direction and subsequent sheath distortion. A cylindrical antenna in a magnetized plasma environment presents geometrical complications even beyond this. Where applicable, experimental impedance curves are compared with analytic and simulation results. The experimental work was performed in the large volume space physics simulation chamber (SPSC) at NRL where the plasma is characterized by electron densities and temperatures of ne = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and Te = 1 eV