Advances in impedance probe applications and design in the NRL space physics simulation chamber

We will present recent progress in plasma impedance probe experiments and design at NRL's Space Physics Simulation Chamber. These include our network analyzer S-parameter methods as well as more portable self-contained diagnostics with an eye towards space vehicle applications. The experiments are performed under a variety of conditions with magnetized and unmagnetized collisionless, cold (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ≈1-2eV ) plasmas in density ranges of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Experimental measurements of plasma parameters are compared using three different diagnostics: the plasma impedance probe, a Langmuir probe with a guard ring, and an emissive probe. Operating conditions for each instrument are explored experimentally with an emphasis on improving space vehicle diagnostics and understanding which devices are most appropriate for use given plasma conditions likely to be encountered. New computational results will provide experimental predictions over a larger parameter space.