Impact of Sensor-to-guard area ratio on Langmuir probes

Langmuir probes have been widely used on rocket and satellite platforms, yet their accuracy is limited by assumptions about sensor geometry. Theory for planar or cylindrical probes assumes uniform electric fields like those caused by infinite surfaces. These are typically approximated by placing a "guard" electrode adjacent to the sensor and at the same potential to mitigate edge effects.
A Wide-Sweeping Langmuir Probe (WSLP) has been developed to investigate the current collection characteristics of several planar probes with varying guard-sensor area ratios in a laboratory with a plasma source generating Low-Earth Orbit (LEO) like conditions (approximately <=0.5eV, 1e10-12 m^-3, with 4 km/s ion streaming velocity). The WSLP features a small form factor, easily programmable sweep rate and profile, and wide sweeping range of +/-30V which make it ideal for investigation of current collection in both ion and electron saturation regions. This work presents the design and calibration of the WSLP, as well as initial data from chamber tests with variety of probe geometries.