Double-Layer-Relevant Laboratory Results

Over the past few years, many double-layer-relevant laboratory experiments have been carried out at the University of Wisconsin. Laboratory stair-step double layers, which resemble three or more weak double layers joined in series, have been produced without ionization for the first time. Double-layer floating potential fluctuations have been investigated and progress has been made in developing a novel technique for measuring electron energy distribution functions in low-density double layers (i.e., λd >> probe dimensions). A new inductive plasma source has been developed. With this source, magnetized double layers can be routinely produced. These magnetized double layers are often weak stair-step double layers that are oblique to the magnetic field. Laboratory data of emitting probe characteristics taken in tenuous plasmas have helped to quantify space-charge-enhanced plasma gradient induced error in double-layer electric field measurements made by satellite double probes. Also, magnetic sheaths have been experimentally studied and compared with theory.