A comparison of current-voltage relationships of collectors in the earth's ionosphere with and without electron beam emission

The CHARGE‐2 sounding rocket flight was designed primarily to measure the vehicle potential of an electron‐emitting payload in the mid‐latitude ionosphere. The experiment was separated into two sections, the larger section carried a 1 keV electron gun and was referred to as the mother vehicle. The smaller section, referred to as the daughter, was connected to the mother by an insulated, conducting tether, and was deployed to a distance of up to 426 m across the geomagnetic field. In addition to performing electron beam experiments, the mother vehicle contained a high voltage power supply capable of applying up to 450 V and 28 mA to the daughter through the tether. Steady state potentials of up to 560 V were measured for the mother vehicle during beam emissions of up to 36 mA. The daughter collected currents up to 6.5 mA and attained potentials of up to 1000 V relative to the background ionosphere. The CHARGE‐2 experiment was unique in that for the first time a comparison can be made of the current collection between an electron beam‐emitting vehicle and a non‐emitting vehicle at high potentials (400 V to 1000 V). The daughter current collection agreed well with the Parker‐Murphy model, while the mother current collection always exceeded the Parker‐Murphy limit and even exceeded the Langmuir‐Blodgett predicted current below 240 km. The additional current collection of the mother is attributed to beam‐plasma interactions. This additional source of collected current may be very important for successful electron beam emission at altitudes below 240 km.