Measurements of the D-region plasma using active falling plasms probes

Kurzfassung

The MEDUSA experiment, as a part of the REXUS/BEXUS project, develops a new in-situ technique probing the lower ionosphere plasma by two daughter payloads. These identical daughter payloads contain sensitive structures which are exposed to the atmosphere. This structure consists of a grid, which surrounds an ion collector that is connected to a electrometer. The collector has a negative potential, the measured current at an electrometer is proportional to the ion density measurements. The grid is on plasma potential and retards the fast ions. At the same time a debye sheath evolves around the grid. The grid and the debye sheath builds a capacitor which is part of a oscillating circuit. Measuring the frequency of this circuit provides a relative measure of the electron density. An acceleration sensor inside each payload can be used to derive neutral gas density profiles from the Navier-Stokes equation. These neutral density profiles can be used to investigate possible correlations with the plasma densites. A GPS receiver on each subpayload provides in-situ horizontal information of all three physical quantities (electron, ion and neutral density) that hasn't been available in this scientific field before. During the REXUS 15/16 campaign a rocket will bring the two probes up to 90 km, which are then ejected from the main payload. In the following, the daughter payloads measure the electron and ion density. The data is stored on the daughter payloads and is sent also to a ground station if a recovery of the probe is not possible. The scientific scope of MEDUSA is measuring small scale fluctuations in the plasma density of the D-region. Enabling investigations on the physics of the atmospheric phenomenon polar mesospheric winter echos (PMWE), which are radar echos in the range of 55-80 km. The measurement is supported by ground based instruments and model studies at winter polar latitudes.