Graphical analysis method for a retarding potential analyzer and its application to the real‐time measurements of ion temperature in space plasmas

摘要

In order to obtain the ion temperature from a voltage‐to‐current characteristic of a retarding potential analyzer (RPA) in a drifted density (106 1/cc), low‐temperature (1 eV) plasma such as an ionospheric plasma, optimum fitting procedures using the digital computer have been used. But these methods must take a lot of time to search the parameters. A graphical method using the sampling of a RPA curve has been developed to obtain the ion temperature quickly. Many diagrams were drawn by calculation to determine the ion temperature. This method is suitable not only for the processing of a large quantity of data but also for the in‐flight data analysis aboard a sounding rocket. By the use of feedback control circuits, ion temperature data could be obtained at a ratio of several tens per second in the ionosphere, where the mass of the ion M varies slowly. The accuracy of this method and the effect of variations of M, angle of attack Θa, and drift velocity v0 is discussed. Also the efficacy of this method is confirmed. This method was examined in the ionosphere aboard a rocket whose velocity was about 2 km/s. The ion temperature data obtained are compared with those obtained by the usual optimum fitting procedure.