[P-CG20] Future missions and instrumentation for space and planetary science

[PCG20-05] Ionospheric Observation using Ion Velocity Analyzer

*Chiaki Kato¹, Takumi Abe², Hirotsugu Kojima³, Akinori Saito⁴, Ayako Matsuoka⁵ (1.Graduate School of Engineering, Kyoto University, 2.Japan Aerospace Exploration Agency Institute of Space and Astronautical Science Department of Solar System Sciences, 3.Research institute for sustainable humanosphere, Kyoto University, 4.Department of Geophysics, Graduate School of Science, Kyoto University, 5.Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University)

Keywords:Ionospheric ions, Ion Drift, Ion Velocity Analyzer

In the ionosphere, there are various phenomena in which the interaction between neutral particles and the ionized atmosphere is important. However, few simultaneous observations of both have been obtained, and sufficient elucidation has not been reached. For example, in the past sounding rocket experiments conducted in the United States in the mid-latitude ionosphere E region during the daytime, while all the parameters in the equation of J=σE+Un×B (σ: electrical conductivity, E: electric field, Un: neutral wind, B: magnetic field) were directly measured, the ion velocity was not measured and was assumed to be equal to the neutral wind velocity. As a result, the current equation calculated by the observed value has no solution. On such a background, we are planning to conduct sounding rocket experiments that can accurately evaluate all the parameters in the current equation above by measuring ion velocity and density, and neutral atmosphere density, as well as indirectly measuring neutral atmospheric temperature, by developing a new instrument for sounding rockets. By measuring and verifying all the parameters, it is expected to elucidate the coupling process between the neutral atmosphere and the plasma.
The ion velocity analyzer (IVA) developed in this research consists of a Retarding Potential Analyzer (RPA) and an Ion Drift Meter (IDM) section, and thereby the drift velocity, density, and temperature of ions can be measured. The RPA section consists of five mesh grids from G1 to G5 and analyzes the energy of ions by applying a voltage to the grid electrodes. The role of each grid is as follows: 1) G1 on the ion incident side is common with GND to prevent leakage of retarding voltage, 2) A retarding voltage is applied to G2 and G3, 3) G4 suppresses the internal effect of the retarding voltage, 4) A negative voltage is applied to G5 to prevent electrons from reaching the collector electrode. The collector electrode is composed of 36 small electrodes, and the surface area of the electrodes varies depending on the position. The angle of incidence of ions is estimated from the current distribution of multiple electrodes. The maximum measured current of one electrode was expected to be 10 nA. The energy range of ions that can be detected by this instrument is up to 4 eV because the sweep voltage of 0~4 V with respect to the rocket potential is applied.
The plasma environment in actual observation was simulated by an ion accelerator, and the performance of the prototype ion drift velocity analyzer was tested. On the circumstance of the ionospheric plasma simulated in a space chamber, the ion current was measured while sweeping the RPA voltage. The results showed that the ion current begins to decrease at a certain RPA voltage, confirming that the IVA can accurately analyze the energy of the incoming ions.
In this research, we will work on the development of new instruments for sounding rockets that enable estimation of ion drift velocity and density to elucidate various phenomena in the ionosphere. On the daytime in the summer of 2024, sounding rocket “S-310-46” will be devoted to make direct observations of the neutral atmosphere, plasma atmosphere, electric field, and magnetic field in the Sporadic E layer at an altitude of 90-130 km.