[P-PS04] Mercury Science and Exploration

[PPS04-07] Beam instability as a plasma diagnostic tool for the Mercury upstream region

★Invited Papers

*Yasuhito Narita¹、Uwe Motschmann¹、Daniel Schmid²、Horia Comisel³ (1.Institute of Theoretical Physics, Technische Universitaet Braunschweig, Germany、2.Space Research Institute, Austrian Academy of Sciences, Graz, Austria、3.Institute of Space Science, Bucharest-Magurele, Romania)

キーワード：Mercury, shock-upstream region, beam instability

Mercury shock-upstream region is unique from the plasma physics point of view. One-dimensional beam instability setup can potentially be realized, in which the interplanetary magnetic field, the solar wind flow, and the beams are all aligned along an axis. Moreover, different ion components can excite the instability at once such as shock-reflected ions and pickup ions of exospheric origin. We revisit the theory of beam instability (in particular, dispersion relation and dielectric response), and construct models and scenarios of the beam instabilities relevant for the Mercury shock-upstream region. We derive a relation between the beam resonance frequency and the flow velocity in the spacecraft frame given that the beam velocity is known, which serves as a useful diagnostic tool for the Mercury upstream region, and so for the in-situ magnetic field data such as the MESSENGER and BepiColombo missions. A scenario of nonlinear wave evolution is also proposed as the lesson from the wave-wave coupling studies.