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Studies of ions in a drift field: laser diagnostics of excited states and measurements of thermochemical properties at equilibrium
A major technique for investigating the thermochemical properties of ions and their related clusters is the high pressure drift/mass spectrometer detection technique. A crucial question in this regard is the extent to which ions drifting in an electric field are thermalized. This paper is divided into two parts, one describing some laser techniques which are enabling an investigation of the possible presence of excited ions in a drift field, and secondly, a reporting of some recent findings and trends in the stability of ion clusters of single and mixed constituents
3D Magnetic Reconnection with a spatially confined X-line extent -- Implications for Dipolarizing Flux Bundles and the Dawn-Dusk Asymmetry
Using 3D particle-in-cell (PIC) simulations, we study magnetic reconnection
with the x-line being spatially confined in the current direction. We include
thick current layers to prevent reconnection at two ends of a thin current
sheet that has a thickness on an ion inertial (di) scale. The reconnection rate
and outflow speed drop significantly when the extent of the thin current sheet
in the current direction is < O(10 di). When the thin current sheet extent is
long enough, we find it consists of two distinct regions; an inactive region
(on the ion-drifting side) exists adjacent to the active region where
reconnection proceeds normally as in a 2D case. The extent of this inactive
region is ~ O(10 di), and it suppresses reconnection when the thin current
sheet extent is comparable or shorter. The time-scale of current sheet thinning
toward fast reconnection can be translated into the spatial-scale of this
inactive region; because electron drifts inside the ion diffusion region
transport the reconnected magnetic flux, that drives outflows and furthers the
current sheet thinning, away from this region. This is a consequence of the
Hall effect in 3D. While this inactive region may explain the shortest possible
azimuthal extent of dipolarizing flux bundles at Earth, it may also explain the
dawn-dusk asymmetry observed at the magnetotail of Mercury, that has a global
dawn-dusk extent much shorter than that of Earth.Comment: 9 pages, 9 figures, submitted to JGR on 01/23/201
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