| 1. |
- Vaivads, Andris, et al.
(författare)
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EIDOSCOPE : particle acceleration at plasma boundaries
- 2012
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 491-527
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Tidskriftsartikel (refereegranskat)abstract
- We describe the mission concept of how ESA can make a major contribution to the Japanese Canadian multi-spacecraft mission SCOPE by adding one cost-effective spacecraft EIDO (Electron and Ion Dynamics Observatory), which has a comprehensive and optimized plasma payload to address the physics of particle acceleration. The combined mission EIDOSCOPE will distinguish amongst and quantify the governing processes of particle acceleration at several important plasma boundaries and their associated boundary layers: collisionless shocks, plasma jet fronts, thin current sheets and turbulent boundary layers. Particle acceleration and associated cross-scale coupling is one of the key outstanding topics to be addressed in the Plasma Universe. The very important science questions that only the combined EIDOSCOPE mission will be able to tackle are: 1) Quantitatively, what are the processes and efficiencies with which both electrons and ions are selectively injected and subsequently accelerated by collisionless shocks? 2) How does small-scale electron and ion acceleration at jet fronts due to kinetic processes couple simultaneously to large scale acceleration due to fluid (MHD) mechanisms? 3) How does multi-scale coupling govern acceleration mechanisms at electron, ion and fluid scales in thin current sheets? 4) How do particle acceleration processes inside turbulent boundary layers depend on turbulence properties at ion/electron scales? EIDO particle instruments are capable of resolving full 3D particle distribution functions in both thermal and suprathermal regimes and at high enough temporal resolution to resolve the relevant scales even in very dynamic plasma processes. The EIDO spin axis is designed to be sun-pointing, allowing EIDO to carry out the most sensitive electric field measurements ever accomplished in the outer magnetosphere. Combined with a nearby SCOPE Far Daughter satellite, EIDO will form a second pair (in addition to SCOPE Mother-Near Daughter) of closely separated satellites that provides the unique capability to measure the 3D electric field with high accuracy and sensitivity. All EIDO instrumentation are state-of-the-art technology with heritage from many recent missions. The EIDOSCOPE orbit will be close to equatorial with apogee 25-30 RE and perigee 8-10 RE. In the course of one year the orbit will cross all the major plasma boundaries in the outer magnetosphere; bow shock, magnetopause and magnetotail current sheets, jet fronts and turbulent boundary layers. EIDO offers excellent cost/benefits for ESA, as for only a fraction of an M-class mission cost ESA can become an integral part of a major multi-agency L-class level mission that addresses outstanding science questions for the benefit of the European science community.
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| 2. |
- Fu, H. S., et al.
(författare)
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Dipolarization fronts as a consequence of transient reconnection : in situ evidence
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union. - 0094-8276 .- 1944-8007. ; 40:23, s. 6023-6027
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Tidskriftsartikel (refereegranskat)abstract
- Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail from X-GSM=-30 R-E to X-GSM=-7 R-E. How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: Transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (X-GSM>-10 R-E) are primarily attributed to jet braking, while the DFs detected in the mid- or far-tail region (X-GSM<-15 R-E) are primarily attributed to transient reconnection or spontaneous formation. In the jet-braking mechanism, the high-speed flow pushes the preexisting plasmas to produce the DF so that there is causality between high-speed flow and DF. In the transient-reconnection mechanism, there is no causality between high-speed flow and DF, because the frozen-in condition is violated.
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| 3. |
- Aunai, N., et al.
(författare)
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The proton pressure tensor as a new proxy of the proton decoupling region in collisionless magnetic reconnection
- 2011
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 29:9, s. 1571-1579
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Tidskriftsartikel (refereegranskat)abstract
- Cluster data is analyzed to test the proton pressure tensor variations as a proxy of the proton decoupling region in collisionless magnetic reconnection. The Hall electric potential well created in the proton decoupling region results in bounce trajectories of the protons which appears as a characteristic variation of one of the in-plane off-diagonal components of the proton pressure tensor in this region. The event studied in this paper is found to be consistent with classical Hall field signatures with a possible 20% guide field. Moreover, correlations between this pressure tensor component, magnetic field and bulk flow are proposed and validated, together with the expected counterstreaming proton distribution functions.
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| 4. |
- Fu, H. S., et al.
(författare)
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Energetic electron acceleration by unsteady magnetic reconnection
- 2013
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Ingår i: Nature Physics. - : Nature Publishing Group. - 1745-2473 .- 1745-2481. ; 9:7, s. 426-430
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares(1,2),substorms(34), and disruptions in fusion experiments(5,6).Observations in the solar chromosphere(1) and the Earth's magnetosphere(7-10) indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent(11). Here we show that energetic electron acceleration is caused by unsteady reconnection. In the Earth's magnetosphere and the solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady(12), so energetic electrons are absent(11). The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain for the peak observed fluxes.
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| 5. |
- Huang, S. Y., et al.
(författare)
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Electron acceleration in the reconnection diffusion region : Cluster observations
- 2012
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 39:L11103
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Tidskriftsartikel (refereegranskat)abstract
- We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong core magnetic fields and density depletion. Intense currents, with the dominant component parallel to the ambient magnetic field, are detected inside the magnetic islands. A thin current sheet is observed in the close vicinity of one magnetic island. Energetic electron fluxes increase at the location of the thin current sheet, and further increase inside the magnetic island, with the highest fluxes located at the core region of the island. We suggest that these energetic electrons are firstly accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration.
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| 6. |
- Khotyaintsev, Yuri V., et al.
(författare)
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Observations of Slow Electron Holes at a Magnetic Reconnection Site
- 2010
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 105:16
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Tidskriftsartikel (refereegranskat)abstract
- We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.
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| 7. |
- Vaivads, Andris, et al.
(författare)
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Suprathermal electron acceleration during reconnection onset in the magnetotail
- 2011
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 29:10, s. 1917-1925
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Tidskriftsartikel (refereegranskat)abstract
- We study one event of reconnection onset associated to a small substorm on 27 September 2006 by using Cluster observations at inter-spacecraft separation of about 10 000 km. We focus on the acceleration of suprathermal electrons during different stages of reconnection. We show that several distinct stages of acceleration occur: (1) moderate acceleration during reconnection of pre-existing plasma sheet flux tubes, (2) stronger acceleration during reconnection of lobe flux tubes, (3) production of the most energetic electrons within dipolarization fronts (magnetic pile-up regions). The strongest acceleration is reached at the location of B(z) maxima inside the magnetic pile-up region where the reconnection jet stops. Very strong localized dawn-dusk electric field are observed within the magnetic pile-up regions and are associated to most of the magnetic flux transport.
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| 8. |
- Vaivads, Andris, et al.
(författare)
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The Alfvén edge in asymmetric reconnection
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 28:6, s. 1327-1331
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Tidskriftsartikel (refereegranskat)abstract
- We show that in the case of magnetic reconnection where the Alfv,n velocity is much higher in the plasma on one side of the current sheet than the other, an Alfv,n edge is formed. This edge is located between the electron and ion edges on the high Alfv,n velocity side of the current sheet. The Alfv,n edge forms because the Alfv,n wave generated near the X-line will propagate faster than the accelerated ions forming the ion edge. We discuss possible generation mechanism and the polarization of the Alfv,n wave in the case when higher Alfv,n speed is due to larger magnetic field and smaller plasma density, as in the case of magnetopause reconnection. The Alfv,n wave can be generated due to Hall dynamics near the X-line. The Alfv,n wave pulse has a unipolar electric field and the parallel current will be such that the outer current on the high magnetic field side is flowing away from the X-line. Understanding Alfv,n edges is important for understanding the separatrix regions at the boundaries of reconnection jets. We present an example of Alfv,n edge observed by the Cluster spacecraft at the magnetopause.
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