| 1. |
- Vaivads, Andris, et al.
(författare)
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Turbulence Heating ObserveR - satellite mission proposal
- 2016
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Ingår i: JOURNAL OF PLASMA PHYSICS. - 0022-3778. ; 82
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Tidskriftsartikel (refereegranskat)abstract
- The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth's magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space - magnetosheath, shock, foreshock and pristine solar wind - featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the 'Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)'. THOR has been selected by European Space Agency (ESA) for the study phase.
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| 2. |
- Varsani, A., et al.
(författare)
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Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 10891-10909
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Tidskriftsartikel (refereegranskat)abstract
- During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high-energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X-line was located relatively close to the Earth, approximately at 16-18 R-E.
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| 3. |
- Aggarwal, M. M., et al.
(författare)
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Event-by-event charged-neutral fluctuations in Pb plus Pb collisions at 158 A GeV
- 2011
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 701:3, s. 300-305
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Tidskriftsartikel (refereegranskat)abstract
- Charged particles and photons have been measured in central Pb + Pb collisions at 158 A GeV in a common (eta-phi)-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have been analyzed to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged-neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the A Delta eta-Delta phi region. (C) 2011 Elsevier B.V. All rights reserved.
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| 4. |
- Aggarwal, M. M., et al.
(författare)
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Photon and eta production in p plus Pb and p plus C collisions at root(NN)-N-S=17.4 GeV
- 2013
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Ingår i: Nuclear Physics, Section A. - : Elsevier BV. - 0375-9474. ; 898, s. 14-23
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of direct photon production in p + Pb and p + C collisions at root(NN)-N-s = 17.4 GeV are presented. Upper limits on the direct photon yield as a function of p(T) are derived and compared to the results for Pb + Pb collisions at root(NN)-N-s = 17.3 GeV. The production of the eta meson, which is an important input to the direct photon signal extraction, has been determined in the eta -> 2 gamma channel for p + C collisions at root(NN)-N-s = 17.4 GeV. (c) 2012 Elsevier B.V. All rights reserved.
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| 5. |
- Aggarwal, M. M., et al.
(författare)
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Pion freeze-out time in Pb plus Pb collisions at 158 AGeV/c studied via pi(-)/pi(+) and K-/K+ ratios
- 2006
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 48:2, s. 343-352
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the final state Coulomb interaction on particles produced in Pb + Pb collisions at 158AGeV/c has been investigated in the WA98 experiment through the study of the pi(-)/pi(+) and K-/K+ ratios measured as a function of T-m- (m)0. While the ratio for kaons shows no significant T-m dependence, the pi(-)/pi(+) ratio is enhanced at small T-m - (m)0 values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the pi(-)/pi(+) ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.
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| 6. |
- Aggarwal, M. M., et al.
(författare)
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Suppression of high-p(T) neutral pion production in central Pb+Pb collisions at root s(NN)=17.3 GeV relative to p+C and p+Pb collisions
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 100:24
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Tidskriftsartikel (refereegranskat)abstract
- Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at root s(NN) = 17.4 GeV at midrapidity (2.3 less than or similar to eta(lab)less than or similar to 3.0) over the range 0.7 less than or similar to p(T)less than or similar to 3.5 GeV/c. The spectra are compared to pi(0) spectra measured in Pb+Pb collisions at root s(NN) = 17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N-part less than or similar to 300), the yield of pi(0)'s with p(T)greater than or similar to 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N-coll), while for central Pb+Pb collisions with N-part greater than or similar to 350, the pi(0) yield is suppressed.
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| 7. |
- Consolini, G., et al.
(författare)
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On the scaling features of magnetic field fluctuations at non-MHD scales in turbulent space plasmas
- 2016
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Ingår i: 15th Annual International Astrophysics Conference. - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- In several different contexts space plasmas display intermittent turbulence at magneto-hydro-dynamic (MHD) scales, which manifests in anomalous scaling features of the structure functions of the magnetic field increments. Moving to smaller scales, i.e. below the ion-cyclotron and/or ion inertial length, these scaling features are still observed, even though its is not clear if these scaling features are still anomalous or not. Here, we investigate the nature of scaling properties of magnetic field increments at non-MHD scales for a period of fast solar wind to investigate the occurrence or not of multifractal features and collapsing of probability distribution functions (PDFs) using the novel Rank-Ordered Multifractal Analysis (ROMA) method, which is more sensitive than the traditional structure function approach. We find a strong evidence for the occurrence of a near mono-scaling behavior, which suggests that the observed turbulent regime at non-MHD scales mainly displays a mono-fractal nature of magnetic field increments. The results are discussed in terms of a non-compact fractal structure of the dissipation field.
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| 8. |
- Plaschke, F., et al.
(författare)
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Magnetosheath High-Speed Jets : Internal Structure and InteractionWith Ambient Plasma
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:10, s. 10157-10175
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, we have studied the rich internal structure of a magnetosheath high-speed jet. Measurements by the Magnetospheric Multiscale (MMS) spacecraft reveal large-amplitude density, temperature, and magnetic field variations inside the jet. The propagation velocity and normal direction of planar magnetic field structures (i.e., current sheets and waves) are investigated via four-spacecraft timing. We find structures to mainly convect with the jet plasma. There are indications of the presence of a tangential discontinuity. At other times, there are small cross-structure flows. Where this is the case, current sheets and waves overtake the plasma in the jet's core region; ahead and behind that core region, along the jet's path, current sheets are overtaken by the plasma; that is, they move in opposite direction to the jet in the plasma rest frame. Jet structures are found to be mainly thermal and magnetic pressure balance structures, notwithstanding that the dynamic pressure dominates by far. Although the jet is supermagnetosonic in the Earth's frame of reference, it is submagnetosonic with respect to the plasma ahead. Consequently, we find no fast shock. Instead, we find some evidence for (a series of) jets pushing ambient plasma out of their way, thereby stirring the magnetosheath and causing anomalous sunward flows in the subsolar magnetosheath. Furthermore, we find that jets modify the magnetic field in the magnetosheath, aligning it with their propagation direction.
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| 9. |
- Roberts, O. W., et al.
(författare)
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Scale-Dependent Kurtosis of Magnetic Field Fluctuations in the Solar Wind : A Multi-Scale Study With Cluster 2003-2015
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:9
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Tidskriftsartikel (refereegranskat)abstract
- During the lifetime of the Cluster mission, the inter-spacecraft distances in the solar wind have changed from the large, fluid, scales (similar to 10(4) km), down to the scales of protons (similar to 10(2) km). As part of the guest investigator campaign, the mission achieved a formation where a pair of spacecraft were separated by similar to 7 km. The small distances and the exceptional sensitivity of the search coil magnetometer provide an excellent data set for studying solar wind turbulence at electron scales. In this study, we investigate the intermittency of the magnetic field fluctuations in the slow solar wind. Using 20 time intervals with different constellation orientations of Cluster we cover spatial scales between 7 and 10(4) km. We compare time-lagged increments from a single spacecraft with spatially lagged increments using multiple spacecraft. As the turbulent cascade proceeds to smaller scales in the inertial range, the deviation from Gaussian statistics is observed to increase in both temporal and spatial increments in the components transverse to the mean field direction. At ion scales, there is a maximum of kurtosis, and at sub-ion scales, the fluctuations are only weakly non-Gaussian. In the compressive component the deviation from Gaussian statistics is variable: it may increase throughout the inertial and sub-ion ranges, but also, it may have a maximum at magnetohydrodynamic scales associated with large scale magnetic holes. The observations show differences in kurtosis of time and space increments when the spacecraft pairs are transverse to the flow, indicating its spatial anisotropy. Plain Language Summary Turbulence in the slow solar wind is investigated using multi-spacecraft measurements for different satellites configurations. Twenty time intervals of more than 1 hr are analyzed. We compare differences in two time-delayed magnetic field measurements (time-lags) and of magnetic field measurements between spacecraft pairs (space-lags). Space-lags give the fluctuations along different satellite baseline directions and scales (from 7 to 9,000 km) while time-lags give the fluctuations along the flow direction. The magnetic field fluctuations' intermittency, which can be thought of as the "patchiness" or "roughness" is investigated. Differences are observed between the time-lagged measurements and the spatially lagged measurements when the spacecraft pairs are transverse to the flow.
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| 10. |
- Teubenbacher, D., et al.
(författare)
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Density Derivation Using Controlled Spacecraft Potential in Earth's Magnetosheath and Multi-Scale Fluctuation Analysis
- 2023
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:3
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Tidskriftsartikel (refereegranskat)abstract
- In situ measurements from the Magnetospheric Multiscale (MMS) mission are used to estimate electron density from spacecraft potential and investigate compressive turbulence in the Earth's magnetosheath. During the MMS Solar Wind Turbulence Campaign in February 2019, the four MMS spacecraft were arranged in a logarithmic line constellation enabling the study of measurements from multiple spacecraft at varying distances. We estimate the electron density from spacecraft potential for a time interval in which the ion emitters actively control the potential. The derived electron density data product has a higher temporal resolution than the plasma instruments, enabling the examination of fluctuation for scales down to the sub-ion range. The inter-spacecraft separations range from 132 to 916 km; this corresponds to scales of 3.5-24.1 ion inertial lengths. As an example, the derived density and magnetic field data are used to study fluctuations in the magnetosheath through time lags on a single spacecraft and spatial lags between pairs of spacecraft over almost one decade in scale. The results show an increase in anisotropy as the scale decreases, similar for the density and the magnetic field. This suggests different drivers in the strongly compressive magnetosheath and the weakly compressive solar wind. Compressive structures such as magnetic holes, compressive vortices and jets might play key roles.
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| 11. |
- Yordanova, Emiliya, et al.
(författare)
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Magnetosheath plasma turbulence and its spatiotemporal evolution as observed by the Cluster spacecraft
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100:20, s. 205003-
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Tidskriftsartikel (refereegranskat)abstract
- We study the plasma turbulence, at scales larger than the ion inertial length scale, downstream of a quasiparallel bow shock using Cluster multispacecraft measurements. We show that turbulence is intermittent and well described by the extended structure function model, which takes into account the spatial inhomogeneity of the cascade rate. For the first time we use multispacecraft observations to characterize the evolution of magnetosheath turbulence, particularly its intermittency, as a function of the distance from the bow shock. The intermittency significantly changes over the distance of the order of 100 ion inertial lengths, being increasingly stronger and anisotropic away from the bow shock.
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