Publications
282 results found
Vigren E, Galand M, Eriksson AI, et al., 2015, ON THE ELECTRON-TO-NEUTRAL NUMBER DENSITY RATIO IN THE COMA OF COMET 67P/CHURYUMOV-GERASIMENKO: GUIDING EXPRESSION AND SOURCES FOR DEVIATIONS, ASTROPHYSICAL JOURNAL, Vol: 812, ISSN: 0004-637X
Matteini L, Hellinger P, Schwartz SJ, et al., 2015, FIRE HOSE INSTABILITY DRIVEN BY ALPHA PARTICLE TEMPERATURE ANISOTROPY, Astrophysical Journal, Vol: 812, ISSN: 1538-4357
We investigate properties of a solar wind-like plasma, including a secondary alpha particle population exhibiting aparallel temperature anisotropy with respect to the background magnetic field, using linear and quasi-linearpredictions and by means of one-dimensional hybrid simulations. We show that anisotropic alpha particles candrive a parallel fire hose instability analogous to that generated by protons, but that, remarkably, can also betriggered when the parallel plasma beta of alpha particles is below unity. The wave activity generated by the alphaanisotropy affects the evolution of the more abundant protons, leading to their anisotropic heating. When both ionspecies have sufficient parallel anisotropies, both of them can drive the instability, and we observe the generationof two distinct peaks in the spectra of the fluctuations, with longer wavelengths associated to alphas and shorterones to protons. If a non-zero relative drift is present, the unstable modes propagate preferentially in the directionof the drift associated with the unstable species. The generated waves scatter particles and reduce their temperatureanisotropy to a marginally stable state, and, moreover, they significantly reduce the relative drift between the twoion populations. The coexistence of modes excited by both species leads to saturation of the plasma in distinctregions of the beta/anisotropy parameter space for protons and alpha particles, in good agreement with in situ solarwind observations. Our results confirm that fire hose instabilities are likely at work in the solar wind and limit theanisotropy of different ion species in the plasma.
Matteini L, Schwartz SJ, Hellinger P, 2015, Cometary ion instabilities in the solar wind, Planetary and Space Science, ISSN: 1873-5088
Matteini L, Horbury TS, Pantellini F, et al., 2015, Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind alfvénic turbulence, Astrophysical Journal, Vol: 802, ISSN: 1538-4357
We investigate the properties of plasma fluid motion in the large-amplitude, low-frequency fluctuations of highlyAlfvénic fast solar wind. We show that protons locally conserve total kinetic energy when observed from aneffective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame canbe reasonably identified by alpha particles which, due to their drift with respect to protons at about the Alfvénspeed along the magnetic field, do not partake in the fluid low-frequency fluctuations. Using their velocity totransform the proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasmamotion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity andmagnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that thisconstraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is the origin of theobserved constancy of the magnetic field; while the constant velocity corresponding to constant energy can only beobserved in the frame of the fluctuations, the corresponding constant total magnetic field, invariant for Galileantransformations, remains the observational signature in the spacecraft frame of the constant total energy in theAlfvén turbulence frame
Archer MO, Turner DL, Eastwood JP, et al., 2014, Global impacts of a Foreshock Bubble: Magnetosheath, magnetopause and ground-based observations, Planetary and Space Science, Vol: 106, Pages: 56-66, ISSN: 1873-5088
Using multipoint observations we show, for the first time, that Foreshock Bubbles (FBs) have a global impact on Earth׳s magnetosphere. We show that an FB, a transient kinetic phenomenon due to the interaction of backstreaming suprathermal ions with a discontinuity, modifies the total pressure upstream of the bow shock showing a decrease within the FB׳s core and sheath regions. Magnetosheath plasma is accelerated towards the intersection of the FB׳s current sheet with the bow shock resulting in fast, sunward, flows as well as outward motion of the magnetopause. Ground-based magnetometers also show signatures of this magnetopause motion simultaneously across at least 7 h of magnetic local time, corresponding to a distance of 21.5RE transverse to the Sun–Earth line along the magnetopause. These observed global impacts of the FB are in agreement with previous simulations and in stark contrast to the known localised, smaller scale effects of Hot Flow Anomalies (HFAs).
Qureshi MNS, Nasir W, Masood W, et al., 2014, Terrestrial lion roars and non-Maxwellian distribution, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, ISSN: 2169-9380
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- Citations: 58
Archer MO, Turner DL, Eastwood JP, et al., 2014, The role of pressure gradients in driving sunward magnetosheath flows and magnetopause motion, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 8117-8125, ISSN: 2169-9380
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- Citations: 39
Schwartz SJ, 2014, Comment on "Electron demagnetization and heating in quasi-perpendicular shocks" by Mozer and Sundkvist, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 1507-1512, ISSN: 2169-9380
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- Citations: 8
Mitchell JJ, Schwartz SJ, 2014, Isothermalmagnetosheath electrons due to nonlocal electron cross talk, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 1080-1093, ISSN: 2169-9380
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- Citations: 12
Schwartz SJ, Zweibel EG, Goldman M, 2014, Microphysics in Astrophysical Plasmas, MICROPHYSICS OF COSMIC PLASMAS, Editors: Balogh, Bykov, Cargill, Dendy, DeWit, Raymond, Publisher: SPRINGER, Pages: 5-23, ISBN: 978-1-4899-7412-9
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- Citations: 1
Krasnoselskikh V, Balikhin M, Walker SN, et al., 2014, The Dynamic Quasiperpendicular Shock: Cluster Discoveries, MICROPHYSICS OF COSMIC PLASMAS, Editors: Balogh, Bykov, Cargill, Dendy, DeWit, Raymond, Publisher: SPRINGER, Pages: 459-522, ISBN: 978-1-4899-7412-9
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- Citations: 2
Ghavamian P, Schwartz SJ, Mitchell J, et al., 2014, Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection, MICROPHYSICS OF COSMIC PLASMAS, Editors: Balogh, Bykov, Cargill, Dendy, DeWit, Raymond, Publisher: SPRINGER, Pages: 557-587, ISBN: 978-1-4899-7412-9
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- Citations: 3
Masters A, Stawarz L, Fujimoto M, et al., 2013, <i>In situ</i> observations of high-Mach number collisionless shocks in space plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 55, ISSN: 0741-3335
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- Citations: 7
Mitchell JJ, Schwartz SJ, 2013, Nonlocal electron heating at the Earth's bow shock and the role of the magnetically tangent point, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 118, Pages: 7566-7575, ISSN: 2169-9380
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- Citations: 9
Pudney MA, Carr CM, Schwartz SJ, et al., 2013, Near-magnetic-field scaling for verification of spacecraft equipment, Geoscientific Instrumentation, Methods and Data Systems, Vol: 2, Pages: 249-255, ISSN: 2193-0864
Magnetic-field measurements are essential tothe success of many scientific space missions. Outside ofthe earth’s magnetic field the biggest potential source ofmagnetic-field contamination of these measurements is emittedby the spacecraft. Spacecraft magnetic cleanliness is enforcedthrough the application of strict ground verificationrequirements for spacecraft equipment and instruments. Dueto increasingly strict AC magnetic-field requirements, manyspacecraft units cannot be verified on the ground using existingtechniques. These measurements must instead be takenclose to the equipment under test (EUT) and then extrapolated.A traditional dipole power law of −3 (with a fieldfall-off proportional to r−3) cannot be applied at these closedistances without risk of underestimating the field emitted bythe EUT, but we demonstrate that a power law of −2 is tooconservative. We propose a compromise that uses a powerlaw of −2 up to a distance equal to 3 times the unit size, beyondwhich a dipole power law can be applied. When extrapolatingfrom a distance of 0.20 m to 1.00 m from the centre ofa 0.20 m wide EUT, we demonstrate that this method avoidsan under prediction of the field, and is at least twice as accurateas performing the extrapolation with a fixed power lawof −2.
Ghavamian P, Schwartz SJ, Mitchell J, et al., 2013, Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection, SPACE SCIENCE REVIEWS, Vol: 178, Pages: 633-663, ISSN: 0038-6308
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- Citations: 71
Krasnoselskikh V, Balikhin M, Walker SN, et al., 2013, The Dynamic Quasiperpendicular Shock: Cluster Discoveries, SPACE SCIENCE REVIEWS, Vol: 178, Pages: 535-598, ISSN: 0038-6308
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- Citations: 82
Schwartz SJ, Zweibel EG, Goldman M, 2013, Microphysics in Astrophysical Plasmas, SPACE SCIENCE REVIEWS, Vol: 178, Pages: 81-99, ISSN: 0038-6308
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- Citations: 7
Masters A, Stawarz L, Fujimoto M, et al., 2013, Electron acceleration to relativistic energies at a strong quasi-parallel shock wave, NATURE PHYSICS, Vol: 9, Pages: 164-167, ISSN: 1745-2473
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- Citations: 63
Pudney MA, Carr CM, Schwartz SJ, et al., 2013, Near equipment magnetic field verification and scaling, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 3, Pages: 437-458, ISSN: 2193-0856
Masters A, Stawarz Ł, Fujimoto M, et al., 2013, Electron acceleration to relativistic energies at a strong quasi-parallel shock wave
Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova [4, 2, 19]. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions) [16, 8, 10, 17, 14]. However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn’s bow shock) where significant local electron acceleration has been confirmed under quasi- parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks [16, 8, 10, 17, 14]. Furthermore, the acceleration led to electrons at relativistic energies (∼ MeV), comparable to the highest energies ever attributed to shock-acceleration in the solar wind [16]. These observations suggest that at high-Mach numbers, like those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators. For full details please see: Nature Physics, Volume 9, Issue 3, pp. 164-167.
See V, Cameron RF, Schwartz SJ, 2013, Non-adiabatic electron behaviour due to short-scale electric field structures at collisionless shock waves, ANNALES GEOPHYSICAE, Vol: 31, Pages: 639-646, ISSN: 0992-7689
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- Citations: 13
Hasegawa H, Zhang H, Lin Y, et al., 2012, Magnetic flux rope formation within a magnetosheath hot flow anomaly, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 117, ISSN: 2169-9380
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- Citations: 20
Vaivads A, Andersson G, Bale SD, et al., 2012, EIDOSCOPE: particle acceleration at plasma boundaries, EXPERIMENTAL ASTRONOMY, Vol: 33, Pages: 491-527, ISSN: 0922-6435
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- Citations: 5
Sundkvist D, Krasnoselskikh V, Bale SD, et al., 2012, Dispersive Nature of High Mach Number Collisionless Plasma Shocks: Poynting Flux of Oblique Whistler Waves, PHYSICAL REVIEW LETTERS, Vol: 108, ISSN: 0031-9007
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- Citations: 31
Pudney MA, Carr CM, Schwartz SJ, et al., 2012, Automatic parameterization for magnetometer zero offset determination, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 2, Pages: 245-266, ISSN: 2193-0856
Mitchell JJ, Schwartz SJ, Auster U, 2012, Electron cross talk and asymmetric electron distributions near the Earth's bowshock, ANNALES GEOPHYSICAE, Vol: 30, Pages: 503-513, ISSN: 0992-7689
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- Citations: 11
Pogorelsky IV, Dover NP, Babzien M, et al., 2012, Ion Acceleration by Laser Hole-Boring into Plasmas, 15th Workshop on Advanced Accelerator Concepts (AAC), Publisher: AMER INST PHYSICS, Pages: 814-819, ISSN: 0094-243X
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- Citations: 6
Pudney MA, Carr CM, Schwartz SJ, et al., 2012, Automatic parameterization for magnetometer zero offset determination, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 1, Pages: 103-109, ISSN: 2193-0856
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- Citations: 12
Schwartz SJ, Henley E, Mitchell J, et al., 2011, Electron Temperature Gradient Scale at Collisionless Shocks, PHYSICAL REVIEW LETTERS, Vol: 107, ISSN: 0031-9007
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- Citations: 73
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