scholarly journals Gyrokinetic stability theory of electron–positron plasmas

2016 ◽  
Vol 82 (3) ◽  
Author(s):  
P. Helander ◽  
J. W. Connor
Keyword(s):  
Laboratory Experiments ◽  
Particle Flux ◽  
Debye Length ◽  
Closed Field ◽  
Stability Threshold ◽  
Electron Positron ◽  
Magnetically Confined ◽  
Closed Field Line ◽  
The Stability ◽  
The Magnetic Field

The linear gyrokinetic stability properties of magnetically confined electron–positron plasmas are investigated in the parameter regime most likely to be relevant for the first laboratory experiments involving such plasmas, where the density is small enough that collisions can be ignored and the Debye length substantially exceeds the gyroradius. Although the plasma beta is very small, electromagnetic effects are retained, but magnetic compressibility can be neglected. The work of a previous publication (Helander, Phys. Rev. Lett., vol. 113, 2014a, 135003) is thus extended to include electromagnetic instabilities, which are of importance in closed-field-line configurations, where such instabilities can occur at arbitrarily low pressure. It is found that gyrokinetic instabilities are completely absent if the magnetic field is homogeneous: any instability must involve magnetic curvature or shear. Furthermore, in dipole magnetic fields, the stability threshold for interchange modes with wavelengths exceeding the Debye radius coincides with that in ideal magnetohydrodynamics. Above this threshold, the quasilinear particle flux is directed inward if the temperature gradient is sufficiently large, leading to spontaneous peaking of the density profile.

scholarly journals Linear gyrokinetics of electron–positron plasmas in closed field-line systems

2020 ◽  
Vol 86 (2) ◽  
Author(s):  
D. Kennedy ◽  
A. Mishchenko ◽  
P. Xanthopoulos ◽  
P. Helander ◽  
A. Bañón Navarro ◽  
...  
Keyword(s):  
Linear Stability ◽  
Debye Length ◽  
Closed Field ◽  
Flux Tubes ◽  
Electron Positron ◽  
Magnetically Confined ◽  
Closed Field Line ◽  
First Time ◽  
Gyrokinetic Simulations ◽  
The Magnetic Field

Linear gyrokinetic simulations of magnetically confined electron–positron plasmas are performed for the first time in the geometry and parameter regimes likely to be relevant for upcoming laboratory experiments. In such plasmas, the density will be sufficiently small as to render the plasma effectively collisionless. The magnetic field will be very large, meaning that the Debye length will exceed the gyroradius by a few orders of magnitude. We show the results of linear simulations in flux tubes close to the current carrying ring and also in the bulk of the plasma, demonstrating the existence of entropy modes and interchange modes in pair plasmas. We study linear stability and show that in the relevant configurations, almost complete linear stability is attainable in large swathes of parameter space.

scholarly journals Predicted signatures of pulsed reconnection in ESR data

1996 ◽  
Vol 14 (12) ◽  
pp. 1246-1256 ◽  
Author(s):  
C. J. Davis ◽  
M. Lockwood
Keyword(s):  
Magnetic Field ◽  
Closed Field ◽  
Background Rate ◽  
Incoherent Scatter ◽  
Dayside Magnetopause ◽  
Cusp Conditions ◽  
Closed Field Line ◽  
Field Lines ◽  
The Magnetic Field ◽  
Open Magnetic Field

Abstract. Early in 1996, the latest of the European incoherent-scatter (EISCAT) radars came into operation on the Svalbard islands. The EISCAT Svalbard Radar (ESR) has been built in order to study the ionosphere in the northern polar cap and in particular, the dayside cusp. Conditions in the upper atmosphere in the cusp region are complex, with magnetosheath plasma cascading freely into the atmosphere along open magnetic field lines as a result of magnetic reconnection at the dayside magnetopause. A model has been developed to predict the effects of pulsed reconnection and the subsequent cusp precipitation in the ionosphere. Using this model we have successfully recreated some of the major features seen in photometer and satellite data within the cusp. In this paper, the work is extended to predict the signatures of pulsed reconnection in ESR data when the radar is pointed along the magnetic field. It is expected that enhancements in both electron concentration and electron temperature will be observed. Whether these enhancements are continuous in time or occur as a series of separate events is shown to depend critically on where the open/closed field-line boundary is with respect to the radar. This is shown to be particularly true when reconnection pulses are superposed on a steady background rate.

Recent advances in the stability theory of toroidal plasmas

1981 ◽  
Vol 300 (1456) ◽  
pp. 559-567
Keyword(s):  
Stability Theory ◽  
Short Wavelength ◽  
Linear Stability Theory ◽  
Long Wavelength ◽  
Toroidal Plasmas ◽  
Toroidal Plasma ◽  
Magnetically Confined ◽  
Eikonal Representation ◽  
The Stability ◽  
The Magnetic Field

Many of the most persistent instabilities of a magnetically confined plasma have short wavelength perpendicular to the magnetic field but long wavelength parallel to it. Such instabilities are difficult to treat in a toroidal system because the simple eikonal representation of short wavelength oscillations X (r) = Y (r) with 8 1 proves to be incompatible with the other requirements of toroidal periodicity and long parallel wavelength (which would require B >VS = 0). A new method of representing perturbations in a torus will be outlined. By using this, the two-dimensional stability problem posed by an axisymmetric toroidal equilibrium can be reduced to that of solving a one-dimensional eigenvalue equation. This technique essentially completes the linear stability theory of magnetohydrodynamic modes in a toroidal plasma, and is also applicable to the investigation of micro-instabilities that are described by the Vlasov-Maxwell equations.

scholarly journals Effects of hot electrons on the stability of a closed field line plasma

2005 ◽  
Vol 12 (3) ◽  
pp. 032101 ◽  
Author(s):  
Natalia S. Krasheninnikova ◽  
Peter J. Catto
Keyword(s):  
Field Line ◽  
Hot Electrons ◽  
Closed Field ◽  
Closed Field Line ◽  
The Stability

scholarly journals Electrostatic stability of electron–positron plasmas in dipole geometry

2018 ◽  
Vol 84 (2) ◽  
Author(s):  
Alexey Mishchenko ◽  
Gabriel G. Plunk ◽  
Per Helander
Keyword(s):  
Debye Length ◽  
Stability Diagram ◽  
Landau Damping ◽  
Point Dipole ◽  
Stability Boundaries ◽  
Singular Behaviour ◽  
Electron Positron ◽  
The Stability ◽  
Electrostatic Stability ◽  
Z Pinch

The electrostatic stability of electron–positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behaviour. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stability boundaries in parameter space. Landau damping is investigated at scales sufficiently smaller than the Debye length, where instability is absent.

scholarly journals The nightside magnetic field line open–closed boundary and polar rain electron energy-latitude dispersion

2015 ◽  
Vol 33 (1) ◽  
pp. 39-46 ◽  
Author(s):  
S. Wing ◽  
Y. L. Zhang
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Open Field ◽  
Magnetic Field Line ◽  
Path Length ◽  
Closed Field ◽  
Open Field Line ◽  
Polar Rain ◽  
Closed Field Line ◽  
The Magnetic Field

Abstract. The polar rain electrons near the open–closed field line boundary on the nightside often exhibit energy-latitude dispersion, in which the energy decreases with decreasing latitude. The solar wind electrons from the last open-field line would E × B drift equatorward as they move toward the ionosphere, resulting in the observed dispersion. This process is modeled successfully by an open-field line particle precipitation model. The existing method for determining the magnetotail X line distance from the electron dispersion underestimates the electron path length from the X line to the ionosphere by at least 33%. The best estimate of the path length comes from using the two highest energy electrons in the dispersion region. The magnetic field line open–closed boundary is located poleward of the highest energy electrons in the dispersion region, which in turn is located poleward of Defense Meteorological Satellite Program (DMSP) b6, b5e, and b5i boundaries. In the four events examined, b6 is located at least 0.7–1.5° equatorward of the magnetic field line open–closed boundary. The energy-latitude dispersion seen in the electron overhang may result from the plasma sheet electron curvature and gradient drifts into the newly closed field line.

scholarly journals Preliminary two-point observations of the mid-altitude cusp by Cluster PEACE and FGM

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1579-1587 ◽  
Author(s):  
I. Krauklis ◽  
A. N. Fazakerley ◽  
C. J. Owen ◽  
P. J. Carter ◽  
M. W. Dunlop ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Closed Field ◽  
Low Latitude ◽  
Magnetic Field Data ◽  
Current Sheets ◽  
Cusp Region ◽  
Closed Field Line ◽  
Current Systems ◽  
The Magnetic Field

Abstract. On 1 October 2000, Cluster spacecraft Samba (Cluster 3) and Tango (Cluster 4) made an outbound crossing of the northern mid-altitude (4.7 RE) cusp region, moving roughly parallel to the noon meridian. We present preliminary observations from this interval made by the PEACE and FGM instruments. The interplanetary magnetic field at the magnetopause is estimated to have turned south at the time of our observations, based on ACE data as well as a rough estimate of the time taken for the solar wind to travel between ACE and the magnetopause. Cluster 3 encountered the low-latitude boundary layer (LLBL) between 12:20:30 to 12:26:00 UT, and the cusp region between 12:26:00 and 12:32:30 UT. Cluster 4 encountered the LLBL between 12:22:00 to 12:29:00 UT, and the cusp region between 12:29:00 and 12:38:00 UT. During the interval between the two spacecraft passages through these regions, the open/closed field line boundary was observed to move equatorward by 0.33° invariant latitude, while the latitudinal extent of the cusp region increased by 0.5°. Both of these observations are consistent with the ongoing reconnection at the sub-solar magnetopause. The magnetic field data indicate that Cluster encountered four field-aligned longitudinally extended current sheets. The most equatorward of these is consistent with the location of a Region 1 current sheet. Two current sheets were observed in the vicinity of the cusp region, though neither of these were thin current sheets. The fourth current sheet was observed in the mantle region and was largely unaffected by the latitudinal expansion of the cusp region.Key words. Magnetospheric physics (current systems; energetic particles, precipitating; magnetopause, cusp and boundary layers)

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

scholarly journals Interplanetary magnetic field control of Saturn's polar cusp aurora

2005 ◽  
Vol 23 (4) ◽  
pp. 1405-1431 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
S. E. Milan
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
High Latitude ◽  
Closed Field ◽  
Vortical Flows ◽  
Dayside Magnetopause ◽  
Closed Field Line ◽  
Lobe Reconnection

Abstract. Dayside UV emissions in Saturn's polar ionosphere have been suggested to be the first observational evidence of the kronian "cusp" (Gérard et al., 2004). The emission has two distinct states. The first is a bright arc-like feature located in the pre-noon sector, and the second is a more diffuse "spot" of aurora which lies poleward of the general location of the main auroral oval, which may be related to different upstream interplanetary magnetic field (IMF) orientations. Here we take up the suggestion that these emissions correspond to the cusp. However, direct precipitation of electrons in the cusp regions is not capable of producing significant UV aurora. We have therefore investigated the possibility that the observed UV emissions are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, akin to flux transfer events seen at the Earth. We devise a conceptual model of pulsed reconnection at the low-latitude dayside magnetopause for the case of northwards IMF which will give rise to pulsed twin-vortical flows in the magnetosphere and ionosphere in the vicinity of the open-closed field-line boundary, and hence to bi-polar field-aligned currents centred in the vortical flows. During intervals of high-latitude lobe reconnection for southward IMF, we also expect to have pulsed twin-vortical flows and corresponding bi-polar field-aligned currents. The vortical flows in this case, however, are displaced poleward of the open-closed field line boundary, and are reversed in sense, such that the field-aligned currents are also reversed. For both cases of northward and southward IMF we have also for the first time included the effects associated with the IMF By effect. We also include the modulation introduced by the structured nature of the solar wind and IMF at Saturn's orbit by developing "slow" and "fast" flow models corresponding to intermediate and high strength IMF respectively. We then consider the conditions under which the plasma populations appropriate to either sub-solar reconnection or high-latitude lobe reconnection can carry the currents indicated. We have estimated the field-aligned voltages required, the resulting precipitating particle energy fluxes, and the consequent auroral output. Overall our model of pulsed reconnection under conditions of northwards and southwards IMF, and for varying orientations of IMF By, is found to produce a range of UV emission intensities and geometries which is in good agreement with the data presented by Gérard et al. (2004). The recent HST-Cassini solar wind campaign provides a unique opportunity to test the theoretical ideas presented here.

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