scholarly journals Boundary-layer Acceleration and Particle Mirroring in Pulsar Magnetospheres

1981 ◽  
Vol 34 (3) ◽  
pp. 317 ◽  
Author(s):  
RR Burman
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Crab Pulsar ◽  
Number Density ◽  
Southern Boundary ◽  
Axis Of Rotation ◽  
Electron Positron ◽  
Electrons And Ions ◽  
Field Lines

Where the number density of a species becomes very small, inertial development of vorticity occurs; so a magnetospheric zone in which a species is contained must be enclosed by a vortical boundary layer. Where zones of corotating electrons and ions abut, there exists a large local non-corotational electric field, directed so as to force a merging of the electron and ion boundary layers. The poloidalaccelerations and azimuthal drift velocities generated in these layers are estimated here. Ions are accelerated to nonrelativistic or mildly relativistic poloidal speeds, then penetrate into the electron corotation zones where they are centrifugally decelerated as they travel approximately along magnetic field lines. They mirror between points above the stellar surface and the boundary layer, resumably moving to lower magnetic field lines until they reach the star. Electrons are accelerated to poloidal speeds that are relativistic for istances from the axis of rotation exceeding about 1/30 of the radius of the light cylinder. They enter the ion corotation zone where they are further accelerated as they travel approximately along outgoing portions of the closed magnetic field lines, and are then decelerated on ingoing portions. They mirror between the northern and southern boundary layers, presumably moving to lower magnetic field lines until they reach the star. The electrons in the outer parts of the ion.zone are very highly relativistic and emit gamma radiation which, in the case of the Crab pulsar, might create electron-positron pairs.

scholarly journals Corotation and Poloidal Flow in Pulsar Magnetospheres

1981 ◽  
Vol 34 (3) ◽  
pp. 303 ◽  
Author(s):  
RR Burman
Keyword(s):  
Boundary Layers ◽  
Functional Form ◽  
Flow Dynamics ◽  
Southern Boundary ◽  
Piecewise Constant ◽  
Dissipative Effects ◽  
Rotation Axes ◽  
Electrons And Ions ◽  
Oblique Rotator ◽  
Field Lines

In recent years, authors have recognized that it is essential to allow for the non-corotational part - '\l(/J of the electric field in pulsar magneto spheres, but have continued to neglect it .in zones of corotation. It is shown here that, in order to understand the flow dynamics and avoid absurdities, it is essential to use the correct functional form for (/J everywhere outside the star-without exception. Implications include a potential difference between zones of corotating electrons and ions, resulting in a large local 'V(/J field in vortical boundary layers separating those zones, directed so as to force a mixing of electrons and ions there. This result clashes sharply with a well-known conclusion of Holloway, based on use of the zero-inertia approximation with (/J piecewise constant on magnetic field lines: he found the electron and ion zones to be separated by evacuated regions. A further consequence of the present analysis is a possible mirroring of electrons between the northern and southern boundary layers, while they drift toward the star because of dissipative effects. These findings are not restricted to the usual axisymmetric case, but are valid for the oblique rotator, with non-aligned magnetic and rotation axes, so long as zones of corotation exist.

scholarly journals Characteristics of the near-tail dawn magnetopause and boundary layer

2005 ◽  
Vol 23 (4) ◽  
pp. 1481-1497 ◽  
Author(s):  
G. Paschmann ◽  
S. Haaland ◽  
B. U. Ö. Sonnerup ◽  
H. Hasegawa ◽  
E. Georgescu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Dynamic Range ◽  
Effective Means ◽  
Field Measurements ◽  
Thickness Variation ◽  
Magnetic Shear ◽  
Important Conclusion ◽  
Average Value

Abstract. The paper discusses properties of the near-tail dawnside and boundary layer, as obtained from Cluster plasma and magnetic field measurements during a single skimming orbit on 4 and 5 July 2001 that included 24 well-defined crossings by all four spacecraft. As a result of variations of the interplanetary magnetic field, the magnetic shear across the local varied between ~0° and ~180°. Using an improved method, which takes into account acceleration and thickness variation, we have determined the orientation, speed, thickness and current for the 96 individual crossings. The orientations show clear evidence of surface waves. Magnetopause thicknesses range from ~100 to ~2500km, with an average of 753km. The speeds range from less than 10up to more than 300, with an average of 48. Both results are consistent with earlier ISEE and AMPTE results obtained for the dayside magnetopause. Importantly, scaling the thicknesses to the ion gyro radius or the ion inertial length did not reduce the large dynamic range. There is also no significant dependence of thickness on magnetic shear. Current densities range from ~0.01 up to ~0.3uA, with an average value of 0.05 . By including some extra crossings that did not involve all four spacecraft, we were able to apply the Walén test to a total of 60 by Cluster 1 and 3, and have classified 19 cases as rotational discontinuities (RDs), of which 12 and 7 were sunward and tailward of an X-line, respectively. Of these 60 crossings, 26 show no trace of a boundary layer. The only with substantial boundary layers are into the plasma mantle. Of the 26 without a boundary layer, 8 were identified as RDs. Since reconnection produces wedge-shaped boundary layers emanating from the X-line, RDs without may be considered close to the X-line, in which case the observed magnetic shear and Alfvén Mach number should be representative of the conditions at the X-line itself. It is therefore important that four of the eight cases had shear angles ≤100, i.e. the reconnecting fields were far from being anti-parallel, and that all eight cases had Alfvén Mach numbers MA>1 in the adjoining magnetosheath. Another important conclusion can be drawn from the without a that were tangential discontinuities (TDs). To observe TDs with no at such large distances from the subsolar point appears to rule out diffusion over large portions of the as an effective means for plasma transport across the magnetopause.

The orbits of electrons and ions in a rotating magnetic field

1983 ◽  
Vol 29 (1) ◽  
pp. 155-171 ◽  
Author(s):  
Waheed N. Hugrass ◽  
Ieuan R. Jones
Keyword(s):  
Magnetic Field ◽  
Rotating Magnetic Field ◽  
Plasma Equilibrium ◽  
Complex Situation ◽  
Axis Of Rotation ◽  
Equivalent Potential ◽  
Realistic Situation ◽  
Electrons And Ions ◽  
Self Consistent ◽  
The Stability

The motion of electrons and ions in a system which consists of a uniform rotating magnetic field and a steady uniform magnetic field which is aligned with the axis of rotation is re-examined. Stable orbits are identified and explicit expressions for these orbits are provided. The more realistic situation of motion in the non-uniform self-consistent fields appropriate to a cylindrical plasma equilibrium maintained by the rotating field is investigated. Again, stable orbits are found. The stability of orbits in this more complex situation is examined using an equivalent potential concept.

Pulsar magnetospheres

1992 ◽  
Vol 341 (1660) ◽  
pp. 93-104 ◽  
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Photon Emission ◽  
Rotation Period ◽  
Primary Electron ◽  
Rotation Axes ◽  
Polar Caps ◽  
Electron Positron ◽  
Field Lines ◽  
Secular Increase

The energy loss from the neutron star - as inferred from the secular increase in rotation period - is much greater than that emitted in either the radio or the other observed wavelengths. A primary motivation of magnetospheric theory is to trace the mode in which this energy and the associated angular momentum are in fact carried off from active pulsars. This review concentrates on the special case in which the magnetic and rotation axes are aligned. Electrons emitted from the polar caps are accelerated to highly relativistic energies by the electric force and simultaneously pick up angular momentum from the magnetic torque. Some process of angular momentum dissipation occurring beyond the light-cylinder is then required, both to yield the continuous spin-down of the star, and also to allow the electrons to cross magnetic field lines and so complete their circuits back to the star. Within the framework of classical physics, this could occur if most of the spin-down energy is lost through incoherent photon emission in an equatorial domain beyond the lightcylinder, but this would generate y-radiation far in excess of that observed. Transport away of the angular momentum via a relativistic wind requires the generation of a quasi-neutral plasma. Gamma-rays emitted by outflowing electrons will produce electron-positron pairs in the strong magnetic field near the star, and highly energetic electrons returning to the star may also generate a mixed plasma by pair production or by surface spallation. Coupling with the circulating primary electron current may then ensure that the dominant angular momentum loss is via the wind rather than through photon emission.

Collisional alpha transport in a weakly non-quasisymmetric stellarator magnetic field

2019 ◽  
Vol 85 (2) ◽  
Author(s):  
Peter J. Catto
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Collision Frequency ◽  
Alpha Particles ◽  
Slowing Down ◽  
Tail Distribution ◽  
Strong Motivation ◽  
Particle Confinement ◽  
Background Ions

Alpha particle confinement is a serious concern in stellarators and provides strong motivation for optimizing magnetic field configurations. In addition to the collisionless confinement of trapped alphas in stellarators, excessive collisional transport of the trapped alpha particles must be avoided while they tangentially drift due to the magnetic gradient (the $\unicode[STIX]{x1D735}B$ drift). The combination of pitch angle scatter off the background ions and the $\unicode[STIX]{x1D735}B$ drift gives rise to two narrow boundary layers in the trapped region. The first is at the trapped–passing boundary and enables the finite trapped response to be matched to the vanishing passing response of the alphas. The second layer is a region that encompasses the somewhat more deeply trapped alphas with vanishing tangential $\unicode[STIX]{x1D735}B$ drift. Away from (and between) these boundary layers, collisions are ineffective and the alpha $\unicode[STIX]{x1D735}B$ drift simply balances the small radial drift of the trapped alphas. As this balance does not vanish as the trapped–passing boundary is approached, the first collisional boundary layer is necessary and gives rise to $\surd \unicode[STIX]{x1D708}$ transport, with $\unicode[STIX]{x1D708}$ the collision frequency. The vanishing of the tangential drift results in a separate, somewhat wider boundary layer, and significantly stronger superbanana plateau transport that is independent of collisionality. The constraint imposed by the need to avoid significant energy depletion loss in the slowing down tail distribution function sets the allowed departure of a stellarator from an optimal quasisymmetric configuration.

A possible mechanism for <theta> aurora formation

1995 ◽  
Vol 13 (7) ◽  
pp. 698-703 ◽  
Author(s):  
B. V. Rezhenov ◽  
I. M. Vardavas
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Plasma Sheet ◽  
Energy Spectra ◽  
System Of Equations ◽  
The Sun ◽  
High Latitudes ◽  
Plasma Sheet Boundary Layer ◽  
Interchange Instability ◽  
Field Lines

Abstract. A mechanism for the formation of <theta> aurora connected with the development of an interchange instability on the plasma sheet boundary layer (PSBL) is suggested. The PSBL is assumed to be deep inside the region of closed magnetic field lines. A system of equations connecting currents in the ionosphere and magnetosphere is solved numerically. It is found, using realistic ionospheric and magnetospheric parameters, that in a period of 8–10 min a system of plasma bars directed to the Sun arises at high latitudes. The system of bars is about 1000 km in width and 3000 km in length and approximates the Θ aurora. The suggested mechanism allows an explanation of a number of Θ aurora features such as the appearance probability, electric field directions, energy spectra of precipitating particles, and its location.

scholarly journals The Nature of Pulsar Subpulse Drift

1991 ◽  
Vol 44 (5) ◽  
pp. 573 ◽  
Author(s):  
AZ Kazbegi ◽  
GZ Machabeli ◽  
GI Melikidze
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Large Scale ◽  
Primary Particle ◽  
Particle Beam ◽  
Drift Waves ◽  
Electron Positron ◽  
Field Lines ◽  
The Magnetic Field ◽  
Open Magnetic Field

A possible mechanism for the explanation of pulsar subpulse drift is suggested. In the region of the open magnetic field lines the existence of an electron-positron plasma penetrated by a primary particle beam is assumed. There is a possibility of excitation of large-scale drift waves propagating transversely to the magnetic field lines. These waves can affect the fulfilment of the radio-wave generation conditions. If the pulsar angular velocity is near to the frequency of the drift waves one should observe regular drift phenomena.

scholarly journals Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures

2001 ◽  
Vol 19 (10/12) ◽  
pp. 1613-1640 ◽  
Author(s):  
M. Lockwood ◽  
A. Fazakerley ◽  
H. Opgenoorth ◽  
J. Moen ◽  
A. P. van Eyken ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Normal Component ◽  
Phase Speed ◽  
Propagation Delay ◽  
Polar Cap ◽  
Transfer Event ◽  
Field Lines ◽  
Pass Through ◽  
The Magnetic Field

Abstract. We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ( [ XGSM, YGSM, ZGSM ] ≈ [ 2, 7, 9 ] RE). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is welldefined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10–15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 RE in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)

scholarly journals On the role of rotation in the outflows of the Crab pulsar

2015 ◽  
Vol 24 (06) ◽  
pp. 1550042
Author(s):  
Gudavadze Irakli ◽  
Osmanov Zaza ◽  
Rogava Andria
Keyword(s):  
Magnetic Field ◽  
Rotation Axis ◽  
Three Dimensional ◽  
Rotating Magnetic Field ◽  
Crab Pulsar ◽  
X Ray ◽  
Field Lines ◽  
The Magnetic Field ◽  
Component Parallel

In order to study constraints imposed on kinematics of the Crab pulsar's jet, we consider motion of particles along co-rotating field lines in the magnetosphere of the Crab pulsar. It is shown that particles following the co-rotating magnetic field lines may attain velocities close to observable values. In particular, we demonstrate that if the magnetic field lines are within the light cylinder (LC), the maximum value of the velocity component parallel to the rotation axis is limited by 0.5c. This result in the context of the X-ray observations performed by Chandra X-ray Observatory seems to be quite indicative and useful to estimate the density of field lines inside the jet. Considering the three-dimensional (3D) field lines crossing the LC, we found that for explaining the force-free regime of outflows the magnetic field lines must asymptotically tend to the Archimedes spiral configuration. It is also shown that the 3D case may explain the observed jet velocity for appropriately chosen parameters of magnetic field lines.

On magnetohydrodynamic flows with aligned magnetic fields

1964 ◽  
Vol 19 (1) ◽  
pp. 49-59 ◽  
Author(s):  
M. B. Glauert
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Magnetic Fields ◽  
Boundary Layers ◽  
Flow Patterns ◽  
Basic Flow ◽  
Conducting Fluid ◽  
Magnetic Diffusivity ◽  
Magnetohydrodynamic Flows ◽  
Aligned Magnetic Field

The boundary layers due to finite viscosity and magnetic diffusivity are studied in relation to two models of the flow of a conducting fluid past a body in an aligned magnetic field. In each case it is deduced that the growth of the boundary layer may have substantial effects, such as to raise doubts about the validity of the assumed basic flow patterns.

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