Ion dynamics in a perpendicular collisionless shock

1977 ◽  
Vol 17 (2) ◽  
pp. 265-279 ◽  
Author(s):  
D. Sherwell ◽  
R. A. Cairns
Keyword(s):  
Magnetic Field ◽  
Shock Waves ◽  
Dissipative Process ◽  
Ion Dynamics ◽  
Collisionless Shock ◽  
Collisionless Shocks ◽  
Ion Heating ◽  
Potential Jump ◽  
Electric And Magnetic Fields ◽  
The Mean

Some properties of perpendicular collisionless shocks are investigated, using a model in which the ion orbits in the shock are assumed to be determined by the average electric and magnetic fields in the shock. These fields are modelled, with the jump in magnetic field across the shock being determined by the conservation relations, and the potential jump determined self-consistently within the model, using the fact that the mean ion velocity downstream of the shock is determined by the conservation relations. Extensive numerical calculations of ion orbits show that effective ion heating can occur in the absence of any dissipative process, with the energy residing in non-Maxwellian velocity distributions in the downstream regions. Results on this and on a number of other features of shock waves, agree well with experiments.

Electron heating in a perpendicular collisionless shock

1971 ◽  
Vol 6 (3) ◽  
pp. 443-448 ◽  
Author(s):  
R. A. Cairns
Keyword(s):  
Shock Waves ◽  
Electric Field ◽  
Qualitative Agreement ◽  
Reasonable Agreement ◽  
Collisionless Shock ◽  
Potential Jump ◽  
Electron Heating ◽  
Gain Energy ◽  
Steady Potential

A model is proposed to explain the observed electron heating in perpendicular collisionless shock waves. This relies on trapping of the electrons by the turbulent electric field to modify their orbits in such a way that they gain energy from the steady potential jump across the shock. With simple assumptions about the nature of this trapping, reasonable agreement with the experimentally observed heating is obtained. In addition, the model provides qualitative agreement with a number of other experimental observations.

A model for precursor structure in supercritical perpendicular, collisionless shock waves

1978 ◽  
Vol 20 (2) ◽  
pp. 265-279
Author(s):  
D. Sherwell ◽  
R. A. Cairns
Keyword(s):  
Magnetic Field ◽  
Shock Waves ◽  
Wave Velocity ◽  
Current Distribution ◽  
Trapped Ions ◽  
Collisionless Shock ◽  
Precursor Structure ◽  
Insight Into ◽  
A Current

Magnetosonic solitons may be given smooth increasing profiles by assuming the presence within the wave of a current distribution Jy(x) of trapped ions perpendicular to Bz(x) and the wave velocity Vx. Suitable ions are found immediately upstream of perpendicular, collisionless shock waves and these are coincident with the often observed ‘foot’ in magnetic field profiles of moderately supercritical shocks. By modelling Jy(x) we apply the theory to previous experiments where Jy(x) is observed, and are able to reproduce reasonably, and thus explain, the profiles in the foot. Insight into a number of features of fast shocks is obtained.

Experimental Study of Electron and ion Heating in High-β Perpendicular Collisionless Shock Waves

1972 ◽  
pp. 327-334
Author(s):  
M. Keilhacker ◽  
M. Kornherr ◽  
H. Niedermeyer ◽  
K.-H. Steuer
Keyword(s):  
Experimental Study ◽  
Shock Waves ◽  
Collisionless Shock ◽  
Ion Heating

Effect of electron thermal anisotropy on the kinetic cross-field streaming instability

1984 ◽  
Vol 32 (1) ◽  
pp. 159-178 ◽  
Author(s):  
S. T. Tsai ◽  
M. Tanaka ◽  
J. D. Gaffey ◽  
E. H. Da Jornada ◽  
C. S. Wu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Shock Waves ◽  
Numerical Solutions ◽  
Collisionless Shock ◽  
Direction Transverse ◽  
Ambient Magnetic Field ◽  
Thermal Anisotropy ◽  
Analytical And Numerical Solutions ◽  
Streaming Instability

The investigation of the kinetic cross-field streaming instability, motivated by the research of collisionless shock waves and previously studied by Wu et al., is discussed more fully in the present work. Since, in the ramp region of a quasi-perpendicular shock, electrons can be preferentially heated in the direction transverse to the ambient magnetic field, it is both desirable and necessary to include the effect of the thermal anisotropy on the instability associated with a shock. The present study has found that Te⊥ > Te‖ can significantly enhance the peak growth rate of the cross-field streaming instability when the electron beta is sufficiently high. Furthermore, the present analysis also improves the analytical and numerical solutions previously obtained.

scholarly journals Theory of the formation of a collisionless Weibel shock: pair vs. electron/proton plasmas

2016 ◽  
Vol 34 (2) ◽  
pp. 362-367 ◽  
Author(s):  
A. Bret ◽  
A. Stockem Novo ◽  
R. Narayan ◽  
C. Ruyer ◽  
M. E. Dieckmann ◽  
...  
Keyword(s):  
Mean Free Path ◽  
Particle Accelerators ◽  
Incoming Flow ◽  
Collisionless Shock ◽  
Collisionless Shocks ◽  
Trapping Time ◽  
Particle In Cell ◽  
The Mean ◽  
The One ◽  
Overlapping Region

AbstractCollisionless shocks are shocks in which the mean-free path is much larger than the shock front. They are ubiquitous in astrophysics and the object of much current attention as they are known to be excellent particle accelerators that could be the key to the cosmic rays enigma. While the scenario leading to the formation of a fluid shock is well known, less is known about the formation of a collisionless shock. We present theoretical and numerical results on the formation of such shocks when two relativistic and symmetric plasma shells (pair or electron/proton) collide. As the two shells start to interpenetrate, the overlapping region turns Weibel unstable. A key concept is the one of trapping time τp, which is the time when the turbulence in the central region has grown enough to trap the incoming flow. For the pair case, this time is simply the saturation time of the Weibel instability. For the electron/proton case, the filaments resulting from the growth of the electronic and protonic Weibel instabilities, need to grow further for the trapping time to be reached. In either case, the shock formation time is 2τp in two-dimensional (2D), and 3τp in 3D. Our results are successfully checked by particle-in-cell simulations and may help designing experiments aiming at producing such shocks in the laboratory.

The generation of interpenetrating plasma flows in an expanding discharge

1976 ◽  
Vol 15 (2) ◽  
pp. 293-307 ◽  
Author(s):  
H. A. Davis ◽  
M. A. Mahdavi ◽  
R. H. Lovberg
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Shock Waves ◽  
Electric Field ◽  
Electric Fields ◽  
Magnetic Disturbance ◽  
Collisionless Shock ◽  
Driving Field ◽  
Piston Speed ◽  
Electron Density And Temperature

We report on an experiment designed to study collisionless shock waves in an inverse pinch discharge using argon. A magnetic disturbance was generated which propagated ahead of the driving field at twice the piston speed. Measurements of the magnetic and electric field structures, electron density and temperature, as well as ion velocities revealed that the disturbance was produced by a beam of plasma moving through the ionized ambient plasma rather than by a true shock wave. Calculations of ion trajectories using measured electric fields demonstrated that the beam originated at small radii and early times, and was not the result of a steady specular reflexion from the piston field. It is concluded that the ions comprising this stream, which were collisionless relative to the ambient ions, did not couple to the background plasma even though a strong magnetic field was applied.

Germination and initial growth of triticale seeds under stationary magnetic fields

2014 ◽  
Vol 2 (2) ◽  
pp. 72-79 ◽  
Author(s):  
Mercedes Florez ◽  
Elvira Martinez ◽  
Victoria Carbonell
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Seed Vigor ◽  
Initial Growth ◽  
Practical Application ◽  
Biochemical Processes ◽  
Mean Germination Time ◽  
Nutrition Value ◽  
The Mean ◽  
Growth Of Seedlings

The main objective of this study is to determine the effects of 125 mT and 250mT magnetic treatment on the germination and initial growth of triticale seeds. This objective has a practical application in agriculture science: early growth of triticale. An increase in the percentage and rate of germination of seeds and a stimulation of growth of seedlings as positive response to magnetic field treatment in rice, wheat, maize and barley seeds have been found in previous studies. Germination tests were carried out under laboratory conditions by exposing triticale seeds to magnetic field for different times. The effect was studied by exposure of seeds prior sowing. The mean germination time were reduced for all the magnetic treatments applied. Most significant differences were obtained for time of exposure of 1 and 24 hours and maximum reductions was 12%. Furthermore, seedlings from magnetically treated seeds grew taller than control. The longest mean total length was obtained from seedlings exposed to 125 and 250 mT for 24 hours. External magnetic fields are assumed to enhance seed vigor by influencing the biochemical processes by stimulating activity of proteins and enzymes. Numerous studies suggested that magnetic field increases ions uptake and consequently improves nutrition value.

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