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Bibcode : PhRvL.. Malcolm Haines' paper" PDF. Retrieved 7 April National Research Council U. Panel on Opportunities in Plasma Science and Technology. Washington, D. Bibcode : SchpJ Plasma-The Fourth State of Matter 3rd ed. Fundamentals of Plasma Physics. Archived from the original on 2 February Elert, Glenn ed.
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Physics of Magnetic Flux Ropes : — Retrieved on Is it a Liquid, Solid, or Gas? Retrieved 21 January Bulletin of the American Astronomical Society. Bibcode : BAAS Geophysical Research Letters. Bibcode : GeoRL.. Journal of Geophysical Research. Bibcode : JGRA.. The Astrophysical Journal. Bibcode : ApJ Archived from the original on 5 October Retrieved 26 January Chinese Astronomy and Astrophysics.
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Rheology Viscoelasticity Rheometry Rheometer. Electrorheological Magnetorheological Ferrofluids. High voltages may lead to electrical breakdown, as can lower pressures in fluorescent lights and neon signs. Very high For many purposes the electric field in a plasma may be treated as zero, although when current flows the voltage drop, though small, is finite, and density gradients are usually associated with an electric field according to the Boltzmann relation.
Any electric currents in the plasma "couple" ie. Collective phenomena are common because the electric and magnetic forces are both long-range and potentially many orders of magnitude stronger than gravitational forces. One All gas particles behave in a similar way, influenced by gravity , and collisions with one another. Two or three Electrons, ions, and neutrals can be distinguished by the sign of their charge so that they behave independently in many circumstances, having different velocities or even different temperatures, leading to phenomenon such as new types of waves and instabilities.
Maxwellian The velocity distribution of all gas particles has a characteristic shape:. Above mA, the measured quasi-directional electron flux averaged over electron energy and As This conclusion is supported by concurrent observations of the radar backscatter and intense very high frequency VHF radioemission from the near-rocket region at frequencies greatly exceeding the plasma frequency of the ambient plasma Mishin and Ruzhin, b ; Dokukin et al.
Figure 7 illustrates the evolution of the VHF spectrum with the injection height and pitch angle during 0. In Zarnitza 2, a broadband continuous spectrum of beam-induced VHF electromagnetic waves was detected by a ground-based radio spectrograph with a 27—51 MHz bandwidth Dokukin et al. It is seen in Figures 7A,B that the radioemission appears during each 0. This modulation is due to the variation of the injection pitch angle cf.
Figures 5B,C and also clearly depends on the spin phase. The radio burst near 50 MHz of a 5—10 MHz width at the beginning of the injection pulse is a rapid drift from lower to higher frequencies within the spectrograph sweeping time of 20 ms. Figure 7. Adapted from Dokukin et al. After Mishin and Ruzhin b. After transition to the second regime and until the plasma generator was turned on, f max is approximated as follows. As shown in Figure 7B , the spectrum has maxima buldges centered at half-integral harmonics of the electron gyrofrequency, f ce , i. At the same time, the VHF radar data show radioemission at the radar frequency of One can see the time delay of a few milliseconds with respect to the start of 20 ms pulses.
Besides the enhanced number of suprathermal electrons in the NRG, strong scattering of beam electrons occurs in the vicinity of a beam-emitting payload Hendrickson et al. Clearly, above km the scattered flux is almost independent of the neutral density, while the SPA predicts the decrease by a factor of By the same token, the Polar 5 data reveal Maehlum et al. Figure 8. After Grandal a and Arnoldy et al.
In summary, the observed near-rocket glow, suprathermal electrons, VHF radioemission, and prompt electron echoes, as well as the fine altitudinal structure of AA rays, point to much stronger interaction of injected electrons with the upper atmosphere than provided by electron collisions. Next, a brief survey is presented of the theory of collisionless beam-plasma interaction BPI resulting in the beam-plasma discharge BPD near beam-emitting payloads and the double-peak structure of artificial and natural aurora rays. Conventionally e. Charged particles in motion generate electromagnetic fields that affect motion of other particles, thereby making a fast remote response to local perturbations.
A symbiotic relationship between plasma particles and fields results in a wide variety of collective motions, i. It is worth noting that in the magnetospheric community such waves, routinely observed in the plasma sheet region associated with diffuse aurora e. It is instructive to recall the well-known wave-particle quantum-mechanical analogy e. That is, the wave vector changes in such a way that the frequency is preserved. Evidently, the cavity plays a role of the potential hole for plasmons that are trapped inside if the Hamiltonian is negative, i. Thus, only a small group of fast particles can be in resonance with the waves, i.
It is instructive to give an example of the resonance wave-particle interaction in isotropic plasmas. Linearizing in the wave field yields the quiver velocity.
The particles exchange energy with the wave. It is negative in a Maxwellian plasma, so the waves are damped. This resonance, collisionless damping is named the Landau damping. In a magnetoactive plasma, oblique waves are subjected to the cyclotron damping as well. In non-equilibrium plasma, the population of fast particles can dominate in a certain velocity domain so that waves in resonance with these particles will gain energy and grow. This process inverse Landau or cyclotron damping is called plasma instability.
In a steady state, the dissipation rate is determined by the energy flux balance. It can be estimated from Equation 16 as follows. Disregarding wave-wave interactions and using the statistical description of waves with random phases, results in the quasilinear approximation Vedenov et al. It is valid only for very tenuous beams irrelevant to our problem.
The next step in w is taking account of the induced scattering, in which electrons interact with beats of different randomly-phased modes e.
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This weak turbulence WT approximation is valid until the beam density exceeds. Galeev, ; Papadopoulos, ; Galeev et al. Then, the beam relaxation is described in terms of strong Langmuir turbulence SLT. As a result, initial modulations grow with time. As trapping inside a cavity leads to strong correlation of the wave phases, such that the WT condition of random phases e.
Cavities with trapped strongly-correlated Langmuir oscillations are termed cavitons and subjected to collapse Zakharov, Their evolution depends on the dimension, d , and can be understood from simple arguments e. The wavelengths of the trapped plasmons are also of the order of l , i. In two three dimensions, the speed of collapse persists accelerates with time. The basic signatures of the SLT development in various beam-plasma systems have been observed in laboratory experiments e. However, as follows from eq. Applying a similar procedure to the electromagnetic version of the Zakharov equation e.
The SLT acceleration of suprathermal tail electrons is, probably, the most important consequence of the BPI for artificial and natural aurora.
Their distribution function along the magnetic field can be found from the kinetic equation. Figure 9 illustrates the wave spectrum and electron distribution in the developed strong Langmuir turbulence. Figure 9. Cartoon depicting the wave spectrum and electron distribution in the developed strong Langmuir turbulence. The blue and red solid lines indicate the bulk and accelerated tail populations, respectively. After Shapiro and Shevchenko Reprinted by permission from Plenum Press.
A remark is in order. Figure 6B. It seems relevant to briefly discuss the SLT acceleration of suprathermal electrons producing artificial aurora and ionization in active space experiments with high-power radio waves Mishin and Pedersen, ; Eliasson et al. Here Langmuir waves are parametrically driven by ordinary O pump waves near the reflection altitude, h 0 , where the pump frequency, f o , matches the local plasma frequency, f pe h 0 the interested reader is referred to Streltsov et al.
Figure 10 exemplifies the results of the Eliasson et al. The simulation details are given in Eliasson et al. Figure Adapted from Eliasson et al. Reprinted by permission from the American Geophysical Union. Omitting the features of their spatial distribution related to the radio wave propagation, we point out that in 1—2 ms the initial Airy structure starts breaking into small-scale turbulence.
In saturation, solitary wave packets in the SLT region are trapped in density cavitons. It is seen that the SLT region of the altitudinal extent, l LT , is sandwiched between the WT regions with turbulent electric fields but without cavitons. This explains the differences in the patches layers of artificial plasma descending from the initial interaction altitude at various input parameters shown in Figure 10e.
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The downward propagation of the artificial plasma produced by the accelerated electron tail is due to the fact that the electrons propagating along the geomagnetic field create the new plasma resonance condition for the incident radio wave below the initial resonance. This way, an ionizing wavefront created by the SLT-accelerated electrons is formed Mishin and Pedersen, ; Eliasson et al.
Furthermore, the presence of the ambient suprathermal population photoelectrons facilitates the SLT acceleration Mishin et al. The consequences of the photoelectrons in the sunlit ionosphere are the decreased threshold, the greater downward speeds, and the decay of the persistent artificial ionization at the terminal altitude after sunlit-to-dark transition.
Balancing the heating rate 27 by inelastic losses gives. Figure 11 illustrates a scenario Mishin et al. The lower peak q i o n c is caused by the collisional ionization of neutral gas by the primary beam electrons, while the upper layer, i. For a few keV beams, both peaks will overlap, so that the observer would see only one thick layer with a sharp upper boundary.
Schematic representation of the Plasma Turbulence Layer PTL indicated by the black rectangle and a double-peaked ionization profile. The dotted curve presents the collisional SPA ionization profile, q i o n c. The dashed curve shows the electron temperature profile of the heated plasma. The solid curves show the altitudinal profiles of the wave energy density, W , and ionization rate of the accelerated electrons, q i o n t. The dashed horizaontal line indicates the PTL upper boundary.
After Mishin Reprinted by permission from the American Institute of Physics. This scenario agrees well with the altitude profile of artificial auroral rays far from the beam-emitting rocket Figure 4 and natural auroral rays section 6. So far our consideration was limited to collisionless interaction of a warm, tenuous bump-in-tail beam pertinent to natural and artificial auroral rays. With regards to the near-rocket plasma, this approximation becomes applicable after the plasma density significantly increases over the background in the beam-plasma discharge, which is described below.
It has long been known that injection of powerful electron beams in neutral gas may result in the avalanche-like ionization accompanied by strong plasma oscillations e. As any discharge, BPD develops under certain breakdown conditions that can be readily obtained in a simplified form. The Townsend criterion requires that an electron must acquire enough energy to produce at least one ionizating impact before disappearing from the gap due to recombination and diffusion. In the BPD, the pump waves are generated via the beam instability. Therefore, the first step is to find the critical beam density, n b c r , necessary for the instability to develop.
The former considers the beam ralaxation to find the input parameters, i. Then, the energization heating and acceleration of plasma electrons with subsequent ionization is calculated. The solution of the first part critically depends on the plasma density and temperature that vary during the breakdown. This yields the criterion for a self-sustained discharge. A finite cross-section of injected beams reduces the growth rate but not quenches the instability e.
Following Alekhin et al. Therefore, the beam expands radially due to electrostatic repulsion. Winckler, , Figure 2. A helical structure rapidly transforms into a pencil-like cf. Using a hollow-cylinder beam does not change the basic results concerning the instability development. This agrees with the laboratory e. The wave growth slows down when the beam electrons become trapped by the wave potential and change the relative phase bouncing back and forth in the potential hole.
Since the wave frequency exceeds the cyclotron frequency, the trapped beam electrons are unmagnetized and pulled by the wave across the magnetic field, ultimately filling the void in the center and expanding over the beam gyroradius. This is consistent with the data concerning the beam structure Bernstein et al. Substituting E 0 t r 41 into v E 10 , yields. It is worth noting that the fast heating was observed in the Bauer et al. High electron temperatures in the near zone were reported by Gringauz et al.
It is worth noting that Vlasenko et al. A few remarks are in order. Numerical simulations Khazanov et al. Thus far, only perpendicular diffusion was considered. Such behavior is typical of laboratory experiments with intense cold beams e. Actually, that can happen even earlier due to radial diffusion of beam electrons scattered off persisting short-scale oscillations at the rate 45 , which is indicated by the prompt electron echo section 3.
There are the principal differences between the stationary and initial BPD regimes. Next, in addition to ionization by the heated thermal plasma electrons, accelerated suprathermal electrons can contribute significantly to the BPD ignition when strong Langmuir turbulence determines the beam relaxation Mishin and Ruzhin, a , ; Rowland et al. As the neutral density in the NRG region varies during the flight, the beam relaxation regime changes accordingly. The ionization by the thermal bulk electrons is determined by a Maxwellian tail, i. However, the main contribution comes from suprathermal electrons The lower BPD boundary is determined by the neutral density, N max , at which collisional damping inhibits the development of the cold-beam instability Mishin and Ruzhin, a ; Dokukin et al.
These results pertain to the beam instability. Here, the strong electron heating is the main contributor to the BPD development. Ashour-Abdalla and Kennel, ; Ashour-Abdalla et al. Figure 12 illustrates the BPD regimes vs. A The different stationary BPD regimes vs. Adapted from Mishin and Ruzhin a. B Altitude and neutral density range over which BPD is expected. The first stripped column indicates the range expected from Mishin and Ruzhin's analysis.
The second stripped column indicates the parameter range over which BPD has been observed in the large tank at the Jonson Space Center. Adapted from Linson Finally, using the heated bulk and accelerated tail electrons it is easy to show that the total power of optical emissions radiated from the NRG is of the order of a few per cent of the beam power Ivchenko et al. The power of VHF radioemission estimated assuming conversion of Langmuir waves on density oscillations inherent in unstable beam-plasma systems also reaches a few percent of the beam power Galeev et al. The distribution of precipitating electrons, F b v , varies significantly in time and space creating various auroral forms with latitudinal scale lengths from tens of kilometers down to hundred meters e.
Some of the measured distributions of auroral electrons do exhibit the bump-in-the-tail feature. Its origin is beyond the scope of this survey. Figure 13 exemplifies auroral beam and suprathermal electron spectra observed over auroral arcs e. These beam parameters easily suffice the BPI conditions described in sections 4.
Therefore, the beam relaxation can be described by the BPI theory outlined there. This explains why the bump-in-tail distributions, such as in Figures 13A,B , are preserved along the path Galeev, ; Papadopoulos, Dots and circles show the observed fluxes, while dashed and solid lines show B a Gaussian approximation and C power-law trends. Adapted from A Arnoldy et al. B Bryant et al. The overall observations show that the spectrum of suprathermal electrons over arcs is not formed solely on account of the collisional interaction but can be explained in terms of the SLT acceleration Papadopoulos and Coffey, ; Galeev, ; Matthews et al.
It is worth to note that recent incoherent scatter radar observations Isham et al. However, Donahue et al. Similarly, ground-based optical imagers detected either double-peaked auroral rays of about the same thickness, displaced in altitude by about 5—15 km, or one thick layer with the sharp upper boundary below about km, with the characteristic scale length of only a fraction of H N Oguti, ; Stenbaek-Nielsen and Hallinan, ; Dzyubenko et al. There were efforts to explain such double-peak profiles by the collisional interaction invoking two precipitating electron populations, i.
However, these efforts failed to fit the upper peak and sharp upper boundary. Figures 14A,B shows double-peaked auroral rays observed near Tixie Bay by a side-looking low-light TV camera, the same as used in Zarnitza 2, and their luminosity profiles Dzyubenko et al. The upper peaks are by a factor of two narrower than the minimum possible from the SPA, while the lower peak matches the SPA predictions cf. Shown below Figure 14C is an example of a rayed arc with the sharp upper boundary Hallinan et al.
A Auroral rays along the magnetic field indicated by the arrow and B their luminosity profiles. Adapted from Dzyubenko et al. C A rayed arc with the sharp upper boundary. After Hallinan et al. One sample is shown in Figures 15A,B , where the thin layers in T e and n e are emphasized by thick lines. A similar double-peaked ionization profile Figure 15C was observed in pulsating aurora Wahlund et al. As for auroral rays, the difference with the SPA profile for the upper peak is evident.
Thin layers of the A elevated electron temperature and B electron density indicated by thick lines after Schlesier et al. After Wahlund et al. A striking resemblance between the Enhanced and Artificial Aurora Figure 4 profiles is evident. Given that the parameters of electron beams far beneath the rocket are close to that of natural beams, it is safe to conclude that their generation mechanisms have much in common.
It is obvious that the sought-for mechanism is the one that creates the plasma turbulence layer. The effects of powerful electron beams injected from sounding rockets into the upper atmosphere to create artificial aurora are outlined. The overall dataset cannot be explained solely by collisional degradation of energetic electrons but demands collisionless beam-plasma interactions BPI be taken into account. A brief survey of the BPI theory in a weakly-ionized plasma is presented. The basic processes of the near-rocket region are described in terms of the beam-plasma discharge BPD ignited by plasma electrons energized by the beam-excited plasma turbulence.
Depending on the ambient plasma and atmospheric densities, there are several regimes of the BPD development. The observations of artificial auroral rays far beneath the rocket indicate that turbulence regime and thus the relaxation of radially expanded beams are strongly affected by collisions of plasma electrons. As a result, the energy density of plasma waves and concomitant energization of plasma electrons are enhanced in a narrow layer termed the plasma turbulence layer PTL.