Lasing without inversion and electromagnetically induced transparency under electron cyclotron resonance conditions

Parametric effects of lasing without inversion and electromagnetically induced transparency in classical systems are considered. The characteristic features of the effect of lasing without inversion in ensembles of classical electrons are analyzed using an “inversionless” cyclotron maser as an example. A theory of the effect of electromagnetically induced transparency is developed for electron cyclotron waves in a high-temperature plasma. Possible applications of these two effects in plasma physics and microwave electronics are discussed.     

Quasilinear modification of the spectra of cyclotron emission from a toroidal plasma near the ECRH frequency

A study is made of the modification of the spectra of electron cyclotron emission from an ECR heated plasma in a toroidal magnetic confinement system into which the heating radiation is launched from the low-field side. It is shown that, at frequencies close to the heating frequency, cyclotron emission can become more intense because of the deformation of the distribution function of the resonant electrons. This effect can be used to diagnose the slightly pronounced quasilinear perturbations of the electron distribution in the thermal energy range, which are typical of experiments on ECR plasma heating. Results of a qualitative analysis carried out for model electron distribution functions are presented, and examples of three-dimensional numerical simulations of a circular tokamak are described.     

Multimode parametric instability during electron cyclotron heating

A study is made of the generation of electron Bernstein waves in the interaction of a microwave field with a magnetized plasma during electron cyclotron heating. Parametric resonance accompanied by simultaneous conversion of microwave-field energy into the energy of numerous waves is analyzed. The relevant dispersion relation is investigated using the Hill method, which has recently been applied for the first time to examine the parametric interaction between high-power microwave radiation and plasmas. It is shown that the dispersion relation can be used to describe the onset of modulational instability at multimode parametric resonance. The growth rate of the modulational instability is obtained. Efficient energy transfer from the microwave field into Bernstein modes and, accordingly, into plasma electrons may be one of the main mechanisms for electron cyclotron resonance plasma heating.     

Modeling of Coulomb collisions in a kinetic description of the electron cyclotron resonance plasma heating

The electron distribution function is modeled numerically with allowance for Coulomb collisions and quasilinear effects under cyclotron resonance conditions by solving a two-dimensional kinetic equation containing the quasilinear diffusion operator and the Coulomb collision operator in the Landau form. Two simplified model collision integrals that make it possible to describe electron heating by microwave radiation are considered. The first model collision operator is obtained by introducing the parametric time dependence of the temperature of the background Maxwellian electrons into the linear collision integral. It is shown that the heating of the bulk electrons can be described in a noncontradictory way if the temperature dynamics of the background electrons is calculated from the equation of energy balance, which is governed by the amount of the microwave power absorbed by the resonant electrons with the distribution function modified due to quasilinear effects. This conclusion is confirmed in a more rigorous fashion by comparing the solutions obtained using the first model Coulomb collision integral with those obtained using the second model integral, namely, the nonlinear operator derived by averaging the distribution function of the scattering electrons over pitch angles. The time-dependent linear collision integral is used to obtain analytic solutions describing quasi-steady electron heating with allowance for the quasilinear degradation of microwave power absorption.     

Ray trajectories near the electron cyclotron resonance surface in an axisymmetric magnetic trap

Characteristic features of the propagation of electromagnetic electron cyclotron waves in the vicinity of the electron cyclotron resonance surface are investigated both analytically and numerically with allowance for variation in the magnetic field strength and a corresponding variation in the magnetic field direction. It is demonstrated that variation in the magnetic field direction can qualitatively change the wave propagation pattern and can markedly affect the efficiency of electron cyclotron resonance plasma heating in an axisymmetric magnetic trap.     

On the feasibility of electron cyclotron heating of overcritical plasma in a magnetic mirror trap

The feasibility of matching electromagnetic radiation in the electron cyclotron frequency range to a dense plasma in an open magnetic trap by producing an inverted (with a minimum on the axis) plasma density profile is discussed. The use of such a profile shows promise for the implementation of efficient cyclotron heating at plasma densities above the critical density, at which the Langmuir frequency is equal to the heating radiation frequency. Examples of the magnetic field and plasma density distributions in a mirror trap are presented for which analysis of the beam trajectories shows the feasibility of efficient electron cyclotron absorption of microwave beams in overcritical plasma.     

Magnetosonic oscillations of thin plasma columns

Oscillations of a plasma column in a longitudinal magnetic field are considered. It is found that eigenmodes with frequencies close to the ion cyclotron frequency can be excited in columns the radii of which are smaller than the characteristic wavelength of magnetosonic oscillations predicted by the theory of homogeneous plasma. The eigenmodes have the form of waves running around the column axis in the direction of electron gyration in the magnetic field. Magnetosonic oscillations can be excited as a side effect when using helical antennas for ion cyclotron resonance heating of plasma. These oscillations should enhance electron heating in the plasma core, as well as both electron and ion heating at the periphery of the plasma column. The spectrum of eigenmodes of inhomogeneous plasma columns includes oscillations of different nature. Comparative analysis of their properties performed in the present paper is useful for understanding the full picture of the physical processes occurring during ion cyclotron resonance heating and clarifying the characteristic features of the magnetosonic oscillations under study.     

Influence of the plasma density and heating power on the intensity of electron cyclotron emission in the L-2M stellarator

Results are presented from experiments on studying the plasma behavior in the L-2M stellarator in regimes with a high power deposition in electrons during electron cyclotron heating at the second harmonic of the electron gyrofrequency (X mode) at heating powers of P _in=120–400 kW and average plasma densities from n _e≤3×10¹⁹ to 0.3×10¹⁹ m^?3. It is shown that, as the plasma density decreases and the heating power increases, the electron cyclotron emission spectrum is modified; this may be attributed to a deviation of the electron energy distribution from a Maxwellian and the generation of suprathermal electrons. At low plasma densities, the emission intensity at the second harmonic of the electron gyrofrequency increases, whereas the plasma energy measured by diamagnetic diagnostics does not increase. This poses the question of the correctness of determining the plasma electron temperature by electron cyclotron emission diagnostics under these conditions.     

Generation of large-scale structures by strong drift turbulence

The previously existing quasilinear theory of the generation of a large-scale radial electric field by small-scale drift turbulence in a plasma is generalized for the case of strong turbulence which is usually observed in experiments. The geostrophic equation (i.e., the reduced Charney-Hasegawa-Mima equation) is used to construct a systematic theory in the two-scale direct interaction approximation. It is shown that, as in the quasilinear case, drift turbulence results in a turbulent viscosity effect and leads to the renormalization of the Poisson bracket in the Charney-Hasegawa-Mima equation. It is found that, for strong drift turbulence, the viscosity coefficient is represented as a sum of two parts, which are comparable in magnitude. As in quasilinear theory, the first part is determined by the second-order correlation functions of the turbulent field and is always negative. The second part is proportional to the third-order correlation functions, and the sign of its contribution to the turbulent viscosity coefficient depends strongly on the turbulence spectrum. The turbulent viscosity coefficient is calculated numerically for the Kolmogorov spectra, which characterize the inertial interval of the drift turbulence.     

Idaten is a new cold-inducible transposon of Volvox carteri that can be used for tagging developmentally important genes

A cold-inducible transposon called Jordan has previously been used to tag and recover genes controlling key aspects of Volvox development, including the process called inversion. In a search for additional genes, we isolated 17 new inversionless mutants from cultures grown at 24 degrees (the temperature that activates Jordan transposition). These mutants were stable at 32 degrees, but generated revertants at 24 degrees . DNA blots revealed that one mutant had a transposon unrelated to Jordan inserted in invA ("inversionless A"). This new transposon, which we named Idaten, has terminal inverted repeats (TIRs) beginning with CCCTA, and upon insertion it creates a 3-bp target-site duplication. It appears to belong to the CACTA superfamily of class II DNA transposons, which includes En/Spm. No significant open reading frames were in the Idaten sequence, but we retrieved another element with Idaten-type TIRs encoding a protein similar to the En/Spm transposase as a candidate for an Idaten-specific transposase. We found that in five of the new inversionless strains we could not find any Jordan insertions causing the phenotype to possess insertions of an Idaten family member in a single locus (invC). This clearly indicates that Idaten is a potentially powerful alternative to Jordan for tagging developmentally important genes in Volvox.     

Waveguide regime of cyclotron maser instability in plasma regions of depressed density

The generation of auroral kilometric radiation from the Earth is studied in a waveguide model that describes the development of cyclotron maser instability in plasma regions of depressed density that have a finite length in one of the directions perpendicular to the magnetic field. A general dispersion relation for waves propagating in an arbitrary direction is derived. Numerical solutions to the dispersion relation show that the instability growth rate increases with wave vector component directed along a tangent to the source boundary in a plane perpendicular to the magnetic field. Waveguide eigenmodes are constructed, and it is shown that, in the general case, the electromagnetic field in the source has an asymmetric structure, the ratio of the electric field components in the source depends on the coordinates, and the electric field component transverse to the source boundary can substantially exceed the component parallel to the boundary. The results obtained are discussed from the standpoint of comparing them with satellite observational data.     

Self-consistent modeling of radio-frequency plasma generation in stellarators

A self-consistent model of radio-frequency (RF) plasma generation in stellarators in the ion cyclotron frequency range is described. The model includes equations for the particle and energy balance and boundary conditions for Maxwell’s equations. The equation of charged particle balance takes into account the influx of particles due to ionization and their loss via diffusion and convection. The equation of electron energy balance takes into account the RF heating power source, as well as energy losses due to the excitation and electron-impact ionization of gas atoms, energy exchange via Coulomb collisions, and plasma heat conduction. The deposited RF power is calculated by solving the boundary problem for Maxwell’s equations. When describing the dissipation of the energy of the RF field, collisional absorption and Landau damping are taken into account. At each time step, Maxwell’s equations are solved for the current profiles of the plasma density and plasma temperature. The calculations are performed for a cylindrical plasma. The plasma is assumed to be axisymmetric and homogeneous along the plasma column. The system of balance equations is solved using the Crank-Nicholson scheme. Maxwell’s equations are solved in a one-dimensional approximation by using the Fourier transformation along the azimuthal and longitudinal coordinates. Results of simulations of RF plasma generation in the Uragan-2M stellarator by using a frame antenna operating at frequencies lower than the ion cyclotron frequency are presented. The calculations show that the slow wave generated by the antenna is efficiently absorbed at the periphery of the plasma column, due to which only a small fraction of the input power reaches the confinement region. As a result, the temperature on the axis of the plasma column remains low, whereas at the periphery it is substantially higher. This leads to strong absorption of the RF field at the periphery via the Landau mechanism.     

Electron cyclotron resonance acceleration of electrons to relativistic energies by a microwave field in a mirror trap

Results are presented from experiments on the acceleration of electrons by a 2.45-GHz microwave field in an adiabatic mirror trap under electron cyclotron resonance conditions, the electric and wave vectors of the wave being orthogonal to the trap axis. At a microwave electric field of ≥10 V/cm and air pressures of 10^?6–10^?4 Torr (the experiments were also performed with helium and argon), a self-sustained discharge was initiated in which a fraction of plasma electrons were accelerated to energies of 0.3–0.5 MeV. After the onset of instability, the acceleration terminated; the plasma decayed; and the accelerated electrons escaped toward the chamber wall, causing the generation of X-ray emission. Estimates show that electrons can be accelerated to the above energies only in the regime of self-phased interaction with the microwave field, provided that the electrons with a relativistically increased mass penetrate into the region with a higher magnetic field. It is shown that the negative-mass instability also can contribute to electron acceleration. The dynamic friction of the fast electrons by neutral particles in the drift space between the resonance zones does not suppress electron acceleration, so the electrons pass into a runaway regime. Since the air molecules excited by relativistic runaway electrons radiate primarily in the red spectral region, this experiment can be considered as a model of high-altitude atmospheric discharges, known as “red sprites.”     

Nonlocal weakly relativistic permittivity tensor of magnetized plasma near electron cyclotron resonances

Compact expressions are derived for the nonlocal permittivity tensor of weakly relativistic plasma in a 2D nonuniform magnetic field near the resonances at the second harmonic of the electron cyclotron frequency for an extraordinary wave and at the first harmonic for an ordinary wave. It is shown that the wave equation with allowance for the obtained thermal correction to the permittivity tensor in the form of a differential operator in transverse (with respect to the external magnetic field) coordinates possesses an integral in the form of the energy conservation law.     

Quasilinear relaxation of a low-density electron beam in a plasma

The quasilinear relaxation of a low-density electron beam under the action of plasma turbulence, which is generated during the development of a beam instability, when the beam is formed due to rapid local electron heating (acceleration) is analyzed in the one-dimensional approximation. It is shown that quasilinear diffusion results in the formation of a local plateau at the top of the electron distribution function without causing any significant spread in velocities of the beam electrons and that the relaxation process proceeds primarily through the spatial expansion of electrons with different velocities.     

Electron cyclotron resonance plasma heating in the CERA-RX facility under a randomly pulsating electric field

The results of the numerical simulation of the electron cyclotron resonance (ECR) heating of plasma particles in the CERA-RX facility under a randomly pulsating electric field (the collective effects taken into account) are presented. Under these conditions, the electron energy spectrum was found to be depleted to the low energy region due to an increase in the number of particles in the high energy region. The obtained effect depends on the polarity of the pulsating electric field.     

Effect of the dipole-dipole interaction of particles in an active medium on the character of superradiation

The motion of a system of interacting nonlinear charged oscillators is investigated numerically. Because of nonlinearity, the total collective electric field gives rise to a phasing effect—correlations in the phases of the oscillators. The consequence is superradiation—the enhanced spontaneous short-term emission of the energy stored in the oscillators. It is shown that the oscillations of the oscillators become stochastic because of the dipole-dipole interaction between them and their nearest neighbors. As a result, as the density of the oscillators increases, distant collective correlations are suppressed, superradiation ceases to be generated, and radiation is shielded in the medium. The phenomena considered in the present paper can play an important role in cyclotron emission from a plasma and thus should be taken into account in emission calculations. The process whereby the energy of the transverse electron motion in electron cooling devices decreases is analyzed as an example. This process occurs as a result of the development of cyclotron maser instability and has the nature of superradiation. The onset of correlations between individual electrons moving in their Larmor circles is the initial, linear stage of instability developing in the plasma. Superradiation is the final, nonlinear instability stage.     

Single minimum-<Emphasis Type="Italic">B</Emphasis> ambipolar trap

A new type of ambipolar trap is proposed, where a minimum-B magnetic field is used to confine the particles radially and to provide plasma macroscopic stability. The particles are confined axially by creating the plug potentials at both end-mirror cells of the ambipolar trap. The plug potential is produced by only electron cyclotron resonance heating, the mechanism of which is proposed.     

Ray trajectories and electron cyclotron absorption in an axisymmetric magnetic confinement system

The propagation and cyclotron absorption of electromagnetic waves lauched into an axisymmetric magnetic confinement system in a quasi-longitudinal direction is studied in the geometrical-optics approximation. Cyclotron absorption in a dense plasma is described by solving an approximate dispersion relation that is valid for small angles between the magnetic field B and the wave vector k. This approach makes it possible to avoid the difficulty associated with a transition from large propagation angles to the case of strictly longitudinal propagation. It is shown that electron cyclotron absorption can be efficient only when the plasma density is below the critical density. The numerical results obtained for the device for producing multicharged ions in experiments at the Institute of Applied Physics of the Russian Academy of Sciences agree qualitatively with the experimental data.     

Broadband Wide-Angle Second Harmonic Generation in Magnetized Plasma: Double Resonant Effect

Conditions for the phase synchronism between high-frequency electromagnetic waves with frequencies ω and 2ω propagating in magnetized plasma are investigated. The variety of the values of the plasma density and magnetic field, as well as of wave polarizations, obeying the synchronism conditions are shown to provide resonant broadband wide-angle nonlinear generation of the second harmonic of the pumping wave. Special attention is given to oblique propagation of interacting waves. The coupling strengths for the resonant mode conversion in magnetized collisional plasma are obtained. The double resonance ensuring efficient nonlinear generation of extraordinary mode in the vicinity of the electron cyclotron resonance (ω(2k) = ω _ce ) is considered. Examples illustrating these nonlinear phenomena for some plasma and radiation parameters are presented.