B. Chakraborty

Axial magnetic field generation by ponderomotive force in a laser‐produced plasma

Axial magnetic field generation in a plasma due to ponderomotive action of an obliquely incident spatially inhomogeneous laser beam is discussed. The theoretical analysis shows that the field can be excited by the collisional as well as the noncollisional processes via ponderomotive action. The collisional contribution, estimated to be in the range of kilogauss, is dominant for lower intensity (I) and shorter wavelength (λ) lasers and scales as λ−2 for both the s‐ and p‐polarized beams. The noncollisional process can excite the field to 0.5–0.6 MG for a p‐polarized intense and longer wavelength laser beam which scales as I4/3λ14/3. Faraday rotation is estimated theoretically to highlight the significance of ponderomotive effect in generating the axial field. Finally, implications of the model are discussed along with its limitations in the context of laser–plasma experiments.

Wave-precession and related nonlinear effects in plasmas

Abstract We present here an overview of the important classical results on the nonlinearly induced wave-precession effect and the complementary nonlinear effect of shift in a wave parameter in cold plasmas including the relativistic corrections. The relativistic Vlasov plasma equations have been considered for a frequency shift of a strong plane polarized wave. The report is somewhat detailed and systematic. Emphasis is placed on an exposition of the differential methods which can be developed for the evaluation of these processes in plasmas described either by a reduced form of the Maxwell-Lorentz equations of electrodynamics or in the Vlasov plasma limit. For the sake of completeness of the presentation, a brief discussion is also provided on (1) these effects in other media, (2) some relevant elementary topics and (3) some other related effects. This effort is expected t enlarge the scope of future research on, and to provide an integrated picture of, various types of self-rotation induced effects in plasmas and other media.

Scaling laws for a self-generated axial magnetic field in laser-produced plasma

The generation of an axial magnetic field caused by the interaction of standing waves formed by two counterpropagating, elliptically polarized electromagnetic waves with a laser‐produced plasma has been investigated. Study of the variation of magnetization with different powers and wavelengths available from Nd–glass and CO2 lasers shows that induced axial magnetization increases linearly with an increase in power for all wavelengths and increases exponentially with the wavelengths for different laser powers at a particular plasma density. The variation of magnetization with plasma density reveals that the peak value of magnetization occurs below the critical density (nc) for a particular wavelength and power. Scaling laws for the induced axial magnetic field have been given. The poloidal fields arising from such mechanisms are important in the lateral energy and axial energy transport mechanisms. Such a field inhibits lateral energy transport, but axial energy propagation may be increased.

Intense magnetization generated by standing waves in a plasma

Nonlinear increments of displacements of electrons in a cold unmagnetized electron plasma due to two strong elliptically polarized electromagnetic waves have been studied. These results have been used to find the induced magnetization due to standing waves formed by the two counterpropagating elliptically polarized electromagnetic waves. The induced magnetization has been found to be strong enough for interest in the investigation of laser‐plasma interaction. For an Nd‐glass laser (λ=1.06 μm, power flux∼1016 W/cm2) interacting with a plasma (N∼1017/cm3), the induced magnetic field is found to be in the megagauss region. The principal effect of the high magnetic field is on the electron thermal conduction. The heat transport is inhibited due to the generated field.

Induced magnetization of Alfven waves

Abstract The induced magnetization of propagating and standing Alfven waves (IMPAW and IMSAW, respectively) in plasmas, due to the inverse Faraday effect, is investigated here. This effect follows from the magnetic moment per unit volume of the ordered motion of charges of both sign, in presence of an electromagnetic wave propagating parallel to an ambient magnetic field in the low frequency limit. Both IMPAW and IMSAW are found to be inversely proportional to the cube of the ambient field. These are expected to be significant in the study of physics of the sun and other stars, including pulsars, and in the programmes of RF heating of plasmas of tokamaks and other laboratory devices.

Physics in rotating frames. I. On uniform rotation about a fixed axis in some holonomic and anholonomic frames

Abstract The principle of equivalence of general theory of relativity provides the possibility of studying rotation at uniform rates about a fixed axis with the help of transformation from an inertial laboratory frame to frames having such rotation. Several metrices of such axial rotation, all of which are permitted by the principle of equivalence, have been enlisted and briefly discussed in the paper. Also enlisted are metrices for some types of screw rotation. Anholonomic differentials for relativistic rotation have also been studied with the help of the theory of exterior differential forms for anholonomic objects, and the theory of local inertial orthonormal tetrads for the same rotation.

Precessional rotation and other nonlinear effects due to standing waves and other two‐wave resonant interactions in a magnetized plasma

When two electromagnetic waves propagate along the fixed direction of an uniform and constant magnetic field in a homogeneous, cold, and collisionally damped plasma, the effects of their nonlinear interaction are large and so important in two special cases. One is the case in which the beat frequency equals the characteristic plasma frequency and moreover, one of the wave frequencies equals the gyration frequency of electrons (or ions). The other is the nonlinear evolution of the wave pattern formed by an appropriate superposition of the two waves in a manner which produces standing waves from them in the linear approximation. These two cases have been theoretically investigated in this paper. Moreover, the nonlinear evolution of the standing‐wave patterns has been discussed with a view to initiate the exploration of the application side of this effect.

Radiative cooling instabilities in the low dense plasma corona of laser‐irradiated solid targets

Plasma jets produced from targets with atomic numbers ranging from 5 to 82 have been investigated in detail. Theoretical modeling based on a radiative cooling instability has been used to successfully explain the experimental results. Optical shadowgrams and x‐ray pinhole pictures strongly indicate a correlation between the jets and x‐ray emission from plasma. Plasma jets are intense in materials such as copper, molybdenum, tungsten, and gold which are characterized by strong x‐ray emission. Interferograms indicate a large increase in electron density in the region of plasma jets.

A theory for Landau damping of ion acoustic waves in dope plasma

Landau damping, free from the influence of other forms of damping, has been experimentally detected in ion acoustic waves in traces of a dope plasma of a light inert gas, when it is introduced into partially ionized plasma of a heavy inert gas. A theory has been worked out of Landau damping for longitudinal waves in Vlasov plasma for study of this and other familiar Landau dampings.

Faraday rotation of spontaneous magnetization in a laser‐produced plasma from solid target

Interaction of elliptically polarized laser radiation with plasma produced from a solid target generates magnetic fields simultaneously along axial and transverse directions. The axial magnetic field induces the plane of polarization of the incident laser beam to rotate due to the Faraday effect. Numerically the Faraday rotation has been calculated for interaction of Nd glass laser (λ=1.06 μm) in the subdense plasma in which the plasma density, temperature, and self‐generated magnetic field vary in the axial direction.