Amiram Ron

Plasmoid propagation in a transverse magnetic field and in a magnetized plasma

The propagation of plasmoids (neutralized ion beams) in a vacuum transverse‐magnetic field has been studied in the University of California, Irvine laboratory for several years [Phys. Fluids 24, 739 (1981); 25, 730, 2353 (1982); 26, 2276 (1983); J. Appl. Phys. 64, 73 (1988)]. These experiments have confirmed that the plasmoid propagates by the E×B drift in a low beta and high beta plasmoid beam (0.01<β<300), where β is the ratio of beam kinetic energy to magnetic field energy. The polarization electric field E arises from the opposite deflection of the plasmoid ions and electrons, because of the Lorentz force, and allows the plasmoid to propagate undeflected at essentially the initial plasmoid velocity. In these experiments, plasmoids (150 keV, 5 kA, 50–100 A/cm2, 1 μ sec) were injected into transverse fields of Bt=0–400 G. Anomalously fast penetration of the transverse magnetic field has been observed as in the ‘‘Porcupine’’ experiments [J. Geophys. Res. 91, 10,183 (1987)]. The most recent experiments ar...

Propagation of a wide ion beam into a magnetic barrier

A fully relativistic and self‐consistent Vlasov equilibrium model is presented and solved for the general problem of the motion of a neutralized ion beam in a transverse magnetic field. The radius of the beam is taken to be much larger than any characteristic length of the system so that the model is, in effect, one‐dimensional. The beam has density n0 and velocity v0 and enters a vacuous region with an externally applied transverse magnetic field B0. It is found that the distance that the ions penetrate into the barrier is determined primarily by the longitudinal electric field produced by the electrons, so that their penetration length is much less than the ion gyroradius. In the case v20/c2≪m/M−B20/16πn0Mc2 the model equations can be solved analytically. In this case the injected plasma is quasi‐neutral and the ions closely follow the electrons. The penetration length of the plasma is then the geometric mean of the electron and ion gyroradii due to the magnetic field Bc= (B20+16πn0Mv02)1/2. A discussio...

Theory of fluorescence and Raman scattering near resonance

Abstract Using a simple model for a molecular system in a bath, the cross section for Raman scattering around resonance is calculated. Without introducing constant relaxation times at the outset, the calculation yields a sharp coherent term, and a broad “hot” luminescence term. The second term is due to dephasing; its relative strength depends on the incident light frequency, and it disappears away from resonance.

The plasma as a phase conjugate reflector

Plasma is a nonlinear medium and two waves propagating in it interact electromagnetically with each other. If the plasma is pumped by two strong counterstreaming waves of equal frequency, and a third wave enters, the nonlinear interaction generates a fourth wave, phase conjugate to the third wave. This interaction becomes very significant if the frequency and wave vector differences between the third wave and one of the pump waves resonate with the frequency and wave vector of the ion acoustic mode of the plasma. This resonance can be predicted from a fluidlike description of the plasma, but it is shown that the Vlasov description can provide more details of behavior near the resonance. Possible applications of the emergent technology range from improved focusing of radiation in hyperthermia therapy of cancer to the formation of a microwave laser between a phase conjugate plasma reflector and a mirror, for improved radar imaging. Another application is cordless, self‐guiding, power transmission.

EFFECT OF NEUTRAL ATOMS ON A CAPILLARY-DISCHARGE Z PINCH

We study the effect of neutral atoms on the dynamics of a capillary discharge Z-pinch, in a regime for which a large soft-x-ray amplification has been demonstrated. We extended the commonly used one-fluid magneto-hydrodynamics (MHD) model by separating out the neutral atoms as a second fluid. Numerical calculations using this extended model yield new predictions for the dynamics of the pinch collapse, and better agreement with known measured data.

Diffraction Elimination: Dragging Slow-Light with Diffusing Atoms

Images imprinted on a laser pulse can be dramatically slowed when traversing an alkali vapor medium via electromagnetically induced transparency.

Slowing and Storing Images in Atomic Vapor

We study slowing and storage of three-dimensional light fields in atomic vapor. We demonstrate a technique which reduces the effect of diffusion on the storage fidelity and prove that the phase pattern was also maintained.

Coherent Storage of 3D Light Fields in Atomic Vapor

Optical Storage: Temporal storage of optical signals is a needed capability in communications.