N. R. Pereira

Nonlinear Schrödinger equation including growth and damping

The nonlinear Schrodinger equation, with complex coefficients that describe growth and damping, is considered. An exact stationary soliton solution is found for arbitrary growth and damping strength.

Algebraic internal wave solitons and the integrable Calogero–Moser–Sutherland N‐body problem

The Benjamin–Ono equation that describes nonlinear internal waves in a stratified fluid is solved by a pole expansion method. The dynamics of poles which characterize solitons is shown to be identical to the well‐known integrable N‐body problem of Calogero, Moser, and Sutherland.

Internal wave solitons

A numerical solution of the Benjamin–Ono equation for internal waves shows soliton behavior. Two and three Lorentzian solitons pass through one another unscathed. An initial Lorentzian with larger than soliton amplitude decays into solitons, with velocities predicted by the five conservation laws.

Soliton in the damped nonlinear Schrödinger equation

A numerical solution of the damped nonlinear Schrodinger equation is compared to analytical predictions that assume invariance of the soliton shape. The agreement is fair for the damping laws of the form γk∞‖k‖b. Good agreement is found for γk∞k2, and this case is studied analytically including second order effects of the damping.

Nonlinear development of lower hybrid cones

The instability of a planar lower hybrid soliton to transverse long wavelength perturbations is investigated numerically. Initially, a kink‐like deformation grows in agreement with linear analysis. In the nonlinear regime the soliton breaks up into bunches which move apart and spread the energy throughout the plasma.

Differential absorption spectrometer for pulsed bremsstrahlung

We describe a differential absorption spectrometer that measures the energy spectrum (from 20 to 800 keV) of flash x rays whose intensity precludes pulse‐height analysis methods. The spectrometer uses individually calibrated thermoluminescent dosimeters, each inside its own spherical absorber, to accommodate isotropic radiation from pulsed bremsstrahlung sources. An iterative perturbation unfolding code determines the spectrum from the detector responses and the computed energy response functions. Unfolding works best with a good guess for the initial spectrum, and data with less than a few percent error.

Damped double solitons in the nonlinear Schrödinger equation

The nonlinear Schrodinger equation modified by a damping term is investigated numerically for initial conditions other than single solitons. With damping, colliding solitons still pass through each other, but the breather can change qualitatively into two continuously interacting but separated solitons. These results are consistent with a slow change in the inverse scattering eigenvalues due to the damping.

Cauchois–Johansson x-ray spectrograph for 1.5–400 keV energy range

A Cauchois–Johansson optical scheme is proposed, based on a specially designed cylindrical quartz crystal. The corresponding x-ray spectrograph is manufactured, which provides high spectral resolution in transmission and reflection regimes and covers the wide energy range of 1.5–400 keV. The device is calibrated with an x-ray tube and is suggested to be used in high-temperature plasma diagnostics.

The reflex-diode HPM source on Aurora

The most recent in a series of experiments to develop the reflex diode as a source of microwaves on the Aurora relativistic electron-beam pulser is described. An overall output has been achieved for radial extraction of approximately 400 J in microwave bursts from approximately 100 to 150 ns at frequencies below 1 GHz. The diagnostics for radial extraction have included directional couplers, card calorimeters, and free-field sensors. The authors have varied the anode-cathode spacing, downstream microwave reflector, and a second anode foil, but, within the range of variations, no strong trends have been noted. >

K-line spectra from tungsten heated by an intense pulsed electron beam

The plasma-filled rod-pinch diode (PFRP) is an intense source of x-rays ideal for radiography of dense objects. In the PRFP megavoltage electrons from a pulsed discharge concentrate at the pointed end of a 1 mm diameter tapered tungsten rod. Ionization of this plasma might increase the energy of tungstens Kα(1) fluorescence line, at 59.3182 keV, enough for the difference to be observed by a high-resolution Cauchois transmission crystal spectrograph. When the PFRPs intense hard bremsstrahlung is suppressed by the proper shielding, such an instrument gives excellent fluorescence spectra, albeit with as yet insufficient resolution to see any effect of tungstens ionization. Higher resolution is possible with various straightforward upgrades that are feasible thanks to the radiations high intensity.