Radiation reaction induced spiral attractors in ultra-intense colliding laser beams

The radiation reaction effects on electron dynamics in counter-propagating circularly polarized laser beams are investigated through the linearization theorem and the results are in great agreement with numeric solutions.For the first time,the properties of fixed points in electron phase-space were analyzed with linear stability theory,showing that center nodes will become attractors if the classical radiation reaction is considered.Electron dynamics are significantly affected by the properties of the fixed points and the electron phase-space densities are found to be increasing exponentially near the attractors.The density growth rates are derived theoretically and further verified by particle-in-cell sim-ulations,which can be detected in experiments to explore the effects of radiation reaction qualitatively.The attractor can also facilitate realizing a series of nanometer-scaled flying electron slices via adjusting the colliding laser frequencies.

Casson Nanofluid Flow with Cattaneo-Christov Heat Flux and Chemical Reaction Past a Stretching Sheet in the Presence of Porous Medium

In the current work,inclined magnetic field,thermal radiation,and the Cattaneo-Christov heat flux are taken into account as we analyze the impact of chemical reaction on magneto-hydrodynamic Casson nanofluid flow on a stretching sheet.Modified Buongiorno’s nanofluid model has been used to model the flow governing equations.The stretching surface is embedded in a porousmedium.By using similarity transformations,the nonlinear partial differential equations are transformed into a set of dimensionless ordinary differential equations.The numerical solution of transformed dimensionless equations is achieved by applying the shooting procedure together with Rung-Kutta 4th-order method employing MATLAB.The impact of significant parameters on the velocity profile f(ζ),temperature distributionθ(ζ),concentration profileϕ(ζ),skin friction coefficient(Cf),Nusselt number(Nux)and Sherwood number(Shx)are analyzed and displayed in graphical and tabular formats.With an increase in Casson fluid 0.5<β<2,the motion of the Casson fluid decelerates whereas the temperature profile increases.As the thermal relation factor expands 0.1<γ1<0.4,the temperature reduces,and consequently thermal boundary layer shrinks.Additionally,by raising the level of thermal radiation 1<Rd<7,the temperature profile significantly improves,and an abrupt expansion has also been observed in the associated thermal boundary with raise thermal radiation strength.It was observed that higher permeability 0<K<4 hinders the acceleration of Casson fluid.Higher Brownian motion levels 0.2<Nb<0.6 correspond to lower levels of the Casson fluid concentration profile.Moreover,it is observed that chemical reaction 0.2<γ2<0.5 has an inverse relation with the concentration level of Casson fluid.The current model’s significant uses include heat energy enhancement,petroleum recovery,energy devices,food manufacturing processes,and cooling device adjustment,among others.Furthermore,present outcomes have been found in great agreementwith already publishedwork.

Entropy analysis in electrical magnetohydrodynamic(MHD) flow of nanofluid with effects of thermal radiation,viscous dissipation,and chemical reaction

The unsteady mixed convection flow of electrical conducting nanofluid and heat transfer due to a permeable linear stretching sheet with the combined effects of an electric field, magnetic field, thermal radiation, viscous dissipation, and chemical reaction have been investigated. A similarity transformation is used to transform the constitutive equations into a system of nonlinear ordinary differential equations.The resultant system of equations is then solved numerically using implicit finite difference method.The velocity, temperature, concentration, entropy generation, and Bejan number are obtained with the dependence of different emerging parameters examined. It is noticed that the velocity is more sensible with high values of electric field and diminished with a magnetic field. The radiative heat transfer and viscous dissipation enhance the heat conduction in the system. Moreover, the impact of mixed convection parameter and Buoyancy ratio parameter on Bejan number profile has reverse effects. A chemical reaction reduced the nanoparticle concentration for higher values.

Newtonian Gravitational Radiation and Waves

In this paper, we review historical Maxwell's equation for gravity and recent studies on the lack of curvature of linear dipole gravitational waves. The extended Newton's gravity necessarily has the continuity equation for the conservation of mass, and with the Gauss' equation associated to gravitational time depending field R, bring about a new field W which resembles the magnetic field in Electrodynamics. Although this field has not been found yet, its existence comes from a strong mathematical statement, and it is shown that linear dipole gravitational waves have their origin in extended Newton theory of gravity. This is a direct mathematical consequence of Gauss' law and the continuity equation for the density of mass and current, and as a direct result of this, any accelerated mass will emit mainly dipole gravitational radiation. Then, one concludes that dipole gravitational waves can have its origin on the extended Newton's gravity equations.

Dense pair plasma generation and its modulation dynamics in counter-propagating laser field

With two-dimensional quantum electrodynamics（QED） particle-in-cell simulations, a dense electron-positron（e^-e~＋） pair generation from laser-solid interactions is demonstrated. When the interaction of two linearly polarized laser pulses with a thin target enters into the relativistic transparency regime, a stable standing wave（SW） field can be formed by the overlap of the two counter-propagating laser pulses directly. The present study aims to clarify the effects of the S W field on the dynamics of e^-e^＋ pair plasmas. Our results indicate that under the combined effect of the SW field and radiation reaction（RR） effect, the created e^-e^＋ pairs can be trapped into the electric field nodes when the field strength is strong.The trapping effect contributes to the generation of γAV≥400 and ultra-dense pair plasmas in the two-side irradiation scheme. Despite different laser intensities, these pair plasmas have a Maxwellian spectral distribution with a peak energy of 150 MeV. Besides, the periodical modulation of the average energy, spatial, phase-space, and angular patterns of the e^-e^＋ pair plasmas can be triggered. In the angular patterns, as long as the SW field exists, pair plasmas can be pinched along the laser polarization direction. These results may offer a better understanding of the laser-solid interactions in the experiments when 10-PW laser facilities come into operation in the future.

Spontaneous Emission of an Inertial Multi-Level Atom in a Spacetime with a Reflecting Plane Boundary

We calculate the contributions of the vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy for a multi-level hydrogen atom in the multipolar coupling scheme in a spacetime with a reflecting boundary. Our results show that, due to the presence of the boundary, the polarizations of the atom in the parallel direction and in the normal direction are weighted differently in terms of their contributions to the spontaneous emission rate, which is an oscillating function of the atom distance from the boundary. The possible experimental implications of our result are briefly discussed.

Accelerated Multi-Level Atoms in an Electromagnetic Vacuum and Fulling-Davies-Unruh Effect

We consider, from the point of view of a coaccelerated frame, a uniformly accelerated multi-level atom in interaction with vacuum quantum electromagnetic fields in the multi-polar coupling scheme, and calculate the rate of change of the atom＇s energy assuming a thermal bath at a finite temperature T in the Rindler wedge. Comparison with the spontaneous excitation rate of the atom calculated in the instantaneous inertial frame of the atom shows that both the inertial and coaccelerated observer would agree with each other only when the temperature of the thermal bath equals the FDU value TFDU = α/2π.

Optimization and control of synchrotron emission in ultraintense laser–solid interactions using machine learning – CORRIGENDUM

Due to an isolated error in the 3D simulation parameters,the laser energy and intensity(calculated using the energy)values were incorrectly stated as 10.9 J and 3×10^(22) W cm^(−2),respectively,in Sections 3.3,7 and 8.The correct values are 39.8 J and 1.1×10^(23) W cm^(−2).Similarly,the values stated for the higher energy case,109 J and 3×10^(23) W cm^(−2) in Section 7,should be 398 J and 1.1×10^(24) W cm^(−2),respectively.

IR radiation characteristics of rocket exhaust plumes under varying motor operating conditions

The infrared（IR） irradiance signature from rocket motor exhaust plumes is closely related to motor type,propellant composition,burn time,rocket geometry,chamber parameters and flight conditions.In this paper,an infrared signature analysis tool（IRSAT） was developed to understand the spectral characteristics of exhaust plumes in detail.Through a finite volume technique,flow field properties were obtained through the solution of axisymmetric Navier-Stokes equations with the Reynolds-averaged approach.A refined 13-species,30-reaction chemistry scheme was used for combustion effects and a k-e-Rtturbulence model for entrainment effects.Using flowfield properties as input data,the spectrum was integrated with a line of sight（LOS） method based on a single line group（SLG） model with Curtis-Godson approximation.The model correctly predicted spectral distribution in the wavelengths of 1.50–5.50 lm and had good agreement for its location with imaging spectrometer data.The IRSAT was then applied to discuss the effects of three operating conditions on IR signatures：（a） afterburning;（b） chamber pressure from ignition to cutoff;and（c） minor changes in the ratio of hydroxyl-terminated polybutadiene（HTPB） binder to ammonium perchlorate（AP） oxidizer in propellant.Results show that afterburning effects can increase the size and shape of radiance images with enhancement of radiation intensity up to 40%.Also,the total IR irradiance in different bands can be characterized by a non-dimensional chamber pressure trace in which the maximum discrepancy is less than 13% during ignition and engine cutoff.An increase of chamber pressure can lead to more distinct diamonds,whose distance intervals are extended,and the position of the first diamond moving backwards.In addition,an increase in HTPB/AP causes a significant jump in spectral intensity.The incremental rates of radiance intensity integrated in each band are linear with the increase of HTPB,and the growth rates of radiance intensities in some bands reach up to 50% as HTPB weight increases by 3%.

Optimization and control of synchrotron emission in ultraintense laser–solid interactions using machine learning

The optimum parameters for the generation of synchrotron radiation in ultraintense laser pulse interactions with planar foils are investigated with the application of Bayesian optimization,via Gaussian process regression,to 2D particle-incell simulations.Individual properties of the synchrotron emission,such as the yield,are maximized,and simultaneous mitigation of bremsstrahlung emission is achieved with multi-variate objective functions.The angle-of-incidence of the laser pulse onto the target is shown to strongly influence the synchrotron yield and angular profile,with oblique incidence producing the optimal results.This is further explored in 3D simulations,in which additional control of the spatial profile of synchrotron emission is demonstrated by varying the polarization of the laser light.The results demonstrate the utility of applying a machine learning-based optimization approach and provide new insights into the physics of radiation generation in laser-foil interactions,which will inform the design of experiments in the quantum electrodynamics(QED)-plasma regime.