1,609 research outputs found
Generation of high-energy monoenergetic heavy ion beams by radiation pressure acceleration of ultra-intense laser pulses
A novel radiation pressure acceleration (RPA) regime of heavy ion beams from
laser-irradiated ultrathin foils is proposed by self-consistently taking into
account the ionization dynamics. In this regime, the laser intensity is
required to match with the large ionization energy gap when the successive
ionization of high-Z atoms passing the noble gas configurations [such as
removing an electron from the helium-like charge state to
]. While the target ions in the laser wing region are ionized
to low charge states and undergo rapid dispersions due to instabilities, a
self-organized, stable RPA of highly-charged heavy ion beam near the laser axis
is achieved. It is also found that a large supplement of electrons produced
from ionization helps preserving stable acceleration. Two-dimensional
particle-in-cell simulations show that a monoenergetic beam
with peak energy and energy spread of is obtained by
lasers at intensity .Comment: 5 pages, 4 figure
Numerical investigation of radiative optically-dense transient magnetized reactive transport phenomena with cross diffusion, dissipation and wall mass flux effects
High temperature electromagnetic materials fabrication systems in chemical engineering require ever more sophisticated theoretical and computational models for describing multiple, simultaneous thermophysical effects. Motivated by this application, the present article addresses transient magnetohydrodynamic heat and mass transfer in chemically-reacting fluid flow from an impulsively-started vertical perforated sheet. Thermal radiation flux, internal heat generation (heat source), Joule magnetic heating (Ohmic dissipation), thermo-diffusive and diffuso-thermal (i.e. cross-diffusion) effects and also viscous dissipation are incorporated in the mathematical model. To facilitate numerical solutions of the coupled, nonlinear boundary value problem, non-similar transformations are employed and the partial differential conservation equations are normalized into a dimensionless system of momentum, energy and concentration equations with associated boundary thermal conditions. An implicit finite difference method (FDM) is utilized to solve the unsteady equations. Verification of the FDM solutions for dimensionless velocity, temperature and concentration functions is achieved with a variational finite element method code (MAGNETO-FEM) and also a network simulation method code (MAG-PSPICE). The influence of the emerging thermo-physical parameters on transient velocity, temperature, concentration, wall shear stress, Nusselt number and Sherwood number is elaborated. The flow is accelerated with increasing thermal radiative flux, Eckert number, heat generation and Soret number whereas the flow is decelerated with greater wall suction, heat absorption, magnetic field and Prandtl number. Temperatures are also observed to be elevated with magnetic parameter, radiation heat transfer, Dufour number, heat generation (source) and Eckert number with the contrary effects computed for increasing suction parameter or Prandtl number. The species concentration is enhanced with Soret number and generative chemical reaction whereas it is depressed with greater wall suction, Schimidt number and destructive chemical reaction paramete
ADM solution for Cu/CuO –water viscoplastic nanofluid transient slip flow from a porous stretching sheet with entropy generation, convective wall temperature and radiative effects
A mathematical modelis presented for entropy generation in transient hydromagnetic flow of an electroconductive
magnetic Casson (non-Newtonian) nanofluid over a porous stretching sheet in a permeable medium. The
Cattaneo-Christov heat flux model is employed to simulate non-Fourier (thermal relaxation) effects. A Rosseland
flux model is implemented to model radiative heat transfer. The Darcy model is employed for the porous media
bulk drag effect. Momentum slip is also included to simulate non-adherence of the nanofluid at the wall. The
transformed, dimensionless governing equations and boundary conditions (featuring velocity slip and convective
temperature) characterizing the flow are solved with the Adomian Decomposition Method (ADM). Bejan’s
entropy minimization generation method is employed. Cu-water and CuO-water nanofluids are considered.
Extensive visualization of velocity, temperature and entropy generation number profiles is presented for variation
in magnetic field parameter, unsteadiness parameter, Casson parameter, nanofluid volume fraction, permeability
parameter, suction/injection parameter, radiative parameter, Biot number, relaxation time parameter, velocity slip
parameter, Brinkman number (dissipation parameter), temperature ratio and Prandtl number. The evolution of
skin friction and local Nusselt number (wall heat transfer rate) are also studied. The ADM computations are
validated with simpler models from the literature. The solutions show that with elevation in volume fraction of
nanoparticle and Brinkman number, the entropy generation magnitudes are increased. An increase in Darcy
number also increases the skin friction and local Nusselt number. Increasing magnetic field, volume fraction,
unsteadiness, thermal radiation, velocity slip, Casson parameters, Darcy and Biot numbers are all observed to
boost temperatures. However, temperatures are reduced with increasing non-Fourier (thermal relaxation)
parameter. Greater flow acceleration is achieved for CuO-water nanofluid compared with Cu-water nanofluid
although the contrary response is computed in temperature distributions. The simulations are relevant to the high
temperature manufacturing fluid dynamics of magnetic nanoliquids, smart coating systems etc
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Laser-driven acceleration of quasi-monoenergetic, near-collimated titanium ions via a transparency-enhanced acceleration scheme
Laser-driven ion acceleration has been an active research area in the past two decades with the prospects of designing novel and compact ion accelerators. Many potential applications in science and industry require high-quality, energetic ion beams with low divergence and narrow energy spread. Intense laser ion acceleration research strives to meet these challenges and may provide high charge state beams, with some successes for carbon and lighter ions. Here we demonstrate the generation of well collimated, quasi-monoenergetic titanium ions with energies ∼145 and 180 MeV in experiments using the high-contrast(<10-9) and high-intensity (6× 1020 W cm-2) Trident laser and ultra-Thin (∼100 nm) titanium foil targets. Numerical simulations show that the foils become transparent to the laser pulses, undergoing relativistically induced transparency (RIT), resulting in a two-stage acceleration process which lasts until ∼2 ps after the onset of RIT. Such long acceleration time in the self-generated electric fields in the expanding plasma enables the formation of the quasi-monoenergetic peaks. This work contributes to the better understanding of the acceleration of heavier ions in the RIT regime, towards the development of next generation laser-based ion accelerators for various applications
Lattice Discretization in Quantum Scattering
The utility of lattice discretization technique is demonstrated for solving
nonrelativistic quantum scattering problems and specially for the treatment of
ultraviolet divergences in these problems with some potentials singular at the
origin in two and three space dimensions. This shows that lattice
discretization technique could be a useful tool for the numerical solution of
scattering problems in general. The approach is illustrated in the case of the
Dirac delta function potential.Comment: 9 page
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