[en] Three-dimensional numerical simulations of a scroll expander were performed with dynamic mesh technology. R245fa was selected as the working fluid in the simulations. The PISO algorithm was applied to solve the governing equations with RNG k-ε turbulent model. The distribution and variation of three-dimensional flow field inside the scroll expander were obtained. The research indicates that the flow field is nonuniform and asymmetrical distributions exist inside the expander. Vortex flows also exist in some working chambers. Dynamic clearance leakage flows and inlet orifice throttling have great effects on the flow field distribution. Transient output torque and the mass flux have periodic fluctuations during the working cycles

[en] Deuteron acceleration from CH/CD/CH layer targets irradiated with PW laser pulses has been studied using. Thomson parabola spectrometers and neutron TOF spectroscopy. The measured ion and neutron spectra reveal significant MeV deuteron acceleration from the deeply buried CD layer, which scales with the thickness of the overlying CH layer. While the neutron spectra reveal the scaling of the thermal heating with target thickness, the ion spectra indicate the presence of an efficient nonthermal acceleration mechanism inside. the bulk. Possible explanations will be discussed. (Author)

[en] The measurement of angularly resolved energy distributions of MeV electrons is vital for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma, especially for fast-ignition laser-fusion research. It is also important when evaluating the production of suprathermal (several 10-keV) electrons through laser-plasma instabilities in conventional hot-spot-ignition and shock-ignition research. For these purposes, we developed a ten-inch manipulator-based multichannel electron spectrometer — the Osaka University electron spectrometer (OU-ESM) — that combines angular resolution with high-energy resolution. The OU-ESM consists of five small electron spectrometers set at every 5°, with an energy range from ~40 keV to ~40 MeV. A low-magnetic-field option provides a higher spectral resolution for an energy range of up to ~5 MeV. We successfully gained angularly resolved electron spectra for various experiments on the OMEGA and OMEGA EP Laser Systems.

[en] Neutron time of flight signals have been observed with a high resolution neutron spectrometer using the Peta Watt arm of the Vulcan laser facility at Rutherford Appleton Laboratory from plastic sandwich targets containing a deuterated layer. The neutron spectra have two elements: a high-energy component generated by beam-fusion reactions and a component around 2.45 MeV, most likely to be thermonuclear in origin. The ion temperatures calculated from the neutron signal width clearly demonstrate a dependence on the front layer thickness and are significantly higher than electron temperatures measured under similar conditions. the ion heating process is intensity dependent and is not observed with laser intensities on target below 10''20 W cm''-2. It is shown that process is also strongly dependent upon the intensity prepulse level. The measurements are consistent with a coupled two-step plasma instability process that cascades the laser energy directly to the ions. The implications for fast ignition will be discussed. (Author)

[en] Fully relativistic collisional Particle-in-Cell (PIC) code, PICLS, has been developed to study extreme energy density conditions produced in intense laser-solid interaction. Recent extensions to PICLS, such as the implementation of dynamic ionization, binary collisions in a partially ionized plasma, and radiative losses, enhance the efficacy of simulating intense laser plasma interaction and subsequent energy transport in resistive media. Different ionization models are introduced and benchmarked against each other to check the suitability of the model. The atomic physics models are critical to determine the energy deposition and transport in dense plasmas, especially when they consist of high Z (atomic number) materials. Finally we demonstrate the electron transport simulations to show the importance of target material on fast electron dynamics

[en] Fast electron generation in the presence of coronal plasma in front of a solid target (typically referred to as preformed plasma) in laser-matter interaction in the intensity range of 10¹⁹-10²¹ W/cm² is studied in a one-dimensional slab approximation with particle-in-cell (PIC) simulations. Three different preformed plasma density scale lengths of 1, 5, and 15 μm are considered. We report an increase in both mean and maximum energy of generated fast electrons with an increase in the preformed plasma scale length (in the range 1-15 μm). The heating of plasma electrons is predominantly due to their stochastic motion in counterpropagating electromagnetic (EM) waves (incident and reflected waves) and the presence of a longitudinal electric field produced self-consistently inside the preformed plasma. The synergetic effects of this longitudinal electric field and EM waves responsible for the efficient preformed plasma electrons heating are discussed.

[en] Results of numerical modeling of the experiment carried out to investigate the effect of long scale pre-plasma on fast electron transport are presented. A peculiar ring-like structure in Cu K_α x-ray emission was seen experimentally when a short pulse laser (intensity ∼3 x 10¹⁸ W cm^-2) interacted with a long scale pre-plasma. The long scale pre-plasma, produced by irradiation of a long pulse laser on a flat target having copper fluorescence layer sandwiched between aluminum layers, is modeled with the radiation hydrodynamic code, h2d. Fast electron transport modeling performed with the hybrid particle-in-cell code, LSP, suggests that the ring structure is due to the refluxing of low energy (∼50 keV) fast electrons traveling in the pre-formed plasma back to the solid target. Modeling shows that the excitation of strong electrostatic fields near the transverse plasma boundary is responsible for this refluxing. Details of the modeling along with the exact mechanism of formation of ring-like K_α x-ray emission are discussed.

[en] Transport of intense proton beams in solid-density matter is numerically investigated using an implicit hybrid particle-in-cell code. Both collective effects and stopping for individual beam particles are included through the electromagnetic fields solver and stopping power calculations utilizing the varying local target conditions, allowing self-consistent transport studies. Two target heating mechanisms, the beam energy deposition and Ohmic heating driven by the return current, are compared. The dependences of proton beam transport in solid targets on the beam parameters are systematically analyzed, i.e., simulations with various beam intensities, pulse durations, kinetic energies, and energy distributions are compared. The proton beam deposition profile and ultimate target temperature show strong dependence on intensity and pulse duration. A strong magnetic field is generated from a proton beam with high density and tight beam radius, resulting in focusing of the beam and localized heating of the target up to hundreds of eV.

No abstract available

[en] Relativistic electron transport in short-pulse laser illuminated nail-wire and foil targets has been studied with the e-PLAS implicit/hybrid plasma simulation code in a cylindrical geometry. The intensities are typical of the Vulcan and Titan petawatt lasers (1.06 μm, 1.7x10²⁰ W/cm²) in 10 μm diameter Gaussian spots, producing hot electrons at a relativistic γ = 3.4 according to Beg scaling, and with 20% absorption assumed. The targets are 200 μm long nail-headed copper wires 20 μm in diameter, and copper foils 120 μm thick. The code dumps energy at constant intensity for a picosecond at the critical surface into an isotropic relativistic Maxwellian particle-in-cell hot electron distribution. The emitted hot particles draw a cold electron return current scattering off the background ions taken as ionized at a fixed Z = 15. Transport of the hot electrons is impeded by the electric field from a Spitzer resistivity acting on the cold electron return current. Assumed emission angle is shown to seriously affect hot e^- penetration in the wires.