[en] A model of moving distributed load with a constant speed is established for vertical vibration analysis of a continuous guideway in maglev transportation system. The guideway is considered as a continuous structural system and the action of maglev vehicles on guideways is considered as a moving distributed load. Vibration of the continuous guideways used in Shanghai maglev line is analyzed with this model. The factors that affect the vibration of the guideways, such as speeds, guideway's spans, frequency and damping, are discussed

[en] A stable relativistic ion acceleration regime for thin foils irradiated by circularly polarized laser pulses is suggested. In this regime, the 'light-sail' stage of radiation pressure acceleration for ions is smoothly connected with the initial relativistic 'hole-boring' stage, and a defined relationship between laser intensity I₀, foil density n₀, and thickness l₀ should be satisfied. For foils with a wide range of n₀, the required I₀ and l₀ for the regime are theoretically estimated and verified with the particle-in-cell code ILLUMINATION. It is shown for the first time by 2D simulations that high-density monoenergetic ion beams with energy above GeV/u and divergence of 10 deg. are produced by circularly polarized lasers at intensities of 10²² W/cm², which are within reach of current laser systems

[en] Radiation Pressure Acceleration (RPA) mechanism is currently attracting a substantial amount of experimental and theoretical attention worldwide. Employing the Petawatt laser of the Rutherford Appleton Laboratory, UK, both the Hole-boring (HB) and Light sail (LS) regimes of RPA have been extensively explored by scanning over wide range of laser and target parameters. The dominant role of laser radiation pressure in such intense interaction conditions resulted in narrow band heavy ion spectra, where the ion energy scales with [Iτ/ξ)¹⁵ (I, τ and ξ stand for laser intensity, pulse duration and target areal density respectively] - significantly faster than the competing 'Target Normal Sheath Acceleration' mechanism (E oc I^0.5). The aftermath of RPA is observed in the late time (0.1 -1 ns) evolution of collimated plasma jets ejected from the target rear surface, detected by ps time resolved transverse interferometry. Significant Improvement in spatial uniformity of the plasma jet density profile observed for circularly polarised laser compared to linear, polarisation is a clear indicative of the role played by circular polarisation towards stability of the RPA. (author)

[en] Due to the rapidly increasing demand of electric power, insulating materials used in electrical components are pushed up to their limits, where their electronic properties are of fundamental importance. Electroluminescence provides an elegant way to investigate electronic properties, high field effects and electrical ageing of polymers although the emission spectrum is still poorly understood. Unlike in organic semi-conductors, electroluminescence spectra of large band gap polymers exhibit specific spectral features that cannot be interpreted on the basis of the photo-physical properties of the material. By irradiating polypropylene thin films with electrons up to a few keV and by analyzing the emitted light, we were able to isolate the elementary components of the emission and to reconstruct the electroluminescence spectrum. For the first time, a comprehensive study of electroluminescence in polymers is provided and the underlying mechanisms of the emission are discussed. The results herein provide an univocal demonstration that the electroluminescence from wide band gap polymers results in part from chemical reactions, opening the way to the diagnosis and prognosis of polymeric materials under electrical stress. (paper)

[en] A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4γ_z², where γ_z=(1- v_z²/c²)^-1/2 is the effective Lorentz factor of the electron sheet along its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame n_e/γ, where γ is the full Lorentz factor.

[en] We have demonstrated the promising radiation pressure acceleration (RPA) mechanism of laser-driven ion acceleration at currently achievable laser and target parameters through a large number of two-dimensional particle-in-cell simulations and experiments. High-density monoenergetic ion beams with unprecedented qualities such as narrow-peaked spectrum, lower-divergence and faster energy-scaling are obtained, compared with the conventional target normal sheath acceleration. The key condition for stable RPA from thin foils by intense circularly polarized lasers has been identified, under which the stable RPA regime can be extended from ultrahigh intensities >10²² W cm⁻² to a currently accessible range 10²⁰–10²¹ W cm⁻². The dependences of the RPA mechanism on laser polarization, intensity and on the target composition and areal density have been studied.

[en] Magnetic reconnection (MR) in the high-energy-density (HED) regime is comprehensively investigated by particle-in-cell simulations. In the HED regime, the MR process is driven by two colliding magnetized plasma bubbles produced by intense lasers, where there are ambiguities in distinguishing the actual MR consequences from the pure bubble squeezing effects, because both lead to similar behaviors. After discerning these similarities, such as two-fluid effects, plasma heating and jetting, we establish the direct relevance between the actual consequences of MR with the electron dissipation region, magnetic energy conversion and the relaxation of plasma density gradient. With additional discussions of the 3D effects and relativistic features, the results will guide the future HED experiments for MR and other laboratory astrophysics studies. (paper)

[en] Full text: The demonstration of the efficient energy conversion from laser to electrons then to protons via the Target Normal Sheath Acceleration (TNSA) mechanism on the Nova PW laser experiments [1] has opened a door to new regimes of high energy density sciences with the laser produced high energy proton beams either as heating sources or probes. One of the most important potential applications is to use proton beams as an ignitor [2,3] to initiate fusion spark in the fast ignition (FI) scheme [4] of inertial fusion energy. Large-scale hybrid particle-in-cell (PIC) simulations using the LSP code [5] with self-consistent laser-plasma interaction (LPI) package have been carried out in an integrated fashion for the proton FI scheme. Unlike modeling previously considered [6], the environment has been included; the thin hemispherical target is attached to the inside of a conical structure, which in turn is surrounded by an imploded fuel configuration for the DT plasma. The respective physical processes occurring in the proton FI scheme, including the proton beam source production, focusing and transport of proton beam from the proton source foil into dense plasma, stopping and deposition of the proton beam energy in hot spot of DT fuel, have been analyzed. The energy delivered by the proton beam to the DT fuel will be compared to Atzeni's ignition conditions [7] and to current results on electron-driven fast ignition scheme. This work also has important implication to other applications of laser produced proton beams because the proton beam dynamics during transitions analyzed here — of a high current proton beam transitioning from the source foil into vacuum and further towards the solid (cone tip), — is of critical importance to virtually all uses of proton beams, whether as probes or heaters. References [1] R. A. Snavely et al., Phys. Rev. Lett. 85 (2000) 2945. [2] M. Roth et al., Phys. Rev. Lett. 86 (2001) 436. [3] M. H. Key, Phys. Plasmas 14 (2007) 055502. [4] M. Tabak et al., Phys. Plasmas 1 (1994) 1626. [5] D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. Sect. A 464 (2001) 134. [6] M. Temporal, J. J. Honrubia and S. Atzeni, Phys. Plasmas 9 (2002) 3098. [7] S. Atzeni, Phys. Plasmas 6 (1999) 3316. (author)

[en] A roadmap is proposed for the production of high-energy (>15 MeV) neutrons using short pulse lasers. Different approaches are suggested for the two limiting cases of small (E₁ ≪ Q) and large (E₁ ≫ Q) projectile energies E₁ depending on the Q-value of the nuclear reaction. The neutron fluence from many converter materials is evaluated for two projectiles: protons and deuterons. We found profound differences between proton- and deuteron-driven reactions with regard to both converter material and generated neutron fluence. The optimum converter material for deuteron-driven reactions is low-Z elements such as Li and Be, while for proton-driven reactions the converter material is not critical. For a projectile energy of 50 MeV the deuteron-driven reactions are two orders of magnitude more efficient compared to the proton-driven reactions. Two-dimensional particle-in-cell simulations have been performed for laser pulses with peak intensity 3 × 10²⁰ W cm⁻², pulse duration 40 fs, spot size 5 µm and energy 3 J interacting with ultrathin (0.1 µm) CD foil. The calculated deuteron beam is highly directional along the laser propagation direction with maximum energy of 45 MeV. The interaction of the deuteron beam with a lithium converter and the production of neutrons is modeled using a Monte Carlo code. The computed neutron spectra show that a forward directed neutron beam is generated with an opening angle of ∼1 sr, maximum energy of 60 MeV and a fluence in the forward direction 1.8 × 10⁸ n sr⁻¹, ∼20% of which are with energy above 15 MeV. (paper)

[en] A method to maintain ion stable radiation pressure acceleration (RPA) from laser-irradiated thin foils is proposed, where a series of high-Z nanofilms are placed behind to successively replenish co-moving electrons into the accelerating foil as electron charging stations (ECSs). Such replenishment of co-moving electrons, on the one hand, helps to keep a dynamic balance between the electrostatic pressure in the accelerating slab and the increasing laser radiation pressure with a Gaussian temporal profile at the rising front, i.e. dynamically matching the optimal condition of RPA; on the other hand, it aids in suppressing the foil Coulomb explosion due to loss of electrons induced by transverse instabilities during RPA. Two-dimensional and three-dimensional particle-in-cell simulations show that a monoenergetic Si¹⁴⁺ beam with a peak energy of 3.7 GeV and particle number $4.8\times <!--\; ??\; -->{10}^9$ (charge 11 nC) can be obtained at an intensity of 7 × 10²¹ W cm⁻² and the conversion efficiency from laser to high energy ions is improved significantly by using the ECSs in our scheme. (paper)