Ultrafast laser-driven x-ray spectrometer for x-ray absorption spectroscopy of transition metal complexes

We report what are to our knowledge the first measurements of an x-ray absorption near-edge structure (XANES) spectrum of solvated iron pentacarbonyl by use of an ultrafast laser-driven plasma x-ray source. This source is operating at a 2-kHz repetition rate. Hard x radiation that might falsify the XANES measurements is suppressed by an x-ray optical setup that consists of a fiber-optic lens and a silicon single crystal.     

Demonstration of high-trapping efficiency and narrow energy spread in a laser-driven accelerator

Laser-driven electron accelerators (laser linacs) offer the potential for enabling much more economical and compact devices. However, the development of practical and efficient laser linacs requires accelerating a large ensemble of electrons together ("trapping") while keeping their energy spread small. This has never been realized before for any laser acceleration system. We present here the first demonstration of high-trapping efficiency and narrow energy spread via laser acceleration. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1 sigma) were demonstrated.     

Temperature profile and heat flux inhibition in laser-driven plasmas

It is shown that the nonlinear heat flux calculated by means of the modified moment method applied to the Vlasov-Landau kinetic equation is adequate to account for the heat flux inhibition in laser-driven plasmas, if the nonlinear heat flux so obtained is used in the steady state energy balance equation to calculate the temperature profile self-consistently. Heat flux limit formulas are obtained for supersonic and subsonic fluid speeds. The flux limit factors have an upper bound of 0.14 in the case of the hydrogen plasma. This bound would be reduced, if the temperature at the sonic surface was less than the electron temperature at the critical density surface.     

Demonstration of a transient-gain nickel-like xenon-ion x-ray laser

We demonstrate a high-gain nickel-like xenon-ion x-ray laser, using a picosecond-laser-irradiated gas-puff target. The elongated x-ray laser plasma column was produced by irradiation of the gas-puff target with line-focused double picosecond laser pulses with a total energy of 18 J in a traveling-wave excitation scheme. Strong lasing at 9.98 nm was observed, and a high gain coefficient of 17.4 cm(-1) was measured on the transient collisionally excited 4d-4p , J=0-1 transition for nickel-like xenon ions with target lengths as great as 0.45 cm. A weak nickel-like lasing line at a shorter wavelength of 9.64 nm was also observed, with a gain coefficient of 5.9 cm(-1) .     

Focusing dynamics of high-energy density, laser-driven ion beams

The dynamics of the focusing of laser-driven ion beams produced from concave solid targets was studied. Most of the ion beam energy is observed to converge at the center of the cylindrical targets with a spot diameter of 30 μm, which can be very beneficial for applications requiring high beam energy densities. Also, unbalanced laser irradiation does not compromise the focusability of the beam. However, significant filamentation occurs during the focusing, potentially limiting the localization of the energy deposition region by these beams at focus. These effects could impact the applicability of such high-energy density beams for applications, e.g., in proton-driven fast ignition.     

Mesoscopic charge density wave in a magnetic flux

The stability of a Charge Density Wave (CDW) in a one-dimensional ring pierced by a Aharonov-Bohm flux is studied in a mean-field picture. It is found that the stability depends on the parity of the number N of electrons. When the size of the ring becomes as small as the coherence length , the CDW gap increases for even N and decreases for odd N. Then when N is even, the CDW gap decreases with flux but it increases when N is odd. The variation of the BCS ratio with size and flux is also calculated. We derive the harmonics expansion of the persistent current in a presence of a finite gap. Received: 16 September 1997 / Received in final form: 12 November 1997 / Accepted: 13 November 1997     

Symmetric inertial-confinement-fusion-capsule implosions in a double-z-pinch-driven hohlraum

An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system.     

Angular dependence of the critical current density and the temperature scaling of the flux pinning force in YBCO thin film

In this paper, the critical current J_c(Θ) have been investigated as a function of magnetic-field angle Θ. Θ is the angle between the c-axis and the applied magnetic field direction. This investigation concerned three temperature values (60?K, 78?K and 81?K). The normalized pinning force f_p versus the normalized magnetic field h was also studied (f_p?=?F_p / F_pmax and h?=?H / H_max). The F_p expression was determined based on the Kramer model.The studied sample was a single crystal of YBaCuO thin film deposited by the ablation laser method on the surface (100) of a SrTiO₃ substrate.The results of this work show the existence of point core pinning of the normal centers in the low field regime and the occurrence of the flux creep in high field regime.     

Demonstration of spectrally resolved x-ray scattering in dense plasmas

We present the first spectrally resolved x-ray scattering measurements from solid-density plasmas. The scattering spectra show the broadened Compton down-shifted feature allowing us to determine the electron temperature and density with high accuracy. In the low temperature limit, our data indicate that the ionization balance reflects the electrons in the conduction band consistent with calculations that include quantum mechanical corrections to the interaction potential.     

Temperature dependence of the x-ray and neutron diffraction from a metallic glass

The amorphous alloy Be_0.4Ti_0.5Zr_0.1 has one of the largest negative temperature coefficients of resistivity known in a metallic glass and thus presents a demanding test case for any theory that would explain this phenomenon. By measuring the temperature dependence of the x-ray and neutron diffraction profiles we have attempted to test the extended Ziman theory for the resistivity of amorphous metals. The observed change in the structure factor is large enough to explain the observed resistivity data in terms of this theory.     

Impulse-scaling in a laser-driven in-tube accelerator

The laser-driven in-tube accelerator (LITA) is a unique device for laser propulsion. It is characterized by the acceleration of a projectile in a tube. The thrust performance can be improved by exploiting a confinement effect. In the experiment, a 3.0-g projectile is vertically launched, and the momentum coupling coefficient is measured for various monoatomic gases. The measured coupling coefficient is almost proportional to the reciprocal of the speed of sound. The same impulse generation characteristics are obtained in simplified situations that are analyzed based on conservation relations. Received: 26 August 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-22/217-5284, E-Mail: sasoh@ifs.tohoku.ac.jp RID="**" ID="**"Present address: also at Institute of Advanced Aerospace Technology, Seoul National University, Seoul, 151-742, Korea     

Heat flux and temperature and density profiles in a gas

Summary Starting from Boltzmann's equation, a method is developed for calculating temperature and density profiles and heat flux in a neutral gas in the presence of a temperature gradient and an external force. A generalized barometric law is obtained. The influence of different cross-section models is also investigated. This work was supported in part by MPI (60%) grants of the Italian Ministry of Education.     

Proton radiography of a laser-driven implosion

Protons accelerated by a picosecond laser pulse have been used to radiograph a 500 microm diameter capsule, imploded with 300 J of laser light in 6 symmetrically incident beams of wavelength 1.054 microm and pulse length 1 ns. Point projection proton backlighting was used to characterize the density gradients at discrete times through the implosion. Asymmetries were diagnosed both during the early and stagnation stages of the implosion. Comparison with analytic scattering theory and simple Monte Carlo simulations were consistent with a 3+/-1 g/cm3 core with diameter 85+/-10 microm. Scaling simulations show that protons>50 MeV are required to diagnose asymmetry in ignition scale conditions.     

Factors influencing the density profiles of granular flux in a two-dimensional inclined channel

The two-dimensional dilute granular flow on a smooth incline bounded by rough sidewalls is investigated experimentally, and the transverse density profiles of granular flux (ζ = ρ v) across the channel are measured. The results show that the transverse density profiles of granular flux are symmetric about the channel center and that the density of granular flux near the boundary is clearly lower than that of the center. There is a critical width of channel W _c for the transition of the density of granular flux. The density of granular flux near the boundary decays with the increasing of inclination (sinθ) of the channel. Supported by the National Natural Science Foundation of China (Grant No. 10274071) and the Department of Education of Zhejiang Province (Grant Nos. 20050916 and y200804093)