Use is made of the Vlasov–Maxwell equations to derive an eigenvalue equation describing the extraordinary–mode stability properties of relativistic, non-neutral electron flow in high-voltage diodes. The analysis is based on well-established theoretical techniques developed in basic studies of the kinetic equilibrium and stability properties of nonneutral plasmas characterized by intense self fields. The formal eigenvalue equation is derived for extraordinary-mode flute perturbations in a planar diode. As a specific example, perturbations are considered about the choice of self-consistent Vlasov equilibrium , where . is the electron density at the cathode (x = 0), H is the energy, and Py is the canonical momentum in the Y-direction (the direction of the equilibrium electron flow). As a limiting case, the planar eigenvalue equation is further simplified for low-frequency long-wavelength perturbations with |ω − kvd, ≪ ωυ where and and ⋯c = eB0/mc, and B0ệz is the applied magnetic field in the vacuum region xb < x ≤ d. Here, the outer edge of the electron layer is located at x = xb; ω is complex oscillation frequency; k is the wavenumber in the y-direction; ωυ is the characteristic betatron frequency for oscillations in the x′-orbit about the equilibrium value x′ = x0 = xb/2; and Vd is the average electron flow velocity in the y-direction at x = x0. In simplifying the orbit integrals, a model is adopted in which the eigenfunction approximated by , where x′(t′) is the x′-orbit in the equilibrium field configuration. A detailed analysis of the resulting eigenvalue equation for , derived for low-frequency long-wavelength perturbations, is the subject of a companion paper.

The evolution of the spot size and amplitude of a circularly polarized laser beam propagating in a plasma channel embedded in an obliquely applied magnetic field has been investigated. The wave equation describing the evolution of the radiation field is set up and a variational technique is used to obtain the equations governing the evolution of the spot size and amplitude. Numerical methods are used to analyze the evolution of the laser beam spot size and amplitude. It is seen that the amplitudes of the two transverse components of the electric field of the laser beam evolve differently, since they are driven by unequal current densities. This leads to the conversion of a circularly polarized laser beam into an elliptically polarized beam, under appropriate conditions.

An experimental investigation on X-ray emission from laser-produced plasmas is presented and the properties of such an emission of interest for application purposes are examined. Plasmas were generated by focusing 1 μm, 3 ns Nd laser pulses onto Al and Cu targets at an intensity of 1013 W/cm2. The temporal evolution of the emission and its spectral features were investigated by using an X-ray streak-camera and an X-ray photodiode. In the case of Cu targets, the analysis of the emission showed two spectral components. The main component was centered at ≈ 1.2 keV and a minor component, whose intensity was measured to be 10-3 of the previous component, was observed at ≈7 keV. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu targets and 0.3% for Al targets.

An atomic model of the laser-produced Al plasma has been developed and used to analyze excitation processes of recombination pumping soft X-ray lasers. A soft X-ray gain for H-like Balmer-α line and He-like 3d-2p transition in short-pulse intense KrF laser (IL = 1014–1015 W/cm2, T = 10–100 ps)-produced Al plasmas are calculated for various laser temporal pulse shapes to find the condition for efficient production of population inversion. Results from different models are compared and requirements for the atomic model for X-ray laser design are discussed.

This paper presents cross-sections and collision strengths for proton-impact excitation of optically forbidden transitions in Al10+. These data, calculated in the impact-parameter formalism, covering the expected range of energies/temperature in laser-produced plasmas, are believed to represent the first such detailed treatment of this system. The cross-sections decrease with energy as E−1, while the collision strengths tend to finite limits as the energy of colliding proton becomes infinitely great. This high-energy limiting value has been evaluated combining results from the semi-classical treatment of ion-impact excitation processes and the Born approximation for high-energy behavior of the collision strength. The effective target size has been estimated from the calculated high-energy limit of the collision strength in the Born approximation.

An infrared laser propagating through a semiconductor waveguide, embedded with a density ripple of wave number q, resonantly excites third harmonic radiation. The phase matching is achieved when q equals difference between third harmonic wave number and three times the wave number of the laser. The excited third harmonic is in higher order radial Eigen mode than the pump laser. The third harmonic efficiency increases with electron concentration and decreases with the frequency of the laser.

To diagnose the implosion of a laser-driven-fusion target such as the symmetry, the hydrodynamic instability at the interface, a high-resolution, large field-of-view kilo-electron-volt X-ray imaging is required. A Kirkpatrick-Baez (K-B) microscope is commonly used, but its field of view is limited to a few hundred microns as the resolution decreases rapidly with the increase of the field of view. A higher resolution could be realized by using a Fresnel zone plate (FZP) for imaging. Presented in this work is a numerical study on the imaging properties of an FZP at Ti-Kα wavelength of 0.275 nm, and a comparison to a K-B imager. It is found that the FZP can realize not only a resolution better than 1 µm, but also a field-of-view larger than 20 mm when the FZP is illuminated by X-rays of spectral bandwidth less than 1.75%. These results indicate the feasibility of applying the FZP in high-resolution, large field-of-view X-ray imaging.

The facilities and activities of inertial confinement fusion research in Japan are reviewed. The key institute is ILE Osaka University where the implosion scheme of the “Cannonball Target” has been investigated in experiments and computer simulations to overcome the critical issues in inertial confinement fusion.

Electromagnetic emission at the plasma frequency ωp and its harmonics nωp has been studied. Although such emission is well known from very low density plasmas (electron density of the order of ne ≈ 108 cm−3) now, for the first time it has also been observed from a high density plasma (electron density of the order of ne ≈ 1023 cm−3) produced by a high-intensity femtosecond laser pulse. This radiation is strongly connected to jets of high energy electrons produced in such steep gradient plasmas by collective mechanisms, and probably to nonlinear Langmuir waves in the overdense plasma region. Theoretical investigations using particle-in-cell simulations have been made to pinpoint the physical origin and properties of the emission. Preliminary results show a very weak scaling of the ωp and 2ωp emission with intensity, which should provide clues for future theoretical analyses. Although not the main subject of the present work, also harmonics up to the 20th of the laser fundamental may have been observed close to the ωp and 2ωp line emission in the present experiment (PACS numbers: 52.40.Nk, 42.65.ky, 52.65.-y, 33.20.Ni, 52.25.Qt).

The heating of the titanium foil in a recent femtosecond laser plasma experiment is investigated theoretically in two different ways. In the first, the energy content and thus the heating efficiency of the central volume of the foil is derived by integrating the transverse temperature profiles obtained in this experiment, using specific heats based on the average atom model. In the second approach target heating by the fast electrons, both by direct energy deposition and by resistive heating is investigated. The latter approach makes use of a specially devised electron flow model which includes a simplified quantitative treatment of multi-refluxing as a crucial component. In all, the calculated results of electron beam heating are consistent with experiment within the limitations of the modeling. Finally, a prediction for the temporal dependence of the Kα pulse from the central volume of the foil based on our electron flow model is given.

We present a numerical study of the stabilization process for a fully correlated two-electron model atom in an intense laser pulse. A comparison with calculations for a “real” 3D He atom is also done. We concentrate on the very high frequency regime, where the photon energy exceeds the ionization energy of both electrons, outer and inner. Our results show that when correlation effects are included the ionization probability (IP) is enhanced. Nevertheless, we still observe a decreasing IP within a certain intensity domain. The results from the fully correlated simulations are compared with those from simpler, approximate models. The full numerical treatment for the He atom is not yet possible. We therefore present results obtained with “single active electron” approximation and time-dependent density functional theory. Our numerical simulations can be useful for the future understanding of the stabilization phenomenon for more-than-one electron atoms.

Numerical simulation of active media nuclear-pumped lasers on noble gases and their mixtures with metal vapors are presented. Prospects of creation of high-power short-wavelength nuclear-pumped excimer lasers are discussed.

In an earlier preliminary design study, we proposed a novel nuclear-pumped laser-driven (NPL) inertial confinement fusion (ICF) power reactor that represents an important variation on the “neutron feedback” concept for ICF. This NPL-driven ICF concept also included an advanced, DT-seeded, D3He-fueled pellet and magnetic protection of the first wall of the reactor chamber. Advantages that were demonstrated for this approach included increased efficiency for laser-to-target energy coupling, increased efficiency for thermalto-electric energy conversion, and reduced neutron activation and waste. The coupling efficiency is enhanced because a nuclear-pumped flashlamp is directly pumped by fission fragments from uranium micropellets within the lamp medium. The thermal conversion efficiency is greater because a large fraction of the ICF pellet&s fusion yield is in charged Finally, the fraction of the fusion yield carried by neutrons is significantly reduced in comparison with pure D-T-fueled pellets; thus, neutron-induced activity in the first wall is decreased and safety is increased. The initial study indicated these factors could result in a required driver energy of 5 MJ (vice 10 MJ currently projected) and a pellet gain of only 50 (vice 100 currently projected) for a feasible l,000-MWe power reactor operating with approximately six pellets per second. The current study includes a refined analysis of an NPL-driven ICF power reactor of this type. A cylindrical design for the fission/NPL blanket is selected as a “natural” geometry for pumping the NPL. Required enrichments and criticalities are then predicted for the multiplication of the fusion neutron yield needed to pump the NPL. Based upon these results, we report a more detailed parametric study of the efficiencies for converting neutron, X-ray, and plasma yields from advanced ICF pellets into electrical and optical energy flows required in this concept. We also examined breeding tritium in a lithium blanket layer. Results from these studies help define topics and parameter spaces for further research on this unique reactor concept.

For ultrafast material analyses, we constructed the time-resolved X-ray diffraction system utilizing ultrashort X-rays from laser-produced plasma generated by the 12-TW–50-fs laser at the Nuclear Engineering Research Laboratory. Ultrafast transient changes in laser-irradiated GaAs crystals were observed as X-ray diffraction patterns. Experimental results were compared with numerical analyses.

Based on the path encoding pulse compression teleology, a novel method for obtaining high-power microwave (HPM) pulse with ultrahigh repetition frequency is proposed in this paper. The mechanism of the path encoding pulse compression teleology is first introduced. And then, the obtained HPM pulse is analyzed. Theoretical analysis shows that the peak power of MW level and the repetition frequency of MHz level for the generated HPM pulse can be easily reached. To demonstrate the effectiveness of this method for obtaining HPM pulse with ultrahigh repetition frequency characteristic, a HPM-obtaining experiment was carried out based on an S-band microwave source. The HPM pulses with the width of 1 ns, 2 ns, and 3 ns are studied, respectively. The measured results show that the HPM pulse with the power higher than 100 kW and the repetition frequency of 250 kHz at the frequency of 2.856 GHz is easily obtained. The repetition frequency of the generated HPM pulse can be easily changed. Because the pulse with the power higher than 100 kW and the repetition frequency of several hundreds of kHz is obtained for the first time, this type of pulse will have a broad prospect of application in the communication, radar, and electronic countermeasure fields. In addition, the effect experiment of interfering communication and control links was carried out by utilizing the ultrahigh repetition frequency characteristic of the generated HPM pulse. Also, the experiment results show the feasibility of this pulse for interfering the communication and control links.

Energy loss of protons with 90 and 100 keV energies penetrating through a hydrogen plasma target has been measured, where the electron density of the plasma is about 1016 cm−3 and the electron temperature is about 1-2 eV. It is found that the energy loss of protons in the plasma is obviously larger than that in cold gas and the experimental results based on the Bethe model calculations can be demonstrated by the variation of effective charge of protons in the hydrogen plasma. The effective charge remains 1 for 100 keV protons, while the value for 90 keV protons decreases to be about 0.92. Moreover, two empirical formulae are employed to extract the effective charge.

Volume 23, Number 1, Pages 55–59, 2005

Below is the complete Reference citation for Neumayer et al. (2005).

Neumayer, P., Bock, R., Borneis, S., Brambrink, E., Brand, H., Caird, J., Campbell, E.M., Gaul, E., Goette, S., Haefner, C., Hahn, T., Heuck, H.M., Hoffmann, D.H.H., Javorkova, D., Kluge, H.-J., Kuehl, Th., Kunzer, S., Merz, T., Onkels, E., Perry, M.D., Reemts, D., Roth, M., Samek, S., Schaumann, G., Schrader, F., Seelig, W., Tauschwitz, A., Thiel, R., Ursescu, D., Wiewior, P., Wittrock, U. & Zielbauer, B. (2005). Status of PHELIX laser and first experiments. Laser Part. Beams23, 87–93.

Electron plasma waves excited and/or modified by finite objects such as laser and charged particle pulses are investigated nonperturbatively using a simple model where the driver is unaffected by the interaction. It is shown that smooth as well as sharply peaked electron plasma wake waves of large amplitude can exist. In particular, two charged pulses moving in tandem can excite a highly localized electron plasma wave without producing the expected long wake wave, a configuration that should be particularly useful for efficient trapping and acceleration of electrons to high energies.

We report on multiphoton ionization experiments using picosecond (ps) and sub-ps UV-laser radiation at focused intensities up to 1018 W/cm2. The experiments are concerned with determining the electron temperature of optically ionized gases produced by intense KrF lasers. Thomson scattering, stimulated Raman scattering (SRS), and X-ray emission measurements have been made and compared with modeling calculations of heating. A particular objective is to identify the respective roles of above-threshold ionization, nonlinear inverse bremsstrahlung absorption, and SRS in determining the temperature of the electrons. Results for 350-fs pulses are compared with previous measurements for 12-ps pulses (for which strikingly different behavior is observed). The importance of using subps, short-wavelength lasers to minimize electron temperature is confirmed.

The possibility of an X-ray laser by irradiation of muon beams on a thin rod of deuterium-tritium mixture is discussed. The excited state of dtμ-mesomolecules (J, v) = (1, 0) can be induced to make radiative chain transitions with photon energy of 90 eV to the ground state (0, 0), evacuated by fusion.