The imaging spectrograph with spherical crystal and transmission grating have been used to obtain the high spectrally and spatially resolved images of plasma X-ray microsources (fast z-pinch) as well as of laser-produced plasma flares up to 5 mm in extent. The spectral resolution λ/Δλ = 2·104 have been achieved using a quartz spherical mirror with the curvature radius 500 mm. Using a transmission grating spectrometer, the spectral density of power about 105 W/A in the “water window” has been measured in experiments with a fast z-pinch large pulse storage facility.

The electric field in the temporal and spectral domain of coherent diffraction-limited transition radiation is studied. An electron bunch, with arbitrary longitudinal momentum distribution, propagating at normal incidence to a sharp metal-vacuum boundary with finite transverse dimension is considered. A general expression for the spatiotemporal electric field of the transition radiation is derived, and closed-form solutions for several special cases are given. The influence of parameters such as radial boundary size, electron momentum distribution, and angle of observation on the waveform (e.g., radiation pulse length and amplitude) are discussed. For a Gaussian electron bunch, the coherent radiation waveform is shown to have a single-cycle profile. Application to a novel THz source based on a laser-driven accelerator is discussed.

We propose a mechanism of highly focused, tunable and high-intensity terahertz (THz) radiation generation by frequency-mixing of two super-Gaussian lasers with frequencies ω1, ω2 and wave numbers k1, k2 (laser profile index p > 2) in a corrugated plasma in the presence of external static magnetic field ${B_0}\hat z$. In this process, a strong nonlinear ponderomotive force is offered to the plasma electrons at frequency ω′ = ω1 − ω2 and wave number k′ = k1 − k2 by laser beams. The ponderomotive force results in a strong, controllable nonlinear transverse oscillatory current, which can be optimized by optimizing the external magnetic field, ripple parameters, and laser indexes. This controllable current produces focused and intense THz radiation of tunable frequency and power along with a remarkable efficiency ~25%.

Volume 23, Number 1, Pages 47–53, 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.

The electrical behavior of exploding wires was obtained by numerically solving the nonlinear differential equation describing the discharge circuit. For metal wires of high conductivity and low sublimation heat, such as copper, aluminum, gold, and silver, the circuit simulation can be well performed based on the resistivity model developed by Tucker in which the resisitivity is expressed by the explicit functions of specific action, i.e., ρ = f(g). For metals such as titanium and zinc with anomalously changing resistivity, i.e., decreasing rather than increasing with the liquid heating, the circuit simulation of the exploding wires can be performed using the implicit relationship between ρ and g that is read out point by point from the experimentally measured curve. Using the circuit simulation, the rate of the energy deposition in the exploding wires before the explosion can be obtained, which is helpful to choose the right experimental conditions for possible overheating that is desirable for getting smaller nano-powders produced by exploding wires.

Intense and stable laser operation with Ni-like Zr and Ag was demonstrated at pump energies between 2 J and 5 J energy from the PHELIX pre-amplifier section. A novel single mirror focusing scheme for the TCE x-ray laser (XRL) has been successfully implemented by the LIXAM/MBI/GSI collaboration under different pump geometries. This shows potential for an extension to shorter XRL wavelength. Generation of high quality XRL beams for XRL spectroscopy of highly charged ions is an important issue within the scientific program of PHELIX. Long range perspective is the study of nuclear properties of radioactive isotopes within the FAIR project.

We have made the first observation of Kα X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.

Numerical simulations and analyses are given for the implosion of a hollow shell target driven by proton beams. The target consists of three layers of Pb, Al and DT. The Pb and Al layers play roles of a tamper and a pusher, respectively. The main part of the beam energy is deposited in the Al layer. But the process of deposition depends strongly on the distribution of incident angles and particle energies. As the Al layer is heated by proton beams, the layer expands and pushes the DT layer toward the target centre. This type of implosion motion is examined by using a similarity solution for the slab model. To obtain an optimum velocity for the DT implosion, the optimum target size and optimum layer thicknesses are determined. The Rayleigh–Taylor instability, accompanied by the implosion motion is investigated, and the implosion is found to be stable with respect to the chosen target structure. The effects of inhomogeneities on implosion are shown to be severe. The initial fluctuation of the temperature or the density in the Al layer must be less than 3% and the maximum amplitude of the ripples on the initial boundary surface should be less than 3 μm with a view to achieving a high target gain.

The generalized theory of terawatt laser pulse interaction with a low-dense porous substance of light chemical elements including laser light absorption and energy transfer in a wide region of parameter variation is developed on the base of the model of laser-supported hydrothermal wave in a partially homogenized plasma. Laser light absorption, hydrodynamic motion, and electron thermal conductivity are implemented in the hydrodynamic code, according to the degree of laser-driven homogenization of the laser-produced plasma. The results of numerical simulations obtained by using the hydrodynamic code are presented. The features of laser-supported hydrothermal wave in both possible cases of a porous substance with a density smaller and larger than critical plasma density are discussed along with the comparison with the experiments. The results are addressed to the development of design of laser thermonuclear target as well as and powerful neutron and X-ray sources.

In the present investigation, the excitation of an upper hybrid wave (UHW) in a hot collisionless magneto-plasma by a relativistic laser beam propagating perpendicular to the static magnetic field and having its electric vector polarized along the direction of the static magnetic field (ordinary mode) is presented. Due to nonuniform intensity distribution of pump laser, the background electron concentration is modified. The amplitude of the UHW, which depends on the background electron concentration, is thus nonlinearly coupled with the laser beam. The effect of nonlinear coupling between the pump laser and UHW is studied. The effect of the relativistic electron mass nonlinearity and the relativistic self-focusing of the pump laser on the excitation of the UHW have been incorporated. The dynamics of the excitation of the UHW in different power domains of the laser beam is accordingly modified. It has been seen that the effect of changing the strength of the static magnetic field on the nonlinear coupling and the dynamics of the excitation of the UHW is significant. The focusing behavior of the UHW may find its relevance in the heating of plasmas near the upper hybrid resonance.

In this paper, we report the first results of dosimetric analysis of broad-spectrum, multi-MeV laser accelerated proton beams obtained during experiments at the Rutherford Appleton Laboratory using the Chirped Pulse beam of the Vulcan laser. The spectra are retrieved by a numerical analysis that allows the reconstruction of the energetic profile of the proton beam from data obtained using radiochromic film.

All preceding hydrodynamic computations of plasmas need correction if the thermal conductivity is used because electronic thermal conductivity is decreased on plasma inhomogeneities due to electrostatic double layers. In the worst case, ionic conductivity remains. We compare this with a possible electronic conductivity by the fast tail of the energy distribution. Using the volume ignition for fusion gain computations, we study the increase of gain by spin-polarization of nuclei for the DT reaction especially in nonlinear ranges. Gain can increase by a factor of 3·1.

Using the PALS iodine laser system, Au ions with the charge state up to 58+ and with the kinetic energy as high as ~300 MeV were generated. The production of these ions was tested in dependence on the laser frequency (1ω, 3ω), on the irradiation/detection angles (0°, 30°), on the focus position with regard to the target surface, and on the target thickness (500 µm, 200 µm, 80 µm). A larger amount of the fastest ions was produced with 1ω than with 3ω, the most of the fast ions were recorded in the direction ~10° from the target normal, the optimum focus position is in front of the target and should be set on with a precision of 50 µm. The forward emission is weaker than the backward one for both of the thinner targets (which burn through) at our experimental conditions.

The production of atomic hydrogen and positive ions in a typical hydrogen thyratron plasma is considered through an analysis of radiative and collisional processes. The production of atomic hydrogen and positive ions in devices such as hydrogen thyratrons is an important and sensitive factor in determining the operational limitations.

A series of specialized multidimensional resistive magnetohydrodynamic (MHD) models have been developed to tackle the different phases of evolution of wire array z-pinch implosions. Two-dimensional (r–z) “cold-start” or “wire initiation” simulations of single wires indicate the persistence of a two-component structure with a cold, dense core embedded within a much hotter, low density, m = 0 unstable corona. Cold-start simulations with similar conditions to wires in an array show a general trend in the plasma structure from discrete wires with large m = 0 perturbation amplitudes to partially merged wires with smaller perturbation amplitudes as the number of wires is increased. Two-dimensional (r–θ) simulations then show how the persistence of dense wire cores results in the injection of material between the wires into the interior of the array, generating radial plasma streams which form a precursor plasma upon reaching the axis. Higher-resolution 2-D (r–θ) simulations show similar behavior for large number wire arrays in use at Sandia National Laboratories. This model is also used to predict which modes of implosion are in operation in nested wire array experiments. Separate r–θ plane simulations of the flux of plasma imploding towards the axis from the outer array and the bombardment of the inner array by this flux are presented. Finally, 2-D (r–z) simulations of the Rayleigh–Taylor instability during the final implosion phase are used to illustrate the effect upon the power and duration of the radiation output pulse. The results of low-resolution 3-D resistive MHD simulations are also presented. The need for much higher resolution 3-D simulations of certain aspects of wire array evolution is highlighted.

A new direction for high-power microwave (HPM) development is to investigate devices capable of producing HPMs with a complicated spectrum. In recent years, some HPM sources with two stable and separate frequencies have been investigated theoretically and experimentally. However, many short-comings still exist in these devices. Especially, the beam-wave interaction efficiency and the output microwave power are low in such devices. This paper proposes a novel dual-frequency HPM generator based on transition radiation. In the device, the electromagnetic fields are localized near the resonator cavities in the form of standing waves, and thus the interference between the different HPM components with different frequencies is weak. Compared with the existing dual-frequency devices, the new structure allows high beam-wave interaction efficiency and high output microwave power. As indicated in particle-in-cell simulation, with an electron beam of 500 kV voltage and 15.0 kA current guided by a magnetic field of 0.8 Tesla, an average power of 1.60 GW with a total power conversion efficiency of 21.3% is obtained, and the frequencies are 1.53 GHz and 3.29 GHz, respectively. Power level between two HPMs is comparable. The simulation results verify the feasibility of the dual-frequency HPM generator.

We describe the next set of experiments proposed in the U.S. Heavy Ion Fusion Virtual National Laboratory, the so-called Integrated Beam Experiment (IBX). The purpose of IBX is to investigate in an integrated manner the processes and manipulations necessary for a heavy ion fusion induction accelerator. The IBX experiment will demonstrate injection, acceleration, compression, bending, and final focus of a heavy ion beam at significant line charge density. Preliminary conceptual designs are presented and issues and trade-offs are discussed. Plans are also described for the step after IBX, the Integrated Research Experiment (IRE), which will carry out significant target experiments.

Laser plasma interaction experiments have been performed using an fs Titanium Sapphire laser. Plasmas have been generated from planar PMMA targets using single laser pulses with 3.3 mJ pulse energy, 50 fs pulse duration at 800 nm wavelength. The electron density distributions of the plasmas in different delay times have been characterized by means of Nomarski Interferometry. Experimental data were compared with hydrodynamic simulation. First results to characterize the plasma density and temperature as a function of space and time are obtained. This work aims to generate plasmas in the warm dense matter (WDM) regime at near solid-density in an ultra-fast laser target interaction process. Plasmas under these conditions can serve as targets to develop X-ray Thomson scattering as a plasma diagnostic tool, e.g., using the Vacuum ultraviolet (VUV) free-electron laser (FLASH) at Dentsches Elektronen-Synchrotron (DESY) Hamburg.

Parametric electron-ion potential for fast estimation of atomic data required for “on-line” calculations in inertial confinement fusion (ICF) driven by heavy ions is presented. Comparisons of our results (outer- and inner-shell ionization energies, oscillator strengths, and logarithmic mean excitation energies) with experimental and self-consistent-field (SCF) calculation values are made. Using the wave functions generated by the previously mentioned potential, generalized oscillator strengths and integrated inelastic collision cross sections are computed within the frame of Born approximation.

The generation of high-energy-density plasmas by the electromagnetic implosion of cylindrical foils (i.e., imploding plasma shells or hollow z-pinches) has been explored analytically and through numerical simulation. These theoretical investigations have been performed for a variety of foil initial conditions (radius, height, and foil mass) for both capacitive and inductive pulsed power systems. The development of the theoretical modeling techniques is presented, covering both circuit models and plasma load models. The circuit models include simple single loop capacitive and multiple loop inductive systems. These circuits are coupled to the imploding plasma loads whose response has been studied by models ranging from simple time varying inductances to complex two-dimensional magnetohydrodynamic numerical simulations. Results from a series of configurations are given, showing the development of modelling techniques used to study the dynamics of the plasma implosion process and the role of instabilities. Interaction between analytic techniques and detailed numerical simulation has led to improvement in all theoretical modeling techniques presently used to study the implosion process. Comparisons of implosion times, shell structure, instability growth rates, and thermalization times have shown good agreement between analytic/heuristic techniques and more detailed two dimensional magnetohydrodynamic simulations. These in turn have provided excellent agreement with experimental results for both capacitor and inductor pulse power systems.