Determining the cryogenic target parameters with high precision calls for the development of a new direction in the area of target characterization based on microtomography methods of data processing. In this report we present our first results in this area.

Multi-coaxial relativistic backward wave oscillator that generates the beating wave of high power microwave pulse driven by a single accelerator and a single guiding magnet system is presented. Making use of the coaxial annular cathodes that can synchronously produce three annular beams at one shot, the average power of 5.88 GW consisting of two frequency components 9.0 and 9.7 GHz is obtained under the diode voltage and current 724 and 19.57 kA, corresponding to the conversion efficiency 41.5%. The conversion efficiency and the beating frequency are considerably stable with the diode voltage. The coaxial transmission supporter developed from our previous experimental research is employed to conductively connect the coaxial structure and to incoherently combine the microwave pulse of two frequencies with little reflection. It is found that the equipotential connection of the coaxial structure modifies the field distribution in the diode structure to facilitate the operation of the coaxial annular cathodes. The coaxial cathodes of different lengths are proved to be efficient at depressing the space charge effect in order to prevent the explosive emission of the inner cathode from being shielded by the outer annular beams.

Surface exfoliation was observed on single-crystal silicon surface under the action of compressed plasma flow (CPF). This phenomenon is mainly attributed to the strong transient thermal stress impact induced by CPF. To gain a better understanding of the mechanism, a micro scale model combined with thermal conduction and linear elastic fracture mechanics was built to analyze the thermal stress distribution after energy deposition. After computation with finite element method, J integral parameter was applied as the criterion for fracture initiation evaluation. It was demonstrated that the formation of surface exfoliation calls for specific material, crack depth, and CPF parameter. The results are potentially valuable for plasma/matter interaction understanding and CPF parameter optimization.

It was shown (Faenov et al., 2015b) that the energy of femtosecond laser pulses with relativistic intensity approaching to ~1021 W/cm2 is efficiently converted to X-ray radiation and produces exotic states in solid density plasma periphery. We propose and show by one-dimensional two-temperature hydrodynamic modeling, that applying two such unique ultra-bright X-ray sources with intensities above 1017 W/cm2 – allow to generate shock waves with strength of up to some hundreds Mbar, which could give new opportunities for studies of matter in extreme conditions.

Interactions of sub-nanosecond pulses of kJ-class iodine laser “PALS” with low-density foams and acceleration of Al foils by the pressure of the heated foam matter are investigated here, both experimentally and theoretically. X-ray streak camera is used for evaluation of the speed of energy transfer through the porous foam material. The shock-wave arrival on the rear side of the target is monitored by optical streak camera. Accelerated foil velocities, measured by three-frame optical interferometers, and shadowgraphs, reach up to 107 cm/s. The accelerated foil shape is smooth without any signature of small-scale structures present in the incident laser beam. Conversion efficiencies as high as 14% of the laser energy into the kinetic energy of Al foil are derived. Experimental results compare well with our two-dimensional hydrodynamics simulations and with an approximate analytical model.

High-power relativistic magnetrons operating in both S-Band and X-Band (4 GHz) and 8·5 GHz) have been developed with a variety of extraction methods. Using a six window radial extraction scheme, the S-Band magnetron produces ∼3·6 GW. The X-Band magnetron produces 0·05 GW with one radial extraction window. Axial extraction from all six vanes produced power in excess of 0·3 GW. Enhanced erosion and gap closure occur in the smaller X-Band resonator.

For the future, we have to develop new sources of energy. These new sources may be based on nuclear fusion with magnetic confinement (as with the ITER experiment) or with a new concept based on inertial confinement. The European community plans to build a facility (HiPER project) which is dedicated to reaching high gain with cryogenic targets, and to test the concepts of target mass production and rep rate shots. The cryogenic system for the 1st phase experiments in HiPER is based on the cryogenic system developed for the French facility Laser MegaJoule (LMJ). The latter must be modified and upgraded for direct drive targets. In particular the target must be protected from the radiation flux from the vacuum vessel by a thermal shroud. In addition, the LMJ system must be equipped with a thermal system to allow layering of the fusion fuel to take place. The new developments concern a leak tightness thermal shroud for direct drive and a fast shroud retractor able to allow the laser shot within few milliseconds.

Two-photon absorption (TPA) of Au-ion irradiated glasses in the femtosecond regime has been analyzed by an open-aperture Z scan technique. Three types of glasses, namely GIL49, BK7, and Glass B were irradiated by using 1700 keV Au+ ion beams. Samples were post-annealed at 600°C for 5 h. Penetration depth and distribution of Au+ ions having 1700 keV energy within glass substrates were estimated by transport of ions in matter (TRIM) simulations. Detailed calculations with full-damage cascades were performed for each sample, taking into account the chemical composition of glass substrates. TRIM results reveal that there is no significant change in ion range, straggling, and ion distribution with the change in the substrate composition. However, Z scan results showed a difference in TPA coefficients for all three glasses. Extent of crosslinking within each of irradiated sample, owing to its chemical composition, may have affected their TPA coefficients.

A new scheme for cone-hollow-assisted fast ignition in inertial fusion is investigated. A hollow is attached to the tip of a conventional gold cone. The transport and heating of the high-current electrons propagating from the cone tip to the compressed fuel core along the hollow is investigated by two-dimensional hybrid simulation. Different hollow geometry sizes are examinized. It is shown that with proper hollow guiding, hot electrons can be collimated between the inner-walls of the hollow by the large interface magnetic fields appearing on the inner surface. When the beam electrons further propagate into the dense region, they are scattered into the gold hollow through collisions with the fuel electrons and ions. The resulting magnetic potential around the hollow then bends beam electrons along the gold hollow to reach the dense core.

A large, high density, high temperature plasma has been produced by using a high power laser with a capillary electrical discharge. The laser beam is synchronized with the discharge to reach the plasma after it emerges several hundred microns from the capillary.

In this paper the results of numerical computations of rippling smoothing basing on the broad-band laser irradiation method for the laser intensity range 1016−1017 W/cm2 and short-pulse (<10 ps) interaction with plasma are described.

The recombination X-ray laser scheme is considered in the case of recombining plasmas produced by laser pulses which are short to such a degree that the condition for inversion in X-ray transitions of the ions is essentially time-dependent. Using an analytic four-level model, applicable for H-like and Li-like ions, we calculate the inversion conditions for the 4→3, 3→2, and 2→l transitions in H-like ions as functions of time. As we have already shown, a drastic change occurs, especially for the 3→2 transition. To achieve inversion, for short times the free-electron density as a function of the temperature Te, Neinv(Te), must be greater than a critical density Nesh (Te), Neinv(Te) > Nesh(Te), whereas for longer times in the quasi-steady state, Neinv(Te) must be smaller than a critical density Neqv(Te), Neinv(Te) < Nequ(Te). We also consider the evolution of the inversion condition in the intermediate time domain. The time duration of the existence of the short-time 3→2 inversion condition–in the time interval from the initial state with unoccupied lower levels to the quasi-steady state—is in the main determined by t α 1/A21; for example, one has t ≈ 730 fs for Na.

In a plasma produced in particular by optical-field ionization, during the initial cascade populating the excited levels, an inversion may be possible in the 2→1 resonance line transition in the transient regime. The inversion in this transition is of interest especially because of the arising possibility to achieve X-ray gain at shorter wavelengths. In the transient case, an inversion occurs for a small time depending on the temperature Te and the density N.

In addition, we discuss generally the time behavior of the population densities (especially of N3) and show that an optimal population density occurs, on the one hand, for very short times (fs region, depending on Z). On the other hand, however, the optimal (ion-)density-temperature relation is determined via a time of the optimal population density required with regard to the experimental conditions.

We present the results of ab initio, nonperturbative, R-Matrix Floquet calculations of laser-induced continuum structures in helium. We compare our results with recent experimental data and good agreement is found.

Production of sharply collimated high velocity outflows – plasma jets from massive planar targets by a single laser beam at PALS facility is clarified via numerical simulations. Since only a few experimental data on the intensity distribution in the interaction beam near the focus are available for the PALS facility, the laser beam profile was calculated by a numerical model of the laser system and the interaction optics. The obtained intensity profiles are used as the input for plasma dynamic simulations by our cylindrical two-dimensional fluid code PALE. Jet formation due to laser intensity profile with a minimum on the axis is demonstrated. The outflow collimation improves significantly for heavier elements, even when radiative cooling is omitted. Using an optimized interaction beam profile, a homogeneous jet with a length exceeding its diameter by several times may be reliably generated for applications in laboratory astrophysics and impact ignition studies.

Time- and space-integrated emission spectra measurements have been performed in plasma produced by 308 nm wavelength XeCl laser radiation (IL = (4–10)·1012 W/cm2, τ = 10 ns) and by 248 nm wavelength KrF laser pulse train radiation (IL = 5·1015 W/cm2, τ = 7 ps, 16 pulses in train) on CF2 plane target. Theoretical modelling of Lyman series and He-like ion resonance series of fluorine and its fit of experimental data show considerable differences in the absorption of laser radiation in the two plasmas.

Chromatin is the complex of deoxyribonucleic acid (DNA) with proteins that exists in eukaryotic cell nuclei. Chromatin was extracted from livers of Wistar rats and subjected to a 248-nm excimer laser radiation, in doses of 0.5–3 MJ/m2. An UV excimer laser Iofan 1701, with 40-mJ dose/pulse and frequency of 30 Hz was used. The radiolysis of chromatin was analyzed by (1) 1H-NMR spectroscopy, (2) steady-state fluorescence, (3) time-resolved fluorescence, and (4) fluorescence resonance energy transfer (FRET) methods. The laser action on chromatin determines bigger values of the transverse relaxation time (T2), which indicates less bound water in the chromatin structure, therefore a more injured one. The chromatin intrinsic fluorescence decreases on laser action, proving the destruction of the chromatin protein structure. By the time-resolved fluorescence we established that the relative contribution of the excited state lifetime of bound ethidium bromide to chromatin DNA diminishes with the laser dose. This denotes single- and double-strand breaks produced in DNA structure. By the FRET method, the energy transfer efficiency and the distance between dansyl chloride and acridine orange coupled at chromatin were determined. The distance increases with laser action. The determination of the chromatin structure modification in an excimer laser field can be of real interest in medical applications.

A review of recent developments in intense ion beam diagnostics used in the international light ion inertial confinement fusion (ICF) programs will be presented. These developments have occurred in each of the several generic classes of diagnostics, namely, imaging diagnostics, particle spectrograph diagnostics, nuclear activation, and visible spectroscopy. Critical beam parameters measured by the new diagnostics include spatial profile, absolute number, species, anode plasma temperature and density, voltage, current density, and power density. A unique feature of most of these diagnostics is that they are capable of operating in hard (multi-MeV) X-ray (bremsstrahlung) backgrounds of some 109–1011 rad/s. The operating principles of each diagnostic will be summarized in the paper with examples of how the diagnostics may be integrated together to form a complete diagnostic system. The paper will close with a discussion of two new data acquisition systems that have been developed for intense beam diagnostics.

Kα radiation from low charge chlorine is examined for cold dense plasma diagnostics. A relativistic atomic structure calculation shows that the transition energies of Kα lines are slightly shifted to a higher-energy side according to the degree of M-shell ionization. Total spectral shift from Cl+ Kα lines up to those with a fully stripped M-shell is about 10 eV. With an assumption that collisional-radiative-equilibrium is valid, spectral calculations were carried out for a C2H3Cl-plasma heated by an ion beam, and clear deformation among spectral line-shapes is found in the range of the electron temperatures of ≤~ 30 eV. Contribution to the composite spectra of Kα lines with an excited electron in the outer-shell is also briefly discussed. Cl-Kα lines with M-shell electrons can be expected to give us distinct understandings for energy deposition by an ion beam in cold dense plasma.

Volume 23, Number 2, Pages 177–182, 2005

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

Limpouch, J., Demchenko, N.N., Gus'kov, S.Yu., Gromov, A.I., M. Kalal, Kasperczuk, A., Kondrashov, V.N., Krousky, E., Masek, K., Pfeifer, M., Pisarczyk, P., Pisarczyk, T., Rohlena, K., Rozanov, V.B., Sinor, M. & J. Ullshmied, J. (2005). Laser interactions with low-density plastic foams. Laser Part. Beams23, 321.

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 effect of surface deformations on laser absorption and transport in overdense plasma targets is investigated with 2D Vlasov simulations. Fractional absorption increases strongly with the deformation depth and scales weakly with density or intensity. Fast electrons generated in the skin layer have high tangential velocity directed toward the deformation center. In the case of a single, smooth deformation, they may be collimated by magnetic fields into a single jet which penetrates deeply into the plasma. Small-scale surface corrugations are able to destroy the collimation of a single jet leading to multiple jets or diffuse electron sprays.