Search

The hybrid model of laser energy deposition is a combination of the geometrical-optics ray-tracing method with the one-dimensional (1D) solution of the Helmholtz wave equation in regions where the geometrical optics becomes inapplicable. We propose an improved version of this model, where a new physically consistent criterion for transition to the 1D wave optics is derived, and a special rescaling procedure of the wave-optics deposition profile is introduced. The model is intended for applications in large-scale two- and three-dimensional hydrodynamic codes. Comparison with exact 1D solutions demonstrates that it can fairly accurately reproduce the absorption fraction in both the s - and p -polarizations on arbitrarily steep density gradients, provided that a sufficiently accurate algorithm for gradient evaluation is used. The accuracy of the model becomes questionable for long laser pulses simulated on too fine grids, where the hydrodynamic self-focusing instability strongly manifests itself.

We present a new double hohlraum target for the creation of a moderately coupled ( 0.1 Γ 1 ) carbon plasma for energy loss and charge state measurements of projectile ions interacting with this plasma. A spherical cavity of 600 μ m in diameter is heated with a 150-J laser pulse ( λ L = 527 nm ) within 1.2 ns to produce a quasi-Planckian X-ray source with a radiation temperature of T r ≈ 100 eV . These X-rays are then used to heat volumetrically two thin carbon foils in a secondary cylindrical hohlraum to a dense plasma state. An axi-symmetric plasma column with a free-electron density of up to 8 × 10 21 cm - 3 , a temperature of T ≈ 10 eV, and an average ionization degree of Z ≈ 3 is generated. This plasma stays in a dense and an almost uniform state for about 5 ns . Ultimately, such targets are supposed to be used in experiments where a heavy ion beam is launched through the sample plasma, and the ion energy losses as well as the charge distributions are to be measured. The present paper is in a certain sense a symbiotic one, where the theoretical analysis and the experimental results are combined to investigate the basic properties and the prospects of this type of plasma targets.

Remaining within the pure hydrodynamic approach, we formulate a self-consistent model for simulating the dynamic behavior of matter passing through metastable states in the two-phase liquid-vapor region of the phase diagram. The model is based on the local criterion of explosive boiling, derived by applying the theory of homogeneous bubble nucleation in superheated liquids. Practical application of the proposed model is illustrated with hydrodynamic simulations of a volumetrically uniformly heated planar layer of fused silica SiO2. Implications for experimentally measurable quantities are briefly discussed. A newly developed equation of state, based on the well known QEOS model and capable of handling homogeneous mixtures of elements, was used in the numerical simulations., 14 pages, 9 figures

A new algorithm for solution of diffusion equations in two dimensions on structured quadrilateral grids is proposed. The algorithm is based on a semi-implicit method for the time discretization and has a nine-point local stencil in space. Our scheme is fast, quite accurate and demonstrates good spatial convergence. The presented numerical tests show that it is well suited for hydrocodes with cell-centered principal variables.

A new experimental area has been set up at the RFQ accelerator at ITEP (Moscow) to investigate the interaction of ions with gases and plasmas. The HIPr-ITEP accelerator provides ion beams at a specific energy of 100 keV/u. This energy is particularly suitable for studying the interaction of ions with cold and ionized matter below the maximum of the stopping power. As a first step, the new installation was used to measure the energy loss of copper ions in the nitrogen and hydrogen gases. Equilibrium stopping power values were determined and (as no previous experimental data for the Cu ions below the stopping power maximum existed) compared to the available semiempirical codes SRIM 2000, SRIM 2003, and with the new STIP code based on a clearly defined theoretical model which is now under development at ITEP.

This paper reports the results of a series of experiments on laser generated ions using the 100 TW laser at the ‘Laboratiore pour l’Utilisation des Lasers Intenses (LULI)’ at the Ecole Polythechnique in Palaiseau, France, and the 30 TW ‘Trident’ facility at Los Alamos National Laboratories in New Mexico, USA. It shows the importance of the ‘Target Normal Sheath Acceleration’ process (TNSA) for short pulse laser generated ion beams and its connection to the influence of target properties on the ion beam quality. It is shown that TNSA-generated protons form an ion beam with superior beam quality, following versatile spatial beam shaping approaches. These insights are set into perspective for a fast ignitor scenario based on short pulse laser generated protons.

The concept of power plant for a fast ignition heavy-ion fusion (FIHIF) is being developed. The characteristics of super-high-energy-ion driver are described. The scenario of 750 MJ fusion yield target compression and detonation is evaluated. The data on reactor chamber response to energy fluxes generated by microexplosion are given. The energy conversion thermal scheme and power plant output parameters are presented.

We report on measurements of the equation-of-state of copper and gold in the multi-ten Megabar range, opacity measurements based on K-shell absorption in aluminium, and X-ray laser studies on a large number of neon-like ions applying the prepulse technique. For these investigations, the one-beam iodine laser facility ASTERIX emitting pulses with energies of up to 1000 J at 1315 nm and of up to 420 J at 438 nm was used. We also give a brief account of experimental and theoretical results referring to the propagation of an ultrashort pulse through underdense hydrogen or nitrogen plasmas and X-ray spectra from an optically field-ionized nitrogen plasma generated either by linearly or elliptically polarized light. For these investigations, 150-fs/200-mJ/800-nm pulses emitted from our titanium:sapphire laser ATLAS were employed.

An overview of current activities on Heavy-Ion Fusion at ITEP is presented. A project called TWAC (TeraWatt Accumulator) is in progress now, aiming at the production of TeraWatt power level (100 kJ/100 ns) of intense heavy-ion beams, concentrated on experimental targets [1] . The project is based on the use of the existing accelerator chain at ITEP: A 2 MV/2.7 MHz heavy-ion injector I-3, a 13 Tm booster ring UK, a 34 Tm synchrotron U-10, a system of beam transfer lines and a laser ion source of He-like medium mass ions. Volume energy deposition of the heavy-ion beam in a target is expected to generate hot, strongly compressed matter with extremely high energy density (>1 MJ/g) in dense plasmas. The scientific program includes a number of challenging issues on accelerator physics, the physics of high energy density in matter and relativistic nuclear physics. The results of numerical simulations relevant to the suggested high energy density in matter experiments with TWAC beams are discussed. A survey of current experiments on beam–plasma interaction using the ITEP 3 MeV proton linac is given here.

The investigation of beam-plasma interaction processes requires the development of plasma parameter diagnostic methods with high temporal and spatial resolution. The basic plasma parameters to be controlled when measuring the ion energy losses in ionized gases are the areal density of free electrons, the degree of ionization and the heavy element impurities during the electrical discharge in hydrogen. We present the relevant experimental results obtained by means of time-resolved, two-wavelength Mach-Zehnder interferometry based on HeNe ( λ = 0.63 μ m) and HeCd ( λ = 0.44 μ m) lasers. Optical emission line spectroscopy allowed us to follow the behaviour of the impurity concentrations with a high temporal resolution. Both methods have been used for diagnostic tests of a hydrogen plasma target.