A Gw-level high-power CO2 laser system has been developed. A short laser pulse is cut out with a double Pockels cell electrooptical shutter from a hybrid CO2 laser oscillator and amplified with a three-stage dual-path TEA preamplifier, a two-stage TEA preamplifier, a large aperture TEA amplifier, and an electron beam-controlled final amplifier. All parts of the laser system are controlled with a control system. The laser output power is up to 3.2 × 109 W and laser pulse width is 4 ns full width at half maximum.

A three-dimensional model to calculate X-ray intensity distribution on an indirectly driven fusion target is presented. The model includes conversion of laser light into X rays, radiation reemission from X-ray-heated wall of a cavity, and influence of an inner pellet (i.e., a fuel capsule) on radiation redistribution. Intensity distribution of an X ray inside a cylindrical cavity heated by intense blue laser light (wavelength 351 nm, energy 5.2 kJ, duration 0.7 ns) was determined by measuring a burn-through signal from a diagnostic foil integrated onto the cavity. The experimental result is well replicated by the model calculation. By using this model, optimum conditions for uniform irradiation of afusion capsule by X-ray radiation are evaluated for use in Gekko XII laser fusion experiments.

The ion flux produced by an obliquely incident Nd Q-switch pulse on a graphite target has been analyzed with regard to its kinetic energy, charge, and angular distribution. The laser intensity has been varied in a range between 109–5·1010 W/cm2, appropriate for many low-irradiance applications. It is observed that for ions of charge state n the emission cone of the number of ions scales with cos2n+1. The angular emission probability of the kinetic energy of the individual ions is found to be independent of their charge and scales as a cosine function. Due to the asymmetrical heating of the expanding plasma by the obliquely incident laser pulse, the maximum of emission is rotated away from the target normal toward the incoming laser, depending upon the ion's charge and the laser energy. The measured kinetic energy spectra are determined by the recombination during the plasma expansion: There are no low-energetic highly charged ions and no high-energetic lowly chargedions. If the laser energy (intensity) is enhanced, it is observed that the additional heating essentially serves only to increase the velocity of the higher charged ions; the energy of the individual singly charged ions is not altered.

We carried out a numerical analysis on the stability of targets designed to produce fusion energy gains close to 100 when irradiated with an appropriate heavy ion beam. To reach such performances, we found that a high-Z radiation shield was necessary to screen the DT fuel from the radiation coming from the surrounding hot material. As opacity of high-Z materials is only weakly density dependent, we considered targets with lead shields both at solid density and with a density equivalent to that of the contiguous external material. The behaviour of both kinds of targets has been studied by introducing a small spatial nonuniformity on the external surface of the lead shield. Targets with low-density shields have been tested with a beam intensity perturbation, too. Because density gradients are very sharp and ablation is practically absent, we have found these implosions to be Rayleigh-Taylor unstable. The evolution has been followed in the nonlinear regime because the full hydrodynamical-radiative model with a nonlinear heavy ion energy deposition and mesh correction was used.

The interaction of ultrashort laser pulses with a fully ionized plasma is investigated in the plane geometry by means of numerical simulation. The impact of the space oscillations in the amplitude of the laser electric field on the shape of the electron distribution function, on laser beam absorption, and on electron heat transport is demonstrated. Oscillations in the absorption rate of laser radiation with the minima coincident to the maxima of the laser electric field lead to a further decrease in the absorption of laser radiation. Heat flux in the direction of increasing temperature in the underdense region is caused by the modification of the electron distribution function and by the density gradient. A limitation of heat flux to the overdense plasma isobserved with the flux limiter in range 0.03–0.08, growing moderately with the intensity 1014–1016 W/cm2 of the incident 1.2-ps laser pulse.

Optically excited active medium at XeF(A)transition(λ = 481 nm) is considered from the viewpoint of its possible application in ultrashort (down to 10 fs) light pulses amplification due to the extremely wide amplification band of the transition. Photolytical pumping of XeF(C–A)by pulsed discharge or shock wave radiation allows one to amplify light beams with the cross-section at least upto ∼1 m2. Taking into account strong bulk and surface nonlinear effects at high-power density, it seemsfeasible to get the output energy up to ∼ 1 kJ and the power density in the focal spot up to 1023 W/cm2. Consideration of spatial-time distributionof the excited XeF(C) molecules, formed in the XeF;2 photodissociation wave under the action of powerful optical pumping, shows a possibility in principle to design multipass amplifiers with the inversion running wave, which are intended for the amplification of ultrashort pulsesup to the energies noted above.

A numerical and analytical estimation and a one-dimensionalhydrodynamic simulation show that a 30%reduction of the tritium content in a D-T pellet still gives sufficient energy output in aD-T inertial confinement fusion reactor.In other words, the tritiumb content can be reduced significantly without a significant reduction in the D-T fusion energy output.This new result also meansthat the tritium inventory can be reduced significantly before and during the reactor operation in the D-T inertial confinement fusion.This result comes from the contribution of a D-D reaction to the D-T reaction.

A new method for fabricating polystyrene ICF targets has been investigated. A solid solution of polystyrene (PS) containing a chemical blowing agent (CBA) is divided into small granules. These granules are blown into spherical shells in a vertical furnace. By varying the type and amount of CBA as well as furnace parameters, we have been able to produce PS shells 200–600 μm in diameter with wall thicknesses from 4–20 μm.

For nonlocal thermodynamic equilibrium (LTE), the equations of state are not well defined and therefore the hydrodynamic equations are not applicable. In this case, the general transport equations (e.g., Boltzmann or Fokker–Planck) should be used. However, the coupling between atomic physics (rate equations) and the transport equations is extremely complicated. This article shows how the information given by the rate equations is translated into an effective potential. This “potential” theory is explicitly shown for two cases: lithium-like iron plasmas and aluminum plasmas. Moreover, it is suggested that the “collision terms,” and all other interactions that are not taken into account by the explicit rate equations, are described by a stochastic force given by a Langevin equation or equivalently by a Fokker-Planck equation in the ion density space.

A nonlinear theory of ion stopping in classical ideal plasmas is formulated on the basis of formalism of higher-order dielectric functions accounting for nonlinear relationship between polarisation and electric fields generated in plasma by the projectile ion. Corrections to the linear theory corresponding to the Barkas effect are evaluated explicitly. The result differs (what concerns the numerical coefficient) from that following from the harmonic oscillator model.

This article describes computer simulations of a longitudinal instability that affects induction linear accelerators for high-power ion beams. The instability is driven by axial bunching of ions when they interact with acceleration gaps connected to input transmission lines. The process is similar to the longitudinal resistive wall instability in continuous systems. Although bunching instabilities do not appear in existing induction linear accelerators for electrons, they may be important for proposed ion accelerators for heavy ion fusion. The simulation code is a particle-in-cell model that describes a drifting beam crossing discrete acceleration gaps with a self-consistent calculation of axial space charge forces. In present studies with periodic boundaries, the model predicts values for quantities such as the stabilizing axial velocity spread that are in good agreement with analytic theories. The simulations describe the nonlinear growth of the instability and its saturation with increased axial emittance. They show that an initially cold beam is subject to a severe disruption that drives the emittance well above the stabilized saturation levels. The simulation results confirm that axial space charge forces do not reduce axial beam bunching. In fact, space charge effects increase the axial velocity spread required for stability. With simple resistive driving circuits, the model predicts velocity spreads that are too high for heavy ion fusion applications. Several processes currently under study may mitigate this result, including advanced pulsed power switching methods, enhanced gap capacitance, and an energy spread impressed between individual beams of a multibeam transport system.

We studied the formation of the collector ion flow in magnetically insulated diodes (MID) with plate-, sphere-, and cone-shaped cathodes. The ions are formed as a result of the ionization of residual gas by electron bombardment and are focused into the cathode plasma region. This effect can negatively influence diode operation in the microsecond range of pulse duration.

When focusing light ions with intense light ion-beam diodes, problems occur with ions emitted at the edge of the anode plasma. Numerical studies investigating this well-known experimental observation are presented. Going beyond the computational simulations introduced by Westermann (1991 Appl. Phys. Lett. 58, 696), two suggestions for the case of the self-magnetically Bθ-insulated ion diode are presented to focus the beamlets emitted from outer parts of the anode. The first one is based upon the idea of changing nonemitting parts of the anode surface and the second one of shifting the emitting anode surface into the anode body.