In energy-oriented ICF, a nondeterministic ignition process can be acceptable, provided the ignition probability be large enough. We present fuel gain calculations for D-T assemblies ignited by a supercritical spark, statistically created within a cluster of many subcritical ones, at the end of an implosion process. It is assigned the total number of sparks and the probability of having at least one of them supercritical. Comparatively to the central, single-spark approach, the multi-spark scheme is characterized by relaxed symmetry requirements. This allows to consider as realistic the achievement of higher fuel densities and gains comparable (or higher) to those typical of the single-spark approach, as evaluated for currently accepted spark convergence ratios.

A NIF-type hohlraum target (Lindl 1995; CEA 1995) is analyzed in an integrated calculation that uses last revision (4.2) of MULTI2D code (Ramis et al. 1992). The numerical simulation includes: Lagrangian mesh, tracking of laser beams, inverse bremsstrahlung absorption, 3D radiation transport, radiation-induced hydrodynamics of casing and window panes, and radiatively driven capsule implosion. Electron heat conduction (Spitzer with flux limiter), tabulated Equations of State (Sesame), and LTE opacities are also included. Detailed results on hydrodynamic evolution of the system, compression symmetry, and energy balance are also provided.

The interaction of short (1−2 ps) laser pulses with solid targets at irradiances of over 1016 Wcm−2, in the presence of a substantial prepulse has been investigated. High absorption of laser energy is found even at high angles of incidence, with evidence for a resonance absorption peak being found for S, P, and circular polarizations. It is considered that this may be a result of refraction and beam filamentation, which causes loss of distinct polarization. Measurements of hard X-ray emission (∼ 100 keV) confirm a resonance absorption type peak at 45−50°, again for all three cases. Typically, 5−15% of the incident light is back-reflected by stimulated Brillouin scatter, with spatially resolved spectra showing evidence of beam hot-spots at high intensity. The possibility that filamentation and refraction of the beam can explain the lack of polarization dependence in the absorption and hard X-ray emission data is discussed.

In the Compton backscattering of laser light from a high-energy electron beam, the scattered photons are, as is well known, much harder than the incident photons. In connection with the inverse Compton effect, the spectral brightness, the brilliance of the backscattered radiation is theoretically investigated. For the brilliance B [photons/(sec × mm2 × sr × 0.1% bandwidth)] of the scattered radiation a defining relation is given. Then, the intensity I0 and the wavelength λ 0 of the incident laser light are assumed such that the intensity parameter η is sufficiently smaller than 1, so that with regard to the scattering process, multiphoton effects need not be considered, and the backscattered photon energy hν and the differential cross section dσ/dω approximately do not depend on η. In this case, the brilliance B linearly scales with I0. Furthermore, it is assumed that the primary electron and the incident laser photon are counterpropagating along a straight line, the head-on incidence of the laser photon. On these assumptions, for the brilliance B of the backscattered radiation, B depending on the back-scattered photon energy hν, an explicit formula is derived; from it, by approximations, a shorter formula for B is obtained.

Review and systematization of our investigations in thermonuclear (TN) plasma particle diagnostic methods are presented. The proposed diagnostic schemes are based on direct numerical simulations of nuclear reaction products kinetics in a dense hot plasma with the following interpretation of the results by means of analytical scaling relations for charged particles energy loss in plasma with arbitrary degeneration of electron gas. The simulations of the kinetic equations system solution for TN particles is carried out by TERAcode based on Monte–Carlo method. The diagnostic schemes are presented in the form of families of isoline curves at the (ρR, T)-plane which are related to the constant values of measured spectrum characteristics. The searching plasma parameters ρR and temperature T are determined by points of interceptions of curves related to the distinct characteristics. The ranges of applicability of different methods of particle diagnostics are investigated in detail.

Detecting highly energetic neutrons produced by suprathermal fusion reactions is expected as a useful method for the areal density diagnosis in future ICF experiments. This paper examines the possibility of ρR diagnosis using suprathermal fusions, on the basis of transport calculations for neutrons and charged particles. Not only neutron elastic scattering but also nuclear elastic scattering of α-particles are considered as the processes producing energetic recoil ions. Since the suprathermal fusion reaction is affected by the plasma temperature through the slowing-down process of energetic α-particles and recoil ions, the yield ratio of highly energetic neutrons emitted from suprathermal fusions to total ones depends considerably on tne temperature. An areal density diagnostic method based on neutron spectroscopy is proposed here that can eliminate the influence of the plasma temperature on the determination of the areal density. Moreover, on the basis of coupled transport/hydrodynamic calculation, we derive a more realistic energy spectrum of neutrons escaping from laser-imploded D-T pellet and examine the usefulness of the diagnosis method proposed in this paper. It is shown that the Method proposed here may be useful for the areal density diagnosis in the ignition-grade ICF Pellets.

Experiments and the associated simulations for the evaluation of the focusibility of spherical Plasma focus diode (SPFD) were carried out. To evaluate the ion beam focusibility, two types of time-integrated Rutherford scattering pinhole camera were used: angle-integrated and angle-resolved type. From the former method, the ion beam has been found to focus in a cylindrical area with 4.5mmφ × 6.0 mm. The ion density profile shows a peak at 2.5 mm downstream from the geometric focusing point. From the latter method, it is found that a large fraction of the ion beam is produced from the downstream region of the diode. In simulations, the influence of an initial ion thermal energy was evaluated on the ion beam focusibility. When the initial energy is 20 eV, the ion beam focused in a cylindrical area of 0.4 mmφ × 2.4 mm. The experimental focusing parameters seem to be much worse than those evaluated numerically presumably due to the aiming error of ion beam.

The performance of a 15-cm-radius applied-magnetic-field ion diode was investigated on the PBFA II accelerator at a power of 23 TW. The power coupling between the accelerator and diode was measured and compared with numerical simulations that show the effects of the electron flow in the MITL. The power coupled to the cathode of the diode was 18 MW. Measurements of the lithium beam generated from an electric-field-emission LiF anode showed a lithium beam power of 9 TW. The lithium beam was ballistically focused in a gas cell filled with 2 torr argon. The resultant focused power density was ∼1.8 TW/cm2 equivalent on a cylindrical target at the centerline of the diode. The focused power was limited by the 20- to 30-mR divergence of the beam caused by the LiF source used and by virtual cathode instabilities in the anode–cathode gap. The ion mode instability in the virtual cathode was studied extensively by measurement of waves in the ion emission pattern from the anode and of the E-P0 correlation between variations in the beam energy and transverse momentum. The instability Played a dominant role in the limitation of the focused lithium power.

The fast ignitor concept for inertial confinement fusion relies on the generation of hot electrons, produced by a short-pulse ultrahigh intensity laser, which propagate through high-density plasma to deposit their energy in the compressed fuel core and heat it to ignition. In preliminary experiments designed to investigate deep heating of high-density matter, we used a 20 joule, 0.5–30 ps laser to heat solid targets, and used emission spectroscopy to measure plasma temperatures and densities achieved at large depths (2–20 microns) away from the initial target surface. The targets consisted of an Al tracer layer buried within a massive CH slab; H-like and He-like line emission was then used to diagnose plasma conditions. We observe spectra from tracer layers buried up to 20 microns deep, measure emission durations of up to 200 ps, measure plasma temperatures up to Te=650 eV, and measure electron densities above 1023 cm−3. Analysis is in progress, but the data are in reasonable agreement with heating simulations when space-charge induced inhibition is included in hot-electron transport, and this supports the conclusion that the deep heating is initiated by hot electrons.