The facilities and activities of inertial confinement fusion research in Japan are reviewed. The key institute is ILE Osaka University where the implosion scheme of the “Cannonball Target” has been investigated in experiments and computer simulations to overcome the critical issues in inertial confinement fusion.

A novel method of utilizing fluorescence generated from the products of nuclear reactions offers the prospect of compact, high efficiency, multi-megajoule lasers. To overcome the problems associated with traditional laser (or energy converter)-fissile material interfaces, such as a uranium coating (low power density and low efficiency) or a gaseous uranium compound (low power density and deleterious effects on the laser kinetics and photon transport), a method suggested elsewhere of employing a reactor using a uranium aerosol fuel, interspersed with a fluorescer medium, is briefly reviewed. The charged particles produced by nuclear reactions in the fuel produce fluorescence in the core region of the reactor, through interactions with the fluorescer. This fluorescence can then be concentrated, to increase the effective power density in the laser medium, and used to drive a photolytic laser.

One key issue in the above process is the charged particle spectrum from the fissile aerosol. These issues can be addressed theoretically based on the Dirac chord length distribution technique and an Arcen's function. The charged particle spectrum from a UO2 coating has been generated and benchmarked with the experimental data of Kahn et al., and Redmond et al. Agreement is generally good except near the end of the fission fragment tracks. The validity of this simple technique in approximating the rate of ion energy loss lends confidence to the generation of fission fragment spectra for other geometries (i.e. spherical in which transport efficiencies of over 60% appear achievable) using U, UO2 and U3O8. Work is also extended to the case of B-10 in a variety of configurations which are frequently used in modern energy conversion experimental devices.

One of the main problems in IC fusion is the efficient transfer of energy from a low energy-density source to the fusion target. Some general concepts of optimum energystaging are described. The applicability of these concepts is illustrated by a few examples. Particular emphasis is put on the use of several liners in series, which permits both the amplification of the liner-velocity and a spatially symmetric collapse.

In this paper we discuss the importance of radiation transport in inertial confinement fusion (ICF) target design. It is shown that a self similar solution of non-linear heat conduction can be used to estimate the penetration depth of radiation thermal waves (Marshak Waves) in ion-beam ICF pellets. An improved numerical treatment of non-linear heat conduction has been incorporated into the hydrodynamic code MEDUSA-KA to simulate radiation transport in ICF target design studies. The numerical results have been checked against self-similar solutions and a comparison between the two is presented in this paper. We find good agreement between the two. The necessity of using a high-z radiation shield to protect the fuel from radiative preheat is also discussed.

Design studies of a laser fusion reactor SENRI-I are presented, including the related analyses and experiments. The unique feature of SENRI-I is the utilization of the static magnetic field to control and guide the liquid Li flow. Neutronics calculations (1D–3D) show that the sufficient T breeding ratio is obtained and the streaming neutrons are reduced by a devised design of laser port. Analysis of damage of the wall covered by an inner Li flow shows that the long lifetime is assured.

Absorption, reflection and scattering of laser radiation have been studied in experiments with oblique incidence of Nd glass laser beams on plane massive targets of polyethylene, aluminium and copper. Time behaviour of 2ω and 3/2;ω harmonic intensities and their angular distributions were measured along with plasma X-ray spectra in the flux density range 1013 to 3×1014 W/cm2 for 3.5 nsec laser pulses. Comparison of the experimental data with the results of the theoretical analysis and numerical calculations is presented and relatively strong absorption of about 10% is estimated in the quarter critical density region of the plasma corona due to the two-plasmon decay instability growth. The hard X-ray component in the X-ray spectrum disappears at large angles of incidence, hence the supra-thermal electron generation and two-plasmon instability are proven to be coupled phenomena.

Experimental results on the compression of shell targets with aspect ratio A = 150–250 in the “Delfin-1” installation are reported. The absorbed laser energy was 0·3 to 0·5 kJ. The maximum compression was 3·5 × 103, the velocity of target compression at the final stage was 2·6 × 107 cm/s, neutron yield was 106 to 107 D-D neutrons per laser shot. The appearence of plasma corona filamentation correlated with compression stability distruction.

An electron gun is being developed which should substantially improve the normalized current density in medium energy pulsed linacs. The gun will accelerate and pre-bunch electrons from a LaB6 cathode using the high electric field in a resonant microwave cavity.

This survey is devoted to a few basic atomic problems associated with the stopping of nonrelativistic pointlike ions in dense and hot matter, and also to the Stark broadening diagnostics of the resulting beam-produced plasmas.

First, we consider the free electron contribution, taken in the RPA approximation with an exact dynamic dielectric function, valid at any temperature. Therefore, we obtain stopping power and straggling for any projectile velocity. The temperature dependence is of special relevance for a projectile energy smaller than 5 MeV/a.m.u.

Next, we revise the Barkas effect (Z3 corrections) through a novel and compact formulation, which is based on an analogy with electron impact broadening theory. It facilitates inclusion of the non hydrogenic and electronic structure of the target ions, in a more selective way. The results may increase the usual Z2-stopping by 15 to 30 per cent corrections.

Then, we show how the Stark broadening diagnostics of the compressed D + T fuel, seeded with high Z species, arising from the surrounding envelopes, may provide accurate determination of the electron number density ne. In this connection, it should be appreciated that the relatively long compression times (≃ 20 nsec) suggested by the HIBALL numerical simulation allow for a nearly Local Thermodynamic Equilibrium (LTE) state in the target, with Te ≃ Ti. As a consequence, spectroscopic measurements are expected to be easier to implement in HIF targets, than in laser ones.

A tentative proposal for the use of Stark broadening diagnostics of inflight excited and highly stripped ion projectiles is displayed in § 5.

Experiments involving an HIB produced by a standard accelerator, and interacting with an independently produced coronal plasma are finally outlined.

In a recent study R. G. Evans developed an analytic model for ICF targets heated by heavy ion beams in order to show the differences to laser beam heating. However, these differences are really not very pronounced. In fact, Evans' model should be directly applicable to describe exploding pusher foil targets. In addition, Evans' scaling law for the ablation pressure PA with target density ρ0 and particle beam intensity Ib,

is identical to the scaling found for laser targets with tamped flow (Ahlborn, 1981).

A one-dimensional model is used to study the hydrodynamic response of thin foils to bombardment by an intense proton beam. The beam targets are single- and multilayer planar foils of gold and polystyrene. The main conclusion of the study is that the efficiency of conversion of incident beam energy to directed kinetic energy of the target is maximized by using a multilayer design. For beam parameters associated with the Gamble II device at the Naval Research Laboratory, the simulations yield payload velocities of over 5 cm/μs and energy conversion efficiencies of over 30%. We discus the implications of these results for inertial confinement fusion research.

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.

A new electro-optical technique has been developed in which a streak camera is coupled to a Pockels cell with a fast risetime. This technique can improve the time resolution of the high voltages observed in laser produced plasmas between one and two orders of magnitude in comparison to the best oscilloscope measurements. This method should prove useful in confirming the existence of electrostatic fields and elucidating the structure of the wave instabilities found in laser produced plasmas.

The charge distribution of an incident ion as a function of projectile velocity, its range and its average equilibrium charge are studied theoretically. The calculations are made only for an atomic hydrogen gas target. The charge of the ion is determined by the equilibrium between electron loss from the ion and electron capature from a hydrogen atom to the ion. The charge states of the ions are calculated in two cases; to assume a local balance condition for electron loss and capture and to solve a rate equation for the charge state fraction function under non-local balance conditions, both only taking into account single electron loss and capture processes. In the calculations we use empirical formulae for electron loss and capture cross section by making some simplifications. Calculations for the charge state fraction as functions of ion ranges under non-equilibrium conditions have been carried out in the cases of Ne, Ar, and Xe ions. Calculations for the charge state under local balance conditions have been made in the cases of C, Ne, Ar, Kr, I, and U ions.

When a heavy ion beam passes through a plasma in reactor chamber, it scatters some plasma electrons in the direction perpendicular to that of beam propagation. The presence of such electrons causes an instability to deflect the beam from the target pellet. The instability is analyzed by coupled equations for density and temperature for the electrons, and numerical results are given.