M. Murakami 교수

The physics of indirectly driven targets for inertial confinement fusion — so-called hohlraum targets — is investigated. Scaling relations for radiation heat waves in high-Z and low-Z materials are derived from one-dimensional multigroup simulation. A two-temperature model is developed for radiation cavities including fusion capsules. The efficiency of X-ray transfer to the capsule by multiple absorption and re-emission inside the cavity is obtained as a function of cavity areas and materials. U

A new self-similar solution is presented which describes nonrelativistic expansion of a finite plasma mass into vacuum with a full account of charge separation effects. The solution exists only when the ratio Λ=R∕λD of the plasma scale length R to the Debye length λD is invariant, i.e., under the condition Te(t)∝[ne(t)]1−2∕ν, where ν=1, 2, and 3 corresponds, respectively, to the planar, cylindrical, and spherical geometries. For Λ⪢1 the position of the ion front and the maximum energy Ei,max of

A simple analytical model is presented for hydrodynamic expansion of laser-produced plasma with a limited mass, which expands quasi-isothermally during laser irradiation and quasiadiabatically after turning off the laser. During the isothermal expansion, the masses undergo entire disintegration under a relatively long laser pulse, while the ions are being kept accelerated. This physical picture significantly contrasts with that described by the orthodox self-similar solution for a semi-infinite

Relativistic laser pulse propagation into homogeneous plasmas has been investigated as a function of plasma density. At first, the propagation features are compared systematically between relativistic transparency (RT) and hole-boring (HB). Paramountly, a considerably broad intermediate regime, namely the incomplete HB regime, has been found between the RT regime and the HB regime for an extremely intense circularly polarized (CP) pulse. In this regime HB proceeds in collaboration with RT, resul

A new ignition scheme is proposed, in which the compressed DT main fuel is ignited by impact collision of another fraction of separately imploded DT fuel, which is accelerated in the hollow conical target to super high velocities of about (1–2) × 108 cm s−1. Its kinetic energy is directly converted into thermal energy corresponding to temperatures >5 keV on the collision with the main fuel, and this self-heated portion plays the role of ignitor. The ignitor shell is irradiated typically by nanos

Symmetrization of the radiation field by multiple absorption and re-emission in hohlraum targets for indirectly driven inertial confinement fusion (ICF) is investigated. The radiation field on the confining wall and on the fusion capsule is calculated self-consistently, taking into account the angular distribution of the X-rays received and emitted by each surface element. Wall physics are described by approximate ablative heat wave relations, giving the absorbed flux, the temperature and the th

A microtube implosion driven by ultraintense laser pulses is used to produce ultrahigh magnetic fields. Due to the laser-produced hot electrons with energies of mega-electron volts, cold ions in the inner wall surface implode towards the central axis. By pre-seeding uniform magnetic fields on the kilotesla order, the Lorenz force induces the Larmor gyromotion of the imploding ions and electrons. Due to the resultant collective motion of relativistic charged particles around the central axis, str

Two different types of irradiation systems based on dodecahedral configuration are proposed for 60, 72, 80, and 92 beams. By optimizing the system, it is expected that enough uniformity (≤1% rms) is provided. Furthermore, it is quantitatively discussed that the number of beams, power imbalance, and the beam pattern must be improved synchronously for a high illumination uniformity.

Intractable low-mode nonuniformities caused by power imbalance or pointing error of beams are studied quasi-analytically based on Skupsky’s axially symmetric model [S. Skupsky and K. Lee, J. Appl. Phys. 54, 3662 (1983)]. These nonuniformities can be improved by decreasing the imperfections σPΩ, or by increasing the number of laser beams NB: deteriorated irradiation uniformity is shown to be proportional to σPΩ/√NB. Criteria of these imperfections for high irradiation uniformity [≤1% root-mean sq

Coulomb explosion of spherical ion clusters is studied, which are composed of homogeneous two-species (light and heavy) ions. A simple analytical model is developed to describe the explosion performance in terms of two dimensionless parameters, the charge-over-mass ratio, and the charge density ratio. One-dimensional kinetic numerical model is performed to compare with the analytical model and to evaluate the energy coupling efficiency of quasimonoenergetic ion generation. It is crucial to prefo