Hikaru Kitamura

Pycnonuclear reactions in dense astrophysical and fusion plasmas

Rates of pycnonuclear reactions in ultradense fluids and solids are evaluated by taking account of recent progress in quantum-statistical formulations of the equations of state and phase transitions in dense matter. New theoretical results are summarized for the reaction rates and the enhancement factors, obtained through systematic studies of the screening effects by relativistic and nonrelativistic electrons, as well as of the thermodynamic properties of dense matter resulting from internuclear cohesion in electron-screened Coulombic fluids and solids; the results prove to be a significant improvement over those in a previous review [S. Ichimaru, Rev. Mod. Phys. 65, 255 (1993)]. On the basis of these theoretical developments, coupled with renovated experiments in ultrahigh-pressure metal physics, outstanding issues of nuclear reactions in stellar and planetary interiors and in terrestrial settings are explored, with inertial-confinement-fusion experiments, and for a novel scheme of fusion studies in den...

Quantum-Mechanical Properties of Protons in Solid Molecular Hydrogen at Megabar Pressures

Quantum distributions of protons in three high-pressure phases of solid molecular hydrogen are investigated by the first-principles path integral molecular dynamics (FP-PIMD) method, in which interatomic forces are calculated precisely based on the density functional theory. The distributions have entirely different symmetries from those predicted by conventional simulation with classical treatment of protons. Especially in phase II, we found that molecular rotation is hindered by quantum fluctuation of protons, having a strong resemblance to a quantum distribution of impurity muonium in crystalline silicon. The mechanism of this “quantum localization” is clarified by a detailed study of the potential energy surface for the molecular rotation.

Enhanced Pycnonuclear Reactions in Ultrahigh-Pressure Metals

By combining the concepts of pycnonuclear reactions at low temperatures and their enhancement due to strong internuclear Coulomb correlations, we predict the possibilities of a novel scheme for fusion in ultrahigh-pressure liquid-metallic hydrogen near the freezing conditions, for the reactions 2 H ( p , γ) 3 H e , 3 H ( d , n ) 4 H e , and 7 L i ( p , α) 4 H e . Time evolution is followed for p - d reaction after a pulsed compression with 1 k J input and the initial conditions of mass density≈20 g / c m 3 , temperature≈1400 K , pressure≈490 Mbar, and radius≈0.017 c m ; an energy yield of 33 k J in 0.03 fs is thus predicted.

Ionic excitation in dense, two-component plasmas: A nonperturbative approach

A nonperturbative formulation of atomic collisional excitation rates in dense plasmas is developed on the basis of the equations of motion for density matrices in a stochastic potential. This model treats the strong scattering between the atom and plasma particles through the many-body correlation functions describing plasma density fluctuations, which are decomposed into the products of dynamic structure factors within the decorrelation approximation and then are summed to infinite order. A simple analytic solution to the density matrix equation is obtained for two-level atoms. The electron-induced transition of a hydrogen-like ion in dense hydrogen plasma is studied as an example. It is demonstrated that, when the plasma density is sufficiently high, low-frequency ion-density fluctuations influence the electron dynamics and thereby cause coherent excitation between close-lying atomic states. The resultant time evolution of the atomic level population differs considerably from the prediction of one-compo...

Ultradense hydrogen in astrophysics, high-pressure metal physics and fusion studies

Phase diagrams of hydrogen are constructed through first-principles calculations of the equations of state for metallic and insulator phases. On the bases of these theories of the equations of state and the electric resistivity, it is shown that the results of recent shock-metallization experiments can be consistently interpreted in terms of first-order metal-insulator transitions, involving discontinuous changes in density, entropy and enthalpy. The first-order transitions then predict a discontinuous distribution of density and resistivity near the Jovian surface, with a large magnetic Reynolds number enough to sustain prominent magnetic activities. A phase diagram for freezing and ferromagnetic transitions provides a basic account of strong magnetization observed in magnetic white dwarfs. Feasibility of a novel scheme of fusion studies in ultradense metallic hydrogen is examined in light of these experimental and theoretical developments.