The chaotic dynamics of comets and the problems of the Oort cloud

The dynamic properties of comets entering the planetary zone from the Oort cloud are discussed. Even a very slight influence of the large planets can trigger stochastic cometary dynamics. Multiple interactions of comets with the large planets produce diffusion of the parameters of cometary orbits and a mean increase in the semi-major axis of comets. Comets are lifted towards the Oort cloud, where collisions with stars begin to play a substantial role. The transport of comets differs greatly from the customary law of diffusion and noticeably alter cometary distribution

The Oort cloud

Views of the large-scale structure of the solar system, consisting of the Sun, the nine planets and their satellites, changed when Oort demonstrated that a gigantic cloud of comets (the Oort cloud) is located on the periphery of the solar system. The following subject areas are covered: (1) the Oort cloud's mass; (2) Hill's cloud mass; (3) angular momentum distribution in the solar system; and (4) the cometary cloud around other stars

Laser acceleration of monoenergetic protons via a double layer emerging from an ultra-thin foil

We present theoretical and numerical studies of the acceleration of monoenergetic protons in a double layer formed by the laser irradiation of an ultra-thin film. The ponderomotive force of the laser light pushes the electrons forward, and the induced space charge electric field pulls the ions and makes the thin foil accelerate as a whole. The ions trapped by the combined electric field and inertial force in the accelerated frame, together with the electrons trapped in the well of the ponderomotive and ion electric field, form a stable double layer. The trapped ions are accelerated to monoenergetic energies up to 100 MeV and beyond, making them suitable for cancer treatment. We present an analytic theory for the laser-accelerated ion energy and for the amount of trapped ions as functions of the laser intensity, foil thickness and the plasma number density. We also discuss the underlying physics of the trapped and untrapped ions in a double layer. The analytical results are compared with those obtained from direct Vlasov simulations of the fully nonlinear electron and ion dynamics that is controlled by the laser light

Energetics and energy scaling of quasi-monoenergetic protons in laser radiation pressure acceleration

Theoretical and computational studies of the ion energy scaling of the radiation pressure acceleration of an ultra-thin foil by short pulse intense laser irradiation are presented. To obtain a quasi-monoenergetic ion beam with an energy spread of less than 20%, two-dimensional particle-in-cell simulations show that the maximum energy of the quasi-monoenergetic ion beam is limited by self-induced transparency at the density minima caused by the Rayleigh-Taylor instability. For foils of optimal thickness, the time over which Rayleigh-Taylor instability fully develops and transparency occurs is almost independent of the laser amplitude. With a laser power of about one petawatt, quasi-monogenetic protons with 200 MeV and carbon ions with 100 MeV per nucleon can be obtained, suitable for particle therapy applications

An interview with Roald Sagdeev: his story of plasma physics in Russia, 1956–1988

This oral history interview presents Roald Z. Sagdeev’s story of plasma physics in Russia. It chronicles the Russian school’s achievements in basic, laboratory, fusion and space plasma physics. The interview begins with memories of Sagdeev’s graduate student days in Moscow and then describes his work at the Kurchatov Institute of Atomic Energy (1956–1961), the Budker Institute of Nuclear Physics in Novosibirsk (1961–1971) and the Space Research Institute (IKI) (1973–1988). The interview examines the development of quasilinear theory, collisionless shocks, wave turbulence, instabilities, drift waves, chaos theory, the early stages of magnetic confinement theory and space plasma physics. Sagdeev and his school made seminal contributions in all of these areas, and all are central topics in plasma physics today. Sagdeev also speaks of his collaborations and friendships with notable scientists, such as M.N. Rosenbluth, M.A. Leontovich, L.A. Artisimovich, L.I. Rudakov, A.A. Galeev, V.E. Zakharov, as well as of the political and institutional challenges of this period. The conversation reflects Sagdeev’s unique and significant influence in modern plasma theory, Russian space exploration and his support of international cooperation for the advancement of humanity

An interview with Roald Sagdeev: his story of plasma physics in Russia, 1956-1988

This oral history interview presents Roald Z. Sagdeev’s story of plasma physics in Russia. It chronicles the Russian school’s achievements in basic, laboratory, fusion and space plasma physics. The interview begins with memories of Sagdeev’s graduate student days in Moscow and then describes his work at the Kurchatov Institute of Atomic Energy (1956–1961), the Budker Institute of Nuclear Physics in Novosibirsk (1961–1971) and the Space Research Institute (IKI) (1973–1988). The interview examines the development of quasilinear theory, collisionless shocks, wave turbulence, instabilities, drift waves, chaos theory, the early stages of magnetic confinement theory and space plasma physics. Sagdeev and his school made seminal contributions in all of these areas, and all are central topics in plasma physics today. Sagdeev also speaks of his collaborations and friendships with notable scientists, such as M.N. Rosenbluth, M.A. Leontovich, L.A. Artisimovich, L.I. Rudakov, A.A. Galeev, V.E. Zakharov, as well as of the political and institutional challenges of this period. The conversation reflects Sagdeev’s unique and significant influence in modern plasma theory, Russian space exploration and his support of international cooperation for the advancement of humanity