A universal instability of many-dimensional oscillator systems

Limit on stably trapped particle fluxes determined theoretically and compared with data from Explorer satellites

/pdf/limit-on-stably-trapped-particle-fluxes-2ui3luegh7.pdf

Limit on stably trapped particle fluxes

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

/pdf/theory-of-star-formation-sol2jzngnw.pdf

Theory of Star Formation

A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave–zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

/pdf/zonal-flows-in-plasma-a-review-3byloag115.pdf

Zonal flows in plasma—a review

Prologue PART 1: The Need for a Theory of Cognitive Evolution Mental Architecture as an Emergent Phenomenon Culture as Evidence for Cognitive Structure The Organization of This Book PART 2:

Origins of the Modern Mind: Three Stages in the Evolution of Culture and Cognition

Nonlinear Plasma Theory

A perturbation theory analogous to that of quasi-linear theory is developed to treat the behavior of magnetic surfaces, in particular to estimate their stability against field irregularities. The method exploits the similarity between the Vlasov equation and the Liouville equation for field lines. We find that a very important role is played by field resonances, that isolated resonances have a limited effect, extended over a finite width which we estimate, but as soon as resonances overlap, a very rapid destruction of flux surfaces may be expected.

https://iopscience.iop.org/article/10.1088/0029-5515/6/4/008/pdf

Destruction of magnetic surfaces by magnetic field irregularities

Collisionless shocks cannot occur naturally on the earth, because nearly all matter here consists of electrically neutral atoms and molecules. In space, however, high temperatures and ultraviolet radiation from hot stars decompose atoms into their constituent nuclei and electrons, producing a soup of electrically charged particles known as a plasma. Plasma physicists proposed that the collective electrical and magnetic properties of plasmas could produce interactions that take the place of collisions and permit shocks to form. In 1964 the theoretical work found its first experimental confirmation. Norman F. Ness and his colleagues at the Goddard Space Flight Center, using data collected from the iMP-1 spacecraft, detected clear signs that a collisionless shock exists where the solar wind encounters the earth's magnetic field. More recent research has demonstrated that collisionless shocks appear in a dazzling array of astronomical settings. For example, shocks have been found in the solar wind upstream (sunward) of all the planet and comets that have been visited by spacecraft. Violent flares on the sun generate shocks that propagate to the far reaches of the solar system; tremendous galactic outbursts create disruptions in the intergalactic medium that are trillions of times larger. In addition, many astrophysicists think thatmore » shocks from supernova explosions in our galaxy accelerate cosmic rays, a class of extraordinarily energetic elementary particles and atomic nuclei that rain down on the earth from all directions.« less

Collisionless shock waves

IN this article we investigate the instability of a homogeneous plasma with ions (or electrons) having a non-Maxwellian velocity distribution. There exist two causes which lead to the instability of such a plasma: 1) the presence of a "beam" and 2) the anisotropy of "temperatures" parallel and perpendicular to the static magnetic field. In this article we investigate the instability due to the "temperature" anisotropy. It has been shown earlier1• 2 in the "drift" approximation that in the case of a sufficiently strong anisotropy of the "temperatures" of the ions (or the electrons), an instability of convective type Re ( w) ;>! 0 can occur. The so--called "drift" approximation utilized in these papers is valid only when the Larmor radii of all the particles are considerably smaller than the wavelengths of the perturbations, and the Larmor frequencies are correspondingly much higher than the oscillation frequencies. In going over to higher frequencies we shall see that an instability of the type of "oscillation with hunting", Re ( w) ;>! 0, will arise. However, it should be noted that even in the case of low frequency plasma oscillations the "tail" of the velocity distribution will generally speaking contain such particles for which the "drift" approximation will not be applicable as a result of the Doppler effect, and these particles cause the oscillations to build up even in the event of a small departure from an isotropic velocity distribution*. We can easily obtain the dispersion equation for the plasma oscillations if we know the expression for the components of the tensor Ea{3(w, k).

R. Z. Sagdeev

Papers

Nonlinear Plasma Theory

Destruction of magnetic surfaces by magnetic field irregularities

Collisionless shock waves

On the instability of a plasma with an anisotropic distribution of velocities in a magnetic field

Nonlinear Plasma Theory