21,589 research outputs found

### Coupling of electromagnetic waves and space charge waves in type O traveling wave tubes

H. Derfler observed that a parameter defined by Pierce's perturbation method does not have the same physical significance as an analogous parameter described by a differently derived equation of W. Kleen. A modification of Pierce's method is proposed, which yields an equation of Derfler's type, and also allows quicker and easier calculation of a given traveling wave tube's parameters

### Model dependence of the neutrino-deuteron disintegration cross sections at low energies

Model dependence of the reaction rates for the weak breakup of deuterons by
low energy neutrinos is studied starting from the cross sections derived from
potential models and also from pionless effective field theory. Choosing the
spread of the reaction yields, caused basically by the different ways the
two-body currents are treated, as a measure of the model dependent uncertainty,
we conclude that the breakup reactions are $\sim$ 2 - 3 % uncertain, and that
even the ratio of the charged to neutral current reaction rates is also $\sim$
2 % uncertain.Comment: 13 pages, 1 figure, 6 tables, version published in Phys. Rev. C 75,
044610 (2007

### Interactions of the solar neutrinos with the deuterons

Starting from chiral Lagrangians, possessing the SU(2)_L x SU(2)_R local
chiral symmetry, we derive weak axial one-boson exchange currents in the
leading order in the 1/M expansion (M is the nucleon mass). We apply these
currents in calculations of the cross sections for the disintegration of the
deuterons by the low energy neutrinos. The nuclear wave functions are derived
from a variant of the OBEPQB potential and from the Nijmegen 93 and Nijmegen I
nucleon-nucleon interactions. The comparison of our cross sections with those
obtained within the pionless effective field theory and other potential model
calculations shows that the solar neutrino-deuteron cross sections can be
calculated within an accuracy of 3.3 %.Comment: 6 pages, 1 figure, 6 tables, conference tal

### A Drift-Kinetic Analytical Model for SOL Plasma Dynamics at Arbitrary Collisionality

A drift-kinetic model to describe the plasma dynamics in the scrape-off layer
region of tokamak devices at arbitrary collisionality is derived. Our
formulation is based on a gyroaveraged Lagrangian description of the charged
particle motion, and the corresponding drift-kinetic Boltzmann equation that
includes a full Coulomb collision operator. Using a Hermite-Laguerre velocity
space decomposition of the gyroaveraged distribution function, a set of
equations to evolve the coefficients of the expansion is presented. By
evaluating explicitly the moments of the Coulomb collision operator,
distribution functions arbitrarily far from equilibrium can be studied at
arbitrary collisionalities. A fluid closure in the high-collisionality limit is
presented, and the corresponding fluid equations are compared with
previously-derived fluid models

### A gyrokinetic model for the plasma periphery of tokamak devices

A gyrokinetic model is presented that can properly describe strong flows,
large and small amplitude electromagnetic fluctuations occurring on scale
lengths ranging from the electron Larmor radius to the equilibrium
perpendicular pressure gradient scale length, and large deviations from thermal
equilibrium. The formulation of the gyrokinetic model is based on a second
order description of the single charged particle dynamics, derived from Lie
perturbation theory, where the fast particle gyromotion is decoupled from the
slow drifts, assuming that the ratio of the ion sound Larmor radius to the
perpendicular equilibrium pressure scale length is small. The collective
behavior of the plasma is obtained by a gyrokinetic Boltzmann equation that
describes the evolution of the gyroaveraged distribution function and includes
a non-linear gyrokinetic Dougherty collision operator. The gyrokinetic model is
then developed into a set of coupled fluid equations referred to as the
gyrokinetic moment hierarchy. To obtain this hierarchy, the gyroaveraged
distribution function is expanded onto a velocity-space Hermite-Laguerre
polynomial basis and the gyrokinetic equation is projected onto the same basis,
obtaining the spatial and temporal evolution of the Hermite-Laguerre expansion
coefficients. The Hermite-Laguerre projection is performed accurately at
arbitrary perpendicular wavenumber values. Finally, the self-consistent
evolution of the electromagnetic fields is described by a set of gyrokinetic
Maxwell's equations derived from a variational principle, with the velocity
integrals of the gyroaveraged distribution function explicitly evaluated

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