Results 1 - 10 of 2127
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[en] We compare two different derivations of the gyrokinetic equation: the Hamiltonian approach in Dubin D H E et al (1983 Phys. Fluids 26 3524) and the recursive methodology in Parra F I and Catto P J (2008 Plasma Phys. Control. Fusion 50 065014). We prove that both approaches yield the same result at least to second order in a Larmor radius over macroscopic length expansion. There are subtle differences in the definitions of some of the functions that need to be taken into account to prove the equivalence.
[en] Toroidal momentum transport mechanisms are reviewed and put in a broader perspective. The generation of a finite momentum flux is closely related to the breaking of symmetry (parity) along the field. The symmetry argument allows for the systematic identification of possible transport mechanisms. Those that appear to lowest order in the normalized Larmor radius (the diagonal part, Coriolis pinch, E x B shearing, particle flux, and up-down asymmetric equilibria) are reasonably well understood. At higher order, expected to be of importance in the plasma edge, the theory is still under development.
[en] Finite Larmor radius stabilization of Z-pinches is discussed. Stability criteria can be derived for a class of equilibria having constant mass and current density. The internal modes can be stabilized provided the line density not exceed a critical value of the order of 1018 ions/m. (Author)
[en] The particle diffusion in the mixed regime where the heavy impurities are in the Pfirsch-Schluter regime and the light ions are in the plateau regime is studied. It is shown that the formula of the intermediate Pfirsch-Schluter regime is recovered when tested by projection upon the exact solutions. The problem of nuclear shapes and band crossing is discussed either from the point of view of projecting particular intrinsic states on the exact solutions or from the quadrupole moment values of excited states. The results demonstrate the importance of angular momentum alignment in the nuclear the failure of determinantal approximations of the yrast line states and the
[en] A set of one-fluid, modified magnetohydrodynamic (MHD) equations is developed that describes magnetized plasmas for which the relevant scale lengths are intermediate between the electron and ion Larmor radii, and the relevant time scales are intermediate between the electron and ion cyclotron frequencies. It is shown that the momentum equation is the same as that of conventional MHD but that the evolution of the magnetic field is strongly affected. The implications of the modified MHD system on the ''frozen-in'' theorem, magnetosonic waves, Alfven waves, and the interchange instability are examined
[en] Quasisymmetric stellarators are a type of optimized stellarators for which flows are undamped to lowest order in an expansion in the normalized Larmor radius. However, perfect quasisymmetry is impossible. Since large flows may be desirable as a means to reduce turbulent transport, it is important to know when a stellarator can be considered to be sufficiently close to quasisymmetry. The answer to this question depends strongly on the size of the spatial gradients of the deviation from quasisymmetry and on the collisionality regime. Recently, criteria for closeness to quasisymmetry have been derived in a variety of situations. In particular, the case of deviations with large gradients was solved in the 1/ν regime. Denoting by α a parameter that gives the size of the deviation from quasisymmetry, it was proven that particle fluxes do not scale with α3/2, as typically claimed, but with α. It was also shown that ripple wells are not the main cause of transport. This paper reviews those works and presents a new result in another collisionality regime, in which particles trapped in ripple wells are collisional and the rest are collisionless. (paper)
[en] The influence of finite ion Larmor radius and equilibrium self-electric fields on the ion resonance instability in a non-neutral plasma column is examined, and a closed algebraic dispersion relation for the complex eigenfrequency ω is obtained. It is shown that finite ion Larmor radius effects can have a strong stabilizing influence for azimuthal mode numbers 1 > - 2, particularly when the equilibrium self electric field is sufficiently weak. (author)
[en] The effects of compressibility and finite ion Larmor radius on the thermal instability of a plasma in the presence of a uniform horizontal magnetic field are investigated. When the instability sets in as stationary convection, the compressibility and finite Larmor radius are found to have stabilizing effects. The case of overstability is also studied leading to the establishment of conditions sufficient for avoiding overstability. (orig.)
[en] The electrostatic flute-type instability in an inhomogeneous magnetic field is one of the most important modes in fusion research. A model of this mode in terms of an equivalent gravitation force has earlier been treated by conventional normal mode analysis, also including finite Larmor radius (FLR) effects. Such an analysis does not apply to the case of large particle excursions, such as those due to large Larmor radius (LLR) effects. At this stage there does not exist any analytic kinetic approach by which the LLR effects can be fully treated in a quasi-neutral plasma. The aim of this paper is not to present a final solution of the LLR effects on the present instability, but merely to formulate the basic equations for a proposed computer analysis. (author)