Nicolae Pometescu

On non-Markovian relative diffusion of stochastic magnetic lines

In this paper we study some aspects related to the spatial relative diffusion of the magnetic-field lines. The nonlinear integral equation for the Lagrangian correlation is transformed into a system of two ordinary differential equations and solved numerically. The system of linear integro-differential equations for the moments is analysed numerically for different values of the -parameter (which is proportional to the ratio of parallel and perpendicular correlation lengths). A critical value for is obtained in a shearless stochastic magnetic-field model. For the rate of damping of the anisotropy becomes complex, that means an oscillatory behaviour for the correlations and anisotropies. For we find the well known behaviour described in the literature for .

The anomalous particle flux induced by electromagnetic turbulence

The aim of this paper is to calculate, in a new manner, a general expression for the anomalous particle flux due to electromagnetic turbulence, including the parallel components of the magnetic field fluctuations. The calculus of the flux uses the anomalous distribution function defined as the difference between the total distribution function and the neoclassical one. Besides the well known low-beta result, we also obtain the transport flux induced by parallel (to the equilibrium magnetic fields) fluctuations. Comparing the different components of the anomalous radial particle flux we specify the conditions when the effect of parallel fluctuations can be important.

Parallel and poloidal fluxes in turbulent non-ohmic plasmas: An ion-cyclotron resonance heating case

The parallel component of the vectorial fluxes, in particular the ion parallel particle flux h∥i(1) and the ion parallel heat flux h∥i(3), in an electrostatic turbulent magnetically confined plasma submitted to an external rf heating are obtained analytically in terms of the thermodynamic forces. Their expressions are derived using the methodology of neoclassical transport theory, the standard model of magnetic field and assuming a non-ohmic heating in the ion cyclotron resonance heating range for which a decoupling of the electron to the ion dynamics may be admitted as a first approximation. It is shown that all but one of the ion parallel turbulent transport coefficients related to a spectrum of electrostatic fluctuations are drastically reduced when the rf power density measured in terms of the Stix parameter is increased. The remaining coefficient, absent for an ohmic plasma increases with the Stix parameter.

Random transition between two temperatures profiles in magnetized plasma

A set of Langevin equations are used to describe the transport of the guiding centers of charged particles perpendicularly to the main magnetic field and the stochastic transition between the two temperature states is described by a randomly interrupted noise. Using this model, the variation of the running diffusion coefficients in the radial direction is analyzed for two cases of temperature profiles with applications to fusion plasma.

Radial and poloidal particle and energy fluxes in a turbulent non-Ohmic plasma: An ion-cyclotron resonance heating case

The combined effect of the turbulence and of the external radio-frequency heating on the radial and poloidal components of the ion particle and energy fluxes in magnetically confined plasma is analyzed analytically from the drift kinetic equation. These two components of the transport are derived in terms of the thermodynamic forces and of correlations of fluctuating quantities using the methodology of neoclassical transport theory based on the tokamak standard model of confining magnetic field. The ion cyclotron heating is specifically considered since, to first order, the electron dynamics may be neglected. The formalism is applied to different types of instabilities in order to quantify the role of the heating versus turbulence on the transport.

Perfectly stirred catalytic reactor

Abstract A heterogeneous, perfectly stirred catalytic reactor with internal recirculation, with the catalyst placed in a fixed bed, was developed in order to characterize several catalysts employed in ammonia industry. For carbon-dioxide methanation on an Ni/Al 2 O 3 catalyst, the perfect mixing was obtained at a stirrer rotation speed of 1000–2600 rpm, which ensured the same reaction rate, regardless of composition and feeding gas flow rate.