The line emission of carbon and lithium beams in the plasma edge of TEXTOR Beigman, I L; Kocsis, G; Pospieszczyk, A; Vainshtein, L A
doi: 10.1088/0741-3335/40/10/003pmid: N/A
The laser blow-off method (LBO) is a useful tool for the analysis of parameters in the boundary layer of a tokamak plasma, particularly in the determination of the electron temperature and density distribution. The interpretation of the experimental data obtained by LBO from neutral carbon and lithium beams, which are commonly used in these cases, requires corresponding collisional radiative models for description of the level populations within these atoms. Such models for the spectral lines observed in TEXTOR are formulated. The number of atomic levels necessary for calculation of the line intensities is discussed.
Far-field approach to the transfer of polarized radiation in anisotropic, spatially dispersive, weakly inhomogeneous and dissipative media Bellotti, U; Bornatici, M
doi: 10.1088/0741-3335/40/10/004pmid: N/A
The transport of polarized radiation in anisotropic, spatially dispersive, weakly inhomogeneous and dissipative media with embedded sources is dealt with in terms of the (second-rank) radiation intensity tensor obtained on the basis of the geometrical optics far-field solution of the wave equation. Such an approach accounts for the effects of both wave energy absorption and emission from the medium, the former being related to the anti-Hermitian part of the dielectric tensor of the medium and the latter being expressed in terms of the autocorrelation of the source current density, which allows one to treat both polarized and unpolarized, as well as coherent and incoherent, sources. The polarization properties of the radiation, described on the basis of the polarization vectors of the two propagating electromagnetic eigenmodes, are investigated with respect to the effects of both the spatial inhomogeneity and birefringence of the medium, the latter, in particular, being connected with the relative change of phase of the two propagating modes over the relevant ray path. Each of the effects is discussed, and the connections with standard notions such as the specific intensity of the radiation and Stokes parameters are investigated, the state of thermodynamic equilibrium being considered as an example. The specific case of the polarization degeneracy in an isotropic medium is addressed in some detail. The case of a non-uniformly magnetized medium is also considered.
Theory of fully developed turbulence in buoyancy-driven fluids and pressure-gradient-driven plasmas Itoh, S-I; Itoh, K
doi: 10.1088/0741-3335/40/10/006pmid: N/A
A new theoretical method is presented to analyse turbulence and associated transport in far-non-equilibrium fluids and plasmas. First, direct nonlinear interactions with background turbulence are renormalized into nonlinear dielectric form. The relation between the turbulent intensity spectra of energy and temperature, E( k) and , and the nonlinear transfer rates (dielectric) of momentum and energy, and , are obtained as recurrent formulae of integral equations. Second, nonlinear marginal stability conditions are examined by introduction of dressed test mode analysis. Solutions have a power law which are analogous to critical exponents in renormalization group theory. The same paradigm is first applied to neutral fluids to recover conventional results. For two-dimensional (2D) buoyancy-driven turbulence, where a supercritical turbulence appears, spectral forms of E( k), and , are obtained in the energy containing range (or subrange). ( is the temperature gradient and g is the gravity.) The relation between global turbulent transport coefficients, such as and , and nonlinear transfer rates and is obtained. A global spatial structure of the turbulent fluid, which is consistent with the spectrum, is solved. The Nusselt number is obtained as and the relations and are obtained. ( is the Rayleigh number and is the critical Rayleigh number.) To turbulence in the magnetized plasma, where a subcritical turbulence appears, this paradigm is applied. The combination of the pressure gradient and magnetic field gradient , characterizes the non-equilibrium form of the plasma. The spectral intensity of the fluctuating fields for the potential, current and pressure and the nonlinear transfer rates are first obtained (symbols and correspond to the ion viscosity, current diffusivity and heat diffusivity, respectively) in the energy containing range. The turbulence level, W, and the transport coefficients, , are derived as and . The dissipation balance is also examined. These analyses demonstrate that this method is applicable to both the supercritical and subcritical turbulences in neutral fluid and plasma turbulences, i.e. in systems which are far from the thermal equilibrium.
Reduction of loop voltage and magnetic field fluctuations due to toroidal rotation in the reversed field pinch Sätherblom, H-E; Schnack, D D; Drake, J R
doi: 10.1088/0741-3335/40/10/008pmid: N/A
Results are presented from a three-dimensional (3D), nonlinear, resistive magnetohydrodynamic (MHD)-code study of thin shell modes (TSM) in a reversed field pinch (RFP), when toroidal plasma flow is introduced by adding a drag force in the toroidal momentum balance. Without this rotation-inducing force, TSM wall-locking develops and the loop voltage and edge magnetic fluctuation level are increased compared to the conducting shell case. Inclusion of drag on the plasma which produces toroidal flow in turn creates a force on the mode perturbation. Above a threshold drag force wall-locking is eliminated, the perturbation rotates and the loop voltage and edge magnetic field fluctuations are reduced to the value of the conducting shell case.
`Profile consistency' features in shaped sawtoothing ohmic TCV plasmas Weisen, H; Behn, R; Furno, I; Moret, J-M; Sauter, O; team, the TCV
doi: 10.1088/0741-3335/40/10/010pmid: N/A
A large variety of plasma conditions has been created in TCV (Tokamak à Configuration Variable, m, a < 0.25 m). They include limited and diverted discharges with elongations in the range 1-2.58, triangularities between -0.7 and 1 as well as `square' shapes with plasma currents in the range 0.1-1 MA. Over the entire range of quasi-stationary ohmic conditions investigated we observe a correlation between electron pressure profiles and conductivity profiles, suggesting that , where refers to an average over the volume or respectively, the cross sectional area of the plasma. The profiles become broader as the average current density is increased. These `profile consistency' features are in apparent agreement with theoretical considerations based on minimum energy states of the plasma or on stationary entropy. Further analysis of the experimental evidence, together with a model of the current profile consistent with neoclassical conductivity in the confinement zone and corresponding to a safety factor inside the sawtoothing core, however, shows that the observations can be accounted for by the effects of sawtooth activity.