[en] Elongated plasmas up to κ=2.5 have been obtained in the Lausanne Tokamak TCV. for κ<2.3, the normalized current limit, I_N=I[MA]/a[m]B[T], increases with elongation and is limited by the standard ideal limit at q_a=2. However for κ>2.3, a disruption occurs at larger values of q_a(κ), such that the current limit stays about constant at I_N≅3. The modes observed at the disruption are typically m/n=2/1 and 3/2 modes. The observed disruption limit is consistent with the prediction of the n=1 ideal MHD limit for analytical plasma shapes. We have computed the ideal and resistive MHD limit for the actual experimental plasma shapes and profiles. We find that the shots which disrupted are indeed very close to the ideal n=1 external kink β-limit. We also see that, including resistivity, the 4/3, 3>/2 and 2/1 modes are unstable even well below this limit, which agrees with the experimental data. For 2.5<κ<3, we have varied the profiles over a wide range and our results confirm the prediction that only by keeping q_a just above 3 and decreasing the plasma inductance, l_i, one can find stable configurations. (author) 3 figs., 10 refs

[en] A simple configuration consisting in a set of toroidal, helical and vertical field coils is used to calculate free boundary equilibria with nonzero plasma current boundary. The amount of helical boundary deformation is controlled by the ratio of the current in the helical field coils to the current in the toroidal field coils. When this ratio is increased the (m,n)=(2,1) external kink is stabilized at β≅1% for inverse rotational transform profiles in the region q<2. (author) 4 figs., 5 refs

[en] The investigation of the global ideal magnetohydrodynamic (MHD) stability of plasmas with helical boundary shape and nonvanishing toroidal plasma current constitutes the principal aim of this work. Global external modes with small values of m,n (typically n = 1,2,3 and m = n+1) are studied, where m and n are the poloidal and toroidal mode numbers, respectively. The first and main part of the work concentrates on fixed boundary equilibria generated by systematically varying parameters such as the type and the magnitude of the boundary deformation, the number of equilibrium field periods N_per, the aspect ratio, the toroidal current density profile, β and the pressure profile. Due to the periodicity of the equilibrium, couplings between Fourier perturbation components with different toroidal mode numbers n occur and lead to the apparition of families of modes. The study of a particular (m,n) mode has to take into account all (m_l, n_l) perturbation components with n₁ belonging to the same family as n. The stability analysis is carried out in the parameter region where the inverse rotational transform (the safety factor in the traditional tokamak notation) q≤2.0 and β≤2%. A particular property of the configurations investigated is that equilibrium Fourier components (m_e, N_pern_e) which are involved in the couplings between the (m,n) mode studied and the (m_k,n_k) perturbation components with m_k>n_k>n (that exhibit resonances in the q>1 region are very small. As a consequence, the contributions of the (m,n)x(m_k,n_k) couplings to the potential energy are very weak. It is shown that a helical boundary deformation can stabilize the n=1,2,3 external modes; if δ is a measure of the plasma boundary deformation, then windows of stability [δ_min, δ_max] may exist for a large variety of equilibrium parameters. (author) figs., tabs., 44 refs

[en] Mode conversion at the second harmonic cyclotron resonance is studied in a toroidal plasma, showing how the ion-Bernstein wave can dramatically affect the power profile and partition among the species. The results obtained with the gyrokinetic toroidal PENN code in particular suggest that off-axis electron and second harmonic core ion heating should become important when the temperatures in JET reach 10 keV. (author) 1 fig., 11 refs

[en] Levinson's theorem on the relation between the number of bound states and the scattering phase shift in any given momentum sector can be generalized to abstract scattering systems. In the present paper this abstract result is applied to a maximally large class of potential scattering systems in three dimensions. In the special case of a spherically symmetric potential Levinson's theorem is recovered. (Auth.)

[en] The various classical or quantum mechanical equations describing a system of N particles with central two-body interactions are invariant under the 10 transformations of the Galilei group, and for interaction potential inversely proportional to the squares of the particle separations also under two further transformations. From the invariance of the corresponding classical and quantum mechanical variation principles under this 12-parameter conformal extension of the Galilei group, the 'Jacobi-Schroedinger group', the 12 well-known conservation laws of Newtonian dynamics as well as 12 local conservation laws implied by the Schroedinger equation are obtained via Noether's theorem. Under appropriate conditions on the wave functions, these local laws yield 12 global conservation laws which are analogous to the Newtonian ones. The Hamiltonian-Jacobi equation implies a classical equation differing from the Schroedinger equation only by a potential-like term involving the Van Vleck determinant, from which 12 local balance equations and the corresponding global equations are obtained, which under certain conditions reduce the true conservation laws. (Auth.)

No abstract available

[en] An optical treatment of hadron-nucleus scattering originally proposed by Watson is reformulated in terms of scattering amplitudes instead of Mueller operators. This multiple scattering formalism although equivalent to the Kerman, McManus and Thaler approach is found to be less involved and can easily be extended to inelastic scattering. The convergence of the optical potential expansion as well as the role of mesonic absorption in the elastic channel are also discussed in this framework. (Auth.)

[en] The electrical resistivity of solutions of strontium in liquid sodium has been accurately determined by a capillary method as a function of both temperature in kelvins (373 < = T < = 773) and strontium concentration (0.00 <=xsub(Sr) <= 0.38). The resistivity varies smoothly with concentration with an increasingly positive (drho/dxsub(Sr))sub(T) and a decreasingly positive (drho/dT)sub(T); the excess resistivity of the solutions over that of the linear interpolation between the pure metals is relatively small but negative. It is predicted that the overall shape of the resistivity-composition isotherms approximates to a sinusoidal curve about the interpolated resistivity, the inversion from concave to convex behaviour occurring at about xsub(Sr) = 0.50. (Auth.)

[en] LiCl-LiF-GdF₃, LiF-GdF₃ and LiF-BaF₂-GdF₃ salts were evaluated for the electrolytic purification of gadolinium. The sum total of the metallic impurities in the final product was found to be less than 50 wt. ppm; less than 100 wt. ppm each of the interstitial elements H, C, N, O and F was present. LiF-GdF₃ yielded the highest purity gadolinium metal with respect to oxygen, even though this electrolyte and its deposits were handled in air. Metallographic and chemical analyses demonstrated that the extraction of fluoride inclusions from the metal was best achieved by electron beam melting. (Auth.)