Table of contents

Experiments indicate that gluons emitted in p-p collisions at s = 40 (GeV)² and detected by their π⁺-π⁻ decay are linearly polarized.

The dynamical pairing correlations are discussed using the rotating harmonic oscillator model and the RPA formalism. The dependence of the pairing strength distribution on rotational frequency and deformation is given special attention. In particular, the influence of coupling between different oscillator shells is analyzed in detail. Explicit formulae are given for the overlap matrix elements between the rotating and nonrotating states of the cranked harmonic oscillator.

Following an earlier observation in F VI we identified the line pair 1s2s2p²⁵P-1s2s2p3d⁵P^o, ⁵D^o for the elements N, O, Mg, and tentatively for Al and Si in beam-foil spectra. Assignment was established by comparison with Multi-Configuration Dirac-Fock calculations along the isoelectronic sequence. Using this method we also identified some quartet lines of lithiumlike ions with Z > 10.

Sixteen C III 1s2l2l'2l" states are calculated with multi-configuration interaction wave function. Relativistic and mass polarization corrections are included. The energies obtained are used to identify high resolution Auger spectra of Mann and of Bruch and collaborators. It is found that these four-electron resonances give the most intense spectral lines in the C⁺ → CH₄ collision experiment. It is interesting to find that all the four-electron lines between 235 eV to 259 eV observed in the multiple-electron-capture experiment can also be identified as coming from these 1s2l2l'2l" resonances. The agreement between the result of this work and experiments is excellent.

The saddle-point method is used to calculate 1s2l2l'2l" resonances of oxygen. The relativistic and mass polarization corrections are calculated with first order perturbation theory. Energies of Auger electrons are calculated for the (1s²2s, e) and (1s²2p, e) decay channels. These results are compared with those from high resolution Auger spectra using zero-degree electron spectroscopy. Excellent agreement is obtained in every instance. Our results are also compared with previous theoretical calculations in the literature. Some of the higher energy resonances calculated in this work have not yet been measured in experiments. We hope our results will be useful in future identifications.

Radiative lifetimes of 8 different multiplets in the visible range in neutral sulphur have been directly measured using the High Frequency Deflection technique. These lifetimes have not been experimentally studied earlier. The results are compared to Coulomb approximation calculations and semiempirical estimates of the associated oscillator strengths.

The core-excited states of Al III have been studied both experimentally and theoretically. The calculation of energy levels and lifetimes was performed by the multiconfiguration Hartree-Fock method, with Breit-Pauli relativistic corrections taken into account, and included the 2p⁵ 3s3p, 3p², 3s3d, and 3s4s configurations. The experimental data were obtained by the beam-foil method. A level scheme involving quartet levels of the 2p⁵ 3s3p, 3p², and 3s3d configurations has been established. Autoionization is the dominant decay channel for the levels belonging to the 2p⁵ 3p² and 3s3d terms, and only for a few levels of these terms, the dominant decay mode is an optical transition to a 2p⁵ 3s3p level. This is in disagreement with preliminary results from a recent optical study of the Al III system [Martinson et al., Nucl. Instrum. Methods B31, 188 (1988)]. Differences and similarities with the recently studied isoelectronic quartet systems of Na I and Mg II are discussed.

Energies, structures, transition wavelengths and probabilities for 1s²2snl and 1s²2pnl' singlet and triplet terms of N IV are calculated and compared with available experimental data. It is suggested that the 2p4d¹D^o and ¹F^o terms have been incorrectly identified, that 2p3p³S lies below 2s4s³S and that several new and unclassified lines in the beam-foil spectrum of nitrogen are due to transitions from previously unknown 2p4f terms. A tentative assignment is provided for the unclassified line at 259.434 nm.

Doppler-limited laser optogalvanic spectroscopic experiments were carried out using an externally stabilized ring dye laser and a La/Ne hollow cathode lamp. The hyperfine structure of ten La I transitions was studied and the magnetic dipole constants (A) for 18 levels were evaluated. The A constants for the four levels at 13260.36, 20197.38, 25378.46 and 30354.32 cm⁻¹ are reported for the first time.

The spectra of lead and bismuth were observed in the 350-260 Å (Pb) and in the 350-240 Å (Bi) region. In these two regions the 5d⁸-5d⁷6p transitions of Pb VII, respectively, Bi VIII are located. In both 5d⁸ configurations eight levels have been identified, while in the 5d⁷6p configurations 69 levels (Pb) and 57 (Bi) levels were established. The structure of the configuration was calculated using conventional Slater-Condon theory.

In this work we have measured lifetimes, oscillator strengths and hyperfine structures in Ho II. Accurate atomic structure data are of importance for element identification in steller atmospheres as well as in atomic structure studies. Lifetimes of 3 excited levels, all observed in stellar spectra, have been measured using electro-optic modulation spectroscopy in the ultraviolet. Oscillator strengths have furthermore been extracted by analyzing the time evolution of the laser excitation in the Rabi-regime. Previous to this study no lifetime and oscillator strength data were known in Ho II. In addition, the hyperfine structures of 3 low odd levels and 2 excited levels, has been accurately measured using fast beam laser spectroscopy. These data are analyzed using Multi-Configuration Dirac-Fock (MCDF) wavefunctions.

An approximate analysis is made of the 1-D thermal balance equation determining the plasma temperature in a fusion reactor plasma. This highly nonlinear transport equation is investigated for equilibrium and stability. Simple approximate equilibrium solutions are found using variational optimization techniques. Comparisons with numerically obtained solutions show good agreement.

Global vortex solutions in a rotating pure electron plasma column are derived within the framework of a dissipationless, cold fluid model. These solutions represent nonlinear steady state diocotron modes and may be of relevance to recent computer simulations on crossed-field electron flow and laboratory experiments on pure electron plasma columns.

By considering the ablatant to be a 4-species (H₂, H, H⁺ and e⁻) reacting gas and assuming the validity of local thermodynamic equilibrium, the ablatant state of a hydrogen pellet during its passage in a tokamak is studied. Results of analysis showed that the pellet ablation rate is sensitive neither to the specific assumption regarding the variation of the ratio of the specific heats, γ in the ablated cloud, nor to the precise ablation process at the pellet surface. Except a proportional constant depending on the effect of dissociation and ionization, the scaling of the pellet ablation rate with respect to the plasma state and pellet radius is similar to that of the 1-species neutral shielding model; the overall ablation rate is reduced by approximately 15%.

The ratio r_i/r_p of the ionization radius, r_i to the pellet radius, r_p is shown to be related to the pressure, p_e and the equilibrium constant of ionization, K_i(T_e) by p_e/K_i(T_e) of the plasma electrons, and approaches a constant value, (≈ 11), when p_e/K_i(t_e) > 2 × 10⁻¹². For combinations of pellet radius, plasma state and magnetic field strength of interest, irrespective of the ionization process, at an ablated cloud radius r ≈ 2r_p, nearly 80% of the ambient electron energy flux is absorbed.

Under some situations when there is a lack of balance between the energy input of the plasma electrons and the heating and expansion of the ablatant, a weak shock (flow Mach number, M = 1) can develop near the pellet during the expansion of the ablatant.

The ideal MHD stability properties of the axisymmetric free-boundary m = 1 mode of toroidal Extrap equilibria with large aspect ratio and weakly non-circular cross-section are investigated. The effect of passive feedback due to induced currents in the external conductors, represented as ideal current loops, and in a surrounding conducting wall, is taken into account in an approximate fashion by using the inductances of the circuits. The dependence of the effect of the feedback on different parameters such as the plasma radius, the radius of the wall and the horizontal position of the equilibrium plasma is studied. It is found that the effect of feedback becomes significant in the Extrap configuration when the plasma radius is not too small. The axisymmetric mode is thereby stabilized over a parameter regime which is roughly corresponding to the experimental situation of the Extrap T1 device.

An analytical treatment of the large scale axisymmetric motion of a z-pinch in an arbitrary transverse magnetic field is given. The analysis is based on an expansion in the non-circularity of the plasma cross-section, but does not involve any assumption of small displacements of the plasma from some equilibrium position. In order to include the effect of a possible internal rotation of the plasma, the pinch is initially modeled by an incompressible, surface current ideal MHD plasma with constant vorticity. The presence of homogeneous, axial magnetic fields B_i and B_e (inside and outside of the pinch, respectively) is shown to have no effect on the axisymmetric motion. One particular application concerns the axisymmetric m = 1 instability (slip mode) of non-circular pinches, relevant for a number of Tokamaks and for the Extrap z-pinch configuration. It is shown that the plasma rotation increases the linear as well as the nonlinear growth of this instability. In a "quasi-static" approximation the method is readily extended to volume current plasmas, and is found to greatly simplify the calculation of linear and nonlinear stability of non-circular pinches, as compared to previous investigations. Some illustrative examples are given. The role of inertia in the time evolution of the plasma non-circularity, leading to the possibility of axisymmetric stability of a z-pinch in a time-varying magnetic field, as well as to the possible existence of "precessing equilibria" of a z-pinch in Extrap geometry, is briefly discussed.

It has been produced a weakly ionized radiofrequency plasma by electron cyclotron resonance in the Mirror Linear Device LISA of the Universidade Federal Fluminense. The plasma is analyzed both analytically and experimentally. It has been shown that the plasma heating rate is a function of the resonant volume, where two volumes have been considered. The collisional plasma heating process due to the magnetic field modulation has also been studied.

Minor corrections have been done on two simple and ideal MHD models for instability, viz., the fixed- and free-boundary Shafranov's [1] models. In the fixed-boundary case, the interval of values of the safety factor at the current channel radius q_a for instability has been enlarged due to a second branch in the dispersion relation, not predicted in Shafranov's work. In the free-boundary case, the interval of q_a for instability is still the same as in reference above but the expression for the maximum growth differs by a multiplication factor which is a function of the azimuthal mode number m. These corrections were only possible after a carefull handling of the MHD instability equations and boundary conditions in both cases simultaneously.

A set of jump conditions have been derived for the relevant perturbed plasma parameters as a consequence of a finite discontinuity in the equilibrium current density taking place inside a diffuse, incompressible and resistive MHD linear pinch. This set can be relevant in applications to numerical modelling of the equilibria and instability of pinches and tokamaks.

Two MHD models for instability, viz., the Shafranov's [1] resistive free-boundary and resistive fixed-boundary step models have been revisited. In the former, a constant longitudinal current density passes through a cylindrical column of a resistive plasma of radius a separated by vacuum from a perfectly conducting wall at a radius b; in the latter, the current density has the same radial profile but the plasma fills the whole cylinder up to the conducting wall.

For the former, the explicit dependence of resistivity η on the maximum normalized growth rate Γ_max is exhibited showing a stabilizing effect on kinks. A fact that is overlooked by some authors is also pointed out here in the form of a correction of the original growth rate γ_max. For the latter, a special code set up to solve the (stiff) system of differential equations for instability in the region a ⩽ r ⩽ b, together with a set of jump conditions at the current channel radius a, yield no solution satisfying the appropriate boundary conditions at the wall.