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A determination of the angular distributions, β, and relative partial photoionization cross sections, σ, of the valence satellite lines of atomic scandium in the region of the 3p → nd, ms excitations has been carried out using electron spectrometry in conjunction with monochromatized synchrotron radiation. This work is complementary to our earlier study of the partial cross sections of the Sc valence satellites but now includes angular distribution measurements of the most intense satellite lines. A correct theoretical description of the experimental satellite σ and β values presented herein should help in rectifying present discrepancies between theory and experiment for the 3d and 4s mainline σ and β values.

This overview of results from the MST reversed field pinch program summarizes physics im- portant for the advancement of the RFP as well as for improved understanding of toroidal magnetic confinement in general. Topics include energetic particle effects, 3D helical equilibria, and density limit studies, microturbulence, ion heating, and magnetic self-organization physics. With neutral beam injection, several bursty energetic particle (EP) modes are observed. The profiles of the magnetic and density fluctuations associated with these EP-modes are measured using an FIR interferometer- polarimeter. Equilibrium reconstructions of the quasi-single-helicity 3D helical state are provided by the V3FIT code that now incorporates several of MST's advanced diagnostics. A predator-prey theoretical model based on sheared flow and/or magnetic field has been developed that captures key QSH dynamics. Upgraded pellet injection permits study of density and limits over MST's full range of operation, and an MST-record line-average density of 0 : 9 10 20 { m 3 ( n { n G 1 : 4 ) has been obtained. Plasma exhibits saturation at tot § 20% for a wide range of density, 0 : 2 + n { n G + 1 : 6 . Gyrokinetic simulations (GENE) based on experimental toroidal equilibrium reconstructions predict unstable trapped electron modes. Nonlinear simulations show that the "Dimits shift" is large and persists at finite . Experimentally, small-scale density fluctuations are detected in improved confine- ment plasmas. Impurity ion temperature measurements reveal a charge-to-mass-ratio dependence in the rapid heating that occurs during a sawtooth crash. Also, a toroidal asymmetry in the ion temper- ature is measured, correlated with 3D magnetic structure associated with tearing modes. Magnetic self-organization studies include measurements and modeling of the dynamo emf in standard RFP operation as well as with an applied ac inductive electric field to investigate the dynamics of oscillating field current drive (OFCD). Extended MHD computation for standard RFP conditions using NIMROD predicts dynamical coupling of current and plasma flow relaxation. The dynamo emf has also been measured when OFCD is applied, strengthening the understanding of and possibility for steady-state current sustainment using inductive current drive.

An overview of recent results from the MST programme on physics important for the advancement of the reversed field pinch (RFP) as well as for improved understanding of toroidal magnetic confinement more generally is reported. Evidence for the classical confinement of ions in the RFP is provided by analysis of impurity ions and energetic ions created by 1 MW neutral beam injection (NBI). The first appearance of energetic-particle-driven modes by NBI in a RFP plasma is described. MST plasmas robustly access the quasi-single-helicity state that has commonalities to the stellarator and 'snake' formation in tokamaks. In MST the dominant mode grows to 8% of the axisymmetric field strength, while the remaining modes are reduced. Predictive capability for tearing mode behaviour has been improved through nonlinear, 3D, resistive magnetohydrodynamic computation using the measured resistivity profile and Lundquist number, which reproduces the sawtooth cycle dynamics. Experimental evidence and computational analysis indicates two-fluid effects, e.g., Hall physics and gyro-viscosity, are needed to understand the coupling of parallel momentum transport and current profile relaxation. Large Reynolds and Maxwell stresses, plus separately measured kinetic stress, indicate an intricate momentum balance and a possible origin for MST's intrinsic plasma rotation. Gyrokinetic analysis indicates that micro-tearing modes can be unstable at high beta, with a critical gradient for the electron temperature that is larger than for tokamak plasmas by roughly the aspect ratio.

An overview of recent results from the MST reversed field pinch programme is presented. With neutral beam injection, bursty energetic particle (EP) modes are observed. The profiles of the magnetic and density fluctuations associated with these EP modes are measured using a far infrared interferometer-polarimeter. Equilibrium reconstructions of the quasi-single-helicity 3D helical state are provided by the V3FIT code that now incorporates several of MST's advanced diagnostics. The orientation of the helical structure is controlled using a new resonant magnetic perturbation technique. Gyrokinetic simulations based on experimental equilibria predict unstable trapped-electron modes (TEMs), and small-scale density fluctuations are detected in improved-confinement plasmas with TEM-like features. Upgraded pellet injection permits study of density and beta limits over MST's full range of operation, and an MST-record line-average density of 0.9 ×1020 m3 (n/nG = 1.4) has been obtained. Impurity ion temperature measurements reveal a charge-to-mass-ratio dependence in the rapid heating that occurs during a sawtooth crash. Runaway of NBI-born fast ions during the impulsive sawtooth event agrees with test-particle theory. Magnetic self-organization studies include measurements of the dynamo emf with an applied ac inductive electric field using oscillating field current drive.

The partial cross sections, σ, and the angular distribution parameters, β, of the photoelectrons originating from the 4f and 6s subshells of atomic thulium have been measured in the region of the 5p excitations (23 eV–38 eV). In qualitative agreement with a previous absorption study, our σ curves show two regions of strong resonance enhancement, one around a photon energy of 27 eV corresponding to 5p3/2 excitations and the other near 32 eV corresponding to 5p1/2 excitations. The β curves show considerable variation between the allowed extremes of −1.0 and 2.0 for many of the 4f photolines. In addition, the 6s photoline shows very marked deviations from β = 2.0 which is indicative of an open-shell atom. We also compare our experimental results with our calculated 4f partial cross sections. While there is excellent qualitative agreement between theory and experiment, quantitative details are not reproduced: (i) the 5p3/2 excitations are too narrow, (ii) while the 5p1/2 excitations have an intensity that is substantially less than what is observed experimentally.

Einkristalle des Mischkristallsystems Wolfram—Molybdän konnten feldionenmikroskopisch mit Heliumionen bei 20 °K hochaufgelöst abgebildet werden. Mit zunehmender Molybdänkonzentration (25, 50, 75 Atom-Proz.) zeigte sich eine verstärkte Auflockerung der Kristallflächen. Neben den von der Herstellung herrührenden Gitterdefekten werden Leerstellen beobachtet, die insbesondere bei dem atomaren Abbau von Kristallflächen durch Feldeinwirkung gebildet und auf bevorzugte Feldverdampfung des Molybdäns aus den Mischkristallen zurückgeführt werden.

Die Bevorzugung des Wolframs bei Feldelektronenemissionsuntersuchungen ist im wesentlichen auf seine sehr gunstigen vakuumtechnischen Eigenschaften und seine sehr hohe Zerreisfestigkeit zuruckzufuhren. Wolfram hat unter den Metallen nicht nur den hochsten Schmelzpunkt, sondern zeichnet sich zugleich durch besonders niedrigen Dampfdruck aus, so das die Entgasung und Oberflachenreinigung relativ leicht durchzufuhren sind. Seine bemerkenswert hohe Zerreisfestigkeit erlaubt uberdies die Anwendung sehr hoher elektrischer Feldstarken, was sich fur die Desorption, Feldverdampfung, Feldionisation und ionenmikroskopische Abbildung groserer Oberflachenbereiche als sehr gunstig erweist.

Die Bevorzugung des Wolframs bei Feldelektronenemissionsuntersuchungen ist im wesentlichen auf seine sehr gunstigen vakuumtechnischen Eigenschaften und seine sehr hohe Zerreisfestigkeit zuruckzufuhren. Wolfram hat unter den Metallen nicht nur den hochsten Schmelzpunkt, sondern zeichnet sich zugleich durch besonders niedrigen Dampfdruck aus, so das die Entgasung und Oberflachenreinigung relativ leicht durchzufuhren sind. Seine bemerkenswert hohe Zerreisfestigkeit erlaubt uberdies die Anwendung sehr hoher elektrischer Feldstarken, was sich fur die Desorption, Feldverdampfung, Feldionisation und ionenmikroskopische Abbildung groserer Oberflachenbereiche als sehr gunstig erweist.

Oberflachen von Wolframstaben mit Zusatzen von Thoriumoxid werden elektronenmikroskopisch abgebildet. Dies geschieht mit einer zweistufigen Abdrucktechnik (Aluminiummatrize, Kohleabdruck), die den Erfordernissen zerklufteter Oberflachen angepast ist. Lichtmikroskopischen Gefugebildern werden Elektronenmikroskopbilder gegenubergestellt. In diesen konnen noch Thoriumoxideinschlusse mit Abmessungen von etwa 0,05 µm erkannt werden. Zwei Grosenklassen von Thoriumoxideinschlussen sind zu unterscheiden: sehr kleine Einschlusse mit Abmessungen um 0,1 µm und grosere von mehreren E.i.m Ausdehnung. Die kleinen Partikel zeigen noch die Grose der Thoriumoxidkristalle im Metallpulver vor dem Sintern, die groseren sind wahrend des Sinterns entstanden.