Resonant interaction of fast particles with Alfven waves in spherical tokamaks

The Spherical Tokamak (ST) concept has become one of the main avenues in magneticnuclear fusion research since STs successfully demonstrated plasma operationat [Beta] = 2P[mu]0=B2~1. Next step ST machines aiming at achieving burning plasmaconditions in high [Beta] plasmas are being planned, such as the Spherical TokamakPower Plant (STPP) and the Component Testing Facility (CTF). Instabilities offast particle-driven Alfven eigenmodes are often observed in present-day STs. Suchinstabilities, driven by fusion-born alpha particles as well as by fast ions producedwith auxiliary heating schemes, in the next step STs may pose a major problem asthese instabilities may affect confinement and losses of the fast ions.A theory of compressional Alfven eigenmodes (CAE) with frequencies above thedeuterium cyclotron frequency,[omega] > [omega]cD, is developed for plasma parameters of aSTPP, and modes in the ion-ion hybrid frequency range, [omega]cT < [omega] < [omega]cD, are alsoinvestigated in order to assess the potential of diagnosing the deuterium-tritium(D-T) ratio. For the 1-D character of a STPP equilibrium with [Beta]~1 , a `hollowcylinder toroidal plasma model is employed for studying CAEs with arbitrary valuesof the parallel wave-vector k[||] = k[.]B/|B|. The existence of weakly-damped CAEs,free of mode conversion, is shown to be associated with the `well in the magneticfield profile, B = B (R), that can exist at the magnetic axis.A significant part of this thesis focusses on the experimentally observed effectsof resonant wave-particle interaction between Alfven waves and fast particles in theMega Amp Spherical Tokamak (MAST) device at the Culham Laboratory, UK, andin the LArge Plasma Device (LAPD) in the University of California, Los-Angeles,USA. New robust experimental scenarios for exciting CAEs in the MAST spherical tokamak are developed, and interpretation of the observed CAEs in the frequencyrange [omega]cD/3 < [omega] < [omega]cD is given in the context of the 1-D ST model and the Dopplershifted cyclotron resonance. The e ciency of the Doppler resonance between coand counter directed fast ions and left and right hand polarised Alfven waves isfurther assessed experimentally on the LAPD device, with probe ions injected inthe presence of Alfv en waves launched by an external antenna.The developed theory of CAEs is then applied to a calculation of the linear kineticdrive of CAEs in the MAST experiments. A model representation of the fast iondistribution function, produced by neutral beam injection (NBI), is used by fittingto the TRANSP Monte-Carlo NBI modelling results. The main free energy sourcesassociated with temperature anisotropy and bump-on-tail are estimated analytically,and the CAE stability boundary is qualitatively assessed.In order to explain the experimentally observed difference between steady-stateand pulsating Alfvenic modes, the non-linear theory of fast particle driven modesnear marginal stability is extended to include dynamical friction (drag). For thebump-on-tail problem, the drag is shown to always give an explosive amplitudeevolution in contrast to diffusion in velocity space in the vicinity of the wave-particleresonance. This is then extended to the case of experimentally observed NBI-driventoroidal Alfven eigenmodes (TAEs) in the MAST machine. The experimentallyobserved differences between TAEs driven by fast ions produced with ion cyclotronresonance heating (ICRH) and NBI are then interpreted. The problem of dragdominated collisions for modes excited by fusion-born alpha particles in burningplasmas such as a STPP and ITER is underlined.Imperial Users onl

First-Order Phase Transitions in an Early-Universe Environment

In first-order phase transitions in the early universe, the bubble wall is expected to be significantly slowed-down by its interaction with the surrounding plasma. We examine the behaviour of the phase of the Higgs field after two-bubble collisions, and find that phase differences equilibrate much more quickly in slow-moving bubbles than in those which expand at the speed of light. This could lead to a significant reduction in the initial density of topological defects formed at a first-order phase transition.Comment: 4 pages, 2 figures, to appear in Proceedings of the International Workshop on Particle Physics and the Early Universe (COSMO 99), Trieste, Italy, September 27 - October 2, 199

Tilt

Poetry by Kate Lilley, Department of English, University of Sydney, Australia

Two Poems

Poetry by Joanna Lilley

Aurora Leadership Institutes: Assisting future leaders to maximise their leadership skills and potential

Paper presented at Oceans of Opportunities: Library and Information Association of New Zealand Aotearoa 2003 Conference, 7 – 10 October 2003 Napier, New ZealandThis paper provides background information on the Aurora Leadership Institutes and the Aurora Foundation. The latter part of the paper focuses on the looming leadership crisis in the library profession in New Zealand and overseas and identifies several strategies that require implementation to ensure that the crisis is averted

Reflections on professional training: A post-Auroran view

Paper presented at Capitalising on Knowledge: Australian Library and Information Association 2000 Conference, 23 – 26 October 2000 Canberra, ACTThis paper looks at the relationship between education for librarianship, professional development and leadership training

Lateral jet injection into typical combustor flowfields

The trajectory, penetration and mixing efficiency of lateral air jet injection into typical combustor flowfields in the absence of combustion were investigated so as to characterize the time-mean and turbulence flowfield for a variety of configurations and input parameters, recommend appropriate turbulence model advances, and implement and exhibit results of flowfield predictions. A combined experimental and theoretical approach was followed, in a modified version of the test facility, equipped initially with one and two lateral jets, located one test-section downstream of the inlet

Closing the gaps: Maori and information literacy

Paper presented at User Education for User Empowerment: Commonwealth Library Association Conference 19 – 20 October 2000 Christchurch, New Zealand.This paper focuses on the reasons why information literacy is a concept that has yet to make an impact on Maori. Although Maori participation as librarians and library users has increased dramatically over the last decade there are still a range of barriers that continue to inhibit access to library and information services for Maori. The relevance of these barriers to the 'information literacy divide' are analysed and actions are identified which will allow a strategy to be created to close the gap

A note on the decay of aircraft trailing vortices

An elementary theory of aircraft trailing vortex decay is presented based on an assumed law for the variation of the mean eddy viscosity with distance from the wing. This law is based on the experimental data of Rose and Dee (1.963). The analysis gives results, as might be expected, in agreement with their data. The justification for the analysis must however be in doubt until more data are available covering a wide range of variables such as aircraft size, distance, incidence, etc

Turbulent Combustor Flowfield Investigation

The 2-D axisymmetric geometries under low speed, nonreacting, turbulent, swirling flow conditions were investigated. The effect of the parameters on isothermal flowfield patterns, time mean velocities and turbulence quantities is determined and an improved simulation in the form of a computer prediction code equipped with a suitable turbulence model is established. This is a prerequisite to the prediction of more complex turbulent reacting flows