FFAGs and synchrotrons for proton therapy: a comparative study

Accelerators play a key role in the delivery of radiotherapy for treatment of cancer and other medical conditions. Proton therapy has the benefit of more localised delivery of dose to deep seated tumour volumes in comparison to treatment using x-rays or electrons. The accelerators currently used for proton therapy are cyclotrons and synchrotrons, which each have certain advantages and disadvantages. It has been proposed that accelerators of a fixed field alternating gradient (FFAG) design may combine some of the advantages and avoid some of the disadvantages of the existing machines. This thesis looks at the use of synchrotrons as a benchmark for the delivery of proton therapy, and then at how FFAGs may improve upon treatment delivery. Particular attention is paid to the beam dynamics issues, including comparisons between simulations and experimental data taken with the EMMA non-scaling FFAG at Daresbury. The results of the comparisons show that simulation is able to predict the behaviour of a particle bunch in a real machine. The simulation tools are then used to evaluate the design of FFAGs incorporating resonant extraction techniques. In principle, resonant extraction could overcome some problems of kicker based extraction methods. The design study highlights technical challenges that would need to be overcome before resonant extraction could be implemented as a beneficial method for a proton therapy FFAG

Reconstruction of lattice parameters and beam momentum distribution from turn-by-turn beam position monitor readings in circular accelerators

In high chromaticity circular accelerators, rapid decoherence of the betatron motion of a particle beam can make the measurement of lattice and bunch values, such as Courant-Snyder parameters and betatron amplitude, difficult. A method for reconstructing the momentum distribution of a beam from beam position measurements is presented. Further analysis of the same beam position monitor data allows estimates to be made of the Courant-Snyder parameters and the amplitude of coherent betatron oscillation of the beam. The methods are tested through application to data taken on the linear nonscaling fixed field alternating gradient accelerator, EMMA

Interaction of intense vuv radiation with large xenon clusters

The interaction of atomic clusters with short, intense pulses of laser light to form extremely hot, dense plasmas has attracted extensive experimental and theoretical interest. The high density of atoms within the cluster greatly enhances the atom--laser interaction, while the finite size of the cluster prevents energy from escaping the interaction region. Recent technological advances have allowed experiments to probe the laser--cluster interaction at very high photon energies, with interactions much stronger than suggested by theories for lower photon energies. We present a model of the laser--cluster interaction which uses non-perturbative R-matrix techniques to calculate inverse bremsstrahlung and photoionization cross sections for Herman-Skillman atomic potentials. We describe the evolution of the cluster under the influence of the processes of inverse bremsstrahlung heating, photoionization, collisional ionization and recombination, and expansion of the cluster. We compare charge state distribution, charge state ejection energies, and total energy absorbed with the Hamburg experiment of Wabnitz {\em et al.} [Nature {\bf 420}, 482 (2002)] and ejected electron spectra with Laarmann {\em et al.} [Phys. Rev. Lett. {\bf 95}, 063402 (2005)]

BAL phosphorus abundance and evidence for immense ionic column densities in quasar outflows: VLT X-Shooter observations of quasar SDSS J1512+1119

We present spectroscopic analysis of the broad absorption line outflow in quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic component in which we identify PV and SIV/SIV* absorption troughs. The shape of the unblended phosphorus doublet troughs and the three SIV/SIV* troughs allow us to obtain reliable column density measurements for these two ions. Photoionization modelling using these column densities and those of HeI* constrain the abundance of phosphorus to the range of 0.5-4 times the solar value. The total column density, ionization parameter and metalicity inferred from the PV and SIV column densities leads to large optical depth values for the common transition observed in BAL outflows. We show that the true CIV optical depth, is about 1000 times greater in the core of the absorption profile than the value deduced from its apparent optical depth.Comment: Accepted for publication in ApJ on August 26, 2012; 33 pages, 8 figure

Distribution and Ecology of Invasive Ants

This project examines exactly how invasive specific types of ants are, and what effect that has on the ecosystem. To do so, most of the research must be compiled for the first time, as there is a lack of knowledge and research on this subject. Through former research, Tillberg finds that there are invasive pavement ants in Oregon state parks, but due to a lack of research on the species, their impact is unknown. The research will follow a paired design, comparing similar areas with and without pavement ants, to discover what differences this invasive species has on habitats

Distribution and Ecology of Invasive Ants

This project examines exactly how invasive specific types of ants are, and what effect that has on the ecosystem. To do so, most of the research must be compiled for the first time, as there is a lack of knowledge and research on this subject. Through former research, Tillberg finds that there are invasive pavement ants in Oregon state parks, but due to a lack of research on the species, their impact is unknown. The research will follow a paired design, comparing similar areas with and without pavement ants, to discover what differences this invasive species has on habitats

The Diverse Bacterial Community in Intertidal, Anaerobic Sediments at Sapelo Island, Georgia

The phylogenetic diversity and composition of the bacterial community in anaerobic sediments from Sapelo Island, GA, USA were examined using 16S rRNA gene libraries. The diversity of this community was comparable to that of soil, and 1,186 clones formed 817 OTUs at 99% sequence similarity. Chao1 estimators for the total richness were also high, at 3,290 OTUs at 99% sequence similarity. The program RDPquery was developed to assign clones to taxonomic groups based upon comparisons to the RDP database. While most clones could be assigned to describe phyla, fewer than 30% of the clones could be assigned to a described order. Similarly, nearly 25% of the clones were only distantly related (<90% sequence similarity) to other environmental clones, illustrating the unique composition of this community. One quarter of the clones were related to one or more undescribed orders within the γ-Proteobacteria. Other abundant groups included the δ-Proteobacteria, Bacteroidetes, and Cyanobacteria. While these phyla were abundant in other estuarine sediments, the specific members at Sapelo Island appeared to be different from those previously described in other locations, suggesting that great diversity exists between as well as within estuarine intertidal sediments. In spite of the large differences in pore water chemistry with season and depth, differences in the bacterial community were modest over the temporal and spatial scales examined and generally restricted to only certain taxa