High gradient acceleration is a core challenge of accelerator physics. Achieving high gradients is made challenging by issues relating to rf breakdown and pulsed surface heating, which are caused by intense surface fields in the accelerating cavities. The excitation of multiple harmonically related modes within a cavity could reduce the onset of these effects. The temperature rise from pulsed surface heating can be reduced by lowering the average magnetic surface field squared and rf breakdown could be avoided by creating an asymmetry between the anode and cathode surface electric fields. This thesis will present several different cavity designs that show a reduction in the temperature rise on the surface of over 10% for second and third harmonic cavity structures or an asymmetry in the surface electric anode and cathode fields of a factor of 2. The harmonic mode could have undesirable consequences for beam stability. A study of the longitudinal beam dynamics is included that will derive the equations governing the longitudinal motion and show that the harmonic mode will have a minor and predictable effect on the rf bucket. The Compact LInear Collider (CLIC) is a major contender for the next generation of lepton linear colliders and is made challenging by high power requirements and distribution throughout the linac. A high current drive beam is decelerated parallel to the main linac in order to create the required rf power, which can overcome some of these issues. This thesis will describe a novel design for a CLIC-like accelerating structure, using collinear acceleration through fundamental mode detuned cavities. The design will accommodate interleaved drive and test bunches, such that the drive bunches are decelerated and the test bunches are accelerated within the confines of the same cavity which can result in high transformer ratios. The analytical theory based on the circuit model will be verified by time domain simulations. A multi-harmonic detuned accelerating structure is introduced that exhibits the properties of pulsed surface heating reduction and can be used for collinear acceleration. Time domain simulations will verify the transformer ratio to within 3% of theoretical predictions and the average magnetic field squared reduction will be within 20% of the value calculated from eigenmode simulations.

Master of Science / Department of Civil Engineering / Alexander P. Mathews / Nanoscale magnetite is being examined for possible uses as an adsorbent of heavy metals and for the enhancement of water treatment processes such as stripping of trichloroethylene (TCE) from contaminated water supplies and wastewaters. Methods for recovering nanoscale magnetite must be developed before the particles can be used in water treatment processes. This is necessary because expelling high amounts of particles into the environment will be unacceptable and costly; if captured they can be reused; additionally, they could potentially cause environmental impacts due to their stability in an aqueous environment and possible toxicity. Nanoscale magnetite is superparamagnetic, so it has a high magnetic susceptibility, and hence it is very attracted to magnetized materials. Utilizing the magnetic properties of magnetite may be one possible means of separating the particles from a treatment process. High Gradient Magnetic Separation (HGMS) has been studied for the separation of micron and even tenths of a micron size particles, but there is little experimental data for HGMS of nanoscale magnetite. This research looks to filter nanoscale magnetite through a HGMS and determine the capture efficiency of the filter. Subsequently, the filter was backwashed to determine particle recover efficiencies. The flow rate was adjusted to determine the dependency of particle capture efficiency on cross sectional velocity through the filter. Additionally, particle loading was changed to better understand the correlation of particle loading with capture efficiency. Filtrations for nanoscale magnetite dispersed with sodium tripolyphosphate were also completed as well as filtrations of nanoscale magnetite coated with silica and magnetite silica composites. Experimental data in this research indicates that magnetite nanoparticles can be captured at 99.8% efficiency or higher in a well-designed filtration system. Capture efficiencies around 99.8% have been found for magnetite. The silica coated magnetite and magnetite silica composites were captured at efficiencies as high as 96.7% and 97.9%, respectively. The capture efficiency of the dispersed magnetite is lower than non-dispersed magnetite and most promising at relatively low fluid flow velocities and particle loadings. The maximum capture efficiency for dispersed magnetite particles was 90.3%. Both magnetite and dispersed magnetite were successfully recovered using backwash at pH of 10 to 11.

The compact linear collider (CLIC) is a leading candidate for the next generation high energy linear collider. As any breakdown would result in a partial or full loss of luminosity for the pulse in which it occurs, obtaining a low breakdown rate in CLIC accelerating structures is a critical requirement for the successful operation of the proposed collider. This thesis presents investigations into the breakdown phenomenon primarily in the low breakdown rate regime of interest to CLIC, performed using the CERN DC spark systems between 2011 and 2014.The design, construction and commissioning of several new pieces of hardware, as well as the development of improved techniques to measuring the inter-electrode gap distance are detailed. These hardware improvements were fundamental in enabling the exciting new experiments mentioned below, which in turn have provided significant additional insight into the phenomenon of breakdown. Experiments were performed o measure fundamental parameters of individual breakdowns, including, the turn-on time and the delay before breakdown in order to gain an improved understanding of how breakdowns are triggered and the underlying process behind them. The turn-on time measurements are the highest bandwidth measurements made to date with the CERN DC systems and are closer than ever before to the value which is expected from the present understanding of breakdown simulations. Another key measurement was that of the breakdown rate scaling with electric field. Previous investigations of this relationship in the DC systems were unable to investigate breakdown rates below 10^3 breakdowns per pulse. These new results are able to investigate this relationship down to a breakdown rate of 10^-8 and are hence a considerable improvement. Thanks to these improved results a remarkable similarity to the scaling of the breakdown rate with electric field in RF cavities was discovered. The conditioning, or change in breakdown rate over time was also studied for the first time in the CERN DC spark systems as well as the newly built fixed gap system. The qualitative conditioning behaviour of the Fixed Gap System again showed interesting similarities to that observed in RF structures. Preliminary studies into the effect of pulse length and magnetic field on the breakdown rate were conducted as well. This is the first time the effect of a DC magnetic field was studied in a DC spark system and in contrast to experiments in RF cavities no statistically significant effect was observed. The dependence of the breakdown rate on pulse length, again the first measurement of its kind in a DC system also revealed a similar scaling law to that observed in RF accelerating structures. Both of these preliminary measurements would need to be repeated to confirm the results.

In recent years investigators have given increased attention to flow in natural, high-gradient, rough, open channels. Studies include work in both the laboratory and in the field. Solutions to the problem are still incomplete; however, continued attention by investigators is needed to answer many questions. Using a laboratory flume, the writer studied one of the questions concerning the relative importance of gross velocity fluctuations versus turbulent mixing, and the ranges of each under different ranges of submergence and kineticity of flow. In the different ranges, the effect of size and concentration of the roughness elements was studied.

ThomX, un démonstrateur de source Compton compacte de rayons X d’énergie réglable entre 45 et 90 keV, est en construction sur le campus de l'Université Paris-Saclay à Orsay. La thèse s’inscrit dans le cadre de l’upgrade du linac de ThomX qui consiste à réaliser une section accélératrice compacte à fort gradient en bande S (3 GHz) pour porter les faisceaux de ThomX de 50 MeV à 70 MeV. Un accord de collaboration R&D est signé entre LAL et PMB-Alcen pour développer une structure accélératrice en cuivre (OFHC) compacte en bande S à fort gradient. Une étude électromagnétique, thermique et dynamique de faisceau a été effectuée au LAL pour proposer une géométrie optimale de la section accélératrice pour atteindre des gradients accélérateurs très élevés. PMB est en charge d’améliorer les processus de fabrication en commençant par la réalisation des prototypes pour valider les choix technologiques et ensuite fabriquer la section finale pour répondre aux spécifications demandées. Dans un premier temps une étude couplée électromagnétique-thermique-structurelle du canon HF a été effectuée en utilisant le Logiciel d'analyse des éléments finis 3D (ANSYS). Ensuite l’étude électromagnétique et l’optimisation de la géométrie des cellules accélératrices ainsi que la conception des coupleurs de puissance pour constituer les prototypes à impédance constante avec un certain nombre de cellules réduit et la section accélératrice compacte à gradient constant ont été effectuées en utilisant les logiciels CST MWS et HFSS. Puis une étude thermomécanique de la structure accélératrice a été réalisée avec ANSYS pour concevoir et optimiser le circuit de refroidissement pour extraire la chaleur générée par la puissance HF dissipée dans les parois de la structure et garantir une répartition uniforme de la température au long de la structure. Les simulations du vide ont été également réalisées avec le code Monte Carlo pour envisager la meilleure solution de pompage pour le prototype de cuivre et la section finale. En outre, les principales étapes suivies dans la fabrication du Canon HF au LAL et le prototype en aluminium à 7 cellules chez PMB-Alcen ont été présentées. Des tests HF bas niveau du prototype ont été effectués afin de valider la géométrie « processus d’usinage ». Compte tenu des résultats expérimentaux, des problèmes techniques et des contraintes technologiques ont été abordées et certaines solutions ont été proposées pour la fabrication des prototypes en cuivre et de la section finale. Les simulations de la dynamique des faisceaux du Linac de ThomX ont été effectuées en utilisant le code ASTRA. Le but est de réduire autant que possible la dispersion en énergie et l’emittance transverse du paquet d’électrons au point d’interaction avec les impulsions laser, pour préserver la pureté spectrale de rayons X produits. Un modèle aussi proche que possible des caractéristiques des composants réels, tels que le canon HF, la section accélératrice à onde progressive (OP) et les solénoïdes a été pris en compte dans les simulations. Des résultats importants ressortent de ces simulations concernant les paramètres du laser (taille et durée du spot), le champ magnétique maximal des solénoïdes pour la compensation de l'effet de charge espace, le déphasage entre l’onde RF et le laser et l'effet du champ électromagnétique sur la dynamique des électrons. Différentes options pour les paramètres de fonctionnement de la machine et une nouvelle configuration de la position des solénoïdes ont été proposées. L’optimisation des caractéristiques du paquet d’électrons a été obtenue en utilisant un algorithme génétique et les performances finales du faisceau d’électrons ont été mises en évidence. / The ThomX source should provide quasi-monochromatic high-quality X-rays (range 45-90 keV). The framework of the thesis is the electron beam linac energy upgrade from 50 MeV to 70 MeV necessary to achieve X-rays of 90 keV. For this purpose, the development of a compact high-gradient S-band electron accelerating structure is needed. It implies a research and development (R&D) activity at LAL in partnership with a French company (PMB-Alcen) in the High-Gradient (HG) technology of accelerating structures. The LAL-PMB-Alcen collaboration aims at the fabrication of a normal-conducting HG S-band structure by tackling the technological aspects that limit the achievement of high-gradient acceleration mostly due to vacuum RF breakdown and pulsed heating fatigue. Basically, the electromagnetic and thermal design of the HG S-band accelerating section has been performed at LAL. Meanwhile, PMB-Alcen was in charge to perform the fabrication, tuning and low power tests of prototypes and the final accelerating section. In this work, a fully coupled electromagnetic-thermal-structural finite element analysis on the THOMX RF gun has been performed with Ansys workbench. The HG accelerating section final regular cell dimensions and the power coupler design have been optimized. In particular, the electromagnetic simulation techniques and outcomes have been applied to constant impedance (CI) TW prototypes and also to a constant gradient (CG) final accelerating section. This allowed to verify the geometry choice, validate the fabrication procedure and check the fulfilment of the normal operating conditions. Moreover, a coupled thermo-mechanical study on a CI copper prototype has been performed. The water cooling system has been simulated to validate the capability to extract the heat generated by the dissipated power on the walls of the structure and guarantee a uniform temperature distribution along the section. Also, vacuum simulations have been performed on a 16-cells CI copper prototype and also on the final CG accelerating section. In addition, the main steps for the fabrication of the RF gun at LAL and a 7-cells aluminium prototype at PMB-Alcen have been presented. RF low power tests on the prototype have been performed in order to validate the 3D geometry design and the machining process. Taking into account the experimental results, mechanical problems and technological constraints have been tackled and some solutions have been proposed for the future copper prototype fabrication. Finally, beam dynamics simulations of the ThomX linac has been carried out by ASTRA code. The aim is to reduce as much as possible the energy spread and the transverse emittance to preserve the spectral purity of the produced X-rays, at the electron-photon interaction point. A model as close as possible to the characteristics of the real components, such as RF gun, TW section and solenoids has been considered. Important results came out from these simulations regarding laser parameters (spot size and duration), the maximum magnetic field of solenoids for high space charge effect compensation, dephasing between the RF and laser in the gun and effect of the travelling wave electromagnetic field on the particle dynamics. Different options for the parameter settings of machine operation and a new configuration of the solenoids position have been proposed. An optimization of the beam dynamics properties has been obtained by using a genetic algorithm and the ultimate performances of the electron beam have been highlighted.

Estimates of the brown trout (Salmo trutta) population were made in two areas of the Blacksmith Fork River, Cache County, Utah, from June 1972 to June 1973. Additional data were obtained on movement, growth, mortality, biomass, production, and yield. Population density was highly variable in the area where habitat alterations had occurred, but was relatively uniform where the habitat was undisturbed. The brown trout exhibited little movement except during spawning season. Instantaneous growth and mortality rates are provided for each age group. Mean annual biomass in the two areas was 12.0 and 10.2 grams per square meter and production was estimated at 9.2 and 7.7 grams per square meter per y ear in the two study areas. Gametes comprised approximately 5 percent of the annual production and angler harvest removed 39 percent of production.

High-Gradient Magnetic Separation (HGMS) is a powerful separation process that has great potential for industrial wastewater treatment, particularly for the removal and recovery of paramagnetic colloidal particles. The chief advantages of HGMS are that the separation is reversible and potentially selective. However, these advantages are compromised if non-magnetic filtration mechanisms influence significantly the capture of particles. The objective of this study was to identify the chief mechanisms responsible for the removal of ferric oxide (Fe2O3) from water by an HGMS process. This objective was achieved by measuring the effects of applied magnetic induction, collector radius, and fluid velocity on the removal efficiency (RE) of a stainless-steel filter column. These factors were tested on the removal of bare Fe2O3 particles and particles treated with a surfactant (sodium dodecyl sulfate, SDS). The results were compared to the predictions of a trajectory model which simulates particle capture by a magnetic force. The experimental results show that non-magnetic force mechanisms are primarily responsible for the removal of bare Fe2O3 particles for the experimental conditions used in this work. For these particles, the three factors tested had no significant effect on the RE, and 90.1% of the particles were removed without a magnetic force. These results differed sharply from modeling predictions. However, the magnetic force mechanism is primarily responsible for the removal of surfactant-treated Fe2O3 particles. The three factors investigated had a marked effect on the RE, and only 10.8% of the particles were removed without a magnetic force. An increase in magnetic induction from 0.2 to 0.5 T increased the RE from 79.9 to 93.4 %; a decrease in wire radius from 49 to 15 Ym increased the RE from 60.2 to 93.4%, and a decrease in fluid velocity from 0.5 to 0.1 cm/s increased the RE from 69.5 to 95.3%. These results agreed closely with the model predictions.This study demonstrates that by reducing the effect of attractive non-magnetic forces on filtration, surfactant treatment of colloidal particles can potentially preserve and enhance these two key advantages, i.e., regeneration and selectivity of HGMS processes.