Thesis (M.A. Sc.)--University of Toronto, 2005.

Samples of pure nickel have been implanted with 500keV helium ions, at a dose of 10[17]ions/cm[2], followed by annealing in vacuo at 750°C (≈0.6T[m]) for various time periods to allow bubble nucleation and growth to occur. A transverse sectioning technique has been developed to allow TEM studies of the complete depth distribution of cavities, hence allowing the mechanisms for bubble growth at 750°C in nickel to be identified. It was found that after 2 hours annealing, a fine layer of cavities developed, corresponding well with the gas deposition profile calculated using the E-DEP-1 code. Subsequent annealing resulted in cavity growth on the periphery of the layer by vacancy collection, the principal vacancy sources being the irradiated surface and grain boundaries in the bulk of the material. Cavity growth in the peak implanted region was found to be suppressed due to the lack of vacancies and with bubble migration being hindered as a result of high bubble pressures, hence migration and coalescence did not occur until cavities approached their equilibrium pressure. The same bubble growth mechanisms were found to prevail after implantation of 5x10[16]ions/cm[2] and also after 250keV He implantation. The growth of helium bubbles has been compared to neon bubbles after implantation with 500keV Ne ions at two doses: 7.8x10[16]ions/cm[2] to obtain the same peak gas concentration and 2.9x10[15]ions/cm[2] to achieve the same peak displacement damage, followed by annealing. The cavity density was found to be established by the gas concentration, the displacement damage apparently having little or no effect, even after an approximately 27-fold increase. The growth mechanisms observed after Ne implantation appeared to be the same as those for He, although the bubbles after low dose Ne implantation achieved equilibrium conditions more rapidly, due to the lack of implanted gas. He and Ne have been compared after high energy implantation at 500°C, in the Variable Energy Cyclotron at Harwell to a peak gas concentration of 250ppm. For 4MeV He, an inhomogeneous cavity distribution was observed, compared to a relatively uniform cavity layer after 17MeV Ne implantation. However, the observed cavity sizes and number densities were found to be similar. Finally, nickel has been irradiated at 500°C with a mixed beam of 51MeVNi[6+]/17MeVNe[2+] ions, to 250ppm Ne together with 30dpa displacement damage, and compared to an irradiation with 51MeVNi[6+] ions without inert gas, as well as with 17MeVNe[2+] ions. The void number density profile resulting from the single heavy ion irradiation was similar to the computed damage profile, although the peak was ≈10% deeper than that predicted. A depression in the swelling profile was observed in this peak region resulting from a reduction in cavity size, a bimodal distribution being observed. The effect of simultaneous gas deposition was to increase the cavity nucleation and reduce cavity size. This phenomenon was found to be dominant in the region corresponding to the implanted gas layer, however the gas appeared to influence cavities produced at greater depths, with an overall reduction in swelling.

Neste trabalho são apresentadas medidas das secções de choque de fusão nuclear para o sistema ANTPOT 27 Al + ANTPOT. 16 0,nas energias de bombardeio do feixe de ANTPOT 16 O de 45.6 MeV e 49 MeV. Também foram calculadas através do estudo do espalhamento elástico de ANTPOT 16 O por ANTPOT. 27 Al (modelo Óptico), as secções de choque de reação na faixa de energia de bombardeio de 30 MeV a 45.6 MeV. Na energia de bombardeio de 45.6 MeV, foi feito um estudo da contribuição de outros tipos de reações para a secção de choque total de reação. Neste esquema foi detetada experimentalmente a reação ANTPOT. 27 Al (ANTPOT. 16 O, C). Os dados da secção de choque de fusão nuclear foram comparados com o modelo de Glas e Mosel e foram obtidos valores do momento angular critico (l IND. Cr ). Contribuições de processos como emissão de pré-equilíbrio e fissão nuclear foram calculadas com o uso do código de evaporação Alice. / In this work we present cross-section measurements for nuclear fusion in the 27 Al + 16 O system, at 16 O bombarding energies of 45.6 MeV and 49 MeV. With the aid of the optical model the elastic scattering of 16 O by 27 Al was used to calculate reaction cross-section from 30 MeV to 45.6 MeV. At 45.6 MeV contributions by reaction mechanisms other than fusion were studied. The nuclear fusion cross-sections were compared with the model of Glas and Mosel and values of the critical angular momentum (l cr ) extracted at the above cited energies. Contributions by fusion and pre-equilibrium emission were calculated with the code \"Alice\".

Steel components within fusion reactors will be subject to high transmutation rates due to high energy neutrons. In iron based alloys such as steels, high amounts of helium accumulate through transmutation. This leads to helium embrittlement through helium accumulating on the grain boundaries of metal. Worst case scenario predictions were made for DEMO, estimating that for a grain size of 5 micro-meters, embrittlement could happen within 2 years of the blanket region of DEMO. This thesis elaborates on previous worst case scenario calculations by including inter-granular tapping mechanisms, within rate theory simulations. A rate theory code was developed for the purpose of this work, tailored towards a fusion environment. Calculations were performed using rate theory that predicted the timescales in which helium embrittlement occurred within a conceptual DEMO design in the first wall region and the blanket region. The calculations used several parameter sets, where preliminary simulations were performed using the parameter sets, that were compared with cluster density data determined using Transmission Electron Microscopy (TEM) and Positron Annihilation Spectroscopy (PAS). The simulations showed that the helium embrittlement time was heavily influenced by the chosen dislocation density, parameter set and grain size. The simulations conducted to represent the blanket region, showed an increase as high as 94% from the 2 years that has previously been predicted under certain scenarios. However results also showed that assuming a certain parameter set with a low dislocation density, showed no significant increase in embrittlement time. This was not a concern since it was concluded that advanced steel concepts would be expected to have a small average grain size, that would dramatically increase the embrittlement time. The work in this thesis also focused on defect interaction with dislocations. A model was constructed that made use of elasticity theory and VASP calculations that produced the interaction energy map for various defects with an edge dislocation. The interaction energy map for helium interstitials with an edge dislocation was compared with molecular dynamics (MD) simulations produced for this work. The model and simulations showed good agreement. Temperature effects were then included in the model that allowed the concentration around a dislocation to be temperature dependent. These temperature dependent interaction energy maps were then implemented into the advection-diffusion equation, that were solved numerically to explore the capture efficiencies and bias towards certain defects within iron. These values were then used within the rate theory simulations to produce temperature effects on the dislocation sink strengths for vacancies, SIA and helium interstitials.

Development of fueling technologies for modern and future tokamak reactors is essential for their implementation in a commercial energy production setting. Compared to the presently available fueling technologies, gas or cryogenic pellet injection, compact torus injection presents an effective and efficient method for directly fueling the central core of tokamak plasmas. Fueling of the central core of a tokamak plasma is pivotal for providing efficient energy production. The central core plasma of a reactor contains the greatest density of fusion processes. For consistent and continuous fueling of tokamak fusion reactors, compact torus injectors must be operated in a repetitive mode.<p> The goal of this thesis was to study the feasibility of firing the University of Saskatchewan Compact Torus Injector (USCTI) in a repetitive mode. In order to enable USCTI to fire repetitively, modifications were made to its electrical system, control system and data acquisition system. These consisted primarily of the addition of new power supplies, to enable fast charging of the many capacitor banks used to form and accelerate the plasma. The maximum firing rate achieved on USCTI was 0.33 Hz, an increase from the previous maximum firing rate of 0.2 Hz achieved at UC Davis.<p> Firing USCTI in repetitive modes has been successful. It has been shown that the CTs produced in any given repetitive series are properly formed and repeatable. This is made evident through analysis of data collected from the CTs' magnetic fields and densities as they traveled along the injector barrel. The shots from each experiment were compared to the series' mean data and were shown to be consistent over time. Calculations of their correlations show that there are only minimal deviations from shot to shot in any given series.

Development of fueling technologies for modern and future tokamak reactors is essential for their implementation in a commercial energy production setting. Compared to the presently available fueling technologies, gas or cryogenic pellet injection, compact torus injection presents an effective and efficient method for directly fueling the central core of tokamak plasmas. Fueling of the central core of a tokamak plasma is pivotal for providing efficient energy production. The central core plasma of a reactor contains the greatest density of fusion processes. For consistent and continuous fueling of tokamak fusion reactors, compact torus injectors must be operated in a repetitive mode.<p> The goal of this thesis was to study the feasibility of firing the University of Saskatchewan Compact Torus Injector (USCTI) in a repetitive mode. In order to enable USCTI to fire repetitively, modifications were made to its electrical system, control system and data acquisition system. These consisted primarily of the addition of new power supplies, to enable fast charging of the many capacitor banks used to form and accelerate the plasma. The maximum firing rate achieved on USCTI was 0.33 Hz, an increase from the previous maximum firing rate of 0.2 Hz achieved at UC Davis.<p> Firing USCTI in repetitive modes has been successful. It has been shown that the CTs produced in any given repetitive series are properly formed and repeatable. This is made evident through analysis of data collected from the CTs' magnetic fields and densities as they traveled along the injector barrel. The shots from each experiment were compared to the series' mean data and were shown to be consistent over time. Calculations of their correlations show that there are only minimal deviations from shot to shot in any given series.

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Masters Research - Master of Philosophy (Physics) / Fluoro-deoxyglucose (FDG) labeled with fluorine-18 is commonly used in positron emission tomography (PET) imaging. PET imaging is a powerful tool used primarily in the diagnosis and management of cancer. The growth of PET has been limited partly by the difficulties associated in producing fluorine-18. This project involves a theoretical investigation of a novel method of producing fluorine-18 utilising proton generation via the 3He(d,p)4He nuclear reaction. Currently the most common method of producing fluorine-18 for PET is with a medical cyclotron that accelerates protons to mega-voltage energies. These protons are then directed onto a target rich in oxygen-18. This initiates the 18O(p,n)18F reaction to produce fluorine-18. The 3He(d,p)4He reaction, utilized for the present study, has a Q-value of 18.35 MeV and this results in protons being produced at energies similar to that produced in a medical cyclotron. This reaction was investigated as an alternative proton source for the 18O(p,n)18F reaction. The expected advantage of this method over the cyclotron is that particles need only be accelerated to keV energies rather than the tens of MeV that a medical cyclotron accelerates protons to. This is expected to significantly reduce the cost and associated size of the system. Two systems based on the 3He(d,p)4He reaction were designed and calculations were performed to determine the respective yields of fluorine-18. The first system involved separate targets for the 3He(d,p)4He and 18O(p,n)18F reactions. Helium-3 ions are initially fired onto a deuterated plastic target. A heavy-water (H2O18) target is placed immediately behind this plastic target to absorb mega-voltage protons produced by the reaction 3He(d,p)4He in the plastic. The second system involved a single, super heavy water (D2O18) target onto which helium-3 is fired so that both the 3He(d,p)4He and 18O(p,n)18F reactions can occur concurrently in the one target. The input parameters of energy and beam current for the helium-3 beam required for the 3He(d,p)4He reaction were selected on the basis of the performance of currently available ion sources and in particular the saddle-field ion source. Practical considerations such as radiation safety, target degradation and lifetime and ultra high vacuum (UHV) issues were also investigated to further determine the feasibility of the two systems. With the beam current and energy at the extreme limits of the saddle-field ion source it was calculated that insufficient fluorine-18 could be produced daily to supply a PET facility with FDG. It was also found that the high helium-3 beam currents and energy required to produce significant amounts of fluorine-18 resulted in prohibitive temperature rises in the targets that would likely result in target vaporization.

Masters Research - Master of Philosophy (Physics) / Fluoro-deoxyglucose (FDG) labeled with fluorine-18 is commonly used in positron emission tomography (PET) imaging. PET imaging is a powerful tool used primarily in the diagnosis and management of cancer. The growth of PET has been limited partly by the difficulties associated in producing fluorine-18. This project involves a theoretical investigation of a novel method of producing fluorine-18 utilising proton generation via the 3He(d,p)4He nuclear reaction. Currently the most common method of producing fluorine-18 for PET is with a medical cyclotron that accelerates protons to mega-voltage energies. These protons are then directed onto a target rich in oxygen-18. This initiates the 18O(p,n)18F reaction to produce fluorine-18. The 3He(d,p)4He reaction, utilized for the present study, has a Q-value of 18.35 MeV and this results in protons being produced at energies similar to that produced in a medical cyclotron. This reaction was investigated as an alternative proton source for the 18O(p,n)18F reaction. The expected advantage of this method over the cyclotron is that particles need only be accelerated to keV energies rather than the tens of MeV that a medical cyclotron accelerates protons to. This is expected to significantly reduce the cost and associated size of the system. Two systems based on the 3He(d,p)4He reaction were designed and calculations were performed to determine the respective yields of fluorine-18. The first system involved separate targets for the 3He(d,p)4He and 18O(p,n)18F reactions. Helium-3 ions are initially fired onto a deuterated plastic target. A heavy-water (H2O18) target is placed immediately behind this plastic target to absorb mega-voltage protons produced by the reaction 3He(d,p)4He in the plastic. The second system involved a single, super heavy water (D2O18) target onto which helium-3 is fired so that both the 3He(d,p)4He and 18O(p,n)18F reactions can occur concurrently in the one target. The input parameters of energy and beam current for the helium-3 beam required for the 3He(d,p)4He reaction were selected on the basis of the performance of currently available ion sources and in particular the saddle-field ion source. Practical considerations such as radiation safety, target degradation and lifetime and ultra high vacuum (UHV) issues were also investigated to further determine the feasibility of the two systems. With the beam current and energy at the extreme limits of the saddle-field ion source it was calculated that insufficient fluorine-18 could be produced daily to supply a PET facility with FDG. It was also found that the high helium-3 beam currents and energy required to produce significant amounts of fluorine-18 resulted in prohibitive temperature rises in the targets that would likely result in target vaporization.