Дисертації з теми "EMISSION STUDIES"

In this thesis studies relating to cyclotron emission in GaAs, InSb, InP and CdxHg1- xTe (C.M.T.) are described. The effect of the electric field bias on the emission intensity and linewidth in GaAs and InP is studied and a theoretical model is proposed. The study indicates the importance of nonparabolicity and polar mode scattering in determining the intensity and linewidth in these materials. Inter-excited state transitions are observed for the first time in emission- Nonparabolicity splitting is observed in InP and that in GaAs, originally observed in by Gornik (1983),is confirmed. The application of hydrostatic pressure to InSb is observed to narrow the emission line by a factor of three. In experiments on the magnetoimpurity effect in GaAs transitions between the 1S and 2P_, 2P0, 3D-2 and 3D-1 impurity states are observed and central cell structure is observed for the first time. In bulk C.M.T. cyclotron resonance is studied as a function of hydrostatic pressure and reasonable agreement is achieved with accepted values for the variation of band gap with pressure. In the surface layer cyclotron resonance is observed as are Shubnikov de Haas oscillations and electric subband energies are calculated for each of these experiments. Finally the use of cyclotron emission as a spectroscopic source is demonstrated and future developments discussed.

Thesis: M.C.P., Massachusetts Institute of Technology, Department of Urban Studies and Planning, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-52).
Massachusetts is one of the US states at the forefront of carbon emission reduction policy, and has the potential to model success to the rest of the country. The state's Global Warming Solutions Act (GWSA) passed in 2008, two years before federal climate legislation floundered in the U.S. Senate. This legislation committed the state to reducing carbon emissions 25% below 1990 levels by 2020 and 80% by 2050. However, progress toward these targets has been uneven, particularly when it comes to transportation and land use. Despite aggressive goals, the number of vehicle trips, the number of vehicle miles traveled (VMT), and the carbon emissions from passenger vehicle trips are all projected to increase over the next several decades. What will it take to put Massachusetts on track to meet its vehicle emission reductions targets? Many of the state's environmental advocates are uniting behind a potential new policy, a revenue-neutral carbon tax or carbon fee. This policy would levy an additional fee on fossil fuel consumption, but would distribute the revenue back to the state's residents instead of adding it to the state budget. This thesis explores the political, technical, and equity-based considerations that must be addressed to make this policy framework a success. Through spatial analysis of passenger vehicle driving patterns in the state of Massachusetts, a case study of British Columbia's successful revenue-neutral carbon tax, and analysis of the current political landscape in Massachusetts, I conclude that environmental advocates should reconsider their decision to advocate for a state level revenue-neutral carbon tax. At first glance, this policy seems elegantly workable -- economist-approved, politically savvy, and equity-conscious. A closer look, however, reveals some serious flaws that are likely to render it at best a huge expense of political capital for limited results. Worse, this policy might actually undermine the case for a nationwide carbon tax.
by Elizabeth J. Irvin.
M.C.P.

Anxiety disorders are very common and the primary feature is abnormal or inappropriate anxiety. Fear and anxiety is often mediated by the amygdala, a brain structure rich in substance P (SP) and neurokinin 1 (NK1) receptors. To learn more about how the human amygdala is modulated by fear and anxiety in event-triggered anxiety disorders and to investigate if the SP/NK1 receptor system is affected, regional cerebral blood flow (rCBF) ([15O]-water; Study I and II) and the SP/NK1 receptor system ([11C]GR205171; Study III and IV) were studied with positron emission tomography (PET). In Study I we investigated the neural correlates of affective startle modulation in persons with specific phobia by measuring rCBF during exposure to fearful and non-fearful pictures, paired and unpaired with acoustic startle stimuli. Fear-potentiated startle was associated with activation of the affective part of the anterior cingulate cortex and the left amygdaloid–hippocampal area. In Study II short-term drug treatment effects on rCBF in patients diagnosed with social phobia was evaluated, comparing the NK1 receptor antagonist GR205171 to the selective serotonin reuptake inhibitor citalopram and placebo. Social anxiety and neural activity in the medial temporal lobe including the amygdala was significantly reduced by both drugs but not placebo. In Study III we investigated if activity in the SP/NK1 receptor system in the amygdala would be affected by fear provocation in individuals with specific snake or spider phobia. Fear provocation was associated with a decreased uptake of the NK1 antagonist [11C]GR205171 in the amygdala, possibly explained by an increase in endogenous SP release occupying the NK1 receptors. Study IV was conducted to explore the resting state NK1 receptor availability in PTSD patients as compared to healthy controls. Increased resting state binding of the tracer [11C]GR205171 in the amygdala of patients with PTSD suggested an increased amount of available receptors. In summary, fear and fear-potentiated startle modulates the human amygdala, possibly through the SP/NK1 receptor system.

Acoustic emissions (AEs) are generated as a result of the creation of, or movement on microcracks in a rock mass. Hypocentres of AEs have been used as a very effective method of visualising the extent (amount and location) of microcrack damage. Studies have used AE locations to investigate both the behaviour of rock failure in laboratory experiments, and to evaluate damage in the Excavation Disturbed Zone (EDZ) around underground openings. The latter has particular significance for the safe storage of nuclear materials in deep underground facilities. Because AEs represent phenomena associated directly with the physical processes occurring in microcracking, then they can also be used to evaluate the fundamental mechanics of the failure. In this thesis a moment tensor (MT) inversion procedure is developed for AEs. This utilises full-waveform records from an array of ultrasonic piezoelectric transducers distributed around the rock mass. The procedure is tested using synthetic amplitudes and is shown to be robust even with high amplitude uncertainties. The inversion is particularly good at resolving the volumetric component in the source. The procedure allows a precise and well-constrained analysis of the forces that are creating the AEs, and, in some cases, that are actually creating the damage. The mechanics can then be related to the stress field in the rock mass, or can be compared to results from dynamic micromechanical models. Three case studies are performed. Two of these investigate the fundamental behaviour of microcracking in the laboratory. A series of laboratory tests are conducted using polyaxial stress to study the mechanics of damage under realistic in situ stress paths. The third case study investigates the mechanics of failure operating in the EDZ. AEs are shown to be truly scaled earthquakes although with often-complex non-double-couple mechanisms.

Striatal dopamine is well known to be involved in reward. Indeed, drug of abuse allowed DA release in the striatum as previous PET experiment demonstrated. Here, is investigated the change of DA in different conditions of monetary reward in healthy subjects to identify which subcomponent of reward provokes Dopamine release using 11C Raclopride of PET. In a first time we scan 10 healthy male subjects 3 times in different conditions: unpredictable monetary reward, novel visual and audio stimuli, and sensorimotor control. In a second time, we compared different amounts of work load to get monetary reward. Unpredictable passive reward as well as novelty failed to release significantly DA in comparison to the sensorimotor control task. Conditions of increasing effort to obtain the reward failed to release DA in comparison to the condition of passive receipt of reward. Limitations of the PET technique, as well as the paradigm's ones are presented.

This thesis presents a study of early type, emission line objects on small angular scales. Spectroastrometry is used to separate the spectra of unresolved Herbig Ae/Be binary systems. The separated spectra allow the mass ratio of the systems to be established. The separation and mass ratio distribution of the systems suggest that they form via disk fragmentation. To test this conclusion, disk and binary position angles are compared to a model in which the circumstellar disk and binary orbits are co-planar. The data are consistent with the coplanar model and thus with the scenario of disk fragmentation. A search for optical outflows associated with Herbig Ae/Be stars is conducted using integral field unit spectroscopy. No outflows are detected. Therefore, the data cannot constrain the location of the proposed transition from collimated to un-collimated outflows, if such a transition exists. Spectroastrometry is used to probe the origin of the Brackett line emission in the data with sub-milli-arcsecond precision. To explore the potential of spectroastrometry to detect circumstellar disks, spectroastrometric observations of Be stars are presented. It is shown that spectroastrometric data with an angular precision of 0.1 milli-arcseconds can detect milli-arcsecond sized disks. Comparing the spectroastrometric signatures to models of disks with different kinematics demonstrates that Be star disks rotate in a Keplerian fashion, which constrains their formation mechanism. Finally, spectroastrometry over CO bandhead emission is employed to search for disks around massive young stellar objects. Fitting the observed overtone profiles with a model of a circumstellar disk allows the spatial distribution of the CO to be predicted. No signatures of disks are detected. This is entirely consistent with the best fitting models of the emission, and thus with the presence of small-scale disks around massive young stellar objects.

The aim of the present research was the development of an optimised secondary electron emission (SEE) diamond film to use as a dynode material. The project was a partnership between the School of Chemistry in the University of Bristol, the Space Research Centre (SRC) at the University of Leicester and Photek, a company specialized in the manufacture of systems for photon detection. The role of Bristol in this project consisted in the preparation of CVD diamond films and their characterization, before supply to the other collaborators. SEE characterisation of the samples was performed at SRC and Photek would proceed to further testing in actual tubes. Besides its participation in the project, Bristol went further and developed the means to do its own SEE measurements. This thesis describes the work undertaken at Bristol using the facilities at the Diamond CVD group. Diamond films were prepared by hot-filament (HF) CVD covering a range of crystallinities, thicknesses and levels of boron (B) doping, on different substrate materials. A new home-built apparatus has been developed for the acquisition of SEE data from diamond films, both in reflection and transmission configurations. The setup consists of a system of phosphor screens acting as detectors and associated to PMTs for the acquisition of signal measured from the diamond samples. A comprehensive study evaluating the effects of B-doping, crystallinity, surface termination, thickness and substrate material of diamond films on yield and yield degradation in the SEE reflection yields has been performed. In addition, SEE yields from commercial CVD diamond samples were analysed, after surface functionalization by hydrogenation, caesiation and lithiation. Moreover, the present study allowed for an improvement in the growth of thin NCD films, essentially through the optimization of the seeding processes. Finally, the development of techniques to manufacture free standing diamond films on silicon substrates were investigated, and preliminary SEE measurements in transmission were undertaken.

This work assesses the potentials of two NDE techniques namely ultrasonic C-scan and acoustic emission for evaluating plasma sprayed coating quality. The coating materials used were aluminium (Metco 54), alumina (Metco 105), molybdenum (Mob3) and self-fusing molybdenum (Mo5O5). It has been established that ultrasonic C-scan imaging can reliably detect thickness variations of the order of 0.05mm in plasma sprayed coatings. Also, by using this technique it is possible to detect the presence of delamination or lack of adhesion between the coating and substrate. Although it was only possible to produce aluminium and alumina coatings with artificially introduced adhesion defects, it has been shown that the presence of such defects in other coatings can also be detected. It has been established that an ultrasonic C-scan technique is not sensitive to the process parameters of plasma spraying. The process parameters investigated were; poor surface preparation, input power and surface cooling. Another major limitation of ultrasonic C-scan technique is the geometrical restrictions where components with high curvatures can not be tested. Acoustic emission activities from plasma sprayed coatings were monitored during four point bend testing. Samples sprayed on poorly prepared surfaces or sprayed without coolant air could be distinguished from control samples using AE characteristics at low strain levels. Also the AE response of the alumina coatings reflected the thickness of the coatings. Thicker coatings produced more AE events. The AE response of the molybdenum (Mo63) and self-fusing molybdenum (Mo5O5) coatings were complex. It was found that they were related to the residual stresses in the coatings. Aluminium coatings showed very little acoustic emission activities.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.
Includes bibliographical references (leaves 124-139).
This thesis investigates the experimental measurement and theoretical simulation of the effects of azimuthal emission non-uniformity of a 96 kV, 40 amp magnetron injection gun (MIG) used in a gyrotron. The accomplishments of this thesis include: Experimental measurement of the azimuthal emission non-uniformity of the MIG gun; Simulation of the beam quality of the MIG gun using MICHELLE 3-D, the first simulation of a MIG electron beam with azimuthal non-uniformity; Benchmarking the MICHELLE 3-D code to other established gun optics codes; Evaluation of the effects on the velocity spread and pitch factor of azimuthal non-uniformity in the MIG gun, showing that the direct effect on the beam quality is very small; Design, fabrication, and testing in the gyrotron of a capacitive probe system divided into four quadrants to measure azimuthal asymmetries of the electron beam; Use of the capacitive probes to measure low-frequency (100 - 160 MHz) oscillations on the beam, the first measurement of such oscillations in a microsecond pulse length gyrotron; First results on testing a new MIG cathode for emission non-uniformity using a special test chamber built by Calabazas Creek Research.
(cont.) This research will contribute to our understanding of the properties of intense electron beams produced by MIG guns in high-power gyrotrons. MIG's are widely used in gyrotron oscillators and amplifiers for fusion applications to create a beam of gyrating electrons generally operating in the temperature limited regime of emission. Due to this dependence on the temperature of the cathode, variation of the emitter surface temperature will result in inhomogeneous emission. Non-uniform emission is attributed to a deviation in the cathode work function as well. Studies have shown this inhomogeneous beam current density can lead to increased mode competition and velocity spread contributing to an overall decreased efficiency of the gyrotron. This research focuses on the effects on velocity spread and in turn the efficiency of the device from non-uniform current emission. Initially, we measured experimentally the detailed azimuthal non-uniformity profile of an existing 110 GHz gyrotron oscillator at MIT. Using a rotating collector current probe the current density of different emitter angles was extracted. These results agreed fairly well with previous measurements of Anderson et al.
(cont.) This non-uniformity profile was then used with a 3-D simulation code to do the first complete 3-D model from the cathode to the cavity of a MIG. In order to investigate these effects of beam non-uniformity with simulation, we use MICHELLE 3-D developed by SAIC. MICHELLE 3-D has been benchmarked to MICHELLE 2-D and EGUN in the case of a uniform beam. The non-uniform beam measurements are entered into MICHELLE and results are computed at four different azimuthal quadrants of different current densities and for the overall beam, giving special attention to the differences in the beam pitch factor and perpendicular velocity spread. MICHELLE found azimuthal non-uniformity to be a fairly small effect on the overall beam quality. Concurrently with the MICHELLE 3-D simulations, segmented pitch factor probes are implemented to measure the pitch factor in the four azimuthal quadrants. In an attempt to compare with MICHELLE's results, these four capacitive probes measure the induced image charge of different azimuthal sections of the electron beam, enabling an estimation of differences in the pitch factor between quadrants.
(cont.) Unfortunately, the experimental error is found to be quite high (±15%) rendering differences in the pitch factor to be contained within the error boundaries. Though the capacitive probes are found to have too much error for adequate resolution of the pitch factor, they are also used to discover the first observations of low-frequency oscillations in a short pulse MW gyrotron. These frequencies, from 100-160 MHz, are found to be dependent on the beam parameters such as the beam voltage, current, magnetic field, and magnetic compression ratio. The frequency range is remarkably close to the frequency of an electron in the adiabatic trap and the experimental as well as the predicted theoretical oscillation behavior of trapped electrons are discussed. Last, initial progress has been made to test three new cathodes on the Calabazas Creek Research cathode tester. This tester is a dedicated test stand for azimuthal non-uniformity able to obtain a measurement directly at the cathode instead of at the collector end of the device. The setup procedure and results on the first cathode test for the 96 kV, 40 amp gun are reported and future tests are summarized.
by Chad D. Marchewka.
S.M.

This thesis reviews in general the topic of electromagnetic compatibility, and electromagnetic interference and their origin and effects in modern electronically controlled motor drives. The measurement techniques for EMI noise are reviewed. The sources of noise of a switching power circuit are described. This thesis investigates the establishment of a procedure for measuring conducted emission produced by motor drives, using a virtual instrument. This procedure is based on the traditional methodology of EMI measurement and the use of simulation techniques. A test bench is designed. The thesis covers the detailed design of a virtual instrument for measuring conducted current produced by motor drives. A line impedance stabilisation network LISN is designed and built. A series of measurements were carried out using the developed instrument. The results show very little difference between the conducted emission produced by induction, permanent magnet and reluctance motor drives. Comparing one of the experimental results with published results from a major test laboratory assesses the validity of the designed instrument. The experimental results refer to drive systems under no load conditions. Useful conclusions are drawn and future research studies recommended.
Master of Engineering (Hons)

The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany.

Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements.

When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m²) and the peak wavelength were maximum luminescence occurred.

The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected.

When irradiance of the excitation light was approx. 8 W/m² the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m². The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample.

The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 231-239).
Electric thrusters are being developed for in-space propulsion needs of spacecraft as their higher specific impulse enables a significant reduction in the required propellant mass and allows longer duration missions. Over the last few decades many different electric propulsion concepts have been proposed and studied. In studying the electric thrusters, in order to improve the thruster performance as well as to understand the underlying physics of thruster's operation, various diagnostics methods were employed. As one unique method, emission spectroscopy provides a non-invasive, fast and economical diagnostic allowing also the ability to access hard to reach locations. In this study, emission spectroscopy is employed as a means to determine the trends in thruster operations as well as diagnosing the plasma parameters. This study presents the spectral measurement results of three different electric thrusters and plasma sources. First, the BHT-200 Hall thruster emission spectra measurements are presented for varying discharge voltage and for various regions of observation.
(cont.) Second, spectral measurements of a TAL type laboratory mini-Hall thruster, MHT-9, were presented. Third, radiation emission measurements of an experimental Helicon plasma source being studied to assess the possibility of using Helicon discharge as a propulsive system are presented and the trends are discussed. Two collisional-radiative (C-R) models are developed for Argon and Xenon plasmas to analyze the experimental spectra. In the C-R models, electron induced excitation, deexcitation and ionization collisions, and spontaneous radiative de-excitation transitions are simulated for neutral and singly charged ion species. The models are validated against measured spectra obtained using different experimental setups. The BHT-200 Hall thruster has insulator ceramic annular walls made of Boron-Nitride (BN). Erosion of ceramic walls is one of the major life limiting factors for Hall thrusters. Emission spectroscopy is used as a means to determine the trends in the thruster wall erosion rate by measuring the radiation emission of the Boron neutral 249.68nm and 249.77nm lines. Discussion about the spectral measurements and relevant analysis are presented.
by Murat Çelik.
Ph.D.

A detailed investigation has been undertaken into the field induced electron emission (FIEE) mechanism that occurs at microscopically localised `sites' on uncoated and dielectric coated metallic electrodes. These processes have been investigated using two dedicated experimental systems that were developed for this study. The first is a novel combined photo/field emission microscope, which employs a UV source to stimulate photo-electrons from the sample surface in order to generate a topographical image. This system utilises an electrostatic lens column to provide identical optical properties under the different operating conditions required for purely topographical and combined photo/field imaging. The system has been demonstrated to have a resolution approaching 1m. Emission images have been obtained from carbon emission sites using this system to reveal that emission may occur from the edge triple junction or from the bulk of the carbon particle. An existing UHV electron spectrometer has been extensively rebuilt to incorporate a computer control and data acquisition system, improved sample handling and manipulation and a specimen heating stage. Details are given of a comprehensive study into the effects of sample heating on the emission process under conditions of both bulk and transient heating. Similar studies were also performed under conditions of both zero and high applied field. These show that the properties of emission sites are strongly temperature and field dependent thus indicating that the emission process is `non-metallic' in nature. The results have been shown to be consistent with an existing hot electron emission model.

In the analysis of solid samples, there are two distinct advantages to performing direct analysis on the solid: (1) minimal sample preparation and (2) avoids potential sample contamination from the reagents used in the dissolution process. The two most common optical techniques for direct solids analysis are arc and spark emission spectroscopy. The most important drawback associated with arc and spark spectroscopy is in the acquistion and interpretation of the spectrum. The development of a custom echelle spectrometer with Charge Injection Device (CID) array detection carried out in these laboratories should be particularly well suited for arc and spark emission spectroscopy. CIDs exhibit many of the best characteristics of photographic film and PMT detection while providing the added advantage of nondestructive readout and Random Access Integration (RAI). This thesis describes the work coupling a spark source to a CID/echelle spectrometer. When properly shielded, the sensitive electronics of the CID function normally in the presence of the spark discharge. The potential for this system to be able to handle the wide variety of spectroscopic situations resulting from the complex spectra typically obtained with this type of excitation is attributed to the flexibility of the instrument which allows the use of alternate line for analysis and internal standard calibration. Additionally, the use of multiple lines has been applied to comparative analysis, monitoring the background for changes in excitation, and determination of the optimum lines to be used for quantification. Effective utilization of the large database of spectral information has lead to the development of sophisticated expert systems such as automated qualitative and semiquantitative analysis routines. Preliminary work with an astigmatism free imaging spectrograph and a Charge Coupled Device (CCD) array detector has shown the ease with which spatial and spectral maps of emission source can be generated. Observation of the spark discharge process in a hope of gaining a clearer picture of the mechanisms of sample excitation seems to be the most rational approach to ultimately obtaining control over the spark process and alleviating the problems associated with sparks excitation.

The limited availability of the present energetic resources and the climate changes induced by the increase of the level of CO2 in the atmosphere are pushing humanity to completely rethink the ways to produce and consume energy. In the long term, a significant contribution to the solution of the world energy issue may come from nuclear fusion: the raw materials, deuterium and lithium, are worldwide accessible and in sufficient quantity to feed the future fusion reactors for several centuries. The largest fusion experiment is ITER, in phase of construction in France. The ITER machine is designed to produce a fusion power of 500 MW, 10 times the input power. Moreover ITER will be the first experiment to continuously operate with deuterium-tritium plasmas, and will have to stand the neutron irradiation produced by nuclear fusion. To reach the desired performances various additional heating systems are foreseen to heat the plasma core up to 10-15 keV. One of the most important heating systems will be composed by 2 neutral beam injectors (NBIs), which produce 2x16.7 MW beams, composed by H/D atoms. To obtain the beams H-/D- ions produced by an ion source will be accelerated at high energy (870 keV for hydrogen, 1 MeV for deuterium) and then neutralized thanks to the charge exchange interaction with the molecules of a H2/D2 gas. The construction of such a system is very challenging and 2 prototypes will be built and tested in Padua at Consorzio RFX. The first one, SPIDER (Source for the Production of Ions o Deuterium Extracted from an Rf plasma), operative in 2016, aims at studying the source part of the NBI, accelerating ions at lower energies, up to 100 keV. The prototype of the full ITER negative NBI system is MITICA (Megavolt ITer Injector Concept and Advancement), it will start operating in 2019. Both SPIDER and MITICA will be equipped with a large number of diagnostics: in particular, the Beam Emission Spectroscopy (BES) will measure the spectrum of the radiation produced by the beam when interacting with the background gas in order to measure the divergence and the uniformity of the beam produced by the ion source. The divergence is a key parameter for the safety of the test facilities, since it is related to the power deposition of the beam on the beam line component. The beam uniformity is crucial for the heating effectiveness of the beam itself. The PhD activity was mostly devoted to develop the BES diagnostics of SPIDER and MITICA, with the target to measure divergence in the range 3- 7 mrad (e-folding) with a relative error below 10%, and values of uniformity in the range 90-100%. In particular, the work consisted in: • developing a set of codes (dBES) for the simulation of the behavior of the BES diagnostics; • studying and improving the methods of analysis for the data that will be collected by BES. • completing the design of the BES diagnostics, also selecting and testing its hardware components; Experimental data of the test facilities BATMAN (BAvarian Test MAchine for Negative ions), MANITU (Multi Ampere Negative Ion Test Unit) and ELISE (Extraction from a Large Ion Source Experiment) at the Max Planck Institut für Plasmaphysik (IPP) in Garching, have been used to validate the numerical model at the base of dBES and to improve the method of analysis of the BES spectra. During my stays at the ITED group of IPP Garching the results of dBES were also benchmarked against those of the BBC-NI code, developed at IPP for similar purposes. Besides SPIDER and MITICA the studies were also addressed to NIO1 (Negative Ion Optimization 1), hosting an RF ion source which produces a 130 mA beam composed by H- ions. The test facility was jointly built by Consorzio RFX and INFN-LNL, with the aim of studying and improving the production of negative ions, as well as testing concepts and instrumentation for SPIDER and MITICA. For NIO1 the BES diagnostic was entirely designed; the tests on NIO1 of this diagnostic will allow a first experimental validation of the design of those for SPIDER and MITICA. The PhD research is described in this thesis as follows: • Chapter [chap:Introduction] gives a briefly describes the ITER reactor. The principle of operation of the neutral beam injectors is then explained, together with the characteristics of the considered experiments: SPIDER and MITICA, BATMAN, MANITU, ELISE and NIO1. The main diagnostics installed in the negative ion sources and more generally in the NBIs are presented, too. • Chapter [chap:Beam-Emission-Spectroscopy] describes the work done on the simulation codes dedicated to Beam Emission Spectroscopy. The physical phenomena at the base of the BES diagnostic operation are explained. The code dBES, developed for the simulation of the BES diagnostic and for the analysis of its measurements, is described. dBES is then benchmarked against the BBC-NI code and with the experimental data of the BES diagnostics in the BATMAN, MANITU and ELISE test facilities. • Chapter [chap:Designtotal] presents the design of the BES diagnostics in the experiments NIO1, SPIDER and MITICA, carried out by means of the dBES code. • Chapter [chap:Experimental-work] presents the experimental activities carried out to test the available instrumentation for the BES and the optical emission spectroscopy diagnostics in NIO1, SPIDER and MITICA; the design activity of some components is also illustrated. • The summary is reported in chapter [chap:Conclusions]. There follows the list of the articles published and of the technical notes written during the PhD.
La disponibilità limitata delle attuali risorse energetiche e i cambiamenti climatici indotti dall’aumento della concentrazione di CO2 nell’atmosfera impongono all’umanità di ripensare completamente i modi di produrre e consumare energia. Nel lungo termine, un contributo importante alla soluzione del problema energetico mondiale potrebbe arrivare dalla fusione nucleare: le materie prime, deuterio e litio, sono accessibili in tutto il globo e in quantità sufficiente per alimentare i futuri reattori a fusione per diversi secoli. Il più grande esperimento a livello mondiale sulla fusione è ITER, in fase di costruzione in Francia. ITER è progettato per produrre dalla fusione fino a 500MW, 10 volte la potenza in ingresso. Inoltre, ITER sarà il primo esperimento a operare permanentemente con plasmi di deuterio e trizio, quindi conterrà materiale radioattivo (il trizio) e dovrà sopportare l’irraggiamento neutronico prodotto dalla fusione nucleare. Per raggiungere le prestazioni volute serviranno varie forme di riscaldamento addizionale, in modo da portare la temperatura centrale del plasma a 10 15 keV. Uno dei sistemi di riscaldamento più importanti sarà costituito da 2 iniettori di neutri (NBI), che producono fasci da 16.7 MW composti da particelle neutre (H/D). Per ottenere i fasci ioni H-/D-, prodotti da un’apposita sorgente, verranno accelerati ad energie elevate (870 keV per l’idrogeno, 1 MeV per il deuterio) e successivamente neutralizzati grazie alle reazioni di scambio carica con le molecole di un gas di idrogeno/deuterio. Costruire un sistema simile è un’operazione complessa, per questo 2 prototipi saranno costruiti e testati a Padova presso il Consorzio RFX. Il primo, SPIDER (Source for the Production of Ions o Deuterium Extracted from an Rf plasma), che sarà operativo dal 2016, verrà utilizzato per studiare la produzione e accelerazione (fino a 100 keV) degli ioni negativi. Il secondo sarà il prototipo di un intero iniettore di neutri per ITER, MITICA(Megavolt ITer Injector Concept and Advancement), che entrerà in funzione nel 2019. Sia SPIDER che MITICA saranno dotati di un gran numero di diagnostiche: in particolare, la Beam Emission Spectroscopy (BES) misurerà lo spettro della radiazione prodotta dall’interazione tra fascio e gas di fondo, con lo scopo di misurare la divergenza e l’uniformità del fascio prodotto dalla sorgente di ioni. La divergenza è un parametro chiave per la sicurezza degli impianti, poichè è legata alla potenza depositata dal fascio sulle strutture degli esperimenti. L’uniformità del fascio è cruciale per l’efficacia del fascio stesso nel riscaldamento del plasma. L’attività di dottorato è stata dedicata in gran parte a sviluppare le diagnostiche BES di SPIDER e MITICA, con l’obiettivo di misurare la divergenza nell’intervallo 3 7 mrad (e-folding) con un errore relativo sotto il 10%, e valori di uniformità nell’intervallo 90 100%. In particolare, il lavoro è consistito nel: • sviluppare un set di codici (dBES) per la simulazione del comportamento della diagnostica BES; • studiare e migliorare i metodi di analisi dei dati che saranno raccolti dalla BES; • completare il design della diagnostica, anche individuando e testando la sua componentistica hardware; Le misure raccolte negli impianti sperimentali BATMAN(BAvarian Test MAchine for Negative ions), MANITU (Multi Ampere Negative Ion Test Unit) ed ELISE (Extraction from a Large Ion Source Experiment) al Max Planck Institut für Plasmaphysik (IPP) a Garching, sono state utilizzate per validare il modello numerico alla base di dBES a per migliorare il metodo di analisi degli spettri BES. Durante le visite al gruppo ITED di IPP Garching i risultati di dBES sono stati confrontati con quelli del codice BBC-NI, sviluppato a IPP per scopi analoghi. Oltre che su SPIDER e MITICA gli studi si sono concentrati anche su NIO1 (Negative Ion Optimization 1), dotato di una sorgente RF che produce un fascio di 130 mA composto da ioni H. L’esperimento è frutto di una collaborazione tra Consorzio RFX e INFN-LNL, con lo scopo di studiare e migliorare la produzione di ioni negativi, nonchè di testare la strumentazione per SPIDER e MITICA. Per NIO1 è stata interamente progettata la diagnostica BES; i test su NIO1 di questa diagnostica permetteranno una prima verifica sperimentale del design delle diagnostiche analoghe per SPIDER e MITICA. Il lavoro di dottorato è descritto nella tesi come segue: • Il capitolo 1 fornisce una breve descrizione del reattore ITER. Viene poi illustrato il principio di funzionamento degli iniettori di neutri, nonchè le caratteristiche dei esperimenti presi in considerazione: SPIDER e MITICA, BATMAN, MANITU, ELISE e NIO1. Vengono inoltre presentate le principali diagnostiche installate nelle sorgenti di ioni negativi e più in generale negli iniettori di neutri. • Il capitolo 2 descrive il lavoro svolto sui codici di simulazione per la Beam Emission Spectroscopy. Vengono illustrati i fenomeni fisici alla base del funzionamento della diagnostica. Viene successivamente presentato il codice dBES, sviluppato per la simulazione della diagnostica BES e per l’analisi dei dati raccolti dalla diagnostica stessa. Segue la verifica delle simulazioni di dBES con i risultati del codice BBC-NI e con i dati delle diagnostiche BES negli esperimenti BATMAN, MANITU ed ELISE. • Il capitolo 3 presenta il design delle diagnostiche BES per gli esperimenti NIO, SPIDER e MITICA, realizzato con il supporto del codice dBES. • Il capitolo 4 presenta le attività sperimentali svolte per caratterizzare la strumentazione disponibile per le diagnostiche BES e optical emission spectroscopy in NIO1, SPIDER e MITICA; viene illustrata anche la progettazione di alcune componenti delle diagnostiche. • Nel capitolo 5 vengono sintetizzati e discussi i risultati presentati nella tesi. Seguono infine la lista degli articoli pubblicati e delle note tecniche scritte durante il dottorato

This thesis presents the research undertaken in time-resolved fluorescence inten¬sity and anisotropy techniques and their application. New information is revealed concerning the emission behaviour of a synthetic multipolar branched chromophore (AF257). Investigation of the relative radiative rates of fluorescing components in fluorescent proteins EGFP and mCherry was carried out using stimulated emission depletion (STED). Previous assumptions in the modelling of both continuous wave (CW) and pulsed STED are shown to be insufficient, and refinements are proposed and tested. The fluorescence techniques employed in this thesis utilise photoselection of an or¬dered excited state through polarised single and two-photon laser excitation, in addition to polarised, time-resolved measurement of sample fluorescence. Chapter one introduces the fluorescence process, the time-evolution of the alignment in the excited state, and the core measurement processes used. Chapter two examines in detail the absorption-emission mechanism of AF257 using both two-photon and single-photon excitation. By combining fluorescence intensity and anisotropy mea¬surements, it was possible to resolve the emission into that from two distinct excited state geometries. Such a thorough analysis has not been previously published for a molecule of this type; this synthesis of information enables the proposition of a new model for the absorption-emission process. The second half of the thesis concerns the use of STED, which incorporates the orientationally sensitive de-excitation of the excited state distribution. Chapter 3 employs CW STED to probe the fluorescence lifetimes and radiative rates of the commonly used fluorescent probes EGFP and mCherry. It is shown that each of these molecules consist of two fluorescing components with individual radiative rates and varying amplitudes (with STED power). A single ‘average’ lifetime and radiative rate is often used for these molecules in biological applications, and the differences observed here could have major implications for the accuracy of results obtained in their application in the biosciences. The chapter goes on to assess the assumption of an average STED rate in CW STED. Using fluorescence anisotropy measurements and numerical simulation, the importance of orientational dependence of fluorescence lifetimes in the analysis of STED measurements is shown. Chapter 4 investigates the effects of pulse stretching and solvent viscosity in pulsed STED. Analysis of this data shows the breakdown of the previously used model with the use of very long (of the order of 2-10 times the rotational correlation time) STED pulses. Revisions to the model are developed and tested. From the results of these revised models it is concluded that the rotation of the higher order spherical harmonic moments in the excited state distribution has a highly significant effect on the observed depolarisation of the excited state alignment, and that further improvements to the model are needed to incorporate this effect.

HI absorption-line studies provide a unique insight into the growth and evolution of galaxies. Next-generation radio telescopes will allow us to conduct the first large, blind absorption-line surveys, studying the evolution of neutral gas at redshifts that are currently largely unexplored. In this thesis, we have conducted a detailed study of HI emission and absorption in nearby galaxies to investigate the expected detection rate of intervening absorption in future surveys and how various factors influence this detection rate. We conducted a survey for intervening absorption using new ATCA observations. 23 sightlines, with impact parameters of 6-46kpc were searched for absorption, resulting in one new detection (a detection rate of 4.3%). Our detection rate is significantly lower than in previous studies, but as our selection criteria much more closely match that of future blind surveys, this suggests our results are far more representative of the true detection rate. We also find that the structure of the background radio sources significantly affects the detection rate, with many sources having complex structures which dramatically reduces the absorption-line sensitivity. In a separate study, we applied the technique of HI spectral stacking to search, for the first time, for a signal of intervening absorption in HIPASS. In particular, we were interested in searching for absorption at impact parameters to large (<100-200kpc) to detect in individual observations. While the presence of HI emission limits the interpretation of our results, we do see possible evidence of absorption at impact parameters <60kpc, and our analysis clearly demonstrates the potential of this new technique to search for weak absorption-line signals in the outskirts of galaxies. Combined, the results in this thesis advance our understanding of the conditions in which intervening absorption arises, and provide important information in the preparation for future large absorption-line surveys.

Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling. The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m. To address concerns on the effect of natural air drying process on EFE, a comparative study was conducted on Nb and the results showed insignificant difference under the experimental conditions. Nb thin films deposited on Cu present a possible alternative to bulk Nb in superconducting cavities. The EFE performance of a preliminary energetically deposited Nb thin film sample are presented.
Ph. D.

Tracer kinetic modeling with Positron Emission Tomography (PET) requires measurements of the time-activity curves in both plasma (PTAC) and tissue (ITAC) to estimate physiological parameters. However, the estimation usually ignores the measurement noise in PTAC while PTAC is assumed to be in the form of the arterial plasma time-activity curve (APTAC) and the traditional sampling schedule used consists of around 20 PTAC measurement points selected during the course of the measurement to construct a smooth curve using piecewise linear approximation. The accuracy and reliability of the physiological parameters estimated by ignoring such errors are not well understood. Feng et a1. [9] recently proposed a PTAC model which fits the complex tracer kinetic behavior in blood vessels and can be used as a driving function for PET kinetic modeling. In this thesis, we apply this PTAC model, in conjunction with the [18F] 2-fluoro-2-deoxy-D-glucose (FDG) experimental data and a 5-parameter FDG model, to systematically study the effects of FDG tracer plasma concentration measurement noise on the estimation of the FDG model’s impulse response function parameters, the rate constants and the physiological parameter, i.e., Local Cerebral Metabolic Rates of Glucose (LCMRGlc). Also, the Optimal Blood Sampling Schedules (OBSS) for PTAC, based on the PTAC model, are investigated by computer simulations and applied to explore the effects of PTAC sampling schedule on the estimation of LCMRGlc. And finally, a more accurate PTAC form, the capillary plasma time-activity carve (CPTAC) is derived and used to study the effects of using APTAC to replace CPTAC on the estimation of physiological parameter. The results of the computer simulations show that all the error sources, e.g., ignoring PTAC measurement noise, using the traditional PTAC sampling schedule and using APTAC to replace CPTAC, increase the unreliability of LCMRGlc estimates.

L’accumulation des filaments appariés en hélices de la protéine tau (PHF tau) entraine un déclin cognitif rencontré dans la démence causée par la maladie d’Alzheimer (MA). Le radiotraceur 18F AV-1451, utilisé dans la tomographie par émission de positons (TEP), permet l’observation de la protéine tau in vivo. Pour déterminer le taux de dépôt des PHF tau dans le cerveau, l'approche classique consiste à effectuer deux scans séparés de 2 à 3 ans et à reconstruire les images TEP séparément. L’image différence obtenue souffre d’une grande variation dans l’intensité du signal. Un essai clinique nécessiterait alors un échantillon plus large pour déceler une différence significative entre un groupe recevant un traitement potentiel et un groupe contrôle. Notre nouvelle approche vise à reconstruire l’image différence directement des données TEP pour réduire la variance en introduisant une dépendance temporelle linéaire et en considérant la différence entre les doses injectées et le recalage entre les deux images. Pour valider la méthode, nous simulons différents niveaux de dépôt accru des PHF tau en créant une image artificielle à partir de données réelles d’un patient. Nous appliquons ensuite la méthode aux données de 123 sujets : 109 sains, 10 atteints de trouble cognitif léger et 4 souffrants de MA. La reconstruction jointe montre un meilleur contraste dans l'image différence créée par les simulations numériques et une variance considérablement réduite dans le changement du ratio de la valeur de fixation normalisée chez les sujets. La variance réduite de notre méthode entraine un échantillon plus petit pour un potentiel essai clinique contre la MA
The accumulation of the paired helical filament tau protein leads to the cognitive decline seen in Alzheimer’s disease (AD). The Positron Emission Tomography tracer, [18F]-AV-1451, permits the observation of PHF tau in vivo. To determine the rate of tau deposition in the brain, the conventional approach involves scanning the subject two times (2-3 years apart) and reconstructing the images separately. Region-specific rates of accumulation are derived from the difference image which suffers from an increased intensity variation making this approach inadequate for clinical trial looking at the effect of a candidate drug on tau because the increased variation leads to a higher sample size required. We propose a joint longitudinal image reconstruction where the tau deposition difference image is reconstructed directly from measurements leading to a lower intensity variation. This approach introduces a linear temporal dependency and accounts for spatial alignment, and the different injected doses. We validate the reconstruction method by simulating higher tau accumulation in real data at different intensity levels. We additionally reconstruct the data from 123 subjects: 109 healthy subjects, 10 suffering from mild cognitive impairment, and 4 diagnosed with AD. The joint reconstruction shows better contrast in the difference image obtained by the numerical simulations and a drastically reduced variance in the change of the Standard Uptake Value Ratio among subjects. The decreased variance of our method leads to a smaller sample size for a potential clinical trial evaluating the effect of a candidate drug against AD

Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008.
Title from PDF t.p. (viewed on Jul 29, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7588. Adviser: Shyh-Yuan Lee.

This thesis is on chronic neck pain after a rear impact car injury, so called whiplash associated disorder (WAD). Three empirical studies using positron emission tomography (PET) with different radioligands have been performed. The first study evaluated resting state regional cerebral blood flow (rCBF) in WAD patients and in healthy, pain-free controls, by use of oxygen-15 labeled water. Patients had heightened resting rCBF bilaterally in the posterior parahippocampal and the posterior cingulate gyri, in the right thalamus and in the right medial prefrontal gyrus. Attenuated tempero-occipital blood flow was also observed in the patient group as compared to healthy controls. Alterations in rCBF were related to patients’ neck disability ratings. Study I suggests an involvement of the posterior cingulate, the parahippocampal and the medial prefrontal gyri in WAD. This altered resting state neural activity may be linked to an increased self-relevant evaluation of pain and stress. The second study evaluated central expression of the neurokinin-1 (NK1) receptor in WAD patients and healthy controls. Using a carbon-11 labeled specific NK1 antagonist, the receptor availability was measured. Patients displayed lowered NK1 receptor availability in the insula, anterior cingulate, frontal lobe, hippocampus, amygdala and in the periaqueductal gray matter, consistent with results from animal models of chronic pain. NK1 receptor availability was most reduced in the ventromedial orbitofrontal cortex, where attenuations were linearly related to patients fear and avoidance of movement. Thirdly, carbon-11 labeled D-deprenyl was used to investigate the presence of locally inflamed soft tissue in the cervical neck in WAD patients. Although the retention mechanism of [11C]D-deprenyl is not known, the results suggest that WAD patients have chronic inflammatory processes in the neck, most commonly in the adipose tissue at the spineous process of the second vertebra. In summary, this thesis provides evidence for altered central blood flow and receptor characteristics in WAD patients. Further, WAD patients may also have signs of persistent peripheral tissue damage. Both central and peripheral pain mechanisms have been demonstrated and visualized in patients with whiplash associated disorder.