Hohenheim, Universität, Thesis (doctoral), 2001.

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The International Thermonuclear Experimental Reactor (ITER) is currently designed to use graphite targets in the divertor for power handling and impurity control. Understanding and quantifying chemical sputtering is therefore key to the success of fusion as a clean energy source. The principal goal of this thesis is to design and carry out experiments, then analyze and interpret the results in order to elucidate the role of chemical sputtering in carbon sources in the DIII-D tokamak. A self-contained gas puff system has been designed, constructed, and employed for in-situ study of chemical erosion. The porous plug injector (PPI) releases methane through a porous graphite surface into the divertor plasma at a precisely calibrated rate, minimizing perturbation to local plasma while replicating the immediate environment of methane molecules released from a solid graphite surface more accurately than done previously. For the first time in a tokamak environment, the methane flow rate used in a puffing experiment was the same order of magnitude as that expected from laboratory experiments for intrinsic chemical sputtering. Effective photon efficiencies for injection are reported; results are found to have significant dependencies on surface conditions and the divertor operating regime. The contribution of sputtering processes to sources of C0 and C+ are assessed through measurement of background and incremental spectroscopic emissions of both physically and chemically-released sputtering products and by CI, 910 nm line profile fitting. Comparison of background and incremental emissions of chemically-released products demonstrate a dramatic drop in production of CH in cold and detached conditions. Finally, the chemical erosion yield is calculated in both attached and cold-divertor conditions and found to be much closer to that measured ex-situ in ion beam experiments than previously determined in DII-D. These observations represent a positive result for ITER which will operate at all times with a detached divertor, i.e., a low chemical sputtering yield. Results and analysis techniques presented here point the direction for future experiments with the PPI for study of chemical sputtering in the tokamak edge environment.

The International Thermonuclear Experimental Reactor (ITER) is currently designed to use graphite targets in the divertor for power handling and impurity control. Understanding and quantifying chemical sputtering is therefore key to the success of fusion as a clean energy source. The principal goal of this thesis is to design and carry out experiments, then analyze and interpret the results in order to elucidate the role of chemical sputtering in carbon sources in the DIII-D tokamak. A self-contained gas puff system has been designed, constructed, and employed for in-situ study of chemical erosion. The porous plug injector (PPI) releases methane through a porous graphite surface into the divertor plasma at a precisely calibrated rate, minimizing perturbation to local plasma while replicating the immediate environment of methane molecules released from a solid graphite surface more accurately than done previously. For the first time in a tokamak environment, the methane flow rate used in a puffing experiment was the same order of magnitude as that expected from laboratory experiments for intrinsic chemical sputtering. Effective photon efficiencies for injection are reported; results are found to have significant dependencies on surface conditions and the divertor operating regime. The contribution of sputtering processes to sources of C0 and C+ are assessed through measurement of background and incremental spectroscopic emissions of both physically and chemically-released sputtering products and by CI, 910 nm line profile fitting. Comparison of background and incremental emissions of chemically-released products demonstrate a dramatic drop in production of CH in cold and detached conditions. Finally, the chemical erosion yield is calculated in both attached and cold-divertor conditions and found to be much closer to that measured ex-situ in ion beam experiments than previously determined in DII-D. These observations represent a positive result for ITER which will operate at all times with a detached divertor, i.e., a low chemical sputtering yield. Results and analysis techniques presented here point the direction for future experiments with the PPI for study of chemical sputtering in the tokamak edge environment.

Remote sensing imaging is a tool for collecting information about the Earth's surface such as soil, vegetation and water. Recent progress in electronics, telecommunications and sensor developments have resulted in the launch of many satellites in the past three decades. Different sensors in remote sensing systems capture a variety of images with differing characteristics. Image fusion has been used to integrate two or more images and provides output images with better accuracy. This research provides a new technique for image fusion using the contourlet transform in combination with the YCbCr color space. The output images preserve both the spectral and spatial characteristics of the input images and they are better for human and machine interpretation. This technique provides solutions to some problems (\emph{i.e.}, ghosting effect, and blocking artifacts) which the traditional image fusion techniques fail to address. The proposed technique is tested on both classical and remote sensing images. Quality metrics are used to evaluate the results of the proposed technique. The results proved significant enhancement of the quality of the output images. More fine details are successfully captured and the original chromaticity information is preserved as well. The proposed technique eliminates the blocking artifacts in the output images. Also, a new metric is presented to measure the blocking artifacts in the fused image. The results showed that increasing the number of contourlet decomposition levels does not degrade the quality of the output image. Therefore, the output images do not lose their chromaticity information when the number of contourlet decomposition levels increases. The proposed technique is tested on a variety of the remote sensing images that have large resolution ratios (\emph{i.e.}, 1:8, 1:16 and 1:32). The proposed technique is robust and suitable for many image applications. The detection of the concealed objects is an example of such applications, where the proposed technique is tested to measure its capability to fuse images with different features. The results of the Contourlet-YCbCr fusion technique are compared with the conventional fusion methods, where the proposed technique is more capable in detecting the hidden objects and preserving the original color components of the input image.

Freehand 3-D ultrasound (US) using a 2-D US probe has the advantage over conventional 3-D probes of being able to collect arbitrary 3-D volumes at a lower cost. Traditionally, generating a volume requires external tracking to record the US probe position. An alternative means of tracking the US probe position is through speckle tracking. Ultrasound imaging has the advantage that the speckle inherent in all images contains relative position information due to the decorrelation of speckle over distance. However, tracking the position of US images using speckle information alone suffers from drifts caused by tissue inconsistencies and overall lack of accuracy. This thesis presents two novel methods of improving the accuracy of speckle-tracked 3-D US through the use of sensor fusion. The first method fuses the speckle-tracked US positions with those measured by an electromagnetic (EM) tracker. Measurements are combined using an unscented Kalman filter (UKF). The fusion is able to reduce drift errors as well as to eliminate high-frequency jitter noise from the EM tracker positions. Such fusion produces a smooth and accurate 3-D reconstruction superior to those using the EM tracker alone. The second method involves the registration of speckle-tracked 3-D US volumes to preoperative CT volumes. We regard registration combined with speckle tracking as a form of sensor fusion. In this case, speckle tracking is used in the registration to generate an initial position for each US image. To improve the accuracy of the US-to-CT registration, the US volume is registered to the CT volume by creating individual US "sub-volumes", each consisting of a small section of the entire US volume. The registration proceeds from the beginning of the US volume to the end, registering every sub-volume. The work is validated through spine phantoms created from clinical patient CT data as well as an animal study using a lamb cadaver. Using this technique, we are able to successfully register a speckle-tracked US volume to a CT volume with excellent accuracy. As a by-product of accurate registration, any drift from the speckle tracking is eliminated and the freehand 3-D US volume is improved. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2009-10-19 00:10:25.717

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No description available.