This dissertation describes the propagation of near atmospheric nitrogen gas that rushes into a liquid helium cooled vacuum tube after the tube suddenly loses vacuum. The loss-of-vacuum scenario resembles accidental venting of atmospheric air to the beam-line of a superconducting radio frequency particle accelerator and is investigated to understand how in the presence of condensation, the in-flowing air will propagate in such geometry. In a series of controlled experiments, room temperature nitrogen gas (a substitute for air) at a variety of mass flow rates was vented to a high vacuum tube immersed in a bath of liquid helium. Pressure probes and thermometers installed on the tube along its length measured respectively the tube pressure and tube wall temperature rise due to gas flooding and condensation. At high mass in-flow rates a gas front propagated down the vacuum tube but with a continuously decreasing speed. Regression analysis of the measured front arrival times indicates that the speed decreases nearly exponentially with the travel length. At low enough mass in-flow rates, no front propagated in the vacuum tube. Instead, the in-flowing gas steadily condensed over a short section of the tube near its entrance and the front appeared to `freeze-out'. An analytical expression is derived for gas front propagation speed in a vacuum tube in the presence of condensation. The analytical model qualitatively explains the front deceleration and flow freeze-out. The model is then simplified and supplemented with condensation heat/mass transfer data to again find the front to decelerate exponentially while going away from the tube entrance. Within the experimental and procedural uncertainty, the exponential decay length-scales obtained from the front arrival time regression and from the simplified model agree. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / February 23, 2016. / accelerator, accident, condensation, shock, superconducting, vacuum / Includes bibliographical references. / Steven W. Van Sciver, Professor Directing Dissertation; David A. Kopriva, University Representative; Eric E. Hellstrom, Committee Member; Wei Guo, Committee Member; Kunihiko Taira, Committee Member.

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Thermal Conductivity studies can provide fundamental information regarding the symmetry of the superconducting energy gap. To perform this kind of experiment, we need to use a very low temperature environment. Also a special mount has been to designed and constructed for the thermal conductivity measurements. This mount will allow holding the sample in different directions with respect to the applied magnetic field. The results are consistent with Wiedemann-Franz law to within 2.5\%. We also discuss a series of thermal conductivity experiments to shed additional light on the symmetry of the superconducting order parameter in the unconventional superconductor PrOs4Sb12.

Thermal Conductivity studies can provide fundamental information regarding the symmetry of the superconducting energy gap. To perform this kind of experiment, we need to use a very low temperature environment. Also a special mount has been to designed and constructed for the thermal conductivity measurements. This mount will allow holding the sample in different directions with respect to the applied magnetic field. The results are consistent with Wiedemann-Franz law to within 2.5\%. We also discuss a series of thermal conductivity experiments to shed additional light on the symmetry of the superconducting order parameter in the unconventional superconductor PrOs4Sb12.

Thesis (Ph. D.) - Harvard University, 1960. / Bibliography: leaves [90-93]