This study examines the effects of cryogenic temperatures on the mechanical properties of carbon, aramid, and poly(p-phenylene-2, 6-benzobisoxazole) (PBO) fibers. Although the mechanical properties are documented for these fibers at ambient and elevated temperatures, there is an absence of data in the open literature for how these fibers behave at very low temperatures. To evaluate the mechanical properties, the ASTM standard method for testing at ambient temperature was used as a baseline. The low temperature tests were conducted inside a double walled cryogenic chamber to evaluate the fiber performance at 100K. Fiber properties at low temperatures displayed differences from room temperature properties in the form of increased ultimate tensile strength (UTS), decreased in elongation to failure, and increased Young’s Modulus. The change in properties due to the effect of temperature was more pronounced in fibers with a higher degree of crystallinity.

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The development, testing, and use of liquid propellant and hybrid rocket propulsion systems for spacecraft and their launch vehicles routinely involves the use of cryogenic propellants. These propellants provide high energy densities that enable high propulsive efficiency and high engine thrust to vehicle weight ratios. However, use of cryogenic propellants also introduces technical problems not associated with other types of propellants. One of the major technical problems is the phenomenon of propellant tank pressurant and ullage gas collapse. This collapse is mainly caused by heat transfer from most of the ullage gas to tank walls and interfacing propellant, which are both at temperatures well below those of this gas. Pressurant gas is supplied into cryogenic propellant tanks in order to initially pressurize these tanks and then to maintain required pressures as propellant is expelled from these tanks. The cryogenic propellants expelled from the tanks feed rocket engine assemblies, subassemblies, and components at required interface pressures and mass flow rates. The net effect of pressurant and ullage gas collapse is increased total mass and mass flow rate requirements of pressurant gases. For flight vehicles this leads to significant and undesirable weight penalties. For rocket engine component and subassembly ground test facilities this results in high construction and operational cost impacts. Accurate predictions of pressurant gas mass transfer and flow rate requirements are essential to the proper design of systems used to supply these gases to cryogenic propellant tanks. While much work has been done in the past for predicting these gas requirements at low subcritical tank pressures, very little has been done at supercritical tank pressure conditions and there are selected cases where errors of analytical predictions are high. The objectives of this study are to develop a new generalized and improved computer program to determine pressurant gas requirements at both subcritical and supercritical tank pressure conditions, and then evaluate and validate the consistent accuracy of this program over a wide range of conditions by comparison of program results to empirical data.

Physical mechanism for high frequency instability in cryogenic engines at low hydrogen injection temperature has been a subject of debate for long time. Experimental and early developmental studies revealed no instabilities and it was only much later when liquid hydrogen at lower initial temperature (~50 to 100 K) was injected into the combustion chamber that instabilities were detected. From the compilations of the experimental data related to the instability of cryogenic engines by Hulka and Hutt, it was found that the instability was strongly connected to the temperature of hydrogen. Experiments conducted with hydrogen temperature ramping from a higher value to lower values indicated that the temperatures in excess of 90 K favor stability under most practical operating conditions. Even though this has been known for over forty years, there has been no clear and simple explanation for this. Many physical mechanisms have been hypothesized to explain how temperature ramping causes instability, but all appear to have limited range of applicability. Current understanding of cryogenic engine combustion instability has been achieved through a combination of experimental investigation and approximate analytical models as well as CFD tools. Various researchers have tried to link the low hydrogen injection temperature combustion instability phenomena with various potential mechanisms for combustion instability. They involve coupling of combustion acoustics with atomization, vaporization, mixing, chemical kinetics or any combination of these processes. Various studies related to the effect of recess, injector hydrodynamics, acoustic damping of gas liquid scheme injectors and effect of drop size distribution on the stability characteristics of cryogenic engines were compiled in the thesis. Several researchers examined fuel droplet vaporization as the rate controlling mechanism. Recently a new method for the evaluation of stability characteristics of the engine using model chamber were proposed by Russians and this is based on mixing as the rate controlling mechanism. Pros and cons of this method were discussed. Some people examined the combustion instability of rocket engines based on chemistry dynamics. A considerable amount of analytical and numerical studies were carried out by various researchers for finding out the cause of combustion instability. Because of the limitations of their analysis, they could not successfully explain the cause of combustion instability at low hydrogen injection temperature. A compilation of previous numerical studies were carried out. A number of researchers have applied CFD in the study of combustion instabilities in liquid propellant rocket engines. In the present thesis, a theoretical model has been developed based on the vaporization of droplets to predict the stability characteristics of the engine. The proposed concept focuses on three dimensional simulation of combustion instability for giving some meaningful explanations for the experimental work presented in the literature. In the present study the pressure wave corresponding to the transverse modes were superimposed on a three dimensional steady state operating conditions. Steady state parameters were obtained from the three dimensional combustion modeling. The conservation equations for mass, momentum and energy are non dimensionalized for facilitating the order of magnitude analysis. In order to do the stability analysis, variables are represented as the sum of their steady values and deviation from the steady state. A harmonic time dependence is assumed for the perturbations. For the transverse mode of oscillations independent variables of the zeroth order equations are r and θ only and the dependant variables are not functions of the axial distance. The axial dependence comes only through the first order equations. In this analysis, the wave motion in the combustion chamber is assumed to be linear, confining the nonlinearity to the vaporization process only. The reason behind making this assumption is that the vaporization process is the major mechanism driving the instability. Vaporization histories of liquid oxygen drops in a combustor with superimposed transverse oscillations were computed and stability characteristics of the engine were estimated. The stability characteristics of the engine are accessed from the solutions of first order equations. Effects of various parameters like droplet diameter, hydrogen injection temperature and hydrogen injection area on the stability characteristics of cryogenic engines are studied. A comparison of predicted and published experimental results was made which showed general agreement between experiment and computation. The present study and experimental results show clearly that hydrogen injection velocity is the critical parameter for instability rather than hydrogen injection temperature. What has happened in actual experiments when hydrogen injection temperature is varied is an effective alteration of the injection velocity that leads to the situation of instability. For higher relative velocity between hydrogen and liquid oxygen, the response of the vaporization rate in the presence of pressure wave is minimum compared to lower relative velocity. Due to this cryogenic engines will go to unstable mode at lower relative velocity.

Low cost cryocoolers suitable for long term use in industrial environments are required for superconducting technologies to be competitive with copper based devices in real world applications. Industrial Research Limited is developing such cryocoolers, which use metal diaphragm based pressure wave generators to convert electrical energy to the gas volume displacement required. This project explores methods of increasing the volume displacement provided by the diaphragms while ensuring the components stay within the acceptable material limits. Various alternative diaphragm shapes are tested against the currently used shape through finite element analysis. In addition to testing alternative diaphragm shapes, each shape’s dimensions are optimised. It is concluded the currently used design can be improved by offsetting the piston rest position and slightly reducing the piston diameter. A more detailed analysis is carried out of the bend radii created during fabrication of the diaphragm, and physical testing is performed to verify unexpected calculated stress concentrations. High stresses are observed, however it is concluded unmodelled material features have a large effect on the final stress distribution. It is recommended advantageous shape changes calculated in the first part of the work be trialled to increase the efficiency of the cryocooler, and that investigation of the material behaviour during commissioning of the pressure wave generator be carried out to better understand the operational limits of the diaphragms.

SuperCDMS is a leading direct dark matter search experiment which uses solid state detectors (Ge crystals) at milliKelvin temperatures to look for nuclear recoils caused by dark matter interactions in the detector. ‘Weakly Interacting Massive Particles’ (WIMPs) are the most favoured dark matter candidate particles. SuperCDMS, like many other direct dark matter search experiments, primarily looks for WIMPs. The measurement of both the ionization and the lattice vibration (phonon) signals from an interaction in the detector allow it to discriminate against electron recoils which are the main source of background for WIMP detection. SuperCDMS currently operates about 9 kgs worth of germanium detectors at the Soudan underground lab in northern Minnesota. In its next phase, SuperCDMS SNOLAB, it plans to use 100-200 kg of target mass (Ge) which would allow it to probe more of the interesting and unexplored parameter space for WIMPs predicted by theoretical models. The SuperCDMS Queen’s Test Facility is a detector testing facility which is intended to serve detector testing and detector research and development purposes for the SuperCDMS experiment. A modified detector called the ‘HiZIP’ (Half-iZIP), which is reduced in complexity in comparison to the currently used iZIP (interleaved Z-sensitive Ionization and Phonon mediated) detectors, is studied in this thesis. The HiZIP detector design also serves to discriminate against background from multiple scatter events occurring close to the surfaces in a single detector. Studies carried out to compare the surface event leakage in the HiZIP detector using limited information from iZIP data taken at SuperCDMS test facility at UC Berkley produce a highly conservative upper limit of 5 out of 10,000 events at 90% confidence level. This upper limit is the best among many different HiZIP configurations that were investigated and is comparable to the upper limit calculated for an iZIP detector in the same way using the same data. A real HiZIP device operated at Queen’s Test Facility produced an exposure limited 90% upper limit of about 1 in 100 events for surface event leakage. The data used in these studies contain true nuclear recoil events from cosmogenic and ambient neutrons. This background was not subtracted in the calculation of the upper limits stated above and hence they are highly conservative. A surface event source was produced by depositing lead-210 from radon exposure onto a copper plate. This source was then used to take data for a surface event discrimination study of the HiZIP detector operated at Queen’s Test Facility. A study of the contribution of the noise from capacitive crosstalk between charge sensors in a HiZIP detector configuration was investigated, confirming the expectation that no significant drop in performance is to be expected due to this effect. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-30 23:48:49.375

Master of Science / Department of Electrical and Computer Engineering / William Kuhn / Studies of Silicon-on-Sapphire (SOS) CMOS device operation in cryogenic environments are presented. The main focus was to observe the characteristic changes in high, medium and low threshold SOS NFETs as well as SOS silicide blocked (SN) resistors when the operational temperature is in the devices’ freeze-out range below 77 Kelvin. The measurements taken will be useful to any integrated circuit (IC) designer creating devices based on an SOS process intended to operate in cryogenic environments such as superconducting electronics and planetary probes. First, a 1N4001 rectifier and a 2N7000 NFET were tested to see how freeze-out effects standard diode and MOS devices. These devices were tested to see if the measurement setup could induce carrier freeze-out. Next, SOS devices were studied. Data was collected at room temperature and as low as 5 Kelvin to observe resistance changes in an SN resistor and kink effect, threshold voltage shifts and current level changes in transistors. A 2μm high threshold NFET was tested at room temperature, 50 Kelvin, 30 Kelvin and 5 Kelvin to observe effects on I-V curves at different temperatures with-in the freeze-out range. A 2μm medium threshold NFET was tested down to 56 Kelvin to see if the behavior is similar to the high threshold FET. A 2μm intrinsic, or low threshold, NFET was also tested with the assumption it would be the most susceptible to carrier freeze-out. All of the devices were found to behave well with only mild effects noted.

Thesis advisor: Michael Naughton / A helium gas-pressure system has been tested and then used to investigate the nature of a phase transition from the normal metallic state to an antiferromagnetic spin density wave state in the quasi-one dimensional molecular organic conductor (TMTSF)2PF6. This metallic state superconducts at low temperature and high pressure, in such a way that the insulating antiferromagnetic state competes with the superconducting state. The physics motivation was to examine the possibility of a ¿quantum critical point¿ near the critical pressure of the sample where these latter two states may coexist. The technical motivation was to make the first tests of the pressure system at cryogenic temperatures to ensure that it is the appropriate tool for the planned investigations. Using temperature sweeps at various fixed pressures on a single crystal sample, we were able to obtain several points on the pressure versus temperature phase boundary separating the metallic and SDW states. We have thus verified that the helium gas-pressure system is indeed capable of facilitating these types of experiments, and future measurements will be done at lower temperatures accessing the superconducting state. / Thesis (BS) — Boston College, 2003. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Physics. / Discipline: College Honors Program.

Materials which are both lighter and stronger have faced an increased demand over the past decades to fulfil the requirements across a range of industrial applications. More specifically, demands for titanium alloys have increased significantly due to its high strength to weight ratio which is particularly attractive for increasing fuel efficiency in aircrafts and cars and is also used in biomedical implants. Despite the increasing demand for titanium made products, machining titanium alloys remains a significant challenge. High material strength and hardness lead to excessive heat generation at the cutting zone which accumulates and results in high cutting temperatures due to the poor thermal conductivity. The high cutting temperatures together with inherent material properties of titanium are responsible for short tool life and poor surface finish. Despite the environmental and health drawbacks, a generous amount of cutting fluids is commonly used to control the cutting temperature in machining titanium alloys. However, conventional cutting fluids evaporate at high cutting temperatures which isolate the cutting zone by forming a vapour cushion resulting in further increases in cutting temperatures. This research investigates the effects of cryogenic cooling on machinability of Ti-6Al-4V alloy in CNC milling as compared to conventional dry and wet machining environments. Two literature reviews were conducted and a methodology has been developed and implemented consisting of three experimental stages of i) design and manufacture of a cryogenic cooling system, ii) comparative study of cryogenic cooling with dry and wet machining and iii) optimisation of cutting parameters for cryogenic machining. The major contribution of this research can be summarised as design, realisation and assessment of a novel cryogenic cooling system for CNC milling, termed cryogenic shower, which is retrofitable to an existing CNC machining centre. In addition, the research provides a thorough study on the effects of cryogenic cooling on machinability of Ti-6Al-4V alloy in comparison with dry and wet machining. The studies range from power consumption and tool wear through to surface topography and surface integrity. Furthermore, the optimum cutting parameters for cryogenic machining are identified. The research demonstrates that using the cryogenic shower has significantly improved machinability of Ti-6Al-4V through realisation of higher material removal rates, reduced tool wear and improved surface finish, surface topography and surface integrity.

This thesis presents details of the design, construction and measurements of an apparatus (Blue Elbow cryostat) for high voltage testing of a full-size cryogenic nEDM cell in liquid helium at 4.2 K SVP. The test cell is cylindrical and of 24 cm internal diameter with stainless steel electrodes and an insulating borosilicate glass spacer. The cylinder axis of the cell is vertical and the insulator is located in grooves in the electrodes. The electrode separation can be varied from 0.2 cmto 2.6 cm and a voltage of up to 260 kV can be applied across the cell. It has long been expected that a nEDM cell immersed in superfluid LHe at 0.5 K should permit E-fields much greater than room temperature experiments. Long et al. (1) showed that over 400 kV/cm was obtainable in a large cell without an insulating spacer at 4.2 K, but that this was reduced dramatically as the temperature, and hence pressure, was reduced to below 2 K in a pumped LHe bath. Subsequent work by Davidson (2) in this laboratory on small spacerless cells showed that the dielectric strength in the superfluid at 1.9 K could be restored to its 400 kV/cm value by pressurising the LHe to 1 bar. Further work in this laboratory by Davidson (2) and Hill (3) shows that the introduction of a dielectric spacer reduces the value of the breakdown field, Ebd , for a given geometry. However, measurements presented here on smaller scales than the Blue Elbow cryostat, overcame the reduced fields through careful groove optimisation and insulator material choice. Ebd data as a function of separation with the Blue Elbow cryostat in LN2 show a clear reduction compared to data from smaller scale cells, due to surface area effects. Breakdown fields in LHe at 4.2 K SVP with this apparatus indicate fields at 120 kV/cm were achievable at 6mm separation but dropped off dramatically as separation was increased to 12 mm then 16 mm. The reason for the drop off is attributed to the geometry of the electrode. This result, together with Davidson's pressure dependence data, should inform the design of a future cryogenic nEDM experiment.