Fermi surface and superconductivity in low-density high-mobility {\delta}-doped SrTiO3

The electronic structure of low-density n-type SrTiO3 delta-doped heterostructures is investigated by angular dependent Shubnikov-de Haas oscillations. In addition to a controllable crossover from a three- to two-dimensional Fermi surface, clear beating patterns for decreasing dopant layer thicknesses are found. These indicate the lifting of the degeneracy of the conduction band due to subband quantization in the two-dimensional limit. Analysis of the temperature-dependent oscillations shows that similar effective masses are found for all components, associated with the splitting of the light electron pocket. The dimensionality crossover in the superconducting state is found to be distinct from the normal state, resulting in a rich phase diagram as a function of dopant layer thickness.Comment: 4 pages, 5 figures, submitted for publicatio

Flexible Foot Test Assembly

A test model of the flexible foot support was constructed early in the design stages to check its reactions to applied loads. The prototype was made of SS 304 and contained four vertical plates as opposed to the fourteen Inconel 718 plates which comprise the actual structure. Due to the fact that the prototype was built before the design of the support was finalized, the plate dimensions are different from those of the actual proposed design (i.e. model plate thickness is approximately one-half that of the actual plates). See DWG. 3740.210-MC-222376 for assembly details of the test model and DWG. 3740.210-MB-222377 for plate dimensions. This stanchion will be required to not only support the load of the inner vessel of the cryostat and its contents, but it must also allow for the movement of the vessel due to thermal contraction. Assuming that each vertical plate acts as a column, then the following formula from the Manual of Steel Construction (American Institute of Steel Construction, Inc., Eigth edition, 1980) can be applied to determine whether or not such columns undergoing simultaneous axial compression and transverse loading are considered safe for the given loading. The first term is representative of the axially compressive stress, and the second term, the bending stress. If the actual compressive stress is greater than 15% of the allowable compressive stress, then there are additional considerations which must be accounted for in the bending stress term

High Voltage Connector

The originally designed high voltage connectors were to be made of brass. However, if treated like a Bellevile spring with the initially given dimensions, the stresses of the connector when crimped were calculated to be much higher than the yield stress of brass. Since the flange and outer diameters of the connector are to remain small, it was necessary to alter the other dimensions and choice of material in order to bring down the stresses applied to the connector

Critical Flow Restricting Orifices

The installation of flow restricting orifices in both the nitrogen gas and instrument air supply lines in the D-Zero Building limits the flow available to the various users. These orifices are strategically positioned along the lines such that no one user can monopolize the gas supply and deprive others of their flow required to operate. Provided that the necessary orifice plates are machined in a manner similar to that of the prototypes, the orifices for the various lines were sized using the discharge coefficient for the round edge orifice because the calculated values were in good agreement with the empirically obtained values for this case. The final calculated orifice diameters for the round edge, sharp edge, and short tube cases are listed in Table 2

RTV 21 Displacements

A seal is needed for the cover of the Nitrogen Test Vessel in order to prevent leakage of the N{sub 2} gas. This seal is to be molded out of RTV 21. In this experiment, the Modulus of Elasticity of the RTV was sought after, and the displacements of the RTV due to various stresses were measured to see if they were large enough to provide a tight seal between the vessel and its cover

OCH Button Test

A test was conducted to make a check on the yield stress of the copper spacer buttons to be used in OCH. The tested button was made from Copper no. 110, cold drawn rod, which has a documented yield stress value of 48,000 psi. The button was put into compression with the load applied to the face of the button. The resulting deflection vs. the applied cross load was then charted with the width of the chart having a 10,000 kg scale. While the chart speed was set at 1 cm/min, the cross head speed was set at .05 cm/min. To find a value of Young's Modulus for the OCH button, the compression test was run again with a chart width scale of 5,000 kg. The chart speed was set at 10 cm/min and the cross head speed at .05 cm/min. The curve generated on the chart was linear in nature until the button reached its yield point. Here, the slope of the curve began to change, increasing over a small area until a new linear curve was established. The point at which the slope changed would be considered the yielding point of the material, but here, there was no single distinct point. Instead there was a smooth transition between the two linear portions of the curve. In order to find where the yield point would occur, two lines were drawn, representing the best fit of each of the two slopes of the curve (before and after the yield point). The intersection of these lines was taken to be the point from which the yield stress could be calculated

Gaseous Nitrogen Heat Exchanger

A heat exchanger is necessary to warm the gaseous nitrogen from the nitrogen dewar from 77 K to ambient temperature for use in the D-Zero Building. The original proposal would use an ambient air vaporizer, but further investigation led to the consideration and evaluation of other possibilities and a different final system. The vaporizer must be able to handle a flow rate of 1200 scfh at 30 psig on a continuous basis subject to local weather conditions. Upon consulting with a representative from Thermax Incorporated, So. Dartmouth, Massachusetts, four different heat exchanging systems were proposed. Their advantages and disadvantages are stated

Gaseous Nitrogen Heat Exchanger

A heat exchanger is necessary to warm the gaseous nitrogen from the nitrogen dewar from 77 K to ambient temperature for use in the D-Zero Building. The original proposal would use an ambient air vaporizer, but further investigation led to the consideration and evaluation of other possibilities and a different final system. The vaporizer must be able to handle a flow rate of 1200 scfh at 30 psig on a continuous basis subject to local weather conditions. Upon consulting with a representative from Thermax Incorporated, So. Dartmouth, Massachusetts, four different heat exchanging systems were proposed. Their advantages and disadvantages are stated

Flexible Support Test Procedure and Results

Upon completion of the fabrication process, the four central calorimeter cryostat flexible support assemblies were sent to Construction Technology Laboratories (CTL) in Skokie, IL, where the required tests were performed for Richmond Lox prior to the installation of the stanchions in the cryostat. These tests were to simulate the simultaneous axial and transverse loading experienced by the stanchions when the cryostat undergoes the cool down process

D-Zero End Cap Calorimeter Annular Piping Analysis

In accoradnce with the ASME Code for Pressure Piping, B31 version of Chemical Plant and Petroleum Refinery Piping, ANSI/ASME B31.3-1984 Edition, the maximum allowable stress for 304 stainless steel piping is 25,500 psi. This 'Allowable Displacement Stress Range' value was calculated using equation (1a) found on page 16 of the above mentioned reference. Each of the lines that comprise the End Cap Calorimeter (BC) piping were modeled on ANSYS and the appropriate constraints were applied. This was done using the Piping Stress Analysis Module of ANSYS. The bending stresses and displacements due to the thermal contraction that occurs in cooling the piping from 300 K to 77 K were calculated by ANSYS. The seven lines involved and their maximum bending stresses are as follows: (1) Rupture Disc - Maximum bending stress is 8335 psi; (2) Argon Relief - Maximum bending stress is 12,619 psi; (3) Gaseous Argon Supply - Maximum bending stress is 5399 psi; (4) Liquid Nitrogen Cooldown Supply - Maximum bending stress is 7049 psi; (5) Liquid Nitrogen Operating Supply - Maximum bending stress is 5774 psi; (6) Nitrogen Exhaust - Maximum bending stress is 1826 psi; and (7) Argon/Nitrogen Vent - Maximum bending stress is 48,364 psi. The maximum bending stress values and their positions are indicated on the attached diagrams. The dashed line indicates the original position of the piping, and the solid line shows the position of the displaced piping. Also attached are copies of the programs used to model the piping configurations. The original analysis was done by J. Wendlandt, but later changes and additions required that the programs be modified and re-run. The maximum bending stress found in each line of the annular piping fell sufficiently below the allowed maximum of 25,500 psi. The maximum bending stress for the Argon/Nitrogen Vent line was 48,364 psi, which is greater than the value of 25,500 psi allowed by the code. This line of piping is located on the outside of the annular space and will be installed at Fermilab. While fabrication of the EC vessel is underway, modifications will be made to the Argon/Nitrogen Vent line in order that its stress values remain within that allowed by the code. The complete Argon/Nitrogen Vent line is analyzed in EN-312, D0 Cryogenic Piping Frame Stress Analysis, and the stresses are below the maximum allowable stress of 25,500 psi