Personal Papers (MS 80-0002)

Letter from S. M. McAshan, Jr. to Harris L. Kempner inviting him and Ruth to a dinner he and Susan are hosting

Nitrogen system for the SSC

The Superconducting Super Collider consists of two parallel magnet rings, each 87,120 m in circumference, constructed in a tunnel 25 m to 74 m below ground level. They are operated at a controlled low helium temperature in order to maintain the magnet windings in the superconducting state. To obtain this condition, the magnet cryostat is designed with a high-quality insulation obtained by a high vacuum chamber, multilayer insulation, and thermal shields at nominal temperatures of 84 K and 20 K. Thermal radiation and the conduction heat load through the supports are intercepted and absorbed by the 84-K shield. Liquid nitrogen provides the refrigeration for these loads. The 84-K shield is anchored to two 63.5-mm stainless-steel tubes. One of the tubes, the ``liquid line,`` serves as a conduit in the distribution system of liquid nitrogen. The other tube, the ``vapor line,`` is used to collect the nitrogen vapor generated in the cooling process and to supply this vapor to,the helium refrigerators for precooling. The vapor line may also be used as a continuous cooler by injecting controlled amounts of liquid nitrogen. The nitrogen system consists of nitrogen supplies; ten nitrogen dewars for the collider and two for the High Energy Booster located on the ground at the main shaft entrances; liquid and vapor transfer lines through the shaft to connect the surface and the tunnel systems; and transfer lines to bypass warm equipment sections of the collider. The nitrogen system is expected to operate at steady state condition except for cooldown, warmup, and system repair, for which transients are expected. During normal operation and standby modes of the collider, temperature, pressure, and mass flow are expected to be constant in all circuits of the nitrogen system. The conceptual design requirements for various flow schemes and the engineering considerations are presented in this report

Design and Measurements of a Deflecting Mode Cavity for an RF Separator

The Fermilab Main Injector can produce intense 120 GeV/c proton beams for fixed target experimentation. Two deflecting mode RF systems can be used to separate charged kaons from a momentum selected secondary beam, consisting of pions, kaons and protons, using a time of flight method. We present the RF design of a 3.9 GHz superconducting cavity which operates in the deflecting (TM110) pi-mode and the dependence of the RF parameters on the cavity shape, as determined with finite difference calculations. End cell compensation has been treated, providing cell-to-cell field flatness. First results from measurements on a prototype cavity are shown. We demonstrated that it is possible to tune the deflecting mode of a five cell cavity with bead pull measurements. Effects relating to the polarization of the modes are discussed

Design and Performance of Cryogenic Enclosures for Long Duration Testing of Large Samples

We have designed a large helium dewar as part of an experiment to investigate gravitational radiation. Two such dewars have been constructed. Our use requires a nonmagnetic dewar to cool an aluminium antenna of approximately 5000 kg to below helium temperatures and to keep the antenna in a stable low temperature environment for extended time. This requires a low temperature volume of 1.5 m inner diameter and 3.1 m length and a cooling system capable of efficiently removing the room temperature enthalpy of 8.5 × 108 J. Our solution to this problem is of wider application than simply gravity wave detection so we have discussed the design philosophy in some detail. As constructed, the apparatus uses less than 1 l of helium per hour when cold

Mechanism of chromosomal transfer of Enterococcus faecalis pathogenicity island, capsule, antimicrobial resistance, and other traits

The Enterococcus faecalis pathogenicity island (PAI) encodes known virulence traits and >100 additional genes with unknown roles in enterococcal biology. Phage-related integration and excision genes, and direct repeats flanking the island, suggest it moves as an integrative conjugative element (ICE). However, transfer was observed not to require these genes. Transfer only occurred from donors possessing a pheromone responsive-type of conjugative plasmid, and was invariably accompanied by transfer of flanking donor chromosome sequences. Deletion of plasmid transfer functions, including the cis-acting origin of transfer (oriT), abolished movement. In addition to demonstrating PAI movement by a mechanism involving plasmid integration, we observed transfer of a selectable marker placed virtually anywhere on the chromosome. Transfer of this selectable marker was observed to be accompanied by chromosome-chromosome transfer of vancomycin resistance, MLST markers, and capsule genes as well. Plasmid mobilization therefore appears to be a major mechanism for horizontal gene transfer in the evolution of antibiotic resistant E. faecalis strains capable of causing human infection