Showing papers on "Shields published in 1980"

Gamma-Ray Buildup Factors for Stratified Lead and Water Shields

Abstract: A one-dimensional gamma-ray transport code BIGGI 4T has been used to calculate gamma-ray attenuation in single layer and multiple layers of lead and water slabs from a plane monodirectional source....

Gamma-ray buildup factors for concrete slab shields under slant incidence conditions

Abstract: Monte Carlo calculations have been made for the penetration of slab shields by gamma radiation of monoenergetic character. The radiation is in the form of parallel, broad beams incident on the fron...

Rotor Cooling System for a 10-MVA Superconducting Generator

Abstract: The Cryogenics Laboratory and the Electric Power Systems Laboratory at MIT are currently involved in an effort funded by the U. S. Department of Energy to develop a 10-MVA superconducting generator. This machine incorporates the most advanced concepts available in order to demonstrate the greatest possible growth in the state of the art. A rotor and stator comprise the generator. Within the rotor are the superconducting field winding and two electromagnetic shields. The winding and shields are kept at liquid helium temperature by the rotor cooling system. The rotor is supported between thin-walled, vapor-cooled torque tubes for thermal isolation, and further isolation is obtained by using an evacuated stator bore containing a stationary thermal radiation shield.

Field emission gun with noise compensation

Abstract: A field emission gun, for either electron or positive ion emission, in which the beam current between source and sample is measured at accelerating voltage potential between two concentric shields that enclose the gun, its power supplies, and the measuring circuitry. The outer shield is directly connected to the high voltage terminal of the accelerating voltage supply while the inner shield is at the local ground reference of the emission source and associated components. The current between the concentric shields is measured, converted to a proportional voltage signal, compared with the reference voltage, and applied to a field strength controlling electrode in the vicinity of the emission source to modulate the emission and to maintain a constant beam current.

Transient Cooling of a Faultworthy Superconducting Electric Generator

Abstract: In order for superconducting generators to be of use in power stations, they must be made faultworthy, or able to withstand the effects of a short circuit on the power lines. The work described herein is part of an MIT-DOE program to design a 2000-MVA generator, the size of commercial interest, and to build and test a 10-MVA prototype. Designs of faultworthy superconducting generators to date have stationary, normally conducting armatures, rotating superconducting field windings, and several rotating electromagnetic shields between the field winding and the armature [1-3]. The MIT design has two electromagnetic shields and is unique in that these are structurally part of the rotor and operate in the steady state at temparatures in the range of 4 to 6 K. A system of cold shields, as opposed to having at least the outermost shield self-supporting and at room temperature, simplifies the structural problem and has other advantages, but it makes the cooling problem much more difficult [1]. For a representative 2000-MVA design, subjected to a severe fault used for design purposes, the time-averaged total losses in the shields are 4 MW during the first 0.1 s and thereafter drop by an order of magnitude and decay exponentially. The transient cooling scheme must prevent this heat input from increasing the temperature of the superconductor to the level where it will go normal.