Showing papers on "Shields published in 1991"

A deployable high temperature superconducting coil (DHTSC) - A novel concept for producing magnetic shields against both solar flare and Galactic radiation during manned interplanetary missions

Abstract: The discovery of materials which are superconducting above 100 K makes possible the use of superconducting coils deployed beyong the hull of an interplanetary spacecraft to produce a magnetic shield capable of giving protection not only against solar flare radiation, but also even against Galactic radiation. Such deployed coils can be of very large size and can thus achieve the great magnetic moments required using only relatively low currents. Deployable high-temperature-superconducting coil magnetic shields appear to offer very substantial reductions in mass and energy compared to other concepts and could readily provide the radiation protection needed for a Mars mission or space colonies.

Personal space shielding apparatus

Abstract: An apparatus 10 for shielding a personal occupancy space 11 from electromagnetic and geopathic fields has a floor shield 15 and two side wall shields 18 and 20. The shields are made of ferrous, wire mesh screening and are erected so as to traverse all three spatial protected space. The shields are grounded with the use of a wall plug 29 that has two non-conductive prongs 32 and a conductive grounding prong.

Effects of uniform magnetic fields on shielded MR sensors

Abstract: Standard thin-film techniques were used to construct the shielded magnetoresistive (MR) sensors with soft-adjacent-layer biasing. The authors show the three shield designs included in these tests: a tall and asymmetric shield pair with magnetic leads, a tall and asymmetric shield without the magnetic leads, and a short and symmetric structure. The authors discuss the effects of an externally applied magnetic field which can change the biasing of a magnetoresistive sensor. Under large-signal conditions, this produces preferential saturation of one polarity of the readback signal and changes the amount of waveform distortion. In a shielding MR sensor for hard disk applications, the sensitivity to external fields is affected by the shapes of the shields: tall shields are more sensitive to axial fields; asymmetrically shaped shields can increase the sensitivity to radial fields by converting them to axial fields at the sensor. Moderate fields can sometimes induce small, systematic changes into the small-signal spatial sensitivity. >

Shield sizing and response equations

Abstract: A consolidated list is presented of meteoroid debris shield equations which have been given in the referenced memorandums. In some cases, equations have been updated; thus, this memorandum supersedes reference 1. The equations are presented in two parts: (1) shield sizing equations which are used to produce preliminary estimates of shielding weights; and (2) response equations to describe the impact conditions (projectile size as a function of velocity, density, and impact angle) causing failure of a given shield that are to be used for probability analyses (such as in the modified BUMPER program). Specific equations are given that are applicable for the following types of shields: aluminum Whipple shields; Nextel multishock (MS) shields; and mesh double bumper (MDB) shields. These equations will be updated in the future as warranted by the results of additional HVI tests, analyses, and shield modeling.

Neutron Probe Standards: Transport Shields or a Large Drum of Water?

Abstract: The use of standards for the normalization of neutron probe count rates is reviewed. There appear to be two main conventions: the use of an “infinite”, common standard (a large drum of distilled water) and the use of the convenient, H-rich shielding built into the housing of most probes. Counts made in infinite standards are not influenced by surrounding material, are less affected by temperature, and are thus less prone to error. Either type of standard can be used to normalize the count rates of a given probe to correct for instrumental drift. The two conventions appear to have given rise to different approaches to calibration: 1) If probes' own shields are used as standards, each probe (even those of the same type) has to have its own calibration because the shields are not identical, although an intercalibration procedure may be used to transfer the calibration of one probe to another; 2) If a large common (water) standard is used as a routine, the count rates of different probes of the same type can be normalized on the same basis, allowing the possibility of using the same soil calibration. The latter approach was examined using several neutron probes from the same manufacturer. Count rates in the soil and in the water standard were measured to very high precision and the resulting count ratios were compared. The most extreme difference between the ratios was equivalent to a volumetric water content difference of 0.003. This was comparable with the differences reported by other authors between water content values given by different, individually calibrated probes. These results strongly indicate that, following the normalization of count ratios using a common water standard, the same soil calibration can be used for probes of the same design. This can save a large amount of time which would otherwise be spent deriving individual calibrations. The results obtained were markedly better than those obtained through the intercalibration of probes using plastic transfer standards. The benefits of using a large water standard outweigh any disadvantages such as lack of portability.

Transmission of Intermediate-Energy Neutrons and Associated Gamma Rays Through Iron, Lead, Graphite, and Concrete Shields

Abstract: Spectral measurements of intermediate-energy neutrons (i.e., En ≤ 65 MeV) transmitted through iron, lead, graphite, and concrete shields are described. Concurrently, transmitted spectra of associat...

Passive magnetic screening.

Abstract: It is shown that a passive magnetic shield for a 1,5-T whole-body magnet requires about 20 tons of iron. Moreover, to first order, the amount of shielding material is independent of the radius of the shield. The choice between a thick shield fitting tightly round the magnet and a thinner shield of larger radius is determined by considerations of available space and the need for the highest uniformity of field in the bore. Very high permeability materials such as mu-metal are useful only in special circumstances. Multiple shields are valuable if a high degree of shielding is required, but the spacing between the shields needs careful attention. Although exact reciprocity of internal and external shielding is not found in the general case, the degree of shielding will be of the same order in both cases. The complete behavior of cylindrical shields around superconducting magnets can be determined by analytical solution of Maxwell's equations; for less regular shapes, solutions may be determined numerically by computer. © 1991 Academic Press, Inc.

Direct heating type calorimetric instrument

Abstract: PURPOSE:To accurately measure heat capacity by surrounding a sample by plural heat insulating shields consisting of the same material as the sample and supplying heating power proportional to the volume of the sample and the shields. CONSTITUTION:The cylindrical sample 1 is surrounded by the double cylindrical heat insulating shields 7a, 7b consisting of the same material as the sample and heated by supplying current from a DC power supply 8 through a variable resistor 8 and the shields 7a, 7b are directly heated by supplying current from a DC power supply 11. Power proportional to respective volume of the sample 1 and the shields 7a, 7b is supplied so that electric energy per unit volume of the sample 1 coincides with that of the shields 7a, 7b and the internal temperatures of the sample 1 and the inner shield 7b are measured through measuring holes 6, 15, 16 at the same period. consequently, the temperature difference between the sample 1 and the external can be reached to zero as close as possible and the heat capacity of the sample 1 can be accurately measured.

Accelerator magnet designs using superconducting magnetic shields

Abstract: The possibility of a superconducting shield for accelerator dipole and quadrupole magnets is explored. It is found that the decentering instability associated with iron shields is avoided by the strong diamagnetic shield. In addition, the shield can be much thinner, occupying less radial space in the cryostat. By avoiding the weight and decentering forces of the iron shield, one can reoptimize the cryostat design and substantially reduce the mass which must be cooled to helium temperatures. Promising applications in which these advantages are important are p-p collider interaction region quadrupoles, corrector dipoles for collider detectors, and high-field accelerator dipoles.

Superconducting shields and manufactured ceramic wares of complex configuration

Abstract: A technology has been developed for fabrication of magnetic shields and other high technological wares of superconducting yttrium-barium-copper ceramic by hot casting under pressure. The method enables to form wares of complex configurations and different sizes without any additional machining. The method of hot casting under pressure allows to obtain superconducting shields with a fair homogeneity of the critical field over the shielding length. At working temperature 77, 4K the shields have a threshold screening field H c ∗ about 1.5 mT, high screening factor (S>10 4 ) and low intrinsic noise level ( −6 mT).

Transmission of Medium Energy Neutrons Through Concrete Shields

Abstract: Transmission measurements of medium energy neutrons through concrete shields are described. Neutrons which were produced by the bombardment of 75 MeV protons on a thick Cu target, were collimated to a 7.5 cm diameter beam, and injected onto concrete shields of 20, 50 and 100 cm thickness. Neutrons transmitted through the shields were measured by an NE-213 scintillator. The Monte Carlo simulation of the neutron transport was made using the MORSE code based on the DLC-87 Hilo multigroup cross sections. It was seen from the comparison between the calculated and measured fluence that the attenuation profile of the integrated fluence above 20 MeV, as well as the penetrated neutron spectra, were well reproduced by the DLC-87

Display tube and manufacturing method of the same

Abstract: PURPOSE: To prevent the vibration of a shadow mask from being transmitted to magnetic shields by interconnecting, using a component element of a nonmagnetic substance, inner magnetic shields comprising two complementary parts, and mounting the magnetic shields inside a display tube. CONSTITUTION: Internal magnetic shields 19 are secured to the support strip 12 of a shadow mask support device at their respective corners by their flanges 21 and have two complementary parts 15, 16 spaced apart by a distance (d) and located face-to-face, magnetic shielding depending on the distance (d). The parts 15, 16 are connected together by a component element 17 of a nonmagnetic substance during manufacture of a picture tube in such a way as to form the magnetic shields 19, and then the magnetic shields 19 are secured to the picture tube. Thereby tire correctness and color purity of an image displayed are guaranteed, and magnetic shielding unaffected by the vibration of a shadow mask 10 is made possible.

Apparatus for vapor epitaxial growth

Abstract: PURPOSE:To enable obtaining a of a high quality-compound semiconductor having clearly divided composition in boundary parts of films by installing porous movable shields in a gas feed passage between a raw material gas feed pipe and a susceptor on which a substrate is placed CONSTITUTION:At least two of the first and second shields 31 and 32 respectively having at least one hole [(31b) and (32b)] are provided in the course of a gas feed passage between a raw material gas feed pipe and a susceptor 11 carrying a substrate 12 for performing vapor epitaxial growth thereon and at least one of the shields is movable Thereby, positions of the mutual holes (31b) and (32b) of the shields 31 and 32 can be superposed to provide an optional flow of raw material gases from the raw material feed pipe to the substrate 12 or the positions of the holes can be shifted to cut off the flow of the raw material gases by controlling the position of the one shield

Corona electrification transferring device

Abstract: PURPOSE:To change a corona discharge distribution and to obtain an optimum corona discharge distribution by providing 2nd shields by which electrical elements, such as grounding resistance, are variably controlled. CONSTITUTION:The 2nd shields 22, 23 by which the electrical elements, such as grounding resistance, are variably controlled are provided. A control section 42 changes the corona discharge distribution by changing the electrical elements of the 2nd shields 22, 23. The corona discharge distribution deviates to a left side if the grounding resistance of the left shield 23 is zero and the grounding resistance of the right shield 22 is extremely large. The control section 42 changes the electrical elements 32 of the 2nd shields 22, 23 according to a change in the optimum transfer point generated by fluctuations in various conditions in such a manner. The corona discharge distribution is changed in this way and the optimum corona discharge distribution is obtd.

Plasma facing components for tj-ii: thermal shields, beam stops and poloidal limiters

Abstract: The scope of this paper is to identify the critical issues related to the development of all the protective elements for the TJ-II vacuum vessel. The design studies include an analysis of the heat deposition patterns in different plasma configurations, transient thermal analyses during the heating and cooling phases and finite element structural analyses. Results show that the shield can properly withstand the predicted loads even without active cooling. Original engineering solutions are presented for the shields locking system and for the graphite tiles bonding technique.

The Electron Optics of the Ideal Cylindrical Field with Space Charge

Abstract: The monochromatic current is limited by the increasing electron-electron repulsive forces in high density beams. A simple analytical model for the effect of the “space charge” on the electron optical properties of cylindrical deflectors is presented. First-order compensation of the space charge effect is obtained by enlarging the deflection angle and by applying an additional negative bias to the top and bottom shields terminating the cylindrical deflectors. In spherical deflectors the azimuthal and radial foci are displaced from each other for high current loads.