Showing papers on "Shields published in 1990"

Experimental Studies of MLI Systems at Very Low Boundary Temperatures

Abstract: Experimental results for various multilayer insulation (MLI) systems are summarized for two sizes of tank calorimeters. The cold side boundary temperature was normal boiling point (NBP) helium (4.2 K) with hot boundaries between 30 and 130 K. Heat rate data were obtained for double aluminized Mylar (DAM) and double goldized Mylar (DGM) radiation shields and for a wide variety of net spacer materials. The data indicate the temperature regimes in which the application of MLI to the tank reduces heat rates below the rate for a low emissivity surface without MLI. These data are useful in the design of long-life systems which incorporate low-temperature vapor-cooled shields, for example, He-II and solid hydrogen cryostats for long-life space operation.

Performance of supersmooth, extra clean semiconductive shields in XLPE insulated power cables

Abstract: Supersmooth (SS), extra-clean semiconductor shields have been demonstrated to be markedly improved in extruded surface smoothness and to contain a minimal level of ionic impurities. In well-accepted accelerated cable aging tests for wet locations, where the SS extra-clean semiconductives are used as conductor shields, substantial improvements in cable performance have been demonstrated. Additional studies have shown that the SS extra-clean shields initiate far fewer vented water trees in the associated insulation. Both the SS ethylene ethyl acrylate (EEA) and SS ethylene vinyl acetate (EVA) products demonstrate these improved properties. When these superior semiconductives are combined with tree-retardant cross-linked polyethylene (TR-XLPE) insulation, the very best cable performance properties were obtained. It is concluded that, for cables that will be subjected to wet service conditions, the use of SS extra-clean conductor shields combined with TR-XLPE insulation will offer high-quality, cost-effective long-life cable construction. >

Screening efficiency of triaxial cables with optimum braided shields

Abstract: An investigation into the shielding effectiveness of triaxial cables employing wire shields with optimum braid constructions is described Several triaxial configurations with different braid designs for inner and outer cables were simulated It is shown that crosstalk performance of the triaxial cables are affected by both absolute values and polarities of the surface transfer impedances of the shields The effect of electric field coupling on the overall crosstalk within the triaxial system has also been studied in both frequency and time domains For triaxial cables with shorted braids, the effects of electric field coupling are limited to high frequencies, and their effects at low frequencies are small >

Optimization Of Cryogenic And Heat Removal System Of Space Borne Magnets

Abstract: Space based superconducting magnets require a refrigerator system to maintain operating temperature at the design value. The magnets use helium gas cooled shields and multilayer insulation. Refrigerator power is determined based on the heat leak to the shields and to the magnet winding, as well as current leads and charging losses. Electric power is supplied by a power source such as a SP-100 type reactor or solar panels. Cryogenic and heat removal system masses included in the optimization are: the insulation and shields, the refrigerator, the power supply and the heat removal panel. The system is optimized to determine the optimum radiator temperature, su­perinsulation thickness, helium mass flow rate and helium inlet temperature to the shields.

Effect of bedside shielding on air-kerma rates around gynecologic intracavitary brachytherapy patients containing 226Ra or 137Cs.

Abstract: An anthropomorphic phantom was implanted with 226Ra or 137Cs gynecologic intracavitary brachytherapy sources. Air-kerma rate measurements were taken at 10-cm increments along a horizontal plane from the side of the bed at 50 cm, 87 cm, and 136 cm heights above the floor. Five portable lead shields were placed at the head, at the foot and along one side of the bed and readings were taken again at the corresponding heights above, below and behind the shields. The readings were normalized to 100-mg Ra equivalence, and air-kerma rate curves were drawn allowing for the comparison of 226Ra and 137Cs with and without lead shields. The data demonstrated that the air-kerma rates for 137Cs were reduced more than those for 226Ra with the use of the portable lead shields. There was four times the transmission with 226Ra than with 137Cs. The optimal placement was with the lateral bedside shields proximal to the head and foot closest to the bed, with the middle shield overlapping in back. The shields at the head and foot should extend out and overlap the bedside shields. The level of the sources should be positioned near the bottom of the shields. This information will provide the medical health physicist with an estimate of air-kerma rates for both 226Ra and 137Cs with and without shielding for evaluating personnel exposures as well as the effectiveness of current shielding in relation to radiation protection requirements in adjacent rooms or hallways.

Stationary induction apparatus

Abstract: PURPOSE:To manufacture an electromagnetic shield easily while relaxing field concentration on the end face of the electromagnetic shield by installing an electrostatic shield covering the electromagnetic shield between an induction apparatus body and the electromagnetic shield. CONSTITUTION:An electrostatic shield 8 is mounted among a winding 4 and electromagnetic shields 5 to a shape that the electromagnetic shields 5 are covered. The electrostatic shield 8 is constituted by bending a wire gauze, and composed of an underside section 8A for covering the electrostatic shields disposed onto the underside of a tank, side face sections 8B for covering the electromagnetic shields arranged onto the side faces of the tank, and mounting sections 8C for fitting to the tank. Accordingly, the wire gauze need not be bent sharply as an edge shape even in a bending section, and the bending section having smooth surfaces can be formed, thus sufficiently reducing an electric field on the electrostatic shield.

Triaxial cable designs with optimum braided shields

Abstract: An investigation into the shielding effectiveness of triaxial cables employing wire shields, with optimum braid constructions, is described. Several triaxial configurations with different braid designs, for inner and outer cables, were simulated. It is shown that crosstalk performances of the triaxial cables are affected by both absolute values and polarities of the surface transfer impedances of the shields. The effect of electric field coupling, on the overall crosstalk within the triaxial system, has also been studied in both frequency and time domains. For triaxial cables with shorted braids, the effects of electric field coupling are limited to high frequencies and their effects at low frequencies are small. >

Fluidised-bed combustion.

Abstract: of EP0349765In fluidised-bed combustion arrangements, the heat exchangers, which are immersed in the fluidised-bed and designed as pipe panels (6), are exposed to heavy erosion. The aim of the invention is to protect the pipe panels (6) against erosion without influencing the heat transmission. On both sides of the pipe panel (6), protective shields (9, 10) are arranged at a distance. On those sides of the protective shields (9, 10) which are turned towards one another, strips (11, 12; 13, 14) are arranged on the upper and lower edges. Between the strips (11, 12), as between the strips (13, 14), there is a narrow gap. The air flow between the two protective shields (9, 10) is choked by means of the two gaps. The hot fluidised-bed material trickles in the intermediate space and transmits heat to the pipes (7) by contact. The invention is used in particular in fluidised-bed combustion arrangements with stationary fluidised-bed.

Intercalated graphite fiber composites as EMI shields in aerospace structures

Abstract: The requirements for electromagnetic interference (EMI) shielding in aerospace structures are complicated over that of ground structures by their weight limitations. As a result, the best EMI shielding materials must blend low density, high strength, and high elastic modulus with high shielding ability. In addition, fabrication considerations including penetrations and joints play a major role. The EMI shielding properties are calculated for shields formed from pristine and intercalated graphite fiber/epoxy composites and compared to preliminary experimental results and to shields made from aluminum. Calculations indicate that EMI shields could be fabricated from intercalated graphite composites which would have less than 12 percent of the mass of conventional aluminum shields, based on mechanical properties and shielding properties alone.

Development of a metallic shield for the TFTR rf probe diagnostic

Abstract: The ceramic shields covering rf probes located on the bottom of the TFTR vessel sustained damage even after 3 cm retraction from the plasma, while those located on the top of the vessel remained unharmed after two years of exposure. New, metallic, optically opaque shields to replace the ceramics were developed, tested, and installed at two locations. The double‐layer, slotted shield was designed to maximize rf transparency to both transverse components of the incident field. rf characteristics are presented, and thermal and stress considerations are discussed.

Optimization of a system of lamellar-vacuum insulation + cooled shields

Abstract: It is shown that the heat influx through a stack of lamellar-vacuum insulation, alternating with cooled shields, can be reduced substantially by an optimum choice of the insulation packing density and the thickness of the layers between shields.