Showing papers on "Shields published in 1983"

Adverse shielding of the heating field and high ohmic loss introduced by electrostatic shields employed in radio‐frequency heating of plasma

Abstract: The electrostatic shields now commonly employed to shield antennas in the heating of plasma in the ion cyclotron frequency range are shown to reduce the specific radiation resistance of a long narrow antenna in the presence of plasma by a significant factor (on the order of 2/3 for a typical double‐array shield) due to the effect of magnetic shielding of the magnetosonic polarization. An allied change in antenna specific inductance is also found. These effects are shown to diminish with increase in antenna width and should pose no major problem for the wide antennas projected for use in fusion experiments. In addition to the foregoing effects which are not ohmically dissipative in essence, electrostatic shields are also shown to introduce surprisingly high ohmic loss, this being of potential importance in shield design. The dependences of the above magnetic and ohmic phenomena on shield parameters are given and a shield design minimizing them is presented. Their repercussion on coupling efficiency and on the excitation voltage necessary for a given power flux from the antenna is discussed.

An approximation of gamma-ray buildup factors for two-layer shields

Abstract: An empirical formula for gamma-ray buildup factors in two-layer shields is proposed The values of the parameters are given for the formula when fitted to the dose buildup factors, calculated by the invariant imbedding method, for normally incident gamma rays penetrating two-layer shields comprised of combinations of water, iron, or lead slabs The results from the present formula are in excellent agreement with the basic data in the 066- to 10-MeV energy range and for total thicknesses up to about20 mfp The parameters used in the formula change smoothly with the source energy Therefore, the buildup factor for any arbitrary energy can easily be estimated by interpolation of the parameters with respect to energy The buildup factors provided by this formula also are in good agreement with those from transport calculations for two-layer shields consisting of water and lead These factors also agree with those measured by two ionization chambers for /sup 60/Co radiation penetrating two-layer shields comprised of water, iron, or lead slabs

Neutron Streaming Through a Slit and Duct in Concrete Shields and Comparison with a Monte Carlo Analysis

Abstract: A series of measurements of about14-MeV deuterium-tritium neutrons streaming through a slit and a duct in concrete shields has been carried out using a Cockcroft-Walton-type neutron generator. Measured neutron energy spectra are compared with calculations in six configurations of the shields. The configurations are the simplified geometries of streaming paths of tokamak reactors, such as a divertor throat and a neutral beam injection port. The measured data were obtained with an NE-213 liquid scintillator using pulse shape discrimination methods to resolve neutron and gamma-ray pulse height data and using a spectral unfolding code to convert these data to energy spectra. The experiments were analyzed by a Monte Carlo code. The calculated neutron energy spectra slightly underestimate the measured data, especially in the range of 6 to 8 MeV. The agreement between the calculated and measured integral flux above 2.2 MeV ranges from 87.5 to 72.% depending on the configurations.

Electrifying device of electrophotography

Abstract: PURPOSE:To discharge ion wind through an opening in the upper part to prevent the deterioration of a photoreceptor by providing an opening in the upper part of a shield and making the ion current flowing in a grid larger than the ion current flowing in the upper part of the shield CONSTITUTION:A corona discharge electrode 1 is enclosed from three sides by a pair of side shields 2, 3 and an upper shield 4, and openings 5, 6 that allow the passage of ion wind are formed between the shield 4 and the shields 2, 3 The shields 2, 3 consists of respectively a grounded upper conductive part 10 and a lower insulating part 9 If corona is discharged under the conditions of l1>l2, d1>d2, h=0-5mm, the electric field is stronger on the upper side of the electrode 1 than on the lower side; therefore, the flow of ions is stronger from the grid 8 toward the shields and the ion wind is blown through from below toward the openings 5, 6

Designing Space Vehicle Shields for Meteoroid Protection - a New Analysis

Abstract: A new analysis for designing dual-layer shields is presented which is based on energy and momentum conservation, fundamental electromagnetic radiation physics, and the observation of results of extensive experimental impact studies performed at relatively low velocities (near 7 km/s). An important finding is that most of the kinetic energy of a meteoroid striking a dual-layer shield is expended as radiation at the stagnation zone on the face plate of the underlying structure. Systematic procedures for evaluating the response of shield designs for a given impact threat are described. It is noted that similar applications of the analysis can be employed to support a mathematically rigorous procedure for optimum shield design.

Thin film forming device

Abstract: PURPOSE:To enable long-time stable operation with simple constitution by using net-like materials which are superposed to a plate-like material as a member for capturing scattering partiles in a vacuum vessel of a thin film forming device. CONSTITUTION:A vacuum vessel 10 is evacuated by an evacuating system 20 and gas is introduced therein with an introducing system 30. Targets T1, T2 are disposed oppositely by holders 15, 16 in the vessel 10, and shields 17, 18 are provided to protect the holders 15, 16, etc. against plasma particles and to prevent abnormal discharge of the targets except the surfaces thereof. A base plate 40 on which a thin magnetic film is to be formed is held in a way as to face the space between the targets T1 and T2 and electric power is supplied by a means 50 to the targets T1, T2 by which sputtering is accomplished. The shields 17, 18 which are plate-like bodies are covered by stainless steel wire nets 61 so that the shields are constituted as capturing members. The generation of an abnormal discharge is thus obviated completely even if the operation is performed continuously or intermittently. When the nets 61 are removed, the film forming material deposited thereon is simultaneously stripped from the shields 17, 18, thus making their cleaning easy.

Measured Transfer Impedance of Metallized Plastic Tape and Knitted Wire Mesh Cable Shields

Abstract: A s e r i e s o f s h i e l d e d c a b le samples were con­ s t r u c t e d u s in g m e t a l l i z e d p l a s t i c and k n i t t e d w ire mesh t a p e s . Measurements o f th e s h i e l d s show t h a t t h e t r a n s f e r impedance o f c i r c u m f e r e n t i a l l y wrapped m e t a l l i z e d p l a s t i c f o i l was r e l a t i v e l y h igh and in c re a s e d w i th f r e q u en c y s u g g e s t in g t h a t t u r n t o t u r n e l e c t r i c a l c o n t a c t was n o t made. L o n g i tu d in a l ly -w ra p p e d m e t a l l i z e d t a p e was s u r ­ p r i s i n g l y e f f e c t i v e . K n i t t e d w i r e mesh p ro v id ed t r a n s f e r impedances t h a t were r e l a t i v e l y f r e q u e n c y in d e p e n d e n t and had v a l u e s o f t h e o r d e r o f t e n s o f m i n i o h m s / m e t e r . The t r a n s f e r imped­ ance o f a com bina t ion copper m e t a l l i z e d t a p e and k n i t t e d w ire mesh was f r e q u e n c y in d e p e n d e n t w i th a v a lu e o f abou t 15 m i l l io h m s / m e t e r .

Convergence of Integral and Differential Cross-Section Data for Structural Materials

Abstract: Nuclear data for structural materials are used in calculations of reactor fuel enrichment, burn-up reactivity variations, kinetics and safety characteristics, irradiation damage and activation of the materials, and the effectiveness of reflectors and shields. The structural materials of interest are those present in reactor cores, reflectors and shields, components in the coolant circuits and in fuel storage,transport and reprocessing facilities (in connection with criticality calculations). Correlations with integral measurements have been used extensively in the design of reactors, and in refining calculations of neutronics properties. Aspects of the present status of the integral and differential data are discussed.

Experimental and analytical studies of shielding concepts for point sources and jet noise

Abstract: : This analytical and experimental study explores concepts for jet noise shielding. Model experiments centre on solid planar shields, simulating engine-over-wing installations and 'sugar scoop' shields. Tradeoff on effective shielding length is set by interference 'edge noise' as the shield trailing edge approaches the spreading jet. Edge noise is minized by (1) hyperbolic cutouts which trim off the portions of most intense interference between the jet flow and the barrier and (2) hybrid shields - a thermal refractive extension (a flame); for (2) the tradeoff is combustion noise. In general, shielding attenuation increases steadily with frequency following low frequency enhancement by edge noise. Although broadband attenuation is typically only several decibels, the reduction of the subjectively weighted perceived noise levels is higher. In addition, calculated ground contours of peak PN dB (perceived noise level) show a substantial contraction due to shielding: this reaches 66% for one of the 'sugar scoop' shields for the 90 PN dB contour.

Lead shielding for electron beams from 6-18 MeV.

Abstract: The penetration through lead of 6–18 MeV electron beams from a linear accelerator has been investigated. Complete transmission curves are presented for lead placed at the patient surface, and within the electron applicator. Geometric considerations cause transmitted dose to be significantly greater in the former case. Transmission through, and scatter around, flat and curved eye shields of 36 mm diameter has also been measured. In cases of inadequate shield thickness the curved shields cause elevated doses to tissue within them. This situation is particularly important when it is desired to place curved shields beneath the eyelid.

TORE-SUPRA: design of thermal radiation shield at 80 K

Abstract: The TORE-SUPRA superconducting toroidal magnet /1/ operating at liquid helium temperature, must be protected against thermal radiation from the vessels. For this purpose, stainless steel heat shields, cooled at 80 K, are positioned between coil casings at 4.5 K and the vessels, and constitute a double stiff toroid which completely surrounds the magnet. Mockups have been manufactured to study their design and operating problems. Calculations have also been made to analyse the mechanical behaviour of these shields.

Measuring device of partial discharge

Abstract: PURPOSE:To elliminate malfunction at the removal of space field noises and to measure partial discharge precisely by covering the whole surfaces of loop antennas detecting the space field with a metallic conductor and by-passing various pulse current to the ground so as to sense only the space field. CONSTITUTION:The whole surfaces of loop antennas 11A, 11B are covered with electrostatic shields 15, 17 consisting of a metallic conductor. In order to prevent surface current from flowing around the loop antennas. insulating gaps 25 are provided to respective antennas 11A, 11B not to erase magnetic flux interlinked with the loop antennas 11A, 11B. The output signals of pre-amplifiers 13A, 13B connected to the respective loop antennas 11A, 11B are connected to detectors 19D, 19E through high frequency cables 12, 14. The whole surfaces of the high frequency cables 12, 14 also are covered with metallic shields 16, 18 respectively. At the both terminals of the shields 16, 18, antenna sides are coupled with the electrostatic shields 15, 17 respectively and the other ends are coupled with a shield box 23.

Magnetic shield structure for stationary induction electric apparatus

Abstract: PURPOSE:To prevent any local overheat, by a method wherein when magnetic shields made from ferromagnetic thin plates are secured to the inner periphery of a tank having straight and curved portions, the magnetic shields secured to the curved portions are made smaller in width than those secured to the straight portions. CONSTITUTION:Magnetic shields 51 each formed by laminating ferromagnetic thin plates and having a width l1 are secured to the inner periphery of each of straight portions 41 of a tank 4. On the other hand, magnetic shields 52 having a width l2 are secured to the inner periphery of each of curved portions 42 of the tank 4. In this case, the relationship between l1 and l2 is determined so as to satisfy l1>l2. The magnetic flux leaking from three-phase windings U, V, W, is larger at the curved portions 42 than at the straight portions 41. Therefore, by setting the relationship, l1>l2, the loss in the magnetic shields 52 in the portions where the leakage magnetic flux is larger is reduced, so that the generation of heat can be suppressed. It is to be noted that if the magnetic shields 52 are increased also in thickness, the magnetic saturation can be prevented similary.