No abstract available

No abstract available

No abstract available

[en] The threshold magnetic field for flux jumping in a bulk irreversible Type-II superconductor is known to be independent of its bulk critical current density. The analysis shows that the flux jump field should be enhanced in a laminated superconductor in which the surface layer has a lower critical current density than the underlayer. Experiments in laminated samples of Nb-48 wt percent Ti alloys demonstrate an improvement in stability which is in good agreement with the theory. The technique may be useful in increasing the overload current rating of an ac superconducting power cable

[en] Creep tests on Alloy 800H in helium and air at 850 to 950°C have shown that rupture ductility (% elongation) was, on average, about three times greater in air than in helium. Metallographie examination showed that this was associated with much more cracking in the air tested specimens and critical crack length (maximum size of surviving creep crack in a ruptured sample) was about five times as great in air as in helium for the conditions used here. However, the greater apparent crack tolerance of the air tested specimens may be potentially misleading since, at advanced states of damage, the air tested specimens were very weak and brittle at room temperature. For uniformly stressed material, time to given creep strain (e.g., 5%) is likely to provide a more reliable indication of creep strength than is time to rupture. For non-uniform stresses, e.g., at flaws, notches or cracks, account should be taken of the observation that critical crack length may be appreciably shorter in a low oxygen potential environment than it is in air. (author)

[en] Design details are given for a typical power amplifier and its control systems to be used for the approximately 80 spiral resonating cavities of the proposed heavy-ion accelerator at Los Alamos Scientific Laboratory. Operational procedures and some experimental results are also described. Plate circuit design is important for maximum efficiency and stability. The original movable-short, fixed-tap design was not optimal, and several improvements are described. Perturbation controllers are required for the cavity rf phase, amplitude, and resonant frequency. The amplitude control is done by varying the power amplifier screen-grid voltage. Typical power amplifier output is 20 kW at 33 percent plate efficiency and 19-dB gain. (U.S.)

[en] Acidic, aqueous, deaerated solutions of pure DMSO, of DMSO-KBr and of DMSO-EtOH in completely filled glass ampoules were irradiated with a ⁶⁰Co γ source. The gases formed were extracted under vacuum and analysed by gas chromatography. Argon and helium were used as carrier gases and the principal gaseous products were CH₄, H₂, C₂H₆: traces of CO₂ and C₂H₄ were also detected. It was shown that both hydrogen atoms and hydroxyl radicals react with dimethylsulfoxide in aqueous acid solution to produce methane. In both cases however only a fraction of the radicals captured gives rise to this product. Thus methane formed in the reaction of DMSO with biological systems is not unequivocal proof of the presence of OH radicals; nor is the yield of methane a direct measure of an OH yield. The rate constants k(H+DMSO)=2.6x10⁷M^-1s^-1 and k(OH+DMSO)=2.1x10¹⁰M^-1s^-1 were determined in the presence of 5x10^-1M sulfuric acid

[en] A vehicle has a body carrying tracked wheels and permanent magnets whereby the vehicle can move over any magnetic material surface irrespective of the orientation of the surface. (author)

[en] In most designs for flexible ac superconducting cables each phase is carried by a co-axial pair of conductor tubes formed from a single layer of helically laid conductor strands. It is shown that the cable current would generate a net axial magnetic flux and hence an alternating circumferential electric field outside each co-axial pair. If, as in some cable designs, each conductor pair is to be contained in its own helium pipe, circumferential currents will be induced in the pipe wall. The losses depend on the pipe material but are typically three orders of magnitude too large. One solution is to line the pipe with superconductor, such as lead, but this could require more niobium in the conductor itself. Alternatively the co-axial pair could be redesigned so that there is no net axial flux. One possibility is to form conductor tubes from two layers of conductor strands laid in helices of opposite sense. The induced current problem is avoided if all three phase conductors are contained in a common helium pipe, provided that there are no zero sequence components to the pase curents. Losses from any zero sequence component could be readily reduced to an acceptable level, for example by laying a ferromagnetic strip alongside the conductors inside the helium pipe. Since circulating currents will also be induced in the electrostatic screens adjacent to the conductor strands the screens must be of semiconducting rather that metallic, tape. (author)

[en] The complex current distribution on the individual strands of a flexible superconducting cable influences the ac loss. Hence reliable loss predictions cannot be made from previous measurements. It is shown that the required current patterns and losses can be simulated by winding the conductor into single or double layer solenoids. Both total and localized losses can be measured with suitably arranged voltage probes. Measurements have been made on five different strip conductors wound into single layer solenoids to simulate losses on the inner conductor of a flexible cable. Measurements on niobium clad copper composite conductor showed that edge losses contributed more to the total loss than had been predicted theoretically for an idealized case. Despite this the total losses averaged only 15mWm^-2 at 40Amm^-1rms, at 4.2K. Measurements were also made on a Nb/Nb-25%Zr/Cu conductor, developed to carry fault currents in the NbZr and fabricated by soldering together Nb clad NbZr and Nb clad Cu composites. A fields below about 100Amm^-1rms, currents were carried by the niobium surface layer and at higher fields flux penetrated into the NbZr underlayer. Thus losses were acceptably low over the entire field range. (author)