Protection device for superconducting magnets with a superconducting switch

A device, operating in the persistent current mode, was developed for quick energy removal from superconducting magnets. A magnet protection circuit which has a superconducting switch and a superconducting power switch connected in series is proposed. The performance of the system tested in connection with a laboratory solenoid (8T, 150 A, 50 kJ) was demonstrated.     

Sweeping a persisting superconducting magnet with a transformer

A method for sweeping a persisting superconducting magnet is described. The field sweep is achieved by including in the superconducting loop of the magnet a coil which acts as the secondary coil of a transformer. Variation of the current in the primary coil of the transformer, controlled from outside the cryostat, causes the field-sweeping action through flux-linking with the superconducting loop. Compared by the ratio of the magnet's inductance to the transformer's inductance. The advantages of using an all-metal vacuum-tight superconducting feedthrough are discussed.     

Miniature sapphire windows for superconducting niobium cavities

Miniature sapphire windows which allow coupling without ? degredation, have been designed for superconducting niobium cavities.     

液压控制堵水开关的设计

 研制了一种新型液压控制可循环调层的堵水开关． 介绍了单元开关和组合液压开关的基本结构和工作原理，说明了开关的设计特点和应用场合，给出了几何参数和力学参数的计算公式，从而为该类井下工具的设计提供了参考．     

Multifilamentary superconducting materials for large scale applications

The February 1971 edition of this journal carried a ten page article by the author and his colleagues reviewing the then ‘state of the art’ in multifilamentary superconducting composites.¹ At the time we attempted to cover in a fairly comprehensive manner the first decade of development of these materials since the construction of the first high field superconducting magnet.² Now more than another decade of development has passed and obviously the field can no longer be reviewed comprehensively in the same few pages. This article will attempt to give a brief overview of these materials from the point of view of one engaged in their development and supply for large applications. Hopefully, the references to books,^3,4 review articles,^5,6 and the proceedings of the various conferences^7–11 will serve as a source of further information for those who require more details.     

Coupling-current loss in a multifilamentary superconducting wire with a normal-metal core

Coupling-current losses in a multifilamentary superconducting wire with a normal metal core were calculated for the case of transverse magnetic fields. The results showed that the dependence of the coupling-current loss of such a wire on the rate of field variation is markedly different from that of a wire without the core, the former being characterized by two time constants while the latter by one. The theoretical result was confirmed experimentally. It was pointed out that in the case when a wire with Cu/CuNi matrices is to be used in a rapidly changing magnet field, Cu for a stabilization should be arranged at the centre of the wire rather than at the surface of the wire in order to reduce the loss.     

Coupling losses in a rectangular multifilamentary superconducting composite

Coupling current losses between filaments of a superconducting multifilament composite subjected to a transverse varying field is highly dependent on the shape of the conductor. The ac loss is evaluated in a conductor of rectangular cross sectional area. It is shown that the loss per unit volume is somewhat different from the loss in an elliptical shaped composite of the same aspect ratio. In addition, the loss in the outer copper sheath is less sensitive to the aspect ratio than the inner filamentary region. Numerous experimental results are given on losses in as-received conductors and in conductors where the outer copper sheath has been partially removed. The anisotropy in the losses caused by a changing field perpendicular or parallel to the wide side of a conductor is in very good agreement with the theory.     

Minimum heat pulse to quench a superconducting magnet

The minimum energy required to quench a fully impregnated superconducting winding has been measured at a constant field of 5 T for various currents. Great care has been taken to match the experimental conditions with those presumed in the minimum propagating zone (MPZ) treatments of the situation. In particular the winding has been designed so that the MPZ is smaller than the heat source thus satisfying the requirement for a point disturbance. The adiabatic requirement has been met with an inductive heating technique in place of the usual resistive heating. As a consequence of these features the minimum quench energies are much smaller than those obtained in previous experiments and agree well with Wilson's theoretical treatment for a point disturbance.     

A simple heat switch for use at millikelvin temperatures

A simple technique is described for fabricating a high conductivity silver-aluminium joint for use in the construction of an aluminium superconducting heat switch which can be operated in the millikelvin temperature range.     

A superconducting magnetic levitation device for the transport of light payloads

A device for the frictionless transport of light payloads, e.g., silicon wafers, using superconducting magnetic levitation has been demonstrated. The device consists of an array of rigidly connected carrier magnets levitating above a corresponding array of superconducting discs. Silicon wafers placed on the carrier have been linearly transported with velocities up to 50 cm/s. The configuration provides for excellent lateral stability. Studies of the height and lateral friction effects (caused by flux pinning) were measured as a function of payload mass. Future applications may include the frictionless transport of silicon wafers in vacuum environments.     

GaAs霍尔开关集成电路的研制

成功地设计并制造出GaAsMESFET霍尔开关集成电路。该电路采用了方形霍尔元件，绝对灵敏度为704mV/T；信号处理电路由差分放大电路和触发电路组成，触发电路结构类似于SCFL的D触发器。结果表明，开关性能良好，工作点合理，达到设计要求。实验结果还表明，霍尔元件和放大电路可构成灵敏度很高的霍尔线性集成电路。     

Design of polarisation-independent bidirectional optical switch

Optical switching plays a vital role in all optical communication and network. Various optical switchings have been developed in recent years as a way to improve reliability problems and to build small size, robust integrated devices. A novel low crosstalk, high switching speed, compact in structure, efficient in performance, polarisation independent, and reversible 2 × 2 optical switching is proposed using a phase spatial light modulator (PSLM), a polarising beam-splitter (PBS), a mirror, a half-wave plate (HWP) and a quarter-wave plate (QWP). The optical switching should be helpful in the design of a large-scale switch matrix, and show considerable promise in the future of fibre optic networks.     

Electrical characteristics of a dc superconducting cable

A dc superconducting cable is ideal for transmitting large blocks of electrical power over a long distance. However, it must be designed to operate reliably within the constraints of the electrical system. Therefore, system analysis must be performed for each application. The conductor losses caused by the harmonics on the dc must be within the design goals; a system fault should not drive the cable normal with eventual damage to the cable and interruption of power flow; and, the dielectric system of the cable must be designed to be compatible with the expected transient voltages by proper insulation coordination. Transient overvoltages are of concern to electrical power systems; these are especially critical to cryogenic cables because of the susceptibility of the cryogenic enclosures to these transients. This paper discusses the electrical system constraints which are particularly applicable to a dc superconducting cable and shows how such a cable can be designed to be compatible with the electrical system.This paper also summarizes the work on low temperature dielectrics performed at Los Alamos. It shows the variation of break down voltage of dielectric materials, in sheet form and cable configuration, with temperature and pressure under dc and impulse voltage. The surface flashover characteristics with large creepage distance as well as electrical conductivity of dielectric materials at cryogenic temperatures are discussed. These studies are essential for the design of high voltage apparatus operating in cryogenic environments.     

A magnetoresistive transducer with superconducting control lines

The design and the static and dynamic response of a thin film magnetoresistive transducer with superconducting control lines cooled at 4.2 K are described. The transducer facilitates a linear transfer of electrical signals by transformation of the impedance level and by perfect electrical insulation between the input and output circuit. In addition, voltage and power amplifications at low frequencies are achieved.The device can be used to sense supercurrents or currents generated by sources of very low impedance, such as superconducting quantum interferometers (SQUID's).     

dc and ac behaviour of a normal joint in a superconducting cable

The application of joints which can be disassembled is studied within the framework of the development of high current (25 kA), high power (0.5 kW) cryogenic current supplies (flux pumps).^1,2 The behaviour of a scale model with currents up to 5 kA will be presented here.Several means of diminishing the joint resistance have been researched with special attention being paid to detection methods to measure the resistance, and their accuracies.The role of the solder has been investigated. A simple model gives good qualitative understanding of the matter.The presence of ac currents in a cryogenic current supply causes considerably higher losses in the joint because of the non-homogeneous distribution of the current. A good impression of this distribution can be obtained by measuring the field along the joint. The measured results are in good agreement with calculated ones. A useful length of the joint under ac conditions can be defined and is helpful for design purposes.     

Design and operation of a protection system for transformers with superconducting windings

Power transformers with superconducting windings need a protection system to prevent damage to the low-loss superconducting winding by an abnormally high current. The generally accepted protection technique which uses auxiliary coils has been analysed using a network representation. The current distribution between main and auxiliary coil is expressed in terms of geometrical parameters. Experimental data on current transfer and main coil recovery in a test transformer are presented and a method of obtaining a very low auxiliary coil current is suggested.     

Plasma opening switch with a ferroelectric plasma injector

A generator with a plasma opening switch employing a ferroelectric plasma injector has been designed, constructed, and studied in operation. The generator was tested in two regimes, being loaded on an electron-beam diode or vircator for the generation of bremsstrahlung (X-ray) or microwave radiation, respectively.     

AC losses in multilayer superconducting tapes

ac losses have been investigated experimentally as well as theoretically in tapes having on the surface several normal conducting and/or superconducting layers. The superconducting layers under investigation have been Nb₃Sn on a niobium substrate and Nb₃Ge on a stainless steel substrate. It has been proved that the layered structure of the tapes is well reflected by the stepwise character of the ac losses dependence on the amplitude of the surface magnetic field. The magnetic flux passing through a surperconducting layer or surface barrier into the inside of the tape enhances the losses in the passed barrier or layer.     

Heat transfer and flow instability in a superconducting machine rotating at 3000 rpm

Heat transfer measurements have been carried out on the liquid He⁴ in a side arm rotating at a speed of 3000 rpm. The heat transfer cell consists of a copper disc mounted perpendicularly to the radial direction at a radial distance of 0.41 m. A correlation of the type: $\text{Nu/(1 + S}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{)}\text{= 0.17}\text{R}{}_{\mathrm{a}}{}^{0.3}$ where S is the stratification factor, has been obtained.The flow pattern of He⁴-gas through a U-tube under a self-pumping system in a rotating frame has been studied analytically. It can be demonstrated that the flow polarity is influenced by the velocity gradient of the friction factor in the region, between stream-line and turbulent motions, which can lead to flow instability of the kind observed experimentally recently. It has been explained that the instability may occur in both increasing and decreasing speed modes or heat inputs.     

Quench back in thin superconducting solenoid magnets

Superconducting magnets with well coupled, low resistance, secondary circuits have been observed to become fully normal faster than quench propagation in the coil would permit. This process is referred to as ‘quench back’. Quench back observed at the Lawrence Berkeley Laboratory (LBL) was caused by heating the secondary circuit from the current induced from the primary circuit as normal region in the superconducting coil propagated. This paper develops the theory for thermal quench back in thin solenoid magnets and compares this theory with measurements made in two one-meter diameter superconducting solenoid magnets.