Superconducting Magnet Technology Research Articles

高エネルギー物理研究における超伝導磁石技術

Superconducting magnet technologies have been developed as the necessary technologies for high-energy physics research. One of the applications is for the high-energy accelerators, which have to be as large as possible. On the other hand, superconducting magnets have been required for particle detectors in order to obtain higher magnetic field and save electric power. Three superconducting accelerators are being operated and a larger machine that uses NbTi coil cooled by He II, the LHC, is under construction. Many particle detector magnets have been developed and constructed to detect and analyze generated particles. Recent key technologies for the particle detector magnets are aluminumstabilized superconductors and an inner winding method. Very thin detector magnets have been developed and successfully used. In this paper, superconducting magnet technologies for accelerators and particle detectors are described.

Effect of a dimensional crossover on the upper critical field of practical Nb–Ti alloy superconductors

Multilayers of a Nb0.37Ti0.63 alloy, a chief material of superconducting magnet technology, and a Cu0.95Sn0.05 or Cu0.70Ni0.30 alloy exhibit a dimensional crossover with a decreasing bilayer period Λ=dN+dS, where dS=3dN. Cusps of Hc2(θ) and square root Hc2∥(T) develop when Λ⩽40 nm, which indicate a crossover to 2D behavior from 3D behavior seen at Λ=60 nm. Full proximity coupling of Cu–Sn layers for Λ=13 nm restores isotropic angular dependence, but with sharply lower Hc2 values. By contrast, proximity coupling was suppressed by magnetic Cu–Ni layers, and 2D behavior was retained while Tc fell below 4 K for Λ<20 nm. The data are consistent with numeric results obtained by Takahashi and Tachiki [Phys. Rev. B 33, 4620 (1986)] when the variation of the Bardeen–Cooper–Schrieffer pairing potential is the primary cause of the dimensional crossover. Since practical Nb–Ti conductors have a layered nanostructure, this result suggests that a dimensional crossover should also be found in wires. However, the 3D–2D crossover occurs when Λ is much greater than the separation of the flux lines at high field (10–20 nm) and above the range where optimum flux pinning is found. This implies that a 2D state (for insulating or magnetic layers) or a 2D strongly coupled state (for normal metals) exists when flux pinning is strongest. These implications are discussed in the context of practical Nb–Ti wires used in superconducting magnet technology.

Study of nuclear reactions with intense, high-purity, low-energy radioactive ion beams using a versatile multi-configuration dual superconducting-solenoid system

A new device (TwinSol) installed at the Nuclear Structure Laboratory at the University of Notre Dame implements a pair of large-bore 6 T superconducting solenoids for producing relatively pure, high-intensity beams of exotic light nuclei at low-energies (10–80 MeV). Typical beams include 8Li and 6He (T 1/2<1 s). The device efficiently produces, collects and focuses beams onto (or implants into) suitable target foils and test materials. The system uses various combinations of the following detection schemes: XY position sensitive gas counters for time-of-flight and ion ray-tracing; multiple stacks of silicon surface barrier detector telescopes mounted at various angles on a rotating table; 2D position-sensitive silicon detectors (PSDs) for high precision angular measurements; multi-annular, multisectored “CD” detectors for large solid angle (nearly 2π in lab frame), high-collection efficiency (multi-hit) particle detection; and ion-implanted stacks of target foils for off-line detection. Also available are a set of HPGe detectors which will be implemented upon completion of a low-background gamma cave. TwinSol represents an advancement in the application of large-bore superconducting magnet technology, capable of running in persistent mode for weeks without liquid helium (LHe) refill or measurable degradation of magnetic field (<0.1%).

Status of ITER technology R&D in Japan

The status of the ITER technology R&D in the Japanese Home Team is reported in this study. The Japanese Home Team contributes to the validation of the ITER engineering design in most of the technology area. It is responsible for the implementation of various R&D, and in particular plays a significant role in the seven large technology R&D projects. These include a highly international collaborative program of superconducting magnet technology, in-vessel component technology and remote maintenance technology. In addition, peripheral advanced technology R&D is underway such as tritium fuel cycle, heating and current drive systems and diagnostic systems.

Physics Capabilities of an Ignition and Moderate-Burn Experiment Based on ITER Physics Guidelines

The physics capabilities of an ignition-and-moderate-burn tokamak to explore the physics of burning plasmas and burn control on ash accumulation time scales are described. The machine provides physics capabilities comparable to those of the International Thermonuclear Experimental Reactor (ITER) for pulse lengths up to 120 s, but lacks the nuclear component testing, superconducting magnet technology, and long-pulse aspects of ITER`s mission. Strong plasma shaping is adopted to reduce the cost relative of ITER. Using ITER guidelines to evaluate the physics performance, this machine has the same ignition margin as ITER`s, and operates within the limits on beta, density (i.e., the Greenwald density limit), and safety-factor specified in the ITER physics guidelines. Acceptable peak heat fluxes to divertor target surfaces are maintained with an attached, high-recycling divertor operating scenario typical of present-day machines. A range of ignited and driven operating modes is available, including advanced modes prototypical of steady-state tokamak operation. 10 refs., 3 figs., 3 tabs.

Construction and Commissioning Test Results of the Test Facility for the ITER CS Model Coil

So as to demonstrate the superconducting magnet technology to be developed for construction of the International Thermonuclear Experimental Reactor (ITER), model coils were designed and are now being fabricated. For testing of these model coils, a world's largest test facility for superconducting magnets was constructed and its test operations were successfully done. This paper describes the test program of the model coils and performance test results of the test facility to achieve the goals of the test program.

Superconducting homopolar motor and conductor development

The U.S. Navy has been developing superconducting homopolar motors for ship applications since 1969; a successful at-sea demonstration of the first motor, using NbTi wire for the magnet, was achieved in the early 1980s. Recently, this same motor was used as a test bed to demonstrate progress in high-critical-temperature superconducting magnet technology using bismuth-strontium- calcium-copper-oxide (BSCCO) compounds. In the fall of 1995, this motor achieved a performance of 124 kW operating at a temperature of 4.2 K and 91 kW while operating at 28 K. Future tests are scheduled using new magnets with conductors of both the 2223 and the 2212 BSCCO phases. This article describes the advantages of superconducting propulsion and recent progress in the development of BSCCO conductors for use in Navy power systems.

An experimental superconducting helical undulator

Abstract Improvements in the technology of superconducting (SC) magnets for high energy physics and recent advancements in SC materials with artificial pinning center (APC) [1], have made a bifilar helical SC device an attractive candidate for a single-pass free electron laser (FEL) [2]. Initial studies have suggested that a 6.5 mm inner diameter helical device, with a 27 mm period, can generate a central dipole field of 2–2.5 T [3]. Additional studies have also suggested that with a stored energy of 300 J/m, such a device can be made self-protecting in the event of a quench. As a first step towards the construction of 2 m long prototype we propose to build and test a small mechanical model that will serve as a proof of principle for such a high current density magnet, will assure its safety and provide dimensional parameters. In this paper we discuss technical issues relevant to the construction and protection of a single layer, low field (1.17 T), short (300 mm) experimental undulator.

Pulsed and high temperature superconducting magnet technology in Oxford

We present a brief account of the Oxford pulsed field facility. Multisection coils for fields of 50 T in 20 mm bores are described and a specific example is discussed. Two design studies for mixing stationary or quasi-stationary platform field magnets with pulsed coils for fields of 75 T and higher are outlined. Work on the application of high temperature superconductors to magnet technology is also reported.

Three decades of superconducting magnet development

Superconducting Magnet Technology was born in the early 1960's after thediscovery by Kunzler of the high field properties of new superconductors, Nb 3Sn and Nb Zr. The technology advanced vigorously, mainly under the strong incentive of High Energy and Plasma Physics, and spread out to many areas of Physics and of practical applications. The paper retraces some of the adventurous developments leading to the present state-of-the-art. The new era of high T c superconductors is still in the expectant stage for such applications.

Large scale superconducting magnet technology at the KfK Karlsruhe

The development activity of superconducting magnets at KfK began in the late sixties with small solenoids. Early in the seventies magnets for accelerators, solenoids for laboratory research and magnets for ore separation and energy storage including superconducting switches were investigated. In the midst of the seventies, development of midsize and large fusion magnet systems started beginning with a six coil torus TESPE of medium size followed by the EURATOM LCT coil within the Large Coil Task (LCT) under the auspices of the International Energy Agency IEA. A conductor development programme for toroidal field (TF) coils within the frame of the ITER/NET project was performed as well as for a poloidal field (PF) coil. A PF model coil POLO with about 3 m average diameter is in construction. The performance of TOSKA, a facility for the test of large forced flow coils, is now being improved for further tests relevant to large fusion magnets.

The impact of fusion on superconducting magnet development in Europe

Within the European fusion programmes the need for the development of superconducting magnets is recognized since about 20 years and strong programmes with several important milestones have been successfully executed. In all phases an early involvement of industry in close collaboration with the laboratories was essential. This was and is seen as a benefit for both sides in using the know-how from or for all other areas of superconductivity applications. Many basic areas of superconducting magnet technology have been improved remarkably by the fusion magnet development, as e.g. optimized SC wires, complex conductors with low AC losses, cable-in-conduit conductor technology, 1.8 K cooling technique and forced-flow He-I cryogenics, vacuum impregnation of large windings, low-temperature high-voltage capability of windings and leads, force transmitting embedment of the coil in thick cases and many other important details. The achieved state of the art facilitated the conceptual design of the W 7-X stellarator with advanced SC coils to a large extent and accelerates required prototype testing because existing facilities can be used. The programmes are still continued towards the manufacturing of NET/ITER model coils and their testing in TOSKA.

Fusion Nuclear Technology Research and Development in Japan

This paper discusses how basic research in various fields of fusion reactor technology has been undertaken since the mid-1970s in Japan. The major topics in the early years were materials research, superconducting magnet technology, and tritium science and technology. Current fusion nuclear technology research and development activities in Japan come under two administrative frameworks: the Science and Technology Agency (STA) and the universities under the control of the Ministry of Education, Science, and Culture. The long-term plan for fusion nuclear reactor technology development is discussed.

Magnetic conditioning in superfluid

Improvements in superconducting magnet technology have reduced to a handful the number of training quenches typical of dipole magnets. The number of training quenches in long (17 m) and short (1–2 m) SSC magnets are now about the same (operating at 6.6 T and 4.4 K), yet the steps necessary to totally eliminate training are in future research and development plans for magnet construction and conductor motion prevention. The accepted hypothesis is that Lorentz forces and poor mechanical properties of superconducting cables are the cause of conductor motion. Conductor motion reduces the stored energy in the cable by converting it into heat. The small amount of heat generated (millijoules) during motion is usually enough to quench the magnet when it is close to short sample. During training, the magnet performance normally improves with the number of quenches. It is not the quench itself that improves magnet performance but rather the fact that once conductor motion has occurred it will probably not repeat itself unless subjected to higher forces. Conditioning is a process that enables the magnet to reduce its stored energy without causing a premature quench 1,2. During the conditioning process, the magnet is further cooled from its operating temperature of 4.4 to 1.8 K by converting He I into He II. As a result, the magnet is placed in a state where it has excess stability as well as excellent heat transfer capabilities 3. Although this does not eliminate motion, if the magnet is now cycled to ≈ 10% above its operating field at 4.4 K (which is above short sample) the excess stability should be enough to prevent quenching and reduce the probability of conductor motion and training once the magnet has been warmed back up to its operating temperature of 4.4 K.

Superconducting technology for nuclear fusino facilities. 3. Superconducting magnet technology.

The common and essential problems to be solved on the superconducting magnet design will be the stability and reliability including safety, fatigue, mechanical characteristics and so on.The present article will discuss those items common to almost all kinds of superconducting magnet, and their problems to be solved will be made clear.

Superconducting technology for nuclear fusion facilities. Introduction to superconducting magnet technology.

The present series of articles provide a brief review on the present status of superconducting magnet technology for nuclear fusion experimental facilities. In this article, a brief introduction is presented on basic studies for electromagnetic properties of multifilamentary superconducting wires.

Superconducting magnet technology for the Tokamak fusion reactor.

The conceptual designs of the International Thermonuclear Experimental Reactor (ITER) are being curried out from 1988. The requirements for the superconducting magnet system are based on the progress of each component performance. However, the development program will be necessary to solve their difficulties : scale-up, reliability, and irradiation effects of insulator.

Niobium demand and superconductor applications: An overview

Niobium applications in applied superconductivity are described under six major categories following an examination of supply and demand to the turn of the century. The demand is relatively small. Somewhere between 500 and 1000 tonnes of niobium are expected to be used in superconducting devices to be produced over the next ten years; the large range in demand being due to the uncertainty about whether or not the latest proposals to build new particle physics colliders will be approved. The impact of possible space programs has not been considered. The quantity of niobium contained in the primary ore needed for alloy and compound production will be about double this amount, to compensate for losses incurred during the various stages of production to final product. By comparison, world-wide steel industry demands for niobium are around 15 000 tonnes per year. Thus the world superconductor industry is very small. Fears that there may be a shortage of niobium for superconducting applications are unfounded. A major world supplier of ferro-niobium and niobium oxide is Companhia Brasileira de Metalurgia e Mineracao (CBMM) of Brazil and most of the raw material used in the practical superconducting alloys comes from this source. Reserves in the CBMM mine alone are adequate to supply projected world needs for all purposes for at least 500 years. Other world sources of niobium exist and some are being worked, but they contain lower concentrations of niobium in the ore than those in the CBMM mine and therefore they cost more to extract. In spite of the importance of niobium in technology it is not a strategic mineral because of its world-wide abundance and the availability of substitutes for its major applications. A new development in superconductivity has been the discovery of the ceramic oxide superconductors in the last two years with critical temperatures close to 100 K, offering the possibility of cheaper and simpler liquid nitrogen cooling, as opposed to liquid helium cooling, for some future superconducting applications. Near-term applications in simple electronic devices are expected but for present day and projected applications, niobium-based alloys and compounds are likely to be the workhorses of superconductivity for the remainder of this century. The major commercial superconductor application, to date, is that for whole-body magnetic imaging as a tool in medical diagnostics. These units began to reach the market-place in 1982 and over one thousand are now in use world-wide. A further recent development is the use of superconducting r.f. cavities using high purity niobium sheet. Machines using these devices will need over 30% of the total niobium demand for applied superconductivity over the next five or six years. A potential demand is that for new colliding beam accelerators proposed for particle physics and nuclear physics research. If they are built, about 600 tonnes of niobium will be needed for these machines. Requirements for energy industry technologies and transportation, so high about 15 years ago, are likely to be dismally low for the next 20 years or so. Other commercial uses for superconducting magnets at present are those for gyrotrons, magnetic separators and research and development activities. In addition to machines for physics research, smaller accelerators with superconducting magnets are under development for use in medical and industrial applications and for the production of high intensity X-ray light sources. The energy related applications are not yet commercial but the required superconducting magnet technology has been developed over the last 25 years. Applications include magnetic fusion, superconducting generators, magnetohydrodynamic power generation, superconducting power transmission and energy storage, current limiters and superconducting transformers. Successful high-speed land transportation systems based on superconducting magnet levitation have been demonstrated, as have superconducting ship drives. A wide range of superconducting instrumentation is in everyday use and the possibilities for superconducting computers continue to be studied. The status of these various technologies is discussed in the following paragraphs.

MRI-superconductivity in the marketplace

Magnets for medical Magnetic Resonance Imaging (MRI) represent the first large scale commercial application of superconductivity. These devices have been in production in the U.S., the U.K., and Europe for several years and the basic designs have stabilized. Since the magnets operate at relatively low fields (generally < 2 Tesla), they have not required advances in basic superconducting materials or magnet technology. Progress has come rather in the areas of cryogen consumption, field homogeneity, transportability, shielding, reliability, and the user interface. This paper reviews the currently available devices and the areas presently under development.

Super conducting magnet technologies for fusion reactor.

Fundamentals and application of superconducting magnet of a fusion reactor are stated. Regarding to a design of the magnet, thermomechanical aspect is referred to in terms of quench phenomena. A relation between stored magnetic energy and mass required to support electromagnetic force is discussed for the superconducting magnets.