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Über dieses Buch

This book, in essence the proceedings of a NATO Advanced Study Institute with the same title, is designed to provide in-depth coverage of many, but not all, of the major current applications of superconductivity, and of many that still are being developed. It will be of value to scientists and engineers who have interests in the research and production aspects of the technology, as well as in the applications themselves. The ftrst three chapters (by Clarke, Vrba and Wikswo) are devoted to an understanding of the principles, fabrication and uses of SQUID magnetometers and gradiometers, with the greatest emphasis on biomagnetism and nondestructive evaluation (NDE). For the most part, traditional low-temperature superconductor (LTS) SQUIDs are used, but particularly for NDE, high-temperature superconductor (HTS) SQUIDs are proving useful and often more convenient. The succeeding three chapters (by Przybysz, Likharev and Chaloupka) cover broader aspects of superconducting electronics. The ftrst two of these deal primarily with digital L TS circuits, while the third discusses in great detail passive component applications using HTS materials. Currently, HTS ftlters are undergoing intense J3-site testing at cellular telephone base stations. While it is clear that HTS ftlters outperform conventional ftlters in reducing signal loss and allowing for more channels in a given bandwidth, it isn't yet certain that the cellular telephone industry sees sufficient economic beneftts to make a ftrm decision to use HTS ftlters universally in its systems. If this application is generally adapted, the market for these ftlters should be quite large.



1. Low- and High-Tc Squids and Some Applications

DC Superconducting QUantum Interference Devices are routinely fabricated from Nb films with an integrated input coil to couple in magnetic flux from the signal source. Typical dc SQUIDs operated at 4.2 K have a magnetic flux noise of 10−6 Φ0 Hz−1/2, where Φ0 is the flux quantum, corresponding to a magnetic noise energy of 10−32 JHz−1. With the aid of a superconducting flux transformer the magnetic field noise can approach 1 fT Hz−1/2. High-Tc dc SQUIDs fabricated from thin films of YBa2Cu3O7-x (YBCO) have achieved noise energies below 10−30 JHz−1 at 77 K and, with multilayer flux transformers, a magnetic field noise below 10 fT Hz−1/2 at frequencies down to a few Hz. An rf SQUID made from YBCO and operated at 77 K at frequencies around 1 GHz has achieved a magnetic field noise of 16 fT Hz−1/2 at frequencies above 100 Hz. A recent theory for rf SQUIDs predicts noise levels in good agreement with experiment. Two issues relevant to the operation of high-Tc SQUIDs in an unshielded environment are the increase in low-frequency noise arising from the entry of flux vortices into the YBCO films and the realization of long-baseline gradiometers. The applications of low-Tc SQUIDs to nuclear magnetic and nuclear quadrupole resonance, and of high-Tc SQUIDs to scanning SQUID microscopy and geophysics are discussed.
John Clarke

2. Multichannel SQUID Biomagnetic Systems

The field of biomagnetism advanced considerably since the first recordings of magnetic fields of the human heart in 1963 and of the human brain in 1968. Since the introduction of whole-cortex magnetoencephalography (MEG) systems in 1992, the number of installed channels has dramatically increased, and the magnetic evaluation of the human brain has been gradually finding its place in clinical work. MEG is presently the most important biomagnetic application, and sophisticated MEG systems with large numbers of channels have been developed commercially. The MEG systems must meet certain specifications on noise, dynamic range, slew rate and linearity because they are exposed to environmental noise even when they are operated within shielded rooms. The systems are designed to meet these specifications through optimized design of SQUID flux transformers, SQUID control electronics and data acquisition, and development of various synthetic noise cancellation techniques. The interpretation of the resulting magnetic data is enhanced by combining the MEG results with information from electroencephalography (EEG) and other imaging modalities. In addition, an engineering effort is devoted to the development of various items of MEG peripheral equipment (stimulators, patient support, head positioning, etc.).
Jiri Vrba

3. Applications of SQUID Magnetometers to Biomagnetism and Nondestructive Evaluation

Since their introduction to biomagnetism in 1970, SQUID magnetometers have been used worldwide to measure magnetic signals from the heart, brain, lungs, liver, nerves, skeletal muscle, stomach, intestines, eyes, and other organs. The majority of the effort in the field has been by university and national-laboratory researchers and by small, high-technology companies, and has been directed towards the development and promotion of this technology. While a SQUID clearly is an accepted and productive research instrument, the application of this technology in routine clinical diagnosis is only now beginning. The challenge is to identify applications for which SQUIDs are ideally suited and there is minimal competition from other technologies. The introduction of high-temperature superconductor (HTS) SQUIDs has led to a resurgence, for example, in measurements of the magnetocardiogram by physicists and new searches for applications. Similar trends are evident in the use of SQUIDs for the nondestructive evaluation (NDE) of aircraft and other structural systems and materials: most of the effort is directed towards instrumentation development and demonstrations in simple systems. Instruments suitable for specific commercial applications are just now being prototyped, and there is a new generation of HTS SQUIDs for NDE. This chapter presents an overview of SQUID magnetometers for biomagnetism and NDE, reviews a number of pertinent applications of SQUIDs, and discusses the criteria for successful application.
J. P. Wikswo

4. Applications of Josephson Electronics in Digital Systems

Whoever would build the future, must first imagine it. A vision of the future is a powerful motivator for the researcher to strive toward a goal. Research money is directed toward the dream. Little support can be found to build a better transistor for its own sake. The systems that will exploit new electron devices to improve communications, enhance safety in travel, secure the common defense, and improve the quality of life, justify the expense of modern electronic research projects.
John X. Przybysz

5. Superconductor Devices for Ultrafast Computing

Mainstream digital electronic technology based on semiconductor transistors keeps demonstrating remarkable progress. A reasonable question to ask, however, would be how long this progress will continue. Throughout the three decades of the exponential growth of this mainstream technology, this question has been the subject of much scientific and pseudo-scientific speculation.
Konstantin K. Likharev

6. Microwave Applications of High Temperature Superconductors

Over the past decade HTS thin-film technology has matured to such a degree as to allow the beneficial implementation of HTS components into operational systems. This chapter is concerned with the application of low conductor losses in epitaxial HTS thin-films to passive RF components. Following a phenomenological introduction to the RF current transport properties of superconductors, application aspects are discussed in three steps. First, realization and properties of HTS components, like resonators, filters, delay lines and antennas are outlined. Next, the impact of superior HTS component performance is investigated on the subsystem level, covering receiver front-ends, wideband cueing receivers and stable oscillators. Finally, the pay-off of an implementation of HTS technology is discussed for two representative system applications, namely communication satellites and terrestrial mobile communication systems.
H. J. Chaloupka

7. MRI Magnets

The first practical superconducting magnets were constructed in the early 1960’s, and a substantial number have since been manufactured for use in scientific or industrial research. However, it was not until the emergence of Magnetic Resonance Imaging (MRI) in the late 1970’s that a commercial application of superconductivity appeared that would take superconductivity out of the laboratory and into everyday use. The strong and stable magnetic fields needed for MRI have meant that almost from the outset the majority of systems have used superconducting magnets, and the widespread acceptance of MRI as a valuable diagnostic tool in modern medicine has resulted in a worldwide installed base today in excess of 10,000 superconducting magnets.
F. J. Davies

8. Power Quality, Micro Superconducting Magnetic Energy Storage Systems, and Fault Current Limiters

Due to widespread use of digital and microprocessor-based electronic equipment, industry has become more sensitive to problems associated with the low quality of electric power. Low power quality can interrupt operation of sensitive or critical loads, and cause system malfunctions and even failure. Superconducting Magnetic Energy Storage (SMES) systems and Fault Current Limiters (FCL) are the most promising superconducting technologies for power quality applications. SMES units with an output power of about 1 MW can be of benefit as sources of pulsed power to a dedicated 480 V user’s critical load and for improvement of power quality. The next generation of micro-SMES could be connected to a medium voltage electrical substation to provide quality power to all critical loads connected to the substation. Micro-SMES operation is illustrated with the example of Intermagnetics’ 6 MJ, 750 kVA unit. A fault current limiter is a device in a transmission or distribution power network which can reduce the magnitude of a fault current and mitigate hazards associated with the faults. High temperature superconducting (HTS) current-limiting devices may offer a technically sound, cost-effective solution over traditional technologies.
Michael Parizh, Eddie Leung

9. High Current Application of Superconductivity

Part I: Applications in Research and Industrial Areas
Research areas such as particle physics and solid-state physics have been vital fields for high-current applications of superconductivity since the 1960s. Superconducting magnet technology, as well as the technology of NbTi- and Nb3Sn-multifilament conductors, have undergone major advances due to challenging projects in these research areas. The applications introduced in this article concern particle-detector magnets, accelerator magnets and high-field solenoids.
P. Komarek

10. High Current Application of Superconductivity

Part II: Superconducting Magnets for Fusion
Nuclear fusion is one of the major long-term options for mankind’s energy supply. Progress in the physics of fusion reactors is already well advanced, and the development of a first experimental reactor has been underway for several years. At present magnetic confinement of the hot plasma is considered as the most promising technology. Consequently, the use of superconducting magnets for generating the required high magnetic field in a large volume is imperative for economic reasons. Even for large prototype experiments currently under construction, one must use superconducting magnets for steady-state or quasi-steady-state operation.
P. Komarek

11. The Mechanical Deformation Processing of High-Temperature Superconducting Composite Tape

Since the discovery of ceramic high temperature superconductors, HTS [1–3], great efforts have been made in order to exploit the new superconductors in commercial applications. The HTS/metal composites, especially the BiSrCaCuO(BSCCO)/Ag composite, have been demonstrated to be a very promising candidate for large-scale applications. Values of the critical current density, Jc, over 60000 A/cm2 have been reached at 77 K for short composite tapes [4, 5]. Jc values over 20000A/cm2 have been reported for long length tapes over 1000 meter [6]. Most of the BSCCO/Ag composites are now made by the powder-intube, PIT, method. In brief: when the PIT method is applied, HTC precursor powder is filled into a pure Ag or Ag alloy tube, which is then mechanically deformed into thin composite wires or tapes. A thin tape is usually chosen as the final shape. The mechanical deformation process most often includes one or more of the following: extrusion, drawing, rolling and pressing. The as-deformed tapes need further annealing (sintering) in order to form the superconducting phase and texturise the material. A second mechanical deformation may be needed between several annealing steps to improve the superconducting properties of the composite further.
Torsten Freltoft, Zhenghe Han

12. Applications of High Temperature Superconductors in Magnetic Bearings and Flywheels

Superconductors are materials with the remarkable capability to carry an electric current without dissipation of energy. These materials are able to levitate or suspend magnets in a stable manner that permits mechanical motion with nearly no loss of the kinetic energy stored in that motion. This single feature makes the superconductor and magnet system a promising starting point from which to fabricate mechanical bearings that have extremely low friction and are free from wear and tear.
Ki Bui Ma

13. Cryogenic Systems for Superconducting Devices

It may happen, sometime, that the reader spends his or her well deserved holidays in the beautiful country of Greece and, sitting on a typically unstable chair in one of the nice taverns, one may ask for “kryo nero”. It may take a while, but you will get a nice jug filled to the top with icy cold water. Indeed, “cryo” means “cold”, and cooling was already known as a means to improve the quality of life in the early times The Egyptians put wet cloths over their foods, and placed them in the sun, so that the heat associated with the evaporation of the water cooled their food and drinks The Romans cooled their foods with ice blocks that were taken from Alpine regions and were stored underground in vaults insulated with straw. Our forefathers in Europe cut ice blocks out of rivers or shipped ice from Norway or Canada. In special ice factories rods of ice were made to be used for instance in butcheries and breweries.
H. J. M. Ter Brake

14. Superconductor Measurement Techniques and Cryostat Design

This introduction to measurement cryostat design includes illustrations of several practical cryostats for testing low-current thin-films and high-current bulk superconductors. Heat transfer is the heart of most cryostat designs and illustrative calculations are given. Other topics that will be discussed include optimal heat sinking of instrumentation leads, wire materials selection, practical vacuum-tight electrical fixtures, vapor-cooled current leads, high-temperature-superconductor current leads, and variable temperature apparatus. A few properties of technical materials for constructing cryostats will be summarized.
Jack Ekin

15. Superconductivity R&D at ISTEC and elsewhere in Japan

Within a few months of the discovery of high-temperature superconductors (HTS), Japan had started two new national R&D programmes, the International Superconductivity Technology Center (ISTEC) and the Multi-Core Programme (MCP). ISTEC carries out basic research with the aim to develop viable future technology. MCP funds basic research at national institutes and universities. A large number of companies have taken part in these and other national research initiatives to develop superconducting materials and products.
In Japan expectations are high and are backed by lavish research funding. The government alone spends $174 million yearly. Japan believes that HTS will be an important part of its future high-technology industries, predicting that by 2010, this will be an industry worth $75 billion. This report reviews the considerable research effort in Japan in both corporate and government institutes. It also covers some of the commercial developments.
G. Pindoria
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