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The use of REBCO coils is a promising approach to achieve super-high field NMR magnets. As the first step in this direction, we have started to develop an LTS/REBCO NMR magnet operated at 400–600 MHz (9.4–14.1 T). In this paper, based on numerical simulations, we describe a study of the thermal runaway of the REBCO innermost coil, which is one of the major problems of this type of magnet. Based on the simulation results, if an LTS coils quench occurs, the current in the REBCO coil continues to increase due to the electromagnetic induction and leads to a natural thermal runaway with a very high current density. The thermal runaway is limited to only the top and bottom ends of the REBCO coil, as the radial magnetic field is highest there and the quench propagation velocity is quite low. The current density for this type of thermal runaway is much higher than that of the operating current, resulting in the catastrophic overheating of the coil. This is the worst case scenario which must be prevented for the LTS/REBCO NMR magnet. An optimal size dump resistor for the REBCO coil can prevent the natural thermal runaway by suppressing the current increase due to electromagnetic induction. [ABSTRACT FROM PUBLISHER]

A nuclear magnetic resonance (NMR) system using a high-temperature superconducting (HTS) magnet and a probe with an HTS radio frequency coil is currently under development. The HTS NMR magnet is expected to reduce the volume occupied by the magnet and to encourage users to install higher field NMR systems. RE-Ba-Cu-O-coated (REBCO-coated) conductors offer the advantages of a higher critical current density than low-temperature superconductors in magnetic fields above 10 T as well as tolerance to high tensile stress. Both of these factors are expected to lead to a reduction in the volume of the magnet. Four REBCO layer-wound test coils were fabricated in order to investigate their properties under electromagnetic forces in an external magnetic field of up to 17. 2 T. The REBCO coils with a practical inner diameter were successfully operated under electromagnetic forces of over 200 MPa in high magnetic fields. [ABSTRACT FROM PUBLISHER]

Using high-Tc superconductors (HTS) is considered to be the only solution to dramatically increase the highest fields of NMRmagnets because of their high critical fields. However, it is not easy to apply HTS to an NMR spectrometer (HTS-NMR) because a persistent-mode operation with HTS cannot satisfy the field stability of 0.01 ppm/h at present. To overcome this problem, we are now developing an HTS-NMR spectrometer in a driven-mode operation. As the first step, a layer-wound coil was fabricated with bronze-reinforced Bi-2223 conductors. Instead of the Nb3Sn coil, the Bi-2223 coil was installed as the innermost part of an existing NMR magnet. The magnet operated at a field of 11.7 T with a highly stabilized power supply. NMR measurements were carried out, and it was demonstrated that the quality of the multi-dimensional NMR spectra on the protein was equivalent to that obtained with a persistent-mode system. The next step will be to demonstrate its usefulness as a high-field NMR system. The upgrade of the 920 MHz NMR system installed at the Tsukuba Magnet Laboratory is underway. Its innermost coil is scheduled to be replaced by a Bi-2223 layer-wound coil for 2010. Its target field is 24.2 T (1.03 GHz). [ABSTRACT FROM AUTHOR]

In this study, we investigated in field properties of high-Tc superconductor (HTS) tapes electrically as well as mechanically. Metallic reinforced Bi-2223/Ag superconductor tapes were used in this work. The critical current (Ia), which is highly dependent on the magnetic field, was measured using fields applied parallel and perpendicular to the tape surface. The conductor was exposed to fields of up to 28 T at 4.2 K. In order to confirm the performance of tapes in practical NMR operation, Ic was also measured around 2 K. The conductor was wound on a large diameter bobbin and mechanical properties were then measured as the coil current was increased. Finally, we verified the conductor properties from coil Ic and maximum stress/strain of it. [ABSTRACT FROM AUTHOR]

For the development of high magnetic field application using high temperature superconductor (HTS), Bi-2223/Ag tape is one of the promising materials because of its high current capacity and upper critical field. However, Bi-2223/Ag tape shows very strong anisotropy and significant deterioration of critical current in the magnetic field. To explore the possibility of HTS in high field applications, we evaluated the critical current and index value of Bi-2223/Ag conductor in high magnetic field. The Bi-2223/Ag tape was characterized as a function of increasing and decreasing field. The temperature dependence was also examined lower than 4.2 K. All measurements were carried out with hybrid magnet system up to 30 T and the experimental results are reported. [ABSTRACT FROM AUTHOR]

A testing coil composed of six pancake-coils with a YBCO coated conductor has been fabricated and its superconducting properties have been investigated. The resulting coil has generated magnetic fields up to 0.65 T at 65 K in zero external magnetic field. In order to enhance capability for transporting current of YBCO coil, superconducting behavior of the multi-tape YBCO conductor has also been investigated. The critical current of the conductor that is formed by bundling two tapes has practically achieved the sum of the critical currents. [ABSTRACT FROM AUTHOR]

Magnetic field dependencies of the Ic of the IBAD/CVD-YBCO short tape sample and its small coil sample were measured in high fields, up to 18 T at 77 K. Compared with the Ic of the tape sample, the Ic of the coil sample at 0.1 μV/cm showed the same tendency in high fields. If YBCO tape is applied to a high-field coil application, the application should be operated at a temperature which is lower than 77 K. Using long CVD-YBCO tape, six stacked pancake coils were fabricated. Various current tests were conducted using one of these stacked coils. In AC current tests, thermal stability of the YBCO coil was estimated. When the peak values of AC current were 1.2 times higher than the maximum DC current in a thermal stable state, Idcmax, and the average electric field of the coil at the first triangular wave was about 10 times higher than 1 μV/cm criterion, the peak values of the built-up voltage did not tend to increase even after the 99th triangular wave current, and thermal run-away in the coil was not observed. In DC current with overlapped pulse current tests, the maximum peak current of the coil in a thermal stable state was obtained as a function of DC current and sweep time. It was 1.3 times higher than Ic and 1.4 times higher than Idcmax in a test condition. These results indicate that the YBCO coil has high potential in short-time, over-current operations at high temperatures. In cases where built-up voltages did not disappear, they began to increase just after the coil currents reverted to the initial DC currents. It was found that DC current influenced the increasing speed of built-up voltages once the pulse current had decreased to zero. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a superconducting magnet for a high-speed and high-resolution Rutherford backscattering spectrometry system that utilizes the ion motion along the cyclotron trajectory in a magnetic field. The superconducting magnet without cryogen consists of a main coil, shim coils, a 4K refrigerator and pole pieces. It generates a 2T magnetic field in the spectrometer of ϕ 340×750mm. The shapes of the pole pieces and the coil arrangements are optimized by a magnetic field analysis to generate a uniform field. The magnetic field distribution is made to be so uniform that the scattered ions can pass through a ϕ 1mm aperture, by ion trajectory calculation. The trajectory of the incident beam is also computed, and the position of a specimen holder is determined so that the incident beam is well focused on the specimen. [Copyright &y& Elsevier]

The first 920 MHz high-resolution NMR (Nuclear Magnetic Resonance) magnet was successfully installed at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. A persistent operation at 21.6 T has continued since April 2002 without any problems. Excellent field stability of 0.31 Hz/h was observed from December 2002 to January 2003. Since July 2002, the magnet was used as an essential part of the only 920 MHz high-resolution NMR spectrometer in the world. The signal-to-noise ratio of 0.1 % ethylbenzene using a proton-selective probe was as high as 2981. An HCN triple-resonance probe is now attached to the spectrometer to contribute to the National Project on Protein Structural and Functional Analysis in Japan. The completion of the second 920 MHz-class NMR spectrometer is scheduled for spring 2004. [ABSTRACT FROM AUTHOR]

Examines the field performance of a high-resolution nuclear magnetic resonance superconducting magnet. Persistent-mode operation of the magnet; Field decay; Field homogeneity.

Abstract: Research and development activities and some recent results related to Nb3Sn superconducting wires in Kobe Steel, Ltd. (KSL) and Japan Superconductor Technology Inc. (JASTEC) are introduced. First, an outline of the activities is described briefly from a historical point of view. Following that, improvements in the characteristics (i.e., critical current density (J c), n-value and mechanical properties) of bronze-processed Nb3Sn wires are reviewed. Finally, the status of development for the Ta–Sn powder-in-tube (TS-PIT) process is briefly discussed. [Copyright &y& Elsevier]

Abstract: We have commenced a project to develop a beyond-1GHz solution NMR spectrometer using a HTS coil. Due to a small residual resistance present in the HTS conductor and joint resistance between conductors, a stable persistent current sufficient for NMR measurements is unlikely. Therefore, a current has to be supplied to the HTS coil from an external power supply. The ripple of an external power supply causes a field fluctuation which must be stabilized. In this study we show results of NMR measurements using a 500–600MHz NMR in such an external current mode: the field fluctuations are stabilized by an internal 2H lock. The field fluctuation from the external power supply comprises a major field fluctuation component at low frequencies, 0.003–0.005Hz, and superimposed minor field ripples at 2Hz and 50Hz. The former limits the time interval of the internal 2H lock, while the latter generates sidebands in the NMR spectrum. Sideband and baseline noise are controlled by appropriate selection of the feedback loop parameters of the lock. The quality of the 1D-solution NMR spectra observed in external current mode is equivalent to that obtained in persistent current mode. However, if the feedback loop time is as short as the gradient pulse width, refocusing of the NMR signal is lost and NMR peaks disappear. The 2D-NOESY and the 2D-HSQC spectra of ubiquitin in an external current mode have been acquired. The quality of the 2D spectra is equivalent to those obtained in persistent current mode; i.e. the internal 2H lock operates stably over an experimental time interval of 40–50min. To realize a beyond-1GHz NMR spectrometer, further investigations must be made of (i) the long term stability of a DC power supply, (ii) the enhancement of the compensation field limit for the internal 2H lock, (iii) the extension of the helium refill time interval, and (iv) a method to correct the field homogeneity in the external current mode. [Copyright &y& Elsevier]

We have developed a 920 MHz NMR system and performed the proton NMR measurement of ethylbenzene and water using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high-resolution NMR. The sensitivity has been examined by 1H NMR of 0.1% ethylbenzene in Wilmad 555 tube and obtained the signal-to-noise ratio as S/N=2981, which is the highest record, to our knowledge, among the room temperature measurements. [Copyright &y& Elsevier]