A. Sato

Operation of a 920-MHz high-resolution NMR magnet at TML

A 920-MHz high-resolution NMR spectrometer has been operating at the Tsukuba Magnet Laboratory (TML) since April 2002. It has proved its effectiveness by determining the 3-D structures of protein molecules. To accelerate studies in structural biology and solid-state NMR, a second high-field NMR magnet was developed and installed at TML. Although its basic design was the same as that of the first magnet, some improvements were made. For the innermost coil, a 16%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor was employed. The increase in the critical current density above that of a 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn conductor made it possible to reduce the conductor size from 3.5 mm /spl times/ 1.75 mm in the first magnet to 2.80 mm /spl times/ 1.83 mm in the second. At the same operating current of the first magnet, the second magnet is expected to operate at 930 MHz. The liquid helium reservoir and the superfluid helium cooler, which were separated in the first system, were united in the same chamber in the new magnet. The latter magnet was energized up to 21.9 T without quenching in March 2004 and has operated in a persistent-mode at that field. It will be utilized mainly for solid-state NMR measurements.

Development of 1 GHz superconducting NMR magnet at TML/NRIM

Development of a 1 GHz superconducting NMR magnet is in progress at the Tsukuba Magnet Laboratory of the National Research Institute for Metals. The magnet will consist of two parts. The outer magnet of LTS coils is designed to generate a field of 21.1 T (900 MHz) in persistent current mode. The inner coil is designed to generate an additional 2.4 T, resulting in a central field of 23.5 T (1 GHz) in a 54 mm diameter bore at room temperature. As a high-resolution NMR magnet, field stability as well as field homogeneity is very important, which is especially difficult to achieve in the inner coil when exposed to extremely high magnetic fields that superconducting magnets have not yet encountered. The engineering design is complete and fabrication of the superconductors has begun. This report presents the results of the engineering design and R&D studies on the candidate superconductors for the inner coil, such as BSCCO, and improved Nb/sub 3/Al and Nb/sub 3/Sn.

Persistent-mode operation of a 920 MHz high-resolution NMR magnet

Development of a high-field NMR magnet has been underway at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. The magnet succeeded in a persistent-mode operation at 21.17 T in December 1999. A 283-day long-term operation was carried out from October 2000 to August 2001. It included a persistent operation at 21.6 T (920 MHz) for 108 days. This was the highest field that the superconducting magnets have ever achieved in a persistent operation. Field decay was less than 2 Hz/h. Field homogeneity after correcting with superconducting shim coils were less than 0.1 ppm in a sample volume. These results confirmed that this magnet had been successfully developed as a high-resolution NMR magnet.

Development and operation of superconducting NMR magnet beyond 900 MHz

As a milestone in the 1-GHz NMR magnet project being carried out at the Tsukuba Magnet Laboratory, a 900-MHz class NMR magnet was successfully manufactured and operated in December 1999. The developed magnet is made of 15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn, Ta-reinforced (Nb,Ti)/sub 3/Sn, and NbTi conductors. The room temperature bore of the cryostat is 54 mm is diameter. All the coils are cooled with pressurized superfluid helium. The magnet generated a field of 21.20 T in a driven mode and then operated in a persistent mode at 21.17 T corresponding to a proton NMR frequency of 902 MHz. The field may be raised to the range of 21.6 T (920 MHz) in the near future.

Development and testing of superfluid-cooled 900 MHz NMR magnet☆

Abstract As the preliminary step for the 1 GHz NMR spectrometer, a 900 MHz class NMR magnet was fabricated and was successfully operated in December 1999. The magnet is made of 15% Sn–bronze-processed (Nb,Ti) 3 Sn, Ta-reinforced (Nb,Ti) 3 Sn, and NbTi conductors. All the coils are cooled with pressurized superfluid helium. The magnet generated a field of 21.20 T in a driven mode and then operated in a persistent mode at 21.17 T corresponding to a proton NMR frequency of 901.2 MHz. During the magnet excitation for 24 h, the superfluid bath temperature was kept constant to below 1.6 K using an automatic control system. After several excitation tests, the magnet was quenched and the rupture disk of the magnet vessel was broken. The size of the cold safety valve and the structure of the rupture disk have been checked and modified. Before the reassembly of the magnet cryostat, the modified superfluid cooler for cooling the magnet bath was tested.

Resistive insert magnet for a 37.3-T hybrid magnet

Abstract A resistive insert magnet consisting of Bitter-type coils was fabricated, incorporated into the 400-mm bore of the superconducting outsert, and tested under a backup field of 14.2xa0T. This hybrid magnet generated a total field of 37.3xa0T in the center of a 32-mm room-temperature bore. At this magnetic field, the operating current of the resistive insert magnet was 33.25xa0kA at a voltage of 431xa0V. This insert magnet is divided into three coaxial coils. The bitter plates of the two inner coils are made of hard-worked Cu–Ag plates, and those of the outermost coil are made of GlidCop AL-25. The thickness of the plates used in the two inner coils was 0.84xa0mm, and the 0.2% proof stress in the direction parallel to the roll work was about 800xa0MPa at 375xa0K. This temperature is designed to be the maximum of the innermost coil at 37.3xa0T. Elongated cooling channels were punched in a staggered formation in these plates. The flow rate of the cooling water was 0.141xa0m 3 /s at the maximum field. Regular operation up to 35xa0T started from June 2000 at the Tsukuba Magnet Laboratory.

Present status of 920 MHz high-resolution NMR spectrometers

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.

Test results of long term operation of the superfluid-cooled cryostat for a 1 GHz NMR spectrometer

A superfluid cryostat for an 1 GHz-NMR magnet has been developed and its performance was tested. The magnet was successfully energized up to 21.6 T corresponding to a resonance frequency of 920 MHz this April. Before the 920 MHz operations, the magnet was operated for 5 months at the 900 MHz field to check the long-term reliability of the cryogenic system. Stable cryogenic performance has been confirmed through this operation. The HeII bath temperature was kept constant below 1.6 K without any trouble related to the cryostat. The resultant heat load at 1.6 K was 0.55 W. The total helium consumption rate was 800 cc/h.

Long term operation of superfluid-cooled cryostat for 920 MHz NMR spectrometer

The 920 MHz NMR magnet which successfully generated its designed magnetic field on April 2001 was installed at Tsukuba Magnet Laboratory (TML) of the National Institute for Materials Science (NIMS). The magnet again generated 920 MHz without a quench, and has been in continuous operation for over one and a half years up to the present time. The cryostat, which houses the superconducting magnet, employs a pressurized superfluid helium cooling process. Its operating temperature is below 1.55 K. The consumption rates of liquid helium and liquid nitrogen are 0.98 L/h and 0.76 L/h, respectively. Liquid helium is manually supplied every week and liquid nitrogen is automatically supplied every week. Although the cryostat has experienced earthquakes more than 70 times and power failure 3 times, there has been no serious trouble related to the cryostat and the cooling operation is still continuing without interruption.

Long term testing of superfluid-cooled 920 MHz NMR cryostat

The design of the cryostat structure has been checked from the point of view of safety of the cryostat. The heat leak to the superfluid bath has been reduced to 0.5 W at 1.7 K by purification of the magnet bath and careful control of the cold valve sheet surface. The magnet was energized up to 21.20 T (901.2 MHz), and then operated in the persistent mode for four months. The magnetic field was successfully increased up to 21.6 T (920.3 MHz) in April 2001, and then operated in the persistent mode for four months. During the long term operation the shield temperature was measured. The minimum temperature changed periodically depending on the liquid nitrogen level of the 80 K shield.