Takeshi Kamikado

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.

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 of 15 T Cryogen-Free Superconducting Magnets

Cryogen-free superconducting magnets are becoming popular due to their simple operation compared with the conventional liquid Helium cooled magnet. However, for higher fields such as those greater than 14 T, the cryogen-free magnet has not become popular yet, because it is difficult to design and manufacture since the critical current is markedly reduced at higher fields and higher temperatures. We have developed two types of 15 T cryogen-free superconducting magnets, which will be among the highest field magnets in operation as cryogen-free with a GM cryocooler. One magnet has a 52 mm room temperature bore with overall dimensions of 820 mm in diameter and 680 mm in height. This magnet is designed so as to be simple in both operation and installation. Therefore, the magnet is cooled with a single 1 W GM cryocooler. Also, all coils are connected in series and charged with a single power supply. The magnet was successfully charged up to 15 T in 30 minutes and then charged slowly to 16 T without quench. The other magnet has a 170 mm room temperature bore with overall dimensions of 980 mm in diameter and 1015 mm in height. This magnet is designed so as to be used with temperature controlled sample cryostats with an outer diameter of 168 mm. The magnet is cooled with four 1 W GM cryocoolers and charged with a single power supply. The magnet was successfully charged up to 15 T in 90 minutes. Both magnets will enable high magnetic field research or application with very easy operation

New 7 T superconducting magnet system for bacterial cultivation

Abstract A new superconducting magnet system for bacterial cultivation has been developed. The superconducting magnet has a horizontal room temperature bore with a diameter of 160 mm, and provides a homogeneous magnetic field of 7 T ± 0.5% for a 200 mm long × 100 mm diameter region. This homogeneous field region contains an incubator, where bacteria are cultivated aerobically at 10–70 °C ± 0.1 °C while being shaken. The culture exposed to the high magnetic field is compared with a control culture incubated at below geomagnetic field strength. Cultivation of Escherichia coli was carried out both in homogeneous and in inhomogeneous fields, and 1.4–3.6 times the number of viable cells of the control culture was observed in a stationary phase.

Development of 7 T Cryogen-free Superconducting Magnet for Gyrotron

We developed a special type of 7 T 240 mm vertical bore cryogen-free superconducting magnet system, which will be used for gyrotron. The magnet system consists of three sets of coils which are charged separately. A set of main coils is wound with NbTi conductor and produces 7 T at the center of the bore tube. A set of gun coils is also wound with NbTi conductor and located below the main coil. It produces up to -1.4 T at a lower part of the bore tube and controls the magnetic field where a gun is located. A set of sweep coils are located inside of the main coil. The sweep coil produces only +/- 0.2 T but is charged and discharged within several seconds so as to control electron trajectory. To avoid quench with the rise of the temperature from the large AC loss, this set of coils are wound with Nb3Sn conductor. Also to reduce the induced current in the main coil, the sweep coil is actively shielded. This magnet system will contribute to the fast control of the gyrotron oscillation frequency.

Quench analysis of multisection superconducting magnet

The numerical quench simulation code includes the effect of the filament coupling loss. We apply this simulation code to two multisection high field magnets. In this paper we describe the modified quench simulation code which includes the effect of filament coupling loss and make comparisons between the experimental and analytical results.<<ETX>>

Development of the 19 T high field magnet system

A high field magnet system, up to 19 tesla at 1.8K, with magnet bore of 75mm was developed. The magnet consists of Nb/sub 3/Sn solenoids (3 sections) and NbTi solenoids (2 sections). A liquid helium vessel is divided into two parts (4.2K upper part and 1.8K lower part) by a fiberglass reinforced plastics separator. The central field is 17 tesla at 4.2K with normal liquid helium and 19 tesla at 1.8K with pressurized superfluid helium. This magnet can be operated in persistent mode and the field stability at that time is less than 10ppm/hour. The field homogeneity is better than 0.1% at 50 mm sphere volume. The stored energy is about 3MJ. A small refrigerator was installed on the top flange of the cryostat to reduce the evaporation rate of liquid helium and to maintain the superconducting magnet at low temperature while pausing. This system is used for the measurement of critical current and other physical properties of superconducting wire and other materials such as high T/sub c/ superconductors. >

R&D studies on mechanical stress of 1 GHz NMR magnet

In order to make a 1 GHz NMR magnet compact, it is operated under high hoop-stress conditions. In our design the hoop-stress of a 1 GHz NMR magnet exceeds 180 MPa. We prepared two types of sample coils. One of them was constructed with niobium-tin superconducting wire, which has a tantalum core. The other one was wound with niobium-titanium superconducting wire. These wires are rectangular in cross-section. The niobium-tin sample coil was energized in a backup magnetic field of 13.5 T and 14 T. It was possible to operate it up to a hoop-stress of 272 MPa. The niobium-titanium sample coil was tested up to 99% of its critical current where the hoop-stress was 226 MPa. These results confirm that our design of the 1 GHz NMR magnet is appropriate.

Development of the superconducting magnet system for a bioreactor

A superconducting magnet for a bioreactor system was developed in order to determine the biotechnical and biomedical responses of microorganisms to a high magnetic field. The magnet has a horizontal bore, and the field strength at the center is 7 tesla at an operating current of 120 Amperes. The room-temperature bore diameter is 160 mm. Persistent current mode and detachable power leads are adopted. A cryocooler was installed to cool the radiation shields, which enable continuous operation for 6 months without the need to resupply liquid helium. Magnetic shields cover the cryostat to minimize the leakage field. Two reactors are installed inside and outside of the bore. Magnetic shields also cover the outside reactor in order to reduce the strength of the magnetic fields to less than the geomagnetic level. The temperatures of the reactors are controllable, ranging from 283K to 343K with /spl plusmn/0.1K. >