Magnetic resonance imaging apparatus

Spectroscopy, and “NMR on a Chip” for Chemistry, Biochemistry, and Industry Sergey S. Zalesskiy,† Ernesto Danieli,‡ Bernhard Blümich,*,‡ and Valentine P. Ananikov*,†,§ †Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991, Russia ‡Institut für Technische Chemie und Makromolekulare Chemie, RWTH Aachen University, Worringerweg 1, D-52074 Aachen, Germany Department of Chemistry, Saint Petersburg State University, Stary Petergof, 198504, Russia

Miniaturization of NMR systems: desktop spectrometers, microcoil spectroscopy, and "NMR on a chip" for chemistry, biochemistry, and industry.

Since the 1960s, Nb-Ti (superconducting transition temperature T/sub c/=9 K) and Nb/sub 3/Sn (T/sub c/=18 K) have been the materials of choice for virtually all superconducting magnets. However, the prospects for the future changed dramatically in 1987 with the discovery of layered cuprate superconductors with T/sub c/ values that now extend up to about 135 K. Fabrication of useful conductors out of the cuprates has been difficult, but a first generation of silver-sheathed composite conductors based on (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (T/sub c//spl sim/110 K) has already been commercialized. Recent progress on a second generation of biaxially aligned coated conductors using the less anisotropic YBa/sub 2/Cu/sub 3/O/sub 7/ structure has been rapid, suggesting that it too might enter service in the near future. The discovery of superconductivity in MgB/sub 2/ below 39 K in 2001 has brought yet another candidate material to the large-scale applications mix. Two distinct markets for superconductor wires exist-the more classical low-temperature magnet applications such as particle accelerators, nuclear magnetic resonance and magnetic resonance imaging magnets, and plasma-containment magnets for fusion power, and the newer and potentially much larger market for electric power equipment, such as motors, generators, synchronous condensers, power transmission cables, transformers, and fault-current limiters for the electric utility grid. We review key properties and recent progress in these materials and assess their prospects for further development and application.

/pdf/superconducting-materials-for-large-scale-applications-2fd5psn19n.pdf

Superconducting materials for large scale applications

Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires is being pursued. Two specific projects are underway. The first is a user magnet with a 17 T YBCO coil set which, inside an LTS outsert, will generate a combined field of 32 T. The second is a 7 T Bi2212 demonstration coil set to be operated in a large bore resistive magnet to generate a combined magnetic field of 25 T. Owing to the substantial technological differences of the two conductor types, each project faces different conductor and magnet technology challenges. Two small coils have been tested in a 38-mm cold bore cryostat inserted in a 31 T resistive magnet: a Bi2212 round-wire layer-wound insert coil that generated 1.1 T for a total of 32.1 T and a YBCO double-pancake insert that generated 2.8 T for a total central field of 33.8 T. Four larger layer-wound coils have been manufactured and tested in a 20 T, 186-mm cold bore resistive magnet: a sizeable Bi-2212 coil and three thin large-diameter YBCO coils. The test results are discussed. The current densities and stress levels that these coils tolerate underpin our conviction that >30 T all-superconducting magnets are viable.

High Field Magnets With HTS Conductors

Recent developments in 2G HTS coil technology are presented highlighting the ability of 2G HTS wire to function under difficult operating conditions without degradation. The challenges of use in various coil constructions and applications are discussed. Several applications where the conductor is subjected to high stress levels include high field insert coils and rotating machinery. While these applications present different challenges, the ability of the conductor to operate under high stress levels has been demonstrated in both direct sample measurement and test coils. The high winding current density that is available with SuperPower's thin 2G HTS wire was utilized in a high field insert coil demonstration generating central fields in excess of 26.8 T . The ability of the wire to be tailored (stabilization, insulation, ac losses) to fit various operating parameters will also be discussed.

Recent Developments in 2G HTS Coil Technology

Development of a 1 GHz superconducting NMR magnet is in progress at the Tsukuba Magnet Laboratory (TML) of the National Research Institute for Metals (NRIM). This magnet will contain a BSCCO inner coil, which should generate a central field of 23.5 T in a backup field of 21.1 T. In order to accomplish this targeted field, we fabricated two Bi-2212 double-pancake coils (Coil A and Coil B). They were installed in the high-field superconducting magnet system at the TML/NRIM. Their performance was measured in a backup field of 18 T. Coil A was made of 20 double-pancakes wound with Ag sheathed Bi-2212 tape conductors. Ag-Mg tape was co-wound for mechanical support. Its winding was 147 mm in outer diameter and 220 mm in height. It generated a central field of 21.4 T in a clear bore of 61 mm. Coil B was located inside Coil A. Its 6 double-pancakes were wound with Bi-2212 tape conductors reinforced with Ag-Mg-Ni alloy sheath. The outer diameter and height of the winding were 48 mm and 63 mm, respectively. Coil B generated the highest field of 23.4 T in a backup field of 21.4 T. This study confirmed that the present performance of the Bi-2212 coils had already satisfied the required conditions for the inner coil of the 1 GHz NMR magnet from the viewpoint of high-field generation.

Generation of 23.4 T using two Bi-2212 insert coils

A magnet for use in a magnetic resonance imaging apparatus. The magnet includes magnetic poles and coils. The shape and positioning of the magnetic poles and coils enables provision of a uniform static magnetic field. The magnetic pole is provided with ring-shaped grooves and/or projections which compensate for axi-symmetric components of an inhomogeneous magnetic field and with partial grooves or partial projections not shaped in a ring which compensate for non-axi-symmetric components of the inhomogeneous magnetic field. Since the arrangement of the projections and grooves for compensating for the axi-symmetric and non-axi-symmetric components can also be optimized in design, a space occupied by the magnetic poles can be decreased.

Magnet, a method of adjustment of magnetic field and a magnetic resonance imaging apparatus

Stator windings for a superconducting motor with MgB2 wires are fabricated and tested. The stator windings are composed of 12 element coils in the form of a racetrack, and located in iron core slots to generate a rotating magnetic field of three phases and four poles. Preliminary estimations by means of numerical calculations with a finite element method indicate that the magnetic-flux distribution in a gap between the stator and rotor cores contains relatively significant components of fifth and seventh harmonics compared with a fundamental component. An MgB2 rotor prepared in the previous work can be rotated at a synchronous speed successfully by energizing the fabricated stator windings with a pulse width modulation inverter and compensating for the higher harmonics with a torque boost voltage.

Development of Stator Windings for Fully Superconducting Motor With $\hbox{MgB}_{2}$ Wires

A configuration of an NMR apparatus is provided. In the NMR apparatus, a magnetic field space of higher uniformity is generated by split superconducting magnets. At the same time, it is provided with a cryo probe excellent in cooling capability and sensitivity between two superconducting solenoid coils constructed in very close proximity to each other. For this purpose, a probe coil provided between the two superconducting solenoid coils is so constructed that the following is implemented: a certain distance is ensured between a substrate with a coil formed thereon and another, and the substrates and spacer substrates for cooling are alternately laminated. The spacer substrates are cooled by a cold head of sapphire. When the probe coil is inserted in the same direction as a sample tube (direction perpendicular to the static magnetic field), the spacer substrates cannot be coupled directly by the cold head of sapphire. Therefore, they are cooled through a fixed substrate for thermal conduction of sapphire coupled with the cold head.

Nuclear magnetic resonance apparatus

A probe coil for an NMR apparatus using a flexible organic polymer substrate on which a magnesium 2-boride superconductor is formed by a vacuum vapor deposition method, the organic material for the substrate containing no hydrogen atoms or containing heavy hydrogen atoms with which all or part of the hydrogen are substituted.

Tsuyoshi Wakuda

Papers

Generation of 23.4 T using two Bi-2212 insert coils

Magnet, a method of adjustment of magnetic field and a magnetic resonance imaging apparatus

Development of Stator Windings for Fully Superconducting Motor With $\hbox{MgB}_{2}$ Wires

Nuclear magnetic resonance apparatus

Superconductor probe coil for NMR apparatus