High Field Research Research Articles

Unveiling new quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2 up to the saturation magnetic field

Under magnetic fields, quantum magnets often undergo exotic phase transitions with various kinds of order. The discovery of a sequence of fractional magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has played a central role in the high-field research on quantum materials, but so far this system could only be probed up to half the saturation value of the magnetization. Here, we report the first experimental and theoretical investigation of this compound up to the saturation magnetic field of 140 T and beyond. Using ultrasound and magnetostriction techniques combined with extensive tensor-network calculations (iPEPS), several spin-supersolid phases are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease of -50%, related to the tetragonal-to-orthorhombic instability of the checkerboard-type magnon crystal. The unveiled nature of this paradigmatic quantum system is a new milestone for exploring exotic quantum states of matter emerging in extreme conditions.

Redesign of the Coils for the 60T Controlled-Waveform Magnet at NHMFL

Driven by the1.4 GW generator, the 60T Controlled Waveform (60 TCW) magnet was the most powerful controlled waveform system in the world and had always been one of most important magnets to the National High Magnetic Field (NHMFL) and high-field research community because of its following unique features: (1) quasi-static field up to 60 T with 100 ms flat-top and total pulse-length of about 2000 ms, (2) variable magnetic field waveforms such as staircase and triangle with flat-top (3) relative large bore (32 mm) and (4) very fast cooling time (20 minutes) between pulses [Boebinger, 2001], [Crooker <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> 2001]. The magnet is composed of nine concentric coils, with each coil consisting of several conductor winding layers reinforced by a high-strength metallic shell. The magnet underwent a catastrophic failure in 2000 and all the coils had to be rebuilt. In late 2014 the second magnet version failed near the mid-plane of coil 7. The simulations afterward that incident indicated that the overall strength of the coil would be increased by replacing a section of the reinforcing shell with Zylon fiber-epoxy composite. This reduces the stress and thus significantly lowers the level of plastic deformation in the windings. The role of the metal and Zylon fiber reinforcing layers in bearing the axial and radial Lorentz forces has been studied to optimize the magnet design. The results of the optimization will be discussed as well as challenges that have been presented in rebuilding the individual coils of the magnet.

Intervertebral disc internal deformation measured by displacements under applied loading with MRI at 3T

Noninvasive assessment of tissue mechanical behavior could enable insights into tissue function in healthy and diseased conditions and permit the development of effective tissue repair treatments. Measurement of displacements under applied loading with MRI (dualMRI) has the potential for such biomechanical characterization on a clinical MRI system. dualMRI was translated from high-field research systems to a 3T clinical system. Precision was calculated using repeated tests of a silicone phantom. dualMRI was demonstrated by visualizing displacements and strains in an intervertebral disc and compared to T2 measured during cyclic loading. The displacement and strain precisions were 24 µm and 0.3% strain, respectively, under the imaging parameters used in this study. Displacements and strains were measured within the intervertebral disc, but no correlations were found with the T2 values. The translation of dualMRI to a 3T system unveils the potential for in vivo studies in a myriad of tissue and organ systems. Because of the importance of mechanical behavior to the function of a variety of tissues, it's expected that dualMRI implemented on a clinical system will be a powerful tool in assessing the interlinked roles of structure, mechanics, and function in both healthy and diseased tissues.

A Study on the Weak Signal Detection System Applied to the High Field Research Based on the Digital Lock-In Technique and Wavelet Filter

An improved digital lock-in technique with a wavelet filter is developed for the weak signals detection. A simulated signal modulated with a frequency of 40 kHz and contaminated by white noise is constructed to estimate the performance of the system. In this study, the selection of the wavelet filter parameters, such as the decomposition level, the wavelet basis and the threshold strategy is discussed. Finally, the performance of the system in different conditions is presented.

Tohoku High Magnetic Field Research Activities Using Cryogen-Free Superconducting Magnets

In order to realize a hybrid magnet with no need of liquid helium for operation, we have designed a 28 T cryogen-free hybrid magnet with a 32 mm room temperature experimental bore, and actually tested to generate the peak field of 27.5 T. An easy-to-operate cryogen-free hybrid magnet is now operating for basic research in high fields up to 27 T at low temperatures down to 40 mK, using a dilution refrigerator. In addition, we are intending to develop a 100 mm wide bore water-cooled resistive insert magnet combined with a cryogen-free superconducting outsert magnet for X-ray diffraction measurements in steady magnetic fields up to 20 T.

High T/sub c/ insert coils for high field superconducting magnets-the Oxford programme

We describe an industry/university collaboration to develop high temperature superconducting insert coils for use in the next generation of high-field research magnets. Using BSCCO-2212 dip-coat tape on thin silver substrate and a wind, react and tighten (WRAT) technique we have achieved extremely high engineering current densities in excess of 150 A/mm/sup 2/. We describe our latest results, discuss some of the problems with the WRAT method and briefly describe a project to build a high T/sub c/ SMES magnet.

Design and operation of a 40-MW, highly stabilized power supply

Four 10 MW highly stabilized power supply modules have been installed at the National High Magnetic Field Laboratory in Tallahassee, FL, to energize water-cooled resistive high-field research magnets. The power supply modules achieve a long-term current stability of 10 ppm over a 12-h period with a short-term ripple and noise variation of <10 ppm over a time period of one cycle. The power supply modules can operate independently, feeding four separate magnets, or two, three, or four modules can operate in parallel. Each power supply module consists of a 12.5-kV vacuum circuit breaker, two three-winding step-down transformers, a 24-pulse rectifier with interphase reactors, and a passive and an active filter. Two different transformer tap settings allow rated DC supply output voltages of 400 and 500 V. The rated current of a supply module is 17 kA and each supply module has a one-hour overload capability of 20 kA. The isolated output terminals of each power supply module are connected to a reversing switch. An extensive high-current bus system allows the modules to be connected to 16 magnet cells. This paper presents the detailed design of the power supply components. Various test results taken during the commissioning phase with a 10 MW resistive load and results taken with the research magnets are shown. The effects of the modules on the electrical supply system and the operational behavior of the power factor correction/harmonic filters are described. Also included are results of a power supply module feeding a superconducting magnet during quench propagation tests.

The national high magnetic field laboratory: A new facility in support of high field research - DC facility in Tallhassee

The National High Magnetic Field Laboratory facility in Tallahassee, FL will offer to both national and international users magnets (superconducting magnets up to 20 T, resistive magnets up to 35/40 T, and hybrid magnets up to 45/50 T) in a variety of configurations. Additional specialized magnet systems to support NMR (720/900/1000 MHz), ion cyclotron resonance (up to 12 T, 150 mm) and electron spin resonance studies at high fields will be installed. Major subfacilities for high field research in infrared optics, visible optics, magnetic properties of solids, and low-temperature studies are being developed.

Science and Techniques Using Pulsed Magnetic Fields

In this article, we examine materials behavior in the magnetic field region from about 40 T to 500 T using pulsed magnet technology. Examples of materials science using two different pulsed magnet technologies are described in this article.Semicontinuous MagnetsSince the late 1960s, the University of Amsterdam has operated a semicontinuous magnetic field installation that produces magnetic fields up to 40 T with typical time constants of about one second. The magnet coil is constructed from hard-drawn copper wire with a reinforcement cylinder of maraging steel positioned at roughly one third of the outer diameter. Before operation, the coil is cooled to 30 K by cold neon gas. The power for this installation is taken directly from a 10 kV connection to the public electricity grid. By means of a thyristor-based power control system, highly flexible field-time profiles can be realized: step-wise pulses can be generated with field levels constant within 10−4 during 100 ms; linearly increasing and decreasing fields as well as exponentially ripple-free decreasing fields are other examples of standard field-time profiles. Among the measuring techniques frequently used are magnetization, magneto-transport, quantum oscillations, relaxation phenomena, etc. Temperatures at which experiments can be performed range from 400 mK to room temperature. In the Netherlands, the Amsterdam High Field Facility has recently been combined with the High Magnetic Field Laboratory in Nijmegen, where static magnetic fields up to 30 T are produced in hybrid magnet systems, to form the Amsterdam-Nijmegen Magnet Laboratory (ANML). The high field research of ANML comprises semiconductors, magnetism in transition-metal compounds, heavy-fermion physics, superconductors, organic conductors, and magnetic separation. We present here a few selected topics.

High-field facilities under development and construction at the National Research Institute for Metals, Japan

Construction of a new high-field research center is in progress at NRIM, Japan. We are developing and constructing many high-field facilities for the research center, which include a 40 T class hybrid magnet, a 20 T class superconducting magnet with large bore, a 80 T class long-pulsed magnet, and several kinds of small superconducting magnets. The present design concept for the hybrid magnet includes a 15 T superconducting magnet with a room-temperature clear bore of 400 mm and a 25 T polyhelix-type water-cooled resistive magnet with a clear bore of 30 mm. The detailed design of the superconducting magnet and the fabrication of the water-cooled magnet are progressing. Recently the middle and outer coils of the 20 T class superconducting magnet have been completed and have successfully generated 18.1 T in a clear bore of 160 mm. We have constructed a 1.6 MJ capacitor bank system as a power source of the long-pulsed magnet. We are now developing the pulsed magnet, and have found that Cu-Ag alloys are very interesting conductor materials because of their high mechanical strength.

High magnetic-field facilities: Opportunities in research and technology (invited)

Recently the NSF Division of Materials Research Panel on Large Magnetic Fields concluded that the opportunities for research and technology in high magnetic fields are compelling for support of a new national magnet laboratory with the following components as goals: (i) dc hybrid magnet facilities (water-cooled magnets surrounded by superconducting magnets) of at least 45 T; (ii) state-of-the-art superconducting magnets and NMR magnet facilities greater than 25 T; (iii) intense pulsed magnet facilities for ms to 75 T and above; (iv) short pulsed magnets for μs intervals to 200 T; (v) a variety of water-cooled magnets reaching 25 T; and (vi) quasistatic magnets for transient fields of 0.5 s or more up to 65 T. A 20-MW highly regulated solid-state power supply is central for the dc magnets and separate pulsed power sources are required for the pulsed facilities. This paper outlines the main conclusions of the panel report and discusses some of the opportunities for high-field research and technology. Active overseas high magnetic facilities also are outlined.

High-field research in China

In China there are several laboratories which have pulsed magnetic fields up to 30–40 T. A study of 50 T pulsed magnets has been carried out. A hybrid-magnet project to obtain steady fields up to 20 T is also being carried out. In various laboratories, research on high-field magnetization processes, anistropy of rare-earth compounds, magnetophonon resonance of two-dimensional electron systems and the high-field properties of superconducting materials is performed.

700mm diameter cryostat operating at 1.8 K and atmospheric pressure

Two devices operational with Teslas NbTi coils have been built in order to undertake developmental programmes in superconducting magnets for fusion and high field research. The inner bore for experiments is in the 300 mm range. This paper describes the cryostat system which enables superfluid helium at 1.8 K and atmospheric pressure to be used. Some constructional details concerning the main components are given. The result of the cryogenics tests are finally presented: a fully automated operation at 1.8 K with a rather small standard pump and a liquid helium consumption less than 4 lh -t-1 fed at 4.2 K.