Progress in Nuclear Magnetic Resonance Spectroscopy Vol. 2. Edited by J. W. Emsley, J. Feeney and L. H. Sutcliffe. Pp. vii + 269. (Oxford, London and New York: Pergamon Press, Ltd, 1967.) 90s. net. Advances in Magnetic Resonance Vol. 2. By John S. Waugh. Pp. xii + 269. (New York: Academic Press, Inc.; London: Academic Press, Inc. (London), Ltd, 1966.) $12.00. Guide to the NMR Empirical Method A Workbook. By Roy H. Bible jun.. Pp. xi + 305. (New York: Plenum Press, 1967.) $9.50.

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Nuclear Magnetic Resonance

Strong geometrical frustration in magnets leads to exotic states such as spin liquids, spin supersolids, and complex magnetic textures. SrCu2(BO3)2, a spin-1/2 Heisenberg antiferromagnet in the archetypical Shastry–Sutherland lattice, exhibits a rich spectrum of magnetization plateaus and stripe-like magnetic textures in applied fields. The structure of these plateaus is still highly controversial due to the intrinsic complexity associated with frustration and competing length scales. We discover magnetic textures in SrCu2(BO3)2 via magnetostriction and magnetocaloric measurements in fields up to 100.75 T. In addition to observing low-field fine structure with unprecedented resolution, the data also reveal lattice responses at 73.6 T and at 82 T that we attribute, using a controlled density matrix renormalization group approach, to a unanticipated 2/5 plateau and to the long-predicted 1/2 plateau.

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Magnetostriction and magnetic texture to 100.75 Tesla in frustrated SrCu$_2$(BO$_3$)$_2$

We describe the construction of a simple, compact, and cost-effective feedback system that produces flat-top field profiles in pulsed magnetic fields. This system is designed for use in conjunction with a typical capacitor-bank driven pulsed magnet and was tested using a 60-T pulsed magnet. With the developed feedback controller, we have demonstrated flat-top magnetic fields as high as 60.64 T with an excellent field stability of ±0.005 T. The result indicates that the flat-top pulsed magnetic field produced features high field stability and an accessible field strength. These features make this system useful for improving the resolution of data with signal averaging.

Generation of flat-top pulsed magnetic fields with feedback control approach

This study presents a novel multistructure power converter capable of generating high current pulses with short rise and fall times, and high precision in the flat-top. The proposed topology is based on the use of three conversion structures operated with current, voltage and switching frequency ratings in line with the different requirements of each pulse stage. In order to achieve the required precision, a switched-mode compensation structure in series with the load is used. Though this structure must handle a high load current, it is designed to deviate most of the load current to an auxiliary inductor; thus reducing the semiconductor devices requirements. Moreover, the use of this compensation strategy results in a first-order model of the circuit, which leads to an oscillation-free response during structures interconnection. This feature minimizes the required flat-top time, which in turn decreases the power losses on the load. Experimental results based on a scaled-down laboratory prototype validate the capability of the proposed topology to produce current pulses according to the specifications of high-precision applications.

Multistructure Power Converter With H-Bridge Series Regulator Suitable for High-Current High-Precision-Pulsed Current Source

A bipolar pulse current source is proposed for a highly inductive load. The current source exploits a noninductive capacitor to store or release the energy back to and from inductive load during switching on or off of power inverter. A boost module is designed at the dc side of inverter to supplement the required energy gap so that edge steepness of the load current can be improved. The capacitor and boost elements are configured based on the analysis of capacitor impact on the load current and boost inductor current. The stability of load current can be guaranteed by the multiple driving pulses generated from closed-loop control of boost switch, regardless of load changes or initial pulse width offset. An experiment prototype is built to generate a flat-top 20 A current with the 200 μs rise/fall time for an inductive load of 2 mH or higher. Due to the steep rising and falling edges, the inductive load can realize high-frequency pulse currents. Moreover, the steep pulse current source can excite strong magnetic field, which make it especially useful for the inductive coils of high-power geophysical transient electromagnetic method (TEM) transmitter.

Bipolar Steep Pulse Current Source for Highly Inductive Load

A high stability flat-top pulsed magnetic field has both high field strength and high field stability simultaneously, which can be used for the high precision scientific experiments. In this paper, we present such a high stability flat-top pulsed magnetic field facility developed in the Wuhan National High Magnetic Field Center. A passive bypass circuit is developed to regulate current up to tens of thousands amperes, as well as a 25 T/200 ms flat-top pulsed magnetic field with a ripple of 250 ppm (0.025%). The main circuit scheme of the facility as well as the preliminary experimental results will be presented in this paper.

Fei Hu

Papers

Development of a High-Stability Flat-Top Pulsed Magnetic Field Facility