I. Stolpe

Megagauss magnetic field generation in single-turn coils: new frontiers for scientific experiments

We report on the design and performance of a megagauss generator at the Humboldt High Magnetic Field Centre. The installation uses the fast capacitor discharge into single-turn coils to produce microsecond pulses of 260 T in 8 mm diameter suitable for low-temperature experiments and 310 T in 5 mm diameter. Simple concepts are applied to substantiate crucial design principles for the generator and the choice of components. The implementation of a high-power/low-inductance circuit operated at 60 kV and other technical questions are discussed in detail. The analysis of experimental field and current data is based on numerical simulations of the magnetic pressure and the nonlinear flux diffusion. It was carried out in order to investigate the limitations and characteristics of the Berlin generator in particular and the single-turn coil technique in general. The paper focuses primarily on field, generator and coil parameters, which can be used for performing routine, reproducible scientific experiments at low temperatures.

The design and performance of a transportable low-cost instrument for the generation and application of megagauss fields

A small megagauss generator which produces 110 T by fast semi-destructive capacitor discharge into a single-turn coil of 10 mm diameter is described. For spectroscopic applications the pulses are adequately resolved by 8 - 12 bit, 200 - 1000 MSa data recording systems. The technical implementation of the 60 kV discharge circuit with a total inductance of less than 26 nH, not including the field coil, is discussed in detail. The performance is characterized in terms of the oscillatory circuit parameters R, L and C with brief references to more fundamental studies on transient field phenomena. Safety features as well as the organization and handling of control units and data recording systems are explicitly described to demonstrate the applicability of the generator.

Magneto-optical investigations on cubic GaN in high magnetic fields

Abstract We report on direct IR–cyclotron resonance (CR) spectra of p-type cubic GaN (c-GaN) using semidestructive single-turn coil megagauss field generation. Two strong temperature dependent CR transitions were detected using measurement techniques with optimized signal to noise ratio resolving transmission changes smaller then 2%. On the basis of group theoretical relations between the valence-band energy-parameters of the effective Rashba–Sheka–Pikus Hamiltonian for the wurtzite and the effective Kohn–Luttinger Hamiltonian for the zincblende structure the Landau level scheme was calculated for c-GaN and compared with the observed transitions.

Solid state applications of a transportable low-cost megagauss generator

A table-top megagauss generator, employing the single-turn coil technique has successfully been applied in solid state physics. Magnetic fields up to 113 T are generated within a useful volume of about 1 cm 3 . A detailed description of techniques for high-quality field measurements under the conditions of a short time duration and the presence of strong transient electric disturbances during the field generation is given. Faraday rotation in CdS as well as cyclotron resonance experiments in n-type PbSe are presented as examples of the efficiency of the generator as a scientific instrument.

HIGH SENSITIVITY MEGAGAUSS SPECTROSCOPY

The present paper describes unique experimental techniques developed for minimizing disturbances due to transient electromagnetic fields during a capacitor discharge into a small single turn coil, generating magnetic fields above the megagauss limit. Results of cyclotron resonance measurements are presented as example of the capability of the experimental set-up to resolve transmission changes being smaller than one percent.

IR cyclotron resonance of solid states in magnetic fields up to 700 tesla

We report on the first successful IR-cyclotron resonance experiment in ultrahigh magnetic fields up to 700 T generated by explosive driven flux compression. The sample under investigation was an epitaxially grown p-type cubic GaN-layer, a material which has become worldwide the subject of extensive experimental and theoretical investigations because of its application in optoelectronic devices operating in the blue-to-violet wavelength range. Three distinct transmission minima at about 90 T, 270 T and 400 T-430 T with a resonance depth of a few percent only, are clearly resolved. The data in the lower field region correspond excellently to results derived previously from experiments in fields up to 275 T generated by use of the single-turn coil technique.

IR-magnetospectroscopy on mercury selenide in ultra high magnetic fields

We report on magnetospectroscopy investigations on HgSe in the infrared wavelength range using very high pulsed magnetic fields. We have observed interband transitions as well as the cyclotron resonance (CR) of quasi free electrons. Transient effects in the resonance intensities are due to hysteresis effects in the spin dependent population and provide a novel tool for the determination of the spin-lattice relaxation time.