Luc Van Bockstal

Strength versus conductivity

Abstract In the development of conductors for high-field coils one has to find a compromise between high strenght (to withstand the Lorentz force) and high conductivity (longer pulse time, minimal power, energy and volume required). The design of coils is a non-linear process that is partly based on educated guesses guided by trial and error. Based on the concept of the “current carrying capability” a simple scheme for optimal choice of wire for the relatively simple cases of energy limited coils (or the innermost parts of power limited coils) is developed. On basis of this criterion, the optimal direction of research on new wires or materials is determined.

Experimental techniques for pulsed magnetic fields

Abstract Recent developments at the K.U. Leuven pulsed field laboratory are reviewed. This includes new 60 T user magnets, pulse shaping, decentralized data recording for multiple experiments, low temperature cryogenics, vibration damping, rotatable sample holders and sensitive magnetization measurements. Experimental results (on semiconductors, super-conductors and organic conductors) are shown to illustrate the improvements in the experimental techniques.

The K.U. Leuven pulsed high magnetic field facility

Abstract The pulsed field installation at the K.U. Leuven is upgraded for the development and use of the new generation of high performance coils with peak fields in the 60–70 T range. New equipment includes an improved coil winding installation, capacitor bank switchgear and electrical diagnostics to enable the running of two experiments in parallel, new cryostats for stabilized temperatures in the 300–0.4 K range, sample holders whixh permit rotation of the sample, and facilities for sample preparation.

Coppersilver wire coils for pulsed magnet

Abstract A newly developed Cu-16 at % Ag alloy wire was evaluated by using it to wind multilayered coils for pulsed magnets with different bore diameters, with and without internal reinforcement by glass fiber composites. These magnets have a long pulse duration in the range 5–10ms. A peak field of 62.7 T was obtained in 15 mm bore of a coil without internal reinforcement but enclosed in an outer metal case. A magnet with optimized layer by layer reinforcement succeeded in generating 73.4 T in the 10 mm bore. It was thus established that this wire is highly promising for the construction of high performance pulsed magnets.

The pulsed field installation at the K.U. Leuven

Abstract The pulsed field laboratory at the University of Leuven is described. The power is obtained from two 500-kJ capacitor banks, one at 5/10 kV (convertible) and one at 10 kV. Instrumentation is avvailable for sensitive electrical measurements and experiments with far infrared radiation.

FIR paramagnetic resonance in high-Tc superconductors

Abstract We measured the far infrared (FIR) resonance absorption from the paramagnetic Gd3+ ion in GdBa2Cu3O7-δ. The g-factor is found to be 2.00. The lineshape shows a broadening at lower temperatures. This indicates that the linewidth contains contributions other than the dipolar interaction.

Switching of a 0.5-MJ capacitor bank with thyristors at surge ratings

Abstract The design of a thyristor switch for a 500-kj, 5-kV capcitor bank is described. Four optically triggered high power thyristors are connected in series-parallel, with protection against overload. They are used repeatedly ar surge ratings in single shot operation.

A non-destructive approach to 100 T

Abstract Based on the existing technology of magnets with internal reinforcement, several designs are discussed to illustrate different routes for obtaining 100 T. The theoretical basis for the behaviour of these magnets is presented, and two designs are worked out in detail: one using glass fibre and soft copper, the other using a strong conductor and stiff reinforcement. These monolithic magnets are capable of generating long pulses and because they require a high power, they are well suited to be driven by a capacitor bank.

The performance of high-field magnets with optimized internal reinforcement

For the performance analysis of pulsed high-field magnets with internal reinforcement, analytical equations are derived for the optimum distribution of the reinforcement in long coils without external reinforcement. Among others, the relation between the stress in the reinforcement, the obtainable magnetic field and the filling factor of the conductor are established. By adjusting the amount of reinforcement for each layer of conductor, optimal use is made of the material strength. Therefore, this type of magnet is a good candidate for obtaining high magnetic fields up to 100 T. Moreover, it is shown that these magnets give the longest pulse duration when used in combination with an energy-limited high-power pulsed energy source.

Long duration pulsed magnetic fields: Achievements and challenges

Abstract The design and use of capacitor-driven pulsed magnets with wire-wound coils are reviewed. Magnet design is governed by two basic factors: the pulse duration which depends on the mass of the coil and the available energy; the peak field which depends on the mechanical strength of building materials and on the geometry. Options for the design of future high performance magnets are discussed. These magnets are characterized by a relatively small bore (10–20 mm) and limited pulse duration (typically 10 ms). It has been established that most solid state experiments can be successfully conducted under these conditions, at temperatures down into the millikelvin range.