Superconducting magnets in the SIS100 particle accelerator require the supply of liquid helium and electric current. Both are transported with by-pass lines designed at Wrocław University of Technology. Bus-bars used to transfer an electric current between the sections of the accelerator will be encased in a steel shell. Eddy currents are expected to appear in the shell during fast-ramp operation of magnets. Heat generation, which should be limited in any cryogenic system, will appear in the shell. In this work the amount of heat generated is assessed depending on the geometry of an assembly of the bus-bars and the shell. Numerical and analytical calculations are described. It was found that heat generation in the shell is relatively small when compared to other sources present in the accelerator and its value strongly depends on the geometry of the shell. The distribution of eddy currents and generated heat for different geometrical options are presented. Based on the results of the calculations the optimal design is proposed.
One of the most important parameters, crucial to applications of superconductors in cryo-electrotechnique, is power loss. Measurements of losses in superconducting long sample wires require AC magnetic fields of a special geometry and appropriate high homogeneity. In the paper part of the theoretical basis for calculations and a simple design method for a race-track coil set are presented. An example of such home-made coils, with a magnetic field uniformity of about 0.2 % over the range of about 8 cm, is given. Also a simple electronic measurement system for the determination of AC magnetization loss in samples of superconducting tapes is presented.
Inductive magnetometers used for measurements in pulsed magnetic fields should have proper frequency characteristics. In the present work we describe the construction of an inductive magnetometer for measurements of the magnetic moment in pulsed magnetic fields, together with the calculation procedures for determination of its sensitivity. We present a method for determination of the effective coefficient of the coupling between the coils set (gradiometer) and cylindrical samples, as well as a method for calculation of the thermal noise in the measuring system. The determination of the effective coupling coefficient permits a straightforward connection of the value of the measured signal with the magnetic moment of the sample and calibration of the gradiometer in absolute units. In the work we also present, as examples, some experimental hysteresis loops of pulse magnetization measurements for some ferromagnetic samples and a single crystal of high temperature superconductor. The results were obtained using our homemade pulse magnet and magnetometer with a gradiometer designed and constructed on basis of presented here calculations.
In the paper we report experimental results of AC magnetization losses in a multi-filamentary BSCCO-2223 superconducting composite tape due to coaxial AC and DC magnetic fields subjected perpendicularly to the plane of the tape. Such superposition of magnetic fields usually leads to some reduction of magnetization losses. A distinguished minimum in the AC loss is observed, at a certain DC bias magnetic field and at a certain fixed magnetic field amplitude. It is shown that the minimum of the AC losses very strongly depends on magnetic history of the investigated tape, which is directly related to the magnetic flux trapping within tape's superconducting filaments region. Measurements were carried out with a sinusoidally varying magnetic fields at amplitudes up to 100 mT and a superimposed DC magnetic field up to 50 mT, at frequency range of 21-113 Hz.
The influence of the shape of voltage signals (excitation and raference) in a RF souio magnetometer, on t h e dynamics of the approach to the stationary state, in response to a jump of magnetic flux, is analysed. The reduced time required for reaching a particular final accuracy has been determined. The best combinations of signal forms, excitation and reference, capable of shortening the settling time without degradation of t h e accuracy have been found.
In the paper we present an analytical calculation method for determination of the sensitivity of a pulse field magnetometer working with a first order gradiometer. Our considerations here are especially focused on a case of magnetic moment measurements of very small samples. Derived in the work analytical equations allow for a quick estimation of the magnetometer's sensitivity and give also the way to its calibration using the sample simulation coil method. On the base of the given in the paper calculations we designed and constructed a simple homemade magnetometer and performed its sensitivity calibration.
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