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It has long been known that for the description of the E(I)-characteristics of composite superconductors a distribution function can be used instead of a power law relation. With this approach, the conductor is represented by a serial connection of short subsections where the electrical resistance of each subsection is given by a parallel connection of the flux flow resistance of the superconductor and the resistance of the normal conducting matrix. Furthermore the local critical currents are assumed to be normally distributed around a mean value with a standard deviation . If the local critical current in a subsection is exceeded a voltage is generated. The current distribution function is then given by the second derivative of the E (I)-characteristics divided by R/L with R being the overall resistance and L the measuring length. In general only the lower part of the distribution function is apparent. By soldering the conductor in a copper bar the whole distribution can be made visible. In this paper we will give examples of the suitability of the description with Gaussian distribution functions for the low temperature superconductors NbTi and Nb 3 Sn as well as for a Bi2223 tape. A comparison will be made between measurements with and without additional copper.

Testing the different superconducting magnets for the Facility for Antiproton and Ion Research requires testing capabilities beyond the necessities of dc superconducting magnets: stable power converters with fast cycles, capabilities for measuring the loss, and abilities to measure the field on the ramp for the magnets of the heavy-ion synchrotron SIS100. On the other hand, the Super Fragment Separator (Super-FRS) magnets are of large aperture and large size. The high-current design of the SIS100 main dipole and quadrupole magnets necessitated upgrading the power converter, the current leads, and different measurement systems. Facilities are being built or refurbished for measuring the SIS100 quadrupole units and the Super-FRS magnets. We describe the abilities of these facilities and the status of preparation. The upgrade of the existing facility at GSI has been completed. We present the performance of the main systems and their accuracies based on the measurements made for the SIS100 dipole.Index Terms-Magnetic field measurement, test facilities.

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