M. Kläser

Manufacture and test of a 5 T bi-2223 insert coil

With the goal of obtaining a magnetic field of 25 T in our facility HOMER II with a superconducting LTS-HTS hybrid magnet, a first prototype 5 T high temperature superconducting (HTS) insert coil has been constructed and tested. The HTS insert consists of 16 double pancakes made of stainless steel reinforced Bi-2223 tapes manufactured by American Superconductor. The HTS coil was operated at 1.8 K and produced 5.4 T at a current of 151.2 A. In a background field of 11.5 T provided by our facility HOMER I, a total field of 16.9 T was obtained several times. No training or quench of the coil was observed during the test, but after warming up a defect in the winding of one double pancake was detected, presumably due to a ballooning of the tape. The design of the coil and the results of the test are presented and discussed.

Superconducting High Field Magnet Engineering at KIT

For over thirty years superconducting high field solenoid coils have been designed, constructed and operated in the High Magnetic Field Laboratory at the Karlsruhe Institute of Technology (KIT). During this time, three generations of experimental facilities have been built and commissioned to routine operation. Using metallic superconductors commercially available at the time, designs were created that enabled maximum field strengths to be achieved within specified boundary conditions. The latest facility is HOMER II, which is unique in its ability to generate a magnetic field strength of 20 T within a free bore of 185 mm. In this article various configurations of the facilities and their physical parameters are presented. Emphasis is placed on the experimental facility HOMER II including its cryogenic system, quench detection and analysis, as well as its protection concept.

Degradation of Bi-2223 Tape After Cooling With Superfluid Helium

Future superconducting magnets for fields of 25 T and above have to be composed of LTS-HTS hybrid coil systems. To obtain a higher field contribution and for reasons of stability, the outer low temperature superconducting (LTS) magnet section is cooled particularly with superfluid helium. In the classical set-up, the high temperature superconducting (HTS) insert is assembled together with the LTS outsert in a common bath, i.e. in our case it is cooled with superfluid helium. Our first 5 T Bi-2223 prototype insert coil was successfully operated and produced 5.4 T in a background field of 11.5 T. After warming up, ballooning was observed in the tape apparently caused by the penetration of superfluid helium. In this paper we investigate the impact of superfluid helium on the superconducting properties of the Bi-2223 tape used for our HTS insert. In particular, the voltage-current relation, U(I), is examined. It is shown that the resulting critical current and the n-value, which is a differential variable, are not adequate to describe the widely degraded U(I)- curves. In addition, we suggest the use of an integral method. The measurement results and the interpretation of the U(I)-curves are presented and discussed.

Usage of Bi-HTS in high field magnets

At present, superconducting high field magnets built up of metallic low temperature superconductors (LTS) like NbTi and ternary/quaternary Nb/sub 3/Sn is near to the upper limit of achievable field strength. Fields above approx. 23 T seem to be only reachable with LTS-HTS hybrid configurations consisting of an outer LTS section and a high temperature superconductor (HTS) insert. Commercially available Bi-HTS wires were investigated for their application in high field facilities like the HOMER II system with the goal of 25 T and in new generations of NMR magnets of 1000 MHz and above. Therefore the superconducting properties of the HTS wires were examined at 4.2 K in magnetic fields up to 10 T. The voltage-current relation was examined resistively using a high resolution four-point measurement technique. The dependence of the critical current and the n-value on the winding diameter, on the field alteration (increasing/decreasing), and on the field orientation to the wire is presented and discussed.

Superconducting In-Vacuum Undulators

During the last years the Research Center Karlsruhe developed novel high-field superconducting in-vacuum undulators with period lengths of 3.8 and 14 mm. The undulators were tested with beam, both in linac type accelerators (Mainzer Microtron MAMI) and storage rings (ANKA). Based on this experience a new generation of superconducting undulators is planned: undulators capable of electrical field error compensation, undulators with electrically variable polarization direction and high brilliance for various accelerators

Technical Report: First Beam Tests of a Superconductive Undulator in a Storage Ring at ANKA

In 2005 a test superconductive undulator was installed in the ANKA storage ring. Since then the undulator has been constantly in operation as the first cold-bore, small-gap superconducting undulator ever installed in a storage ring. The aim of this experiment was to demonstrate that such a device can be operated under normal user conditions. Compared with permanent magnet undulators, superconducting undulators have a higher magnetic field strength (for a given period length and a given gap width) and can be tuned electrically. The higher field strength allows the production of photon beams with higher brilliance and higher photon energy.

One Year Operation of a Superconductive Undulator in the Storage Ring ANKA

In spring 2005 the worldwide first cold‐bore superconductive undulator was installed in the storage ring ANKA. In this paper the obtained results concerning the measured spectra and the heat load from the beam are described. Future developments in the field on superconductive undulators at ANKA are summarized.