Hans Mueller

Mechanical and Magnetic Design of the Superferric Dipoles for the Super-FRS of the FAIR Project

The Superconducting FRagment Separator (SuperFRS) is a part of the Facility for Antiproton and Ion Research, a new international accelerator facility for the research with antiprotons and ions to be built in Darmstadt, Germany. The Super-FRS is a two-stage fragment separator consisting of a PreSeparator and a Main-Separator, which includes 24 superferric H-type dipole magnets with trapezoidal structure and large aperture. The dipole magnets of the separator will have a deflection radius of 12.5 m, a magnetic field of up to 1.6 T, and an effective length of more than 2 m to bend ion beams with a rigidity from 2 T · m up to 20 T · m. Two trapezoidal-shaped Nb-Ti coils will be located inside a cryostat cooled with liquid helium, but the dipole will have a warm iron yoke with a wide air trim slot. This air trim slot and four chamfered removable poles are designed to meet the required field homogeneity. This paper reports on the current status of the mechanical and magnetic design of such a dipole. The structural stability of the coil case based on 3-D finite-element analysis and the magnetic field simulations of the magnet are presented in detail.

Testing of the Superconducting Magnets for the FAIR Project

The Facility for Antiproton and Ion Research (FAIR) is currently being constructed at GSI Darmstadt. Around 500 superconducting magnets are being procured for the heavy ion synchrotron SIS100, and around 180 are being procured for the Super Fragment Separator (Super-FRS). All these magnets have to be tested at cryogenic temperature in order to verify and guarantee their performances before they are installed in the tunnel. Test stations, measurement equipment, and the required infrastructure are being built up at the host laboratory and, due to the large number of magnets and testing requirements, at CERN and JINR. We report on the plans, testing strategy, developments, and, particularly, the status of preparations for testing of the SIS100 dipoles at GSI.

Low-Temperature Test Capabilities for the Superconducting Magnets of FAIR

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.

Critical Current Distribution in Composite Superconductors

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 mu with a standard deviation sigma. 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 Nb3Sn as well as for a Bi2223 tape. A comparison will be made between measurements with and without additional copper.

A New Cryogenic Test Facility for Large and Heavy Superconducting Magnets

CERN has recently designed and constructed a new cryogenic facility for testing large and heavy superconducting magnets at liquid helium temperatures. The facility, erected in a large assembly hall with cranes capable of up to 100 t, provides a cooling capacity of 1.2 kW at 4.5 K equivalent, 15-kW LN2 cooling and warming capabilities for up to three magnets in parallel. The facility provides the required technical infrastructure for continuous and reliable operation. Test capabilities comprise electrical, cryogenics, vacuum and mechanical verification, and validation at ambient and liquid helium temperatures. A comprehensive survey and magnetic measurement system, comprising a hall-probe mapper, a rotating-coil magnetometer, a stretched wire, a translating fluxmeter, and a laser tracker, allows the detailed measurement of the magnetic field strength and quality on a large volume. The magnetic axes of the quadrupoles can be established within ± 0.2 mm at 1σ accuracy. The facility has been equipped with power supplies, three converters of ± 500 A/120 V, and six converters of ± 600 A/40 V, as well as the required energy extraction, quench protection, data acquisition, and interlocks for the testing of superconducting magnets for the FAIR project, currently under construction at the GSI Research Center, in Darmstadt, Germany. The versatile design of the facility, its layout, and testing capabilities complements CERNs other test infrastructures for large superconducting magnets. We report on the design, construction, and commissioning of the facility as well as the expected capabilities and performances for future tests of large and heavy superconducting magnets.

Design Studies for the Extraction Septa of FAIR's SIS100 Synchrotron

The system for slow extraction of the SIS100 comprises an electrostatic septum, a Lambertson septum and three final extraction septa. The latter will be treated within this paper. Due to the unusual small septum coil widths and the high magnetic field strengths required, the design of these magnets is challenging. The third magnet, for example, has to integrate a main field of 1.85 T and an auxiliary steering dipole of 0.25 T perpendicular. Additionally, all these magnets have to be removable to allow to bake out the vacuum chambers for the extracted and the circulating beam, respectively.

Design Study for the SIS 300 Main Quadrupoles

Various models for the main dipole of the SIS 300 have been manufactured by GSI and Brookhaven (GSI001), IHEP (a 1 m long 6 T model magnet currently under construction) and INFN (a 4.5 T curved magnet for the actual FODO lattice, also under construction). These different magnets reflect the design changes of the SIS 300 over the recent years. Based on the current lattice design studies for the main quadrupoles were started at GSI. In the presentation the actual status of the work on these magnets will be reviewed. Magnetic field quality, AC losses and quench protection aspects of the current design will be addressed.

Magnetic Design for the Superferric Multipole Magnets of the Super-FRS

The superconducting fragment separator (super-FRS) to be built at the Facility for Antiproton and Ion Research, GSI, Darmstadt, Germany, is a two-stage in-flight fragment separator comprising 24 superferric dipoles and 31 multiplets. In each multiplet, quadrupoles and sextupoles will be arranged together with octupoles and steering dipoles in a common cryostat. The design of all the magnets for the multiplets is completed and the first unit of the series production is under construction in the industry. During the development of the magnets, the greatest challenge was to fulfill the field quality requirement of a type 3 quadrupole with a large aperture of 380 mm and a short length of 800 mm. In this paper, the magnetic design of two main multipole magnets, the quadrupole and the sextupole, will be presented with a highlight on the design study of the type 3 quadrupole. Quench calculation results and magnetic interference when the adjacent quadrupole and sextupole are simultaneously operated are also presented.

Superferric Dipoles for the Super-FRS of the FAIR-Project

The Super conducting FRagment Separator (Super-FRS) is a part of Facility for Antiproton and Ion Research, a new international accelerator facility for the research with antiprotons and ions to be built in Darmstadt, Germany. The Super-FRS includes 24 super ferric H-type dipole magnets with trapezoidal structure and large aperture, deflection radius of 12.5 m, magnetic field of up to 1.6 T, and effective length of more than 2 m for bending ion beams (with a rigidity from 2 to 20 Tm). Two Nb-Ti coils will be located inside the cryostat in order to be cooled with liquid He, but the yoke will remain at room temperature (RT). A chamfered-pole was designed to meet the required field homogeneity. This paper reports on the status of such a dipole.