Egbert Fischer

Design of new hollow superconducting NbTi cables for fast cycling synchrotron magnets

Two new options for a hollow NbTi superconducting cable were considered. The first one is based on keystoned wires wrapped around a copper-nickel tube 5 mm in diameter. The second one is a hollow cable of rectangular cross section. The data from cable short sample tests are presented. Some problems with the production technology are discussed. This work is part of the R&D for the Future Accelerator Facility, at GSI in Darmstadt.

Fast Ramped Superferric Prototypes and Conclusions for the Final Design of the SIS 100 Main Magnets

The 100 Tm synchrotron SIS 100 is the core component of the Facility of Antiproton and Ion Research (FAIR). An intensive R&D allowed reducing the AC losses considerably as well as improving the field quality. High priority was also given to the investigation of the mechanical stability of the superconducting coil to guarantee a long term life time of at least 20 years with more than 2middot108 operation cycles and to position the cable windings precisely. Prototype magnets were built last year with the first dipole magnet completed by Babcock Noell GmbH and currently being under preparation for intensive testing. After a brief description of the main R&D results the key features of three full scale dipoles and a quadrupole prototype are given as well as the expected heat load at 4 K for the 3 m long dipoles for the most important operation modes requested for the SIS100 accelerator. During prototyping additional, more intensive operation cycles were requested by beam dynamics and more cooling power by the vacuum requirements. The consequences for the cooling stability of the dipoles were estimated and preliminary tested on a hydraulic equivalent magnet system and will be verified by the upcoming measurements of the full size models. Necessary modifications for the series production are discussed and the actual chosen SIS100 dipole design fulfilling also the additional operation requirements is outlined.

3-D Transient Process Calculations For Fast Cycling Superferric Accelerator Magnets

Fast cycling superferric magnets are planned for use in the new International Accelerator Facility for Antiprotons and Ion Research (FAIR) at GSI, Darmstadt. The efficiency of this magnet is basically defined by the AC loss at liquid helium temperatures in the construction elements of the dipoles and quadrupoles (iron yoke, coil, beam pipe restraints and suspension). A detailed knowledge of the 3D magnetic field, the eddy current distributions and their transient behavior is necessary to minimize the hysteresis and the eddy current losses through the use of an appropriate design. Methodical problems are considered for finite element calculations (ANSYS) of eddy currents in a laminated iron yoke. The results for window-frame dipoles and quadrupoles of the Nuclotron type are given. We present the influence of nonlinear and anisotropic magnetic and electrical properties of laminated steel and of bulk restraint elements

Some aspects of cable design for fast cycling superconducting synchrotron magnets

The worlds experience in application and manufacturing of superconducting cables for fast cycling synchrotrons (operating frequency f = 1 Hz) is limited up to now to a hollow multifilament NbTi cable cooled with two-phase helium flow. The cable of 7 mm in diameter has critical current of 8400 A at B = 2.5 T and dB/dt = 4 T/s. The degradation of critical current does not exceed 10% up to dB/dt = 8 T/s. The cable was designed and has been used for the magnets of the Nuclotron superconducting synchrotron at JINR in Dubna. The recent R&D was motivated by the new project of a superconducting synchrotron SIS100 at GSI in Darmstadt. Besides the basic option, i.e., the present Nuclotron-type cable, other design options are proposed. Their suitability for application in the conditions specified for the SIS 100 are considered. The improved characteristics of the Nuclotron-type cable and the magnet coil parameters are also presented.

Magnetic Field Analysis for Superferric Accelerator Magnets Using Elliptic Multipoles and Its Advantages

The Facility for Antiproton and Ion Research (FAIR) will build a set of accelerators and storage rings at the Gesellschaft fur Schwerionforschung (GSI). Nearly all of them transport beams of elliptical shape (SIS 100, CR, NESR, RESR, SuperFRS). Magnetic field calculations as well as magnetic measurements provide precise field information, which is used to improve the properties of the machines using numerical simulations. In this report we develop elliptical multipoles fulfilling the Laplace equation which enable us to describe the field within the whole aperture consistently. Further we show how circular multipoles valid within the elliptic aperture can be derived. We illustrate the advantage of this data representation on the FEM calculations performed during the SIS 100 R&D along with an approach to measure such fields using rotating coils and estimate the influence of measurement artifacts.

Superferric model dipole magnet with the yoke at 80 K for the GSI future fast cycling synchrotron

Experimental data of a fast cycling (f=1 Hz) 2T dipole magnet based on a superconducting NbTi multi filament hollow cable cooled with forced two phase helium flow at T=4.5K and iron yoke at T=80 K are presented. A new magnet design is proposed. The magnet yoke made of laminated steel consists of two parts: the internal smaller part has close mechanical and thermal contact with the coil while the outer part is separated from the cold mass with a gap of 1 mm and cooled with liquid nitrogen.

Full Size Model Magnets for the FAIR SIS100 Synchrotron

The planned FAIR synchrotron SIS100 has to deliver high intensity beams. Following the JINR Nuclotron, GSI has chosen to build this machine using fast-cycling 4 T/s, 2 T superferric magnets. Cycle repetition rates of about 1 Hz cause high AC power losses in the magnet components. Eddy currents deteriorate the field quality. After millions of operation cycles and high radiation flux the coil support structure can loose mechanical stability. Therefore these effects were analyzed to warrant the magnets performance over its lifetime. Following intensive experimental and computational investigations on short test models three full size dipoles and a 1.2 m long quadrupole with a maximum field gradient of 27 T/m in the aperture of 135 mm 65 mm will be manufactured until the end of 2007. Two of the dipoles are straight 2.7 m long 2.1 T magnets with a beam aperture of 130 mm 60 mm (width x height), while the third one is a curved 1.9 T dipole 3.0 m long with a reduced horizontal aperture of 115 mm. All the models use a superconducting hollow NbTi/Cu composite cable cooled with two-phase helium flow. The main design features and estimated operation parameters are given. In parallel preliminary tests of a 2.8 m SIS100 equivalent dipole system was performed. The cooling stability of the system at different SIS100 operation cycles was checked experimentally for the first time. These results are discussed as well as possible design options to fulfil additional operation requirements.

New Design for the SIS100/300 Magnet Cooling

Two superconducting synchrotrons, SIS100 and SIS300, are planned for the new International Accelerator Facility of Antiprotons and Heavy Ions (FAIR) at GSI, Darmstadt. These accelerator rings, operating at liquid helium temperatures, are placed in one tunnel of 1100 m length. The SIS100 structural superferric dipoles and quadrupoles are based on the Nuclotron-type hollow NbTi composite multi wire cable and cooled in parallel with two-phase helium flows. The peak operating mode for the SIS100 dipoles corresponds to Bmax=2 T, dB/dt=4 T/s, f=1 Hz. Fast-ramped dipoles ( dB/dtap1 T/s, fap0.05 Hz) with a field strength of 4 T and above are required for the SIS300 ring. A 4.5 T, costhetas-style, curved magnet with a coil made of a high current hollow cable cooled with two-phase helium flow is proposed for SIS300. The necessary modifications of the magnet cooling scheme are presented and discussed. General optimization of the SIS100/300 cryogenic system namely cooling with three refrigerators, the number of parallel channels, the length of helium transfer lines, and a closed nitrogen loop for the heat shield cooling is considered. The new design will make it possible to reduce the FAIR project cost

Investigation of the power losses in a laminated dipole magnet with superconducting coils

Dynamic processes in a window-frame dipole with superconducting windings and a cold, laminated iron yoke have been investigated experimentally at JINR (Dubna, Russia), and theoretically at GSI (Darmstadt, Germany). The main aim of these investigations was a reduction of energy losses in the yoke during ramping. These losses are produced mainly by energy dissipation due to eddy currents and hysteresis effects in the laminations. Both effects were investigated theoretically. As a result, special end blocks were proposed to reduce eddy current losses. For eddy currents simulation we used a model developed at GSI and St. Petersburg State Polytechnical University (Russia). This model is based on an integro-differential approach to eddy currents in laminated structures and a volume integral method for the magnetization vector in ferromagnetic objects. To test this model, a series of experiments were performed at GSI on a normal conducting Heavy Ion Synchrotron dipole magnet. The magnetic field in the aperture of this magnet was controlled with a point coil during the current ramping in the winding. The same transient processes were simulated using software, developed on the basis of the integro-differential method. The theoretical calculations were in reasonable agreement with the measurements.

Superconducting SIS100 Prototype Magnets Test Results and Final Design Issues

The SIS 100 synchrotron is based on Nuclotron type superconducting magnets. These are operated with 4 T/s up to a maximum field of 2 Tesla (dipoles). Based on the experience of the R&D period three full scale dipoles as well as one quadrupole were built. The first dipole was tested intensively this year. We present the operation performance of the first magnet next to the AC losses and apply a concise description of the magnetic field within the complete elliptical beam pipe. We analyse the static and dynamic field quality of the dipoles and compare them to the calculated ones. These test results allow us describing the parameters of the final dipole design for the machine and the field distortions the vacuum chamber creates along with investigations to reduce these artefacts. Based on our preliminary theoretical R&D and the recent measurement results we conclude on the expected operation parameters of an optimized curved dipole with a high current single layer coil and we describe the actual work topics for this magnet.