Gebhard Moritz

Optimization of a superferric nuclotron type dipole for the GSI fast pulsed synchrotron

GSI plans to upgrade its accelerator facilities. A fast-pulsed synchrotron (rigidity 100 Tm, dipole field/ramp rate 2T/4T/s) is one of the main parts of the GSI future project. Superconducting magnets of the Nuclotron type are foreseen for this synchrotron. R&D work has been done in order to improve the DC field quality and to reduce the cryogenic AC losses. Linear 2-D calculations were used to optimize the pole shape of the dipole magnet. Consequently, a negative shimming was introduced. Subsequent nonlinear extension led to the introduction of air slits in the iron yoke which improved the field quality at higher levels. Nonlinear 3-D simulations were then used to optimize the homogeneity of the integral field, by varying the ratio between the yoke and coil length. We built a model magnet with this optimized iron lamination cross section. In order to reduce the AC losses, we used stainless steel end plates, low coercitivity iron, better insulated iron lamination sheets and reduced the superconductor filament size to 6 /spl mu/m. Various contributions to the losses of the magnet were analyzed. Numerical calculations of the eddy current effects due to field components perpendicular to the iron laminations at the end of the magnet showed that this part must not be neglected. The magnet test results are presented and compared with the expected field quality and losses.

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.

Superconducting magnets for the "International Accelerator Facility for Beams of Ions and Antiprotons" at GSI

The concept for GSIs planned future facility is based on two superconducting synchrotrons, SIS 100 and SIS 200. The two accelerators are in the same tunnel and have the same radius R, for operation at BR=100 Tm and 200 Tm respectively. Superconducting magnets are necessary to reach the appropriate magnetic field and may considerably reduce the investment and operating costs, in comparison with conventional magnets. An R&D program was initiated to develop dipole magnets with maximum fields of 2 and 4 Tesla and dipole ramp rates of 4 T/s and 1 T/s, respectively. These requirements were chosen to achieve high average beam intensities. The SIS 100 dipole is a window-frame Nuclotron-type dipole and is being developed in collaboration with JINR (Dubna, Russia). This magnet has been operated at 4 T/s up to a field of 2 Tesla. Reduced losses and improved magnetic field quality are required for the SIS 100 accelerator. In a separate collaboration with BNL (Upton, USA), the one coil layer cos/spl theta/-type RHIC arc dipole, originally designed for operation at 3.5 Tesla with a rather slow ramp rate of 0.042 T/s, will be upgraded for the SIS 200 accelerator to operate at a ramp rate of 1T/s, up to a field of 4 T. R&D for a 6 Tesla dipole was started in collaboration with IHEP (Protvino, Russia), to further increase the rigidity of the SIS 200 ring to 300 Tm. Alternative schemes have been investigated. Besides the synchrotrons, the planned facility will consist of several storage rings and the Super Fragment Separator (SFRS), which have mainly DC magnets with large apertures. NSCL (East Lansing, USA) prepared a feasibility study for these superconducting magnets. The main results of the R&D are presented.

Design of a superferric dipole magnet with high field quality in the aperture

A project to design and construct a new international accelerator was proposed by GSI (Darmstadt, Germany). This project includes the design of several new facilities. One of them is a collector ring (CR). The magnets of the CR operate at constant field (DC), but the level of this field varies for different operational tasks. The magnet system of the CR includes 24 deflecting dipole magnets. The maximum operating field in the aperture is 1.6 T, with a deflection angle of 15 degree, and a bending radius of 8.125 m. The most important requirement for this dipole is a high field uniformity (better than /spl plusmn/0.01% over a volume of 380 mm /spl times/ 150 mm). This requirement must be met for all levels of magnetic flux density in the aperture. Several magnet designs have been investigated including window frame and H-type versions with normal and superconducting coils. The best economical and technical parameters were obtained for a superferric H-type magnet with a wide air filter in the pole. The field homogeneity requirements were fulfilled in such a magnet for field range of 0.2-1.63 T. The effects of the field distortion in the end parts of the magnet, as well as influence of the end plates on the field quality, were also investigated.

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

The FAIR China Group (FCG), consisting of the Institute of Modern Physics (IMP Lanzhou), the Institute of Plasma Physics (ASIPP, Hefei) and the Institute of Electric Engineering (IEE, Beijing) developed and manufactured in cooperation with GSI, Germany a prototype of a superferric dipole for the Super-Fragment-Separator of the FAIR-project. The dipole magnets of the separator will have a deflection radius of 12.5 m, a field up to 1.6 T, a gap of at least 170 mm and an effective length of more than 2 meters to bend ion beams with a rigidity from 2 T · m up to 20 T · m. The magnets operate at DC mode. These requirements led to a superferric design with a yoke weight of more than 50 tons and a maximum stored energy of more than 400 kJ. The principles of yoke, coil and cryostat construction will be presented. We will also show first results of tests and measurements realized at ASIPP and at IMP.

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

Design studies on superconducting Cos /spl theta/ magnets for a fast pulsed synchrotron

The new heavy ion synchrotron proposed by GSI will comprise two superconducting magnet rings in the same tunnel, having rigidities of 200 T.m and 100 T.m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and field distortion. This paper discusses the 200 T.m ring, which will use Cos /spl theta/ magnets based on the RHIC dipole design. We describe options for the low loss Rutherford cable that will be used, together with a novel insulation scheme designed to promote efficient cooling. Measurements of contact resistance in the cable are presented and the results of these measurements are used to predict the ac losses, temperature rise and field distortion in the magnets during fast ramp operation.

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.

Commissioning of the Prototype Test Facility for Rapidly-Cycling Superconducting Magnets for FAIR

For testing rapidly-cycled superconducting magnets in the framework of the FAIR project (Facility for Antiprotons and Ion Research) a test facility was set up at GSI to test model and prototype superconducting magnets for different machines (SIS100, SIS300, Super-FRS). We are able to perform the following magnet tests: quench training, magnetic measurements, measurements of AC losses (calorimetric and V-I methods), temperature distributions in the magnet, and long-term stability tests. The forced-flow and bath-cooled scheme can be applied for the superconducting magnets. The facility consists of the following components: a refrigerator (400 W at 4 K); a distribution box for different cooling schemes (supercritical and two-phase flow); 2 feed-boxes providing electrical and cryogenic supply for the magnets; an all-purpose horizontal magnet cryostat which can be used for all kinds of different magnets (max. 3 m length and 0.8 m diameter); a power converter (11 kA) including the quench protection system; a quench detection system adapted from the LHC-series test facilities. The results of the AC loss measurements and the quench training for the first tested superconducting magnet are presented.

Measured and calculated losses in model dipole for GSI's heavy ion synchrotron

The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 300 T /spl middot/ m and 100 T /spl middot/ m. Fast ramp times are needed. These can cause problems of ac loss and field distortion in the magnets. For the high-energy ring, a 1-m model dipole magnet has been built, based on the RHIC dipole design. This magnet was tested under boiling liquid helium in a vertical dewar. The quench current showed very little dependence on ramp rate. The ac losses, measured by an electrical method, were fitted to straight-line plots of loss/cycle versus ramp rate, thereby separating the eddy current and hysteresis components. These results were compared with calculated values, using parameters which had previously been measured on short samples of cable. Reasonably good agreement between theory and experiment was found, although the measured hysteresis loss is higher than expected in ramps to the highest field levels.