The production of all 110 superconducting dipole magnets has been completed at FAIR in Darmstadt, Germany, marking an important step at one of the world’s biggest scientific research projects. In another development related to the new facility’s massive SIS100 ring accelerator, GE Power Conversion has been selected to provide power converters for the main dipole and quadupole magnets for it.
The production of all 110 superconducting dipole magnets for the new heavy ion accelerator with a circumference of 1.1 kilometers was completed in early August, along with corresponding cold tests at the final operating temperature of -269 degrees. Various sophisticated magnets and entire magnet systems will ensure that the ion beam is precisely guided and focused. The dipoles, mainly needed for deflecting the particle beam, make up more than a quarter of all 415 fast ramped superconducting magnets utilized in the SIS100.
The successful production of the modules and their testing represents the largest series of accelerator components ever manufactured by order of GSI. The completion is an important milestone on the way to installation in the tunnel, which is scheduled to begin in the second half of next year. Bilfinger Noell in Wurzburg, one of the few European manufacturers of superconducting magnets, was contracted for series production.
The dipoles are superferric magnets, consisting of a superconducting coil and an iron yoke to guide the magnetic field. The particular feature of the magnets is the superconducting coil, in which a special superconducting cable is used. This nuclotron cable, originally developed for the ring accelerator Nuklotron at the Joint Institute for Nuclear Research in Dubna, Russia, is particularly suitable for generating rapidly ramped magnetic fields.
The cable consists of a copper-nickel tube. Around this tube strands of niobium-titanium, a common superconductor, are coiled. The original design was optimized with regard to the requirements of FAIR. It is cooled with liquid helium and operated at a temperature of 4.5 Kelvin. The design of the magnets allows to integrate vacuum chambers for the ion beam, whose wall temperature is also just above absolute zero. Thus, the chamber walls act like a super pump onto which the remaining particles of the beam vacuum keep attached. The extremely low remaining gas pressure made possible by is a mandatory precondition for the acceleration of heavy ion beams with highest intensities. Highest particle intensities are part of the specifications of the FAIR facility, which offers a wide variety of new experimental possibilities.
Each of the magnets, which weigh about three tons and are three meters long, is subjected to a comprehensive test program. The quality control of the production as well as several tests under room temperature conditions are performed in Wurzburg before shipment to Darmstadt. Among other things, the geometric precision of the inner aperture and the electrical properties of the coil were measured as part of the so-called FAT (Factory Acceptance Test). Bilfinger Noell succeeded in making the production so precise over the entire series that the deviations of the geometry of the field-determining pole shoes were always less than 50 micrometers from the nominal geometry.
After delivery to GSI, all 110 dipole modules were subjected to testing at the final operating temperature of 4.5 K. To cool the magnets down to this temperature, GSI has built an elaborate, almost 700-square-meter test facility with cryogenic equipment for superconducting accelerator magnets. It has four so-called feed boxes to connect the dipole modules for parallel testing in different phases. Using a specially procured high-power power supply unit, the modules could be supplied during the performance test with amperage up to 17 kiloamperes at rise rates of 28,000 amperes per second.
At FAIR (Facility for Antiproton Ion Research), matter that usually only exists in the depths of space will be reproduced in a lab for research. Scientists will be able to gain new insights into the structure of matter and the evolution of the universe from the Big Bang to the present. FAIR is under construction at GSI Helmholtz Center for Heavy Ion Research. Its existing accelerator facilities will serve as first acceleration stage.
The power converters project was awarded in June. GE will supply low-voltage IGBT inverters from its LV8 power electronics platform, a high-performance modular drive for industrial applications that can address research, development and technical challenges flexibly. It can be customized for either AC drives with rotating machinery or DC loads such as magnetic power supplies, each with single- or multi-quadrant capability. In addition, particularly powerful IGBT switches are provided for quench protection of the superconducting magnets. The power electronics will be implemented with system components such as power transformers, medium-voltage switchgear, surge arresters and fast semiconductor fuses.
These new switch-mode power supplies replace earlier generations of thyristor power supplies with their fast FET (field-effect transistor) ripple compensators. Switching power supplies have enhanced functionality, providing both power current to the magnets (formerly thyristor power converters) and smoothing the ripple of the same (formerly FET arrays). The total power of the switch-mode converters is about 40 MW for the main dipole magnets and their quadrupole magnets.
“We are proud to be part of this ambitious research project, requiring our technologically advanced solutions and know-how. In addition, we are working with the challenging requirements of both limited space and reconciling our power converters with the water-cooling consumption and air conditioning constraints,” noted Joerg Nuttelmann, general manager of GE Power Conversion Germany.