Selected Composites for High Field Magnets
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0977-FF02-01
Selected Composites for High Field Magnets Ke Han, Jingping Chen, Baozhi Cui, Charney A Davy, and Peter N Kalu National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32301
ABSTRACT The US national high magnetic field laboratory builds and uses various high field magnets for fundamental research. In building high field magnets, a variety of high strength composites are required because of the Lorentz stresses generated by high field exceeding the strength of most of the materials, particular conductors. For example, a field of 60 T can generate a magnetic pressure that corresponds to a stress in the conductor of 1.5 GPa, which is at the limit of known conducting materials with conductivity higher than 70% International Annealed Copper Standard and sizes suitable for building high field magnets. The design of high field magnets is limited by these forces and, consequently, by the available materials. At the same time, the materials need to have excellent physical properties. For instance, the conductors need to have high electrical conductivity and high specific heat and the superconductors should have high critical current in field and low alternative current losses. This paper outlines our requirements and research on metal matrix composite materials for building high field magnets. The discussions include both the macrocomposite and microcomposite. The scales of the structures in the composites are from millimeters to nanometers. INTRODUCTION Scientists and researchers come to the USA high magnetic field facilities to undertake research in physics, biology, bioengineering, chemistry, geochemistry, biochemistry, materials science, and engineering. Among all these research areas, materials science research related to high magnetic field is one of the most active ones. In fact, the high magnetic field facility is one of the critical tools for development of new materials that impact nearly every modern technology and research. Two types of materials related to the high magnetic field are very important in high magnetic field research: the magnet materials for building high field magnets and materials whose properties can be influenced by high magnetic fields. The second type materials are so broad that this paper cannot cover all the areas. Therefore, this paper discusses only selected engineering materials, whose properties can be improved by treatment in magnetic field. The first types materials are mainly the high strength materials for building high field magnets and will be focused in this paper. High field magnets which operate in the range 5-100 T require high strength materials to resist the Lorentz forces, which arise when the magnet is energized and low electrical resistivity to minimize the temperature raise due to Joule heating. The design of the coil often requires consideration of the combination of the conductors, structure materials, and insulators. This paper focuses mainly on composite conductors. The high strength conductors addressed in this paper are use
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