Design and Construction of a 38 T Resistive Magnet at the Nijmegen High Field Magnet Laboratory

Abstract

The Nijmegen High Field Magnet Laboratory (Nijmegen HFML) presently offers to its users 33 T in two 32 mm bore resistive magnets, 32 T in a 50 mm bore resistive magnet and 30 T in a 50 mm bore hybrid magnet. To comply with the users' demand for ever higher magnetic fields without having to resort to hybrid magnets, a new resistive 20+ MW magnet has been designed and is now being constructed, which will deliver 38 T in a 32 mm bore. The magnet consists of five Florida-Bitter coils and one outer Bitter coil. The two innermost coils ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm A}_{1}$</tex> </formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm A}_{2}$</tex> </formula> , CuAg conductor) are electrically in parallel. The outer coil (E, Cu conductor) has an outer diameter set to 1 m. The length of this coil is about 670 mm and it weighs almost 3000 kg, indicative of the huge amount of conductor material needed for 40 T class resistive magnets. An important issue is the necessity to reduce the slit factor, i.e. the locally high current density in a winding at a slit in a Bitter disk. We therefore decided to implement the modified Weggel stacking scheme for the A, B and C coils, implying a noninteger number of disks per turn, e.g. 11 13/25 for the B coil. Also, a new compact (1.3 m outer diameter, 1.4 m height) housing has been designed, able to withstand the combined stress due to the maximum fault force of 2.1 MN (occurring when the C coil fails) and the effect of 40 bar differential water pressure. The new magnet is expected to be commissioned in the fourth quarter of 2012.