High specific energy beryllium coils

Cryogenic inductors made of beryllium (Be) have the potential for lower mass compared with aluminum (Al) projected state-of-the-art technology. Beryllium and Al specific stored energy was investigated as a function of conductor resistivity for a given stored energy and coil time constant. One of the initial concerns about the use of Be was that its required resistivity might be so low (and purity so high) as to make its manufacture very expensive. The authors determined what the resistivity had to be so that the mass of a Be coil would equal the mass of an Al coil. The system chosen for investigation was a liquid hydrogen-cooled (20 K) solenoid inductor with a given stored energy and time constant ( tau ). The nominal inductor chosen was one storing 100 MJ of energy, with a tau of 5 s. The coil geometry chosen was a long, thin solenoid that uses a composite reinforcing structure. Producibility of a Be coil is also discussed.