Design limit of the superconducting solenoid for high energy colliding beam experiments

Practical design limit on a superconducting solenoid, in particular, of thin coil for high energy colliding beam experiments was investigated. Heat generation and electricity consumption force to limit a magnetic field produced by a conventional solenoid to be about 0.5 T. It, therefore, requires to employ superconducting technology to produce even higher magnetic field. By using NbTi superconductor which is still an only material that is commonly available, we may seem to be able to produce a magnetic field of as high as 6T using conventional liquid helium cooling at 4.2K. The mechanical as well as thermal constraints, however, put a practical limit on thin solenoid design in the combination of size, thickness and operating magnetic field. The thin solenoid of which stored energy is smaller than around 200 MJ, made from mostly aluminum, must satisfy the following inequality; B2(T)·r(m)≤135xt(m)=∼10·X0 for E<∼200MJ. For the magnet of the larger stored energy (E≥∼200 MJ), the above constraint may become too optimistic. We should carry out the more realistic analysis regarding a local heat up of a conductor due to a magnet quench. It can be generally said, however, that the larger operating current and the relatively smaller current density, which result in a conductor of the larger cross-section, must be required in designing the superconducting magnet of the larger stored energy. (author)