It is essential for high field magnet to have high current density conductor. The efficiency of the current decreases when the coil is wound thick. Conductor development toward high current density conductor is under way hoping it can make a break through in the construction of high field magnet. However, the limitation is not only in the characteristics of the superconductor. The amount of copper in the cable has to be increased when the current density of the superconductor is increased to protect the magnet through a quench. As a result, generation of high field is not as economical as what is assumed with high performance conductors.
This report summarises the relationship among conductor amount and magnetic field under the condition of quench protection. The accelerator design should be considered taking these factors in the selection of the magnet field.