Manufacturing method for coil conductors to generate strong magnetic field

A cylindrical member comprising copper/chromium alloy steel is formed. A central hole is perforated at the center of the cylindrical member for passing coolants. A wedge is attached to the central hole and struck by a static pressure press to extend the central hole. In this case, pressing force of the wedge is applied to the inner surface of the central hole of the cylindrical member, by which the central hole undergoes cold working to provide a metal tissues with large intramolecular density, and the inner surface of the central hole is hardened. Mechanical fabrication and electric discharge machining are applied to the outer surface of the cylindrical member and the wall surface of the central hole. Subsequently, spiral grooves are formed on the surface of the cylindrical member. A durability in view of strength is increased by hardening the inner surface of the central hole of the coil conductor, the coil conductor has sufficient resistance against strong magnetic fields if occur. (I.N.)