Central Solenoid for Spherical Tokamak Globus-M

The central solenoid is a critical component of the spherical tokamak Globus-M (plasma major radius R = 0.36 m, plasma minor radius a = 0.24 m, aspect ratio R/a = 1.5, toroidal magnetic field B_T 0.62 T, plasma current I_p 0.5 MA). The two-layer solenoid, 1312 mm long with a 200-mm outer diameter, is located between the 112-mm-diam inner rod of the toroidal field coils and the 217-mm-diam inner cylinder of the vacuum vessel. Strong magnetic and thermal cyclic loads acting on the solenoid require that it be manufactured from a high-strength hollow conductor. The conductor material selected for the solenoid winding is CuAg0,1(OF). Advanced manufacturing technology has made it possible to increase the continuous length of conductor (with an ~20 × 20 mm² cross section) up to the 66 m that is required for Globus-M. To verify the winding procedure, a one-sixth-length solenoid prototype has been constructed and tested with loads exceeding the design loads acting on the full-scale solenoid. The tests included magnetic and strain measurements. The results are in satisfactory agreement with structural analysis.