Alcator C-Mod non-axisymmetric control coils design and fabrication

A set of non-axisymmetric coils has been added to Alcator C-Mod tokamak to control resonant helical fields. These coils will be used to correct or induce stationary magnetic perturbations, for optimizing stability and exploring the error-field effects on plasma rotation. Sets of four coils above and below the mid-plane (8 in all) enable the helicity and the m-spectrum to be adjusted. The coils are composed of three layers each with an average of 8.875 turns, enclosed in an aluminum case. The conductor used is 4/0 welding cable. The coils were secured to the C-Mod igloo blocks (concrete radiation shielding blocks) with encore bolts. Depending on the needs of each pulse, the coils electrical configuration is easily changed through the use of a patch panel. Presently the system is designed to use a single power supply providing 3000 A 300 volts and developing a field of approximately 0.07 tesla at the center of the coil. This paper will describe the design, fabrication and installation of these coils.