A small rectangular edge localized mode control coil design able to withstand a 400°C environment

Recently, an Edge Localized Mode (ELM) control coil was developed for use on the DIII-D tokamak. The coil design represented a significant challenge due primarily to the requirement for the coil insulation to withstand bakeout temperatures of 400°C for extended periods. This requirement ruled out most common organic insulating systems and necessitated a significant prototyping and development effort, leading to the selection of an advanced high temperature glass/polyimide resin system. The development included developing a heating mechanism that provided the discrete temperature ramp cycles and cure cycles required by this exotic resin. To complicate matters, the resin had a limited shelf life. Additionally the coil was small and rectangular in shape with rather small corner radii. This created a corner buildup that was not previously encountered and made dimensional control difficult. Another unique design requirement was the need to apply a sufficient internal pre-load to the wound and cured coil to insure there will be no relative motion between the coil and the Inconel case due to Lorentz forces from the 4 Tesla toroidal field on the vessel center post. This led to development of very unique leaf springs and a significant research and development effort coupled with an equally arduous finite element analysis effort. A satisfactory prototype was produced. This paper will focus primarily on the manufacturing challenges and discuss the prototyping effort.