Design, control and operation of the vacuum and gas systems for Alcator C-Mod

The torus vacuum system for the Alcator C-Mod tokamak is composed of two 1000 l/s vertical axis turbomolecular pumps and one 8" cryogenic pump. Since the vacuum vessel port connections are inside a liquid nitrogen dewar and are subjected to large temperature gradients during cooling, a double seal arrangement with inner Helicoflex seals and outer indium coated copper seals has been implemented. The gas fueling system provides mixtures of six supply gases to an array of fill valves with complete flexibility of gas mixture and feed location. Fully remote operation and monitoring of the vacuum and gas systems is required and has been implemented using a programmable logic controller. Design details, test results and operational experience are presented.