Accelerating electrode made of molybdenum
Prototype electrode and support frame for NBI (neutral beam injection) device to be installed at ITER (International Thermonuclear Experimental Reactor). To induce nuclear fusion, plasma has to be heated up to one hundred million degrees C. One method to heat up the plasma is NBI heating where “hot” particles are injected. The electrode functions as part of an electrostatic acceleration device, changing the ions from the ion source into a high-energy ion beam. To ensure the static state of the plasma, the electrode is made of molybdenum with internal water channels for hot fluid of constant temperature to withstand the long time beam radiation.
Dimensions of the product: the measurements of the electrode are 520mm×230mm×9mm, the support frame isφ1800mm×60mm. The electrode is made of molybdenum and has internal water channels for temperature-controlled fluid to keep a temperature of 200℃ during operation. MTC manufactured the water channels by vacuum brazing. We managed to process the difficult-to-process-material molybdenum with an accuracy of ±0.05mm, machining 216 holes for the ions. The support frame is made of SUS316L with a sealed structure to keep the vacuum and pipes to allow the feeding with hot fluid to the electrode. The structure to absorb thermal expansion due to the temperature rise in the pipes and the large-scale flange with thermal shield structure to prevent heat transfer to the flange have been built with MTC’s large-size machining equipment and our expert welding technique.