Design of impurity influx monitor (divertor) for ITER

Because of the changes of interfaces between ITER and the Impurity Influx Monitor (divertor) accompanied with the change of the ITER design to a reduced size machine, changes in the design of the monitor are required. In this design work, optics compatible with new interfaces, a calibration system and an alignment system of the optical axis and the focus were designed and investigated. The design of the optical systems was simplified to save the cost. To simplify the optics, the design of the collection optics was changed from an off-axis aspherical mirror system, which is a previous design, to a simple Cassegrain telescope system composed of simple spherical mirrors and lenses. In addition, a micro lens array is inserted just in front of the fiber bundle to increase the light detected. The ray-trace analysis shows that the spatial resolution of ITER requirement (50 mm) will be achieved by these optical systems designed here. The in-situ sensitivity calibration will be realized by applying the light on a micro retro-reflector array installed in front of the plasma facing first mirror from the outside the vacuum chamber through the same optics for plasma measurement and measuring the intensity of the reflected light from the array by using the same optics. In addition, optical design of an adjustment system and a focusing system, and a conceptual design of the shutter system of the monitor were carried out. Moreover, the detector system for the monitor was investigated and designed. (author)