Aberrations in preliminary design of ITER divertor impurity influx monitor

•Divertor impurity influx monitor for ITER (DIM) is procured by JADA.•DIM is designed to observe light from nuclear fusion plasma directly.•DIM is under preliminary design phase.•The spot diagrams were suppressed within the core of receiving fiber.•The aberration of DIM is suppressed in the preliminary design.

Divertor impurity influx monitor for ITER (DIM) is a diagnostic system that observes light from nuclear fusion plasma directly. This system is affected by various aberrations because it observes light from the fan-array chord near the divertor in the ultraviolet–near infrared wavelength range. The aberrations should be suppressed to the extent possible to observe the light with very high spatial resolution. In the preliminary design of DIM, spot diagrams were suppressed within the core of the receiving fiber's cross section, and the resulting spatial resolutions satisfied the design requirements.