1 alignment and calibration schemes for iter cxrs pedestal diagnostic

Charge exchange Recombination Spectroscopy (CXRS) diagnostic is responsible for the key measurement for ITER advanced plasma control and physics studies. ITER CXRS Pedestal has a primary role of edge ion temperature, plasma rotation (velocity) and impurity density measurements in the pedestal region (r/a=0.85 -1.0). In the paper, developments of alignment & calibration scheme for the ITER CXRS Pedestal diagnostic system will be discussed in the suitable transmission system, this includes the ZEMAX ray-tracing tool, used for optimum light transmission path analysis including various optical components. Conventionally, the calibration source is placed in front of the optical diagnostics, however, in ITER, this is not possible. An alternative scheme for intensity calibration has been considered and is being analyzed. In this scheme, the light source will be placed in the diagnostic area and retroreflector will be located behind the shutter (used for protecting the First Mirror). The main advantage of this scheme is that the complete transmission system (first mirror to the detector) will be calibrated without any additional optics. This will eliminate the need for premium space requirement in the port plug which is very limited in ITER due to multiple diagnostic and other support services. In this scheme the intensity calibration mainly relies on the design & properties of the retroreflector, therefore the retroreflector performance is studied using the ZEMAX for vertically and horizontally grooved orientations for aluminum and molybdenum. Further, an experiment was performed to ensure the feasibility and achieving the performance as predicted by ZEMAX for retroreflector, and the flat mirror. Regarding the alignment, the effect of optics displacement on the system performance is also studied using ZEMAX. This helps to assess the required alignment for efficient coupling in the image plane. Tolerance analysis is performed to identify the most affected component for optical transmission in the interspace support structure to ensure the required accuracy of measurements.