Industry Quality Assurance

Quantifying alignment of particle accelerator discs using Fourier domain short coherence interferometry

We apply Fourier domain short coherence interferometry (FDSCI) to quantify alignment of particle accelerating structures (AS) of the future compact linear collider (CLIC). Even micrometer-level misalignments inside the AS, composed of stacked copper discs, reduce the CLIC performance. Thus submicron accuracy across at least 8.6 mm measurement range is required from the quality assurance tester. To measure the internal alignment we insert a fiber-optic probe into the AS to illuminate and collect reflected light from the internal walls, Fig. 1. Our measurement technique bases on detecting a spectral interferogram that reveals after Fourier transform the distance between the wall and the probe end. The internal shape is then scanned point-by-point by rotating and pulling back the AS. In Fig. 2 we show preliminary data by measuring mirror position from several mirror-to-probe distances.

Fig. 1. Fiber-optic FDSCI setup.

Fig. 2. Mirror position measured from several mirror-to-probe distances.