New solution for the high accuracy alignment of accelerator components

Several state-of-the-art metrology measurement methods have been investigated and combined for a fiducialization of accelerator components in the micrometric regime. The PACMAN project at CERN applied stretched-wire measurement methods to Compact Linear Collider quadrupole and cavity beam position monitor prototypes, to locate their magnetic, respectively, electromagnetic, axis using a dedicated test stand and to determine the position of the wire with respect to external alignment targets (fiducials) testing different methods, such as coordinate measuring machine measurements and microtriangulation. Further studies have been performed using a nanopositioning system, verifying the absolute accuracy and repeatability of the fiducialization method within a few micrometers.

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Figure 1

The FPAB and its technical systems.

Figure 2

Details of the modes excited in the position cavity.

Figure 3

(a) Front view of the nanopositioning system; the magnet rests on the inclined piezoelectric actuators. (b) The base needs to remain light but extremely stiff and consists of two plates connected by several transverse and longitudinal stiffener elements.

Figure 4

View of the FPAB as finally assembled in the metrology lab. Two of the four microtriangulation network towers are also visible.

Figure 5

(a) BPM and (b) MBQ magnet mechanical axis definition.

Figure 6

3D model views of the MBQ-BPM joints.

Figure 7

(a) Temperature variation and mean value as measured by four sensors mounted on the CMM. (b) Horizontal and vertical angle observations from four theodolites to a target on top of the magnet. The red line depicts the simulated vertical angle variation according to the temperature variation and the geometrical configuration.

Figure 8

Magnetic axis coordinate definition in the local reference frame of the wire stages.

Figure 9

Vibrating-wire measurement results for the localization of the magnetic axis. Blue circles: measurements at 4 A magnet excitation current; green squares: measurements at $-4\mathrm{A}$ excitation. (a) Horizontal codirectional scan. (b) Vertical codirectional scan. (c) Horizontal counterdirectional scan. (d) Vertical counterdirectional scan.

Figure 10

S41 parameter pattern resulting from a 2D position sweep between the wire and BPM.

Figure 11

(a) Vertical and (b) horizontal coordinate of the electrical center located through S41 observation, $\mathrm{\Delta }=50\mu \mathrm{m}$.

Figure 12

(a) Vertical and (b) horizontal coordinate of the electrical center located through S41 observation, $\mathrm{\Delta }=1\mu \mathrm{m}$.

Figure 13

Differences in the results of fiducialization between the CMM and microtriangulation.

Figure 14

Fiducialization and initial alignment of DB quadrupoles.