Compact Linear Collider (CLIC) is a study of a 3 TeV linear electron-positron (e+ e-) accelerator and it is a successor candidate for CERN's Large Hadron Collider (LHC). CLIC luminosity target is 5.9 × 1034 cm−2s−1 , which causes unprecedented pre-alignment requirements of its main linear accelerator (main linac). Along the 50 km long tunnel, the main components of any 200 m long section have to be positioned within 10 μm from a straight reference line. The pre-alignment challenge has been studied at CERN since the 1990s and main technical challenges have been solved. This article summarises the positioning strategy and presents it to an audience outside the particle accelerator community. The methods can be of interest especially in the field of large-scale metrology. The positioning strategy consists of several steps or subsystems. Development of a straight reference line over tens of kilometres allows absolute positioning of accelerator components while a process called fiducialisation defines component reference axes with regards to alignment targets. Emphasis is on a support pre-alignment network that acts as a link between the straight reference line and fiducialisation. The subsystems and remaining challenges in their development are presented. The chosen strategy's potential is demonstrated experimentally by building a short test setup.

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IOP : CLIC pre-alignment — status and remaining challenges

Pulsed-wire measurement of a magnetic field has been developed by many groups. A pulsed-wire system has been set up and used to measure an in-vacuum undulator magnetic field at NSRRC. A copper zirconium wire (length 4 m, diameter 100 μm) has been selected. The pulse current is generated with an in-house power supply. A high-resolution and fast-feedback laser-photodiode system served to detect the displacement of the wire. Construction of an in-vacuum NdFeB-permanent-magnet undulator (period 22 mm, magnetic length 2 m) has been completed for Taiwan Photon Source. In this work, we applied a highly stiff, thin copper zirconium wire to diminish the maximum sag during measurement of a long undulator. We also demonstrate that the distance between the location of a wire dispersion sensor and a fixed point of the wire is an important issue to separate the main and weak reflection signals in pulsed-wire measurement. From the results of the undulator measurement, we obtained the magnetic field performed with the pulsed wire and Hall probe measurements, which are compared. 

Pulsed-wire system for magnetic-field measurements on an in-vacuum undulator at NSRRC

The precision of magnet alignment in next-generation light sources is critical. To achieve this, the multipole magnets on a common girder of SPring-8-II, an upgrade of SPring-8, are planned to be aligned using the vibrating-wire technique. We developed an alignment monitoring system to monitor the magnet positions in the tunnel where the vibrating-wire technique cannot be executed while the magnets are not energized or when there are vacuum chambers in the magnet center. The alignment monitoring system utilizes a non-contact capacitive sensor embedded in a ceramic ball to measure the wire position relative to the center of the ball and derives the wire sag by measuring a higher mode eigenfrequency. The constitution of this system is illustrated for relevant studies, including the investigation of wire sag against the eigenfrequency, observation of the actual wire sag at a test bench, and validation of the system on the girders for the prototype magnets of SPring-8-II. The system measured the positions of a series of magnets with a precision of ±4 µm (peak to peak) in a 4 m range, in both the horizontal and vertical directions, meeting the requirement of SPring-8-II.

https://iopscience.iop.org/article/10.1088/1361-6501/abe5e4/pdf

Yasuhiro Takemura

Papers

Magnet alignment monitoring system with eigenfrequency-based wire sag correction