Large-scale accelerator alignment using an inclinometer

•71-m-long straightness was evaluated with standard deviations of less than 49 μm.•The derived straightness was in good agreement with the other results.•Reversal measurements were effective in eliminating offsets and drifts of our system.•The estimated errors agree well with the obtained ones.•This method can be applied for several hundred-meter-long objects.

A precise inclinometer (Talyvel 4) was adopted for evaluating aligning straightness of the first 71 m of the KEK electron/positron injector linear accelerator (linac). The straightness could be evaluated with a standard deviation of less than 49 μm. It is in good agreement with those obtained using a conventional alignment telescope and our laser-based alignment system.Error estimation based on the rules of error propagation shows that shape evaluation with a standard deviation of 0.3 mm for a distance of 500 m can be achieved using the proposed method. It indicates that this method is suitable for evaluating straightness of several hundred meters of linacs with sub-millimeter of accuracy.