Abstract
We propose a novel method to align accelerating structures such as those used in the Compact Linear Collider (CLIC) by exploiting a mode that copropagates with the normal accelerating mode. This mode has an octupolar dependence in the transverse direction and is caused by radial waveguides intended to damp higher-order modes. The nonlinear dependence of the octupolar mode makes it possible to determine the center of the structure from the nonlinear dependence of the transverse kick, observed on a downstream beam position monitor, while changing the transverse position of the beam with respect to the accelerating structures. We discuss the method, its tolerances and disentangling the individual misalignments of two adjacent accelerating structures that are powered from a single source.
Highlights
The Compact Linear Collider (CLIC) [1] is a candidate for a future lepton collider to probe physics on the TeV scale beyond LHC
The beam size depends to a large extent on the beam emittance that is initially determined by the damping rings
By moving the girders with the accelerating structures or by moving the beam with two steering magnets or quadrupole movers while switching the rf power on and off we can measure the beam position shifts for different transverse positions in the accelerating structure. This eliminates many systematic errors since we measure position shifts and not absolute positions, and since we can measure the shifts from consecutive shots without moving the beam
Summary
The Compact Linear Collider (CLIC) [1] is a candidate for a future lepton collider to probe physics on the TeV scale beyond LHC. In the power extraction structures there is a mechanism that allows rf to be switched on and off [16], which means beam position measurements for deflected and nondeflected beam can be made shot-to-shot This eliminates many systematic errors and lowers the sensitivity to beam jitter. 9 10 600 10 render the method impractical at high energy This problem, can be circumvented by powering only one of the 24 drive beam sectors at a time and running the entire linac at or close to the injection energy of 9 GeV. Assuming that the magnetic centers of the magnetic elements are unaffected by this scaling the alignment of the acceleration structures works for the entire linac. We first show the method for a single structure [18] and we expand the error analysis and apply the method to two consecutive structures
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