Experimental demonstration of a global dispersion-free steering correction at the new linac test facility at SLAC

A Latina,N Lipkowitz,J Pfingstner,F J Decker,D Schulte,E Adli

doi:10.1103/physrevstab.17.042803

Abstract

The performance of future linear colliders will depend critically on beam-based alignment and feedback systems. In ILC and CLIC it is planned to perform dispersion-free steering in the main linacs. To this end the beams are accelerated with different gradients to evaluate the dispersion. The steering is performed by minimizing the average offset of the different beams in the beam position monitors and, at the same time, the difference between the beam trajectories. The experimental verification of the dispersion-free steering algorithm is essential to prove its effectiveness and to prepare the commissioning of such machines. The algorithm should take an orbit measurement at every cycle (train to train), estimate the correction from this information, and, from the system response matrices, apply the correction. We have successfully tested dispersion-free steering at FACET, including an adaptive system-identification algorithm, where the system response matrix is measured dynamically and automatically.

Highlights

The proposed high-luminosity, electron-positron linear colliders CLIC [1] and ILC [2] require normalized vertical emittances of the order of 10 nm at the interaction point in order to reach the target luminosities of 1034=cm2=s
Two of the main sources of emittance growth are: the emittance dilution due to spurious dispersion in the quadrupoles, which scales as the absolute misalignment of the beam position monitors (BPMs) squared, and the emittance dilution due to transverse wake fields which scales as the square of the accelerator structure offset [3]
In Ref. [9] we have successfully studied the possibility of using many small excitations over time to gradually improve the system knowledge with the help of system identification algorithms that optimally reduce the effects of the measurement noise

Summary

Introduction

The proposed high-luminosity, electron-positron linear colliders CLIC [1] and ILC [2] require normalized vertical emittances of the order of 10 nm at the interaction point in order to reach the target luminosities of 1034=cm2=s. Two of the main sources of emittance growth are: the emittance dilution due to spurious dispersion in the quadrupoles, which scales as the absolute misalignment of the beam position monitors (BPMs) squared, and the emittance dilution due to transverse wake fields which scales as the square of the accelerator structure offset [3]. In order to align such linacs in a robust and more practical way, global correction algorithms have been studied intensively during the last decades [4,5,6,7]. For both CLIC and ILC global dispersion-free correction algorithms [4]

Methods

Results

Conclusion