Abstract
The ATF2 beam line at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $\ensuremath{\sim}10%$ of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of ${10}^{10}{e}^{\ensuremath{-}}$. We present studies of the impact of wakefields on the production of ``nanobeams'' at the ATF2. Wake potentials were evaluated for the ATF2 beam line elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and beam position monitor resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and interaction point tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity dependence of the beam size.
Highlights
In order to achieve their design luminosities in excess of 1034 cm−2 s−1, future electron-positron linear colliders such as CLIC [1,2] and ILC [3] require nanometer-sized beams to collide at the interaction point (IP)
The final focus system (FFS) of these colliders is based on a local chromaticity correction scheme [4], a novel concept that has not so far been deployed at a high-energy particle collider
The effect of a wakefield on an electron bunch, namely the amplitude of the wakefield kick, characterized by the wake potential, depends on the aperture of the wakefield source and on the position offset of the beam relative to the source axis. Devices such as C-band cavity beam position monitors (C-BPMs), flanges, and bellows lead to significant wakefield kicks that affect the beam quality by inducing emittance growth and orbit deflection, which increase the beam size at the IP
Summary
In order to achieve their design luminosities in excess of 1034 cm−2 s−1, future electron-positron linear colliders such as CLIC [1,2] and ILC [3] require nanometer-sized beams to collide at the interaction point (IP). Demonstrate the effectiveness of the local chromaticity correction scheme to achieve an IP vertical beam size as small as 37 nm, and (2) to demonstrate the feasibility of beam orbit stabilization to the nanometer level. The effectiveness of the local chromaticity correction scheme was successfully demonstrated [7,8], and the potential for direct beam orbit stabilization to the nanometer level has been shown [9,10,11,12]. We have developed mitigation techniques to recover a small vertical beam size at the IP and these are presented These results and techniques are applicable to obtaining ultrasmall beams at the FFS of future linear colliders
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