Speaker
Description
Relativistic charged-particle beams which generate intense longitudinal fields in accelerating structures also inherently couple to transverse modes. The effects of this coupling may lead to beam break-up instability, and thus must be countered to preserve beam quality in applications such as linear colliders. Beams with highly asymmetric transverse sizes (flat-beams) have been shown to suppress the initial instability in slab-symmetric structures. However, as the coupling to transverse modes remains, this solution serves only to delay instability. In order to understand the hazards of transverse coupling in such a case, we describe here an experiment characterizing the transverse effects on a flat-beam, traversing near a planar dielectric lined structure. The measurements reveal the emergence of a previously unobserved skew-quadrupole-like interaction when the beam is canted transversely, which is not present when the flat-beam travels parallel to the dielectric surface. We deploy a multipole field fitting algorithm to reconstruct the projected transverse wakefields from the data. We generate the effective kick vector map using a simple two-particle theoretical model, and particle-in-cell simulations provide further insight for realistic particle distributions.
Acknowledgments
The authors acknowledge insightful discussions and
contributions from S. Baturin. This work is supported
by the U.S. Department of Energy, Office of High Energy
Physics, under Contracts DE-SC0017648 (UCLA), DE-
SC0018656 (NIU), and DE-AC02-06CH11357 (ANL).
