Manifold damping of transverse wakefields in high phase advance traveling wave structures and local damping of dipole wakefields in standing wave accelerators

Operating the SLAC/KEK DDS (damped detuned structure) X-band linacs at high gradients (in excess of 70 MV/m) has recently been found to be limited by the accelerator structures breaking down and as a consequence severe damage occurs to the cells which makes the structures inoperable. A series of recent experiments at SLAC indicates that arcing in the structures is significantly reduced if the group velocity of the accelerating mode is reduced and additionally it has been discovered that reducing the length of the accelerating structure also limits the number and intensity of breakdown events. However, in designing new accelerating structures care must be taken to ensure that the beam-induced transverse wakefields do not cause the beam to become unstable. Here, we report on damping transverse wakefields in two different short structures: a 90 cm traveling wave structure in which the wakefield is coupled out to four attached manifolds and secondly, in a standing wave structure in which a limited number of cells heavily damp down the wakefield