R.M. JONES* (SLAC), N.M. KROLL* ** (UCDS & SLAC), R.H. MILLER*, and G.V. Stupakov* (SLAC)
In damping the wakefield generated by an electron beam traversing several thousand X-band linacs in the NLC we utilize a Gaussian frequency distribution of dipole modes to force the modes to deconstructively interfere, together with moderate damping by coupling out the field to four attached manifolds. The modes towards the upper frequency end of the lower dipole band distribution are well damped. However, the modes towards the end of the lower dipole frequency band are not so well damped due to mechanical fabrication requirements that the last few cells not be coupled to the manifold. Here, we consider the effect of locally damping a limited number of cells. Additionally, in the present design RDDS1  the waveguide which couples out the accelerating mode also loads down the dipole mode and this enables a number of high Q modes with high kick factors to be damped. Here, we report on the damping of the wakefield provided by both the fundamental coupler (as has already been fabricated) and on a proposed scheme of locally damping a limited number of cells. The effect of the latter on the wakefield is quite dramatic.
 R.M.Jones et al, 'The Transverse Long-Range Wakefield in RDDS1 for the JLC/NLC X-Band Linacs', Proc IEEE 1999 Particle Accelerator Conference (PAC99), p3468,(1999)
*Work supported at SLAC under U.S. Department of Energy grant number DE-AC03-76SF00515.
**Work supported at SLAC under U.S. Department of Energy grant number DE-FG03-93ER40759
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