A dielectric-loaded circular waveguide structure is a potential high-gradient linear wake-field accelerator. A complete solution is given for the longitudinal electric and magnetic fields excited by a 6 function and a Gaussian charge distribution moving parallel to the guide axis. The fields are then given in the limit of particle velocity equal to the speed of light. Example calculations are given for a structure with inner radius of 2 mm, outer radius of 5 mm, dielectric constant of 3, and total charge of 100 nC. Peak wake fields in excess of 200 MV/m are found. Azimuthal modes 0 and 1 are investigated for the particular interest of acceleration and deflection problems.The electromagnetic radiation of a charged particle passing through a structure containing dielectrics' has many applications to accelerator physics. The next generation of electron-positron linear collides will require high-accelerating-gradient ( ) 100 MV/m) structures.Recently a new acceleration scheme, called the dielectric wake-field accelerator, has been proposed. The concept of dielectric wake-field acceleration is very simple. It is a dielectric-lined waveguide and because of its slow wave characteristics it can be used as a wake-field device. In order to make the dielectric structure a practical wakefield acceleration device, however, one has to have high gradients and manageable transverse wake fields. The estimation of the transverse wake-field amplitudes in the dielectric structure is essential because it is directly related to the beam instability (or beam break-up mode) problem. In this paper we calculate both the longitudinal and transverse wake fields produced in a dielectric structure by passing a charged particle. First we give a general expression for the wake fields corresponding to any particle velocity P=U/c including all azimuthal modes m, then discuss the implication of the results under the limit of P~1, in particular for m =0 and l.We should point out that in our previous calculation of the transverse wake field in the dielectric structure, we assumed that the vector potential A was proportional to the scalar potential P. The implication of this assumption was that only TM-like wake fields would be excited, and that no TE-like wake field would exist. The consequence of this was that the higher-order azimuthal-mode m~1 wake fields vanish when the electron beam is ultrarelativistic. This unexpected result attracted much interest in the community. Since then we continued calculations without preassurnptions, as shown in this paper. In the meantime many other people have also investigated this problem, and the results are that both TE and TM waves exist in the dielectric structure for m ) 1 modes. The conclusion of all these works is that the transverse wake fields do not vanish even in the ultrarelativistic limit.Consider the configuration of a metallic tube with inner radius 6, partially filled with isotropic material with dielectric constant e, containing a hole of radius a at the center which allows charged particles to ...

In experimental studies of the Plasma Wake-field Accelerator performed to date at the Argonne Advanced Accelerator Test Facilit,y, significant nonlinearities in both plasma and beam behavior have been observed. The plasma wares driven in the make of the intense driving beam in these experiments exhibit three-dimensional nonlinear behavior which has as yet no quantitative theoretical explanation. This nonlinearity is due in part to the self-pinching of the driving beam in the plasma, as the the denser self-focused beam can excite larger amplitude plasma waves. Th e se lf-pinching is a process with interesting nonlinear aspects: the initial evolution of the beam envelope and the subsequent approach to Bennett equilibrium through phase mixing.

We have directly measured the damping of wake-field deflection modes in a slow-wave accelerating structure consisting of a dielectric-lined waveguide with segmented conducting boundaries wrapped with rf absorbing material. Such damping of deflection modes is desired to prevent beam breakup instabilities. Attenuation e-folding times of 246 ps were recorded for deflection modes at the Advanced Accelerator Test Facility while the quality of the desired accelerating mode remained unaffected.

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