Report of EM working group

Concepts of various types of linear accelerators for electron-positron colliders are compared and discussed and some proposals for research and development to realize a linear collider in the multi-Tev region are described. As for the normal conducting linear accelerators, the traveling-wave and the standing-wave linacs are compared based on the major parameters of existing or proposed accelerators. As for the superconducting linac, it is deduced that the total length to achieve 1 Tev amounts to 167 km and the ac-power to keep the whole system at the liquid helium temperature amounts to 315 MW under the appropriate assumptions. It is concluded that the superconducting structure is not adequate for the linear collider. As the third possibility, the wake-field accelerator is considered. In order to make the linear collider in the multi-Tev region feasible early in 1990's, it is proposed to start the R and D of the normal conducting traveling-wave linac with high group velocity and the pulsed rf-source with high peak power. It is also proposed that the study of the wake-field accelerator should be started. (Aoki, K.)