  Recent simulation shows that a self-modulated high energy proton bunch can
excite a large amplitude plasma wakefield and accelerate an externally injected
electron bunch to the energy frontier in a single stage acceleration through a
long plasma channel. Based on this scheme, future colliders, either an
electron-positron linear collider (e+-e- collider) or an electron-hadron
collider (e-p collider) can be conceived. In this paper, we discuss some key
design issues for an e+-e- collider and a high energy e-p collider, based on
the existing infrastructure of the CERN accelerator complex.
