Single Positron Damping Ring for ILC
Surrounded by the beautiful mountains and bay of Vancouver, Canada, the damping ring group made an important decision during the recent International Linear Collider (ILC) Workshop VLCW06.
In the ILC damping rings, bunches of positrons or electrons are stored for a fraction of a second prior to being injected in the main accelerator. The damping rings squeeze the emittances of the bunches to prepare them for the final collision. To maximize the bunch storing capacity and luminosity, the damping rings of the ILC are typically very long and thus... expensive.
Until the Vancouver meeting, the baseline configuration design specified that the damping ring complex should consist of three rings, each 6 km long: two positron rings in a single tunnel and one electron ring. When this baseline was adopted in 2005, electron-cloud effects were of sufficient concern to make a single positron ring unattractive.
Since then, simulation studies of electron cloud suppression in the damping rings have continued at SLAC and abroad. Two new techniques appear to be possible solutions to suppress the electron cloud: a grooved chamber surface or clearing electrodes in the beam chambers (see symmetry article). The new results were presented and discussed at Vancouver. They were so convincing that a decision was taken to submit a change request on the baseline design to a single positron damping ring, significantly reducing the cost.
Although very promising in simulation, these solutions still need to be fully tested and demonstrated. R&D on electron cloud mitigation techniques must remain a very high priority for the ILC program.