20 October 2005
As I have discussed the past couple of weeks, the baseline ILC design will be guided and flow from a set of overall requirements. These requirements began from the science goals or requirements that were then translated into technical requirements for an accelerator. With these requirements established, the choices for the different subsystems of the ILC are being determined as consistently as possible with the technical parameters.
In some cases, the requirements can be met with a technically sound and economical choice, while in other cases meeting the requirements might prove to be too difficult, require extensive R&D, be too costly, or perhaps suggest that some modifications be made in the requirements or other subsystems. The process of determining a complete consistent design that meets a challenging set of requirements is necessarily an iterative process.
The design of the individual subsystems begins with the sources of particles, in this case electrons and positrons. For the ILC, producing electrons consistent with the requirements is the more straightforward. Therefore, I will begin with a brief summary of the electron source. Before Snowmass, we split working group 3 (WG3) into two working groups, where WG3a, led by M. Kuriki, J. Clarke, J. Sheppard and P. Piot, concentrated on the positron and electron sources and bunch compressors.
The baseline recommendation for the electron injector consists of direct current guns incorporating photocathodes illuminated by a Ti:Sapphire drive laser. The long electron micro bunches are then bunched in a bunching section and accelerated in a room-temperature linac to an energy of approximately ~100 MeV. The beam is then further accelerated in a standard ILC-type superconducting accelerating module to 5 GeV prior to injection in the damping ring. This recommended source can meet the design requirements of 4 1010 electrons/bunch for 2820 bunches per pulse with a 5 Hz rep rate. In order to achieve the required 80% polarization, the proposed photocathode material is a GaAs/GaAsP strained superlattice cathode. Some R&D will be required on the photocathode drive-laser, the generation of a long pulse train from photocathode and on a higher voltage DC gun.
The details of the parameters, proposed configuration, alternative technologies and associated R&D program will be given for each subsystem of the baseline, including the electron source, in the BCD document that we are creating this fall. I will give brief discussions of the main features and issues of the other subsystems in the coming weeks, in anticipation of determining the baseline configuration for the entire machine.