Accelerator Physics

To obtain the desired luminosity, the ILC must collide in the Interaction region long trains of bunches that have transverse dimensions of roughly 300nm by 5nm. To do this the required the normalized emittance of the beam should be extremely small. For example, the vertical emittance is about ~20 nm*rad. It is a challenge task to create and damp beams with such a small emiitances in the Main Damping Ring and then preserve it during the transportation and acceleration along ~25 km low emittance transport line (LET) before collision. The Low Emittance Transport is the region from the MDR extraction to the IP, and contains as sub-regions the Bunch Compressor (BC), Main Linac (ML), Beam Delivery System (BDS), and Interaction Region (IR).

Unlike many other accelerators, ILC linac cant count on initial alignment of the all accelerator components only. Static and dynamic imperfections in the LET impact the luminosity performance; examples are the survey errors of beamline components and ground motion. Preserving the ultra-small emittances requires component alignment tolerances far beyond that which can be achieved by traditional mechanical and optical alignment techniques, hence the use of beam-based alignment and tuning techniques are essential in obtaining the design luminosity. The corresponding sensitivity to ground motion and vibration mandates the use of continuous trajectory correction feedback systems in maintaining that luminosity. Fast intra-train feed back system will care on beam stability in the collision point. Pulse-to-pulse stability will be provided by slow feed-back system. In the interaction region high resolution nano-BPMs and luminosity monitor together with ultra-fast kickers will keep beam in collision.

The accelerator physics group must develop the necessary procedures, specify the required hardware and assess the potential luminosity degradations. Fermilab group in collaboration with other groups from SLAC, Cornell University, DESY, CERN, Daresbury/UK, KEK is working on LET lattice design and beam studies in ILC linacs.