Normal Conducting CLIC Technology

The CLIC (Compact Linear Collider) multi‐lateral study group based at CERN is studying the technology for an electron‐positron linear collider with a centre‐of‐mass energy up to 5 TeV. In contrast to the International Linear Collider (ILC) study which has chosen to use super‐conducting cavities with accelerating gradients in the range of 30–40 MV/m to obtain centre‐of‐mass collision energies of 0.5–1 TeV, the CLIC study aims to use a normal‐conducting system based on two‐beam technology with gradients of 150 MV/m. It is generally accepted that this change in technology is not only necessary but the only viable choice for a cost‐effective multi‐TeV collider. The CLIC study group is studying the technology issues of such a machine, and is in particular developing state‐of‐the‐art 30 GHz molybdenum‐iris accelerating structures and power extraction and transfer structures (PETS). The accelerating structure has a new geometry which includes fully‐profiled RF surfaces optimised to minimize surface fields, and hybrid damping using both iris slots and radial waveguides. A newly‐developed structure‐optimisation procedure has been used to simultaneously balance surface fields, power flow, short and long‐range transverse wakefields, RF‐to‐beam efficiency and the ratio of luminosity to input power. The slotted irises allow a simple structure fabrication by high‐precision high‐speed 3D milling of just four pieces, and an even easier bolted assembly in a vacuum chamber.