CLIC-a compact and efficient high energy linear collider

Abstract

A description of the original CLIC two-beam scheme is given in [1]. The overall layout of the 1 TeV machine is shown in Fig.1. The main linac consists of normal conducting travelling wave accelerating structures operating at a frequency of 30 GHz and a gradient of 80 MV/m. One in ten of these sections have an asymmetric geometry and act as microwave quadrupoles for BNS damping. For multi-bunch operation damped and/or detuned structures would be required. The 30 GHz RF power is supplied by transfer structures which extract energy from a 3 GeV high-intensity electron drive linac running parallel to the main linac in the same tunnel. The transfer structure consists of a 11.5 mm diameter circular beam tube coupled through two diametrically-opposite ≈5mm wide slots to two periodicallyloaded rectangular waveguides. Each 50 cm long section produces two simultaneous 11.6 ns long 44.6 MW power pulses which drive two accelerating structures. This output power corresponds to 95% of the energy extracted from the beam. Two full-length (84 cell) constant impedance undamped accelerating section have been tested to an average accelerating gradient of 94 MV/m without any signs of breakdown and the periodically-loaded output waveguides of a full-length transfer structure have withstood 60 MW of 30 GHz RF power without breakdown but the structure itself has not yet been tested with a bunched beam Prototype diamond machined discs with the asymmetric geometry required for microwave quadrupole sections have been successfully produced by industry, and studies of damped structures for multibunch operation are underway. High gradient tests have also been made at SLAC on a 26-cell CERN-built X-band section [2]. Average accelerating gradients of 125 MV/m (a peak surface field of 285 MV/m) were obtained after 10 7 shots at 60 Hz with a pulse length of 150 ns. After conditioning, the dark current was 2µA at 50 MV/m and 150µA at 80 MV/m.

CLIC Test Facility developments and results

“…The beam exits the gun with a momentum of 4.5ÊMeV/c and is then accelerated up to 92ÊMeV/c by the S-band travelling wave accelerating section. 30ÊGHz power is generated when the beam is passed through the -un-powered -prototype CLIC main linac accelerating section [1]. The power is fed to the second prototype main linac accelerating section and the accelerating gradient produced in it is directly measured by reaccelerating the lead bunch of the drive train.…”

Pre-alignment of CLIC using the double-wire method

“…Transverse alignment tolerances of about 10μ (rms) are required for the Compact Linear Collider (CLIC) [1] in order to limit the emittance blow-up due to transversely deflecting wakefields to reasonable values. An active alignment system using precision micromovers is proposed to achieve these tight tolerances.…”

Generation of a 30 GHz train of bunches using a magnetic switch-yard

“…The CLIC project of a e + elinear collider is based on the two-beam accelerator scheme [1]. The electron and positron beams are accelerated in 30 GHz accelerating structures, the needed rf power being generated by the interaction of a high power relativistic electron beam (the Drive Beam), running parallel to the main linac, with appropriate rf structures resonant at 30 GHz (transfer structures).…”