The International Workshop on Linear Colliders (IWLC2010) recently brought together many experts involved in research and development for an electron–positron linear collider – the favoured future facility to complement the LHC. Organized by the European Committee for Future Accelerators (ECFA) and hosted by CERN, the meeting took place on 18–22 October and attracted 479 registered participants.
Two complementary technologies are currently being developed for a future linear collider: the International Linear Collider (ILC), based on superconducting RF technology in the tera-electron-volt energy range for colliding beams; and the Compact Linear Collider (CLIC), based on a novel scheme of two-beam acceleration to extend to energies of multi-tera-electron-volts. Taking advantage of a large number of synergies, the two studies are already collaborating closely on a number of technical subjects. These include: beam-delivery systems and machine-detector interfaces; physics and detectors; positron generation; beam dynamics; damping rings; civil engineering and conventional facilities; and cost and schedule.
IWLC2010 merged previously separate workshops on CLIC and ILC for the first time. Covering accelerators as well as detectors and physics, it provided an environment where researchers could exchange ideas, inform their peers about recent achievements and work together on common issues. It also took full advantage of synergies between the two studies, with common working groups to discuss the many shared challenges. The lively discussions, together with the scientific and technical presentations, showed the progress that has been made towards unifying the two study teams into a single linear-collider community.
While the opening and final plenary sessions were held at CERN to facilitate participation and information flow beyond the linear-collider community, the parallel sessions (up to a maximum of 16 simultaneously) were held in the International Conference Centre Geneva. Scheduled activities and satellite meetings started half a day before the workshop formally began and continued throughout. For example, Steinar Stapnes, CERN’s Linear Collider studies leader, presented a colloquium, “Towards a future linear collider”, as an introduction for CERN staff.
CERN’s director-general, Rolf Heuer, introduced the workshop with a presentation on “The LC roadmap” in which he referred to the active role that CERN can play towards defining global linear-collider governance and siting. A plenary session followed that reviewed the physics prospects of linear colliders, the status of the ILC and CLIC accelerators, the concepts for detectors (ILD, SiD and CLIC) and R&D activities for detectors. Another plenary session addressed the potential impact of LHC and Tevatron physics on the linear collider.
Three days were filled with parallel sessions. Some took place as separate accelerator or physics and detector sessions, but many came together in various combinations, with strong interaction between the two communities. In particular, there was a lively discussion session on the scientific imperative to vary the machine energy over a wide range and to scan over energy thresholds, while maintaining adequate luminosity. The progress of the machine designs towards this goal was reviewed and discussed. Excellent progress has been made on both studies towards their next milestones: CLIC will present its Conceptual Design Report for accelerator and detectors in 2011, while the ILC accelerator and the two validated ILC detector concepts – ILD and SiD – will publish a more advanced technical design report and a detailed baseline design, respectively, in 2012.
In particular, the ILC study has achieved its 2010 goal of demonstrating that half of the superconducting accelerating structures produced for the ILC reach the desired acceleration gradient. The successful operation of two advanced test facilities, CESR-TA at Cornell, in the US, and ATF2 at KEK, in Japan, have led to major advances across a range of subjects. The work at CESR-TA has significantly deepened understanding of electron-cloud effects, leading to several promising ways in which they could be mitigated. ATF2 continues to produce important results in many areas of beam instrumentation and beam optics.
As far as CLIC is concerned, the CTF3 test facility, which adresses the major feasibility issues of the novel CLIC technology, is near completion and is being commissioned. There has been important progress on the high-intensity drive-beam generation, which uses complex beam manipulation; on the use of this beam to produce RF power with special power-extraction and transfer structures (PETS); and on the use of this power to accelerate a probe beam, thus demonstrating the feasibility of the two-beam acceleration scheme. First measurements of the beam quality have shown current stability better than the demanding CLIC requirements. Accelerating structures that include waveguide damping features have achieved performances close to CLIC’s target in the first tests at KEK and SLAC. Measurements on a model of the mechanical quadrupole-stabilization system showed good decoupling from ground motion with a residual level consistent with the beam stability specifications.
Regarding the ILC detectors, community-wide detector R&D has led to important advances on high-precision vertex technology, highly granular calorimetry for particle flow, as well as developments in time-projection chambers based on micro-pattern gas detectors. Many of these efforts now proceed together with the CLIC study. For the CLIC detector study, recent simulations of detector performances under CLIC beam conditions have allowed the detector geometries for the CLIC_ILD and CLIC_SiD concepts to be fixed for presentation in the conceptual design report.
In all, this first joint linear-collider workshop was unanimously considered a great success, fostering mutual co-operation on both a regional and a global basis. The next joint workshop is planned to take place in Grenada on 26–30 September 2011.
• For more about IWLC2010, see https://espace.cern.ch/LC2010/default.aspx.
