Successful test for CLIC

The CLIC collaboration has commissioned its new installation and put the first beam into operation.

A view of beam lines in the CLIC experimental hall (CLEX).

One week before the spectacular start-up of the LHC, a much smaller operation team was also celebrating the success of a first beam. Early in the afternoon on 3 September, all eyes in the CTF3 collaboration control room were fixed on the camera display showing a small beam profile screen installed at the far end of their accelerator complex. A few minutes later the first bundle of electrons was lighting up the beam profile screen. The end of the drive beam line had been reached!

A first bundle of electrons lighting up the beam profile screen.

This first beam circulating in the completed facility is an important milestone for the CLIC project, which aims to study the feasibility of an electron-positron collider with a centre-of-mass energy of 3 TeV. The 48 kilometre-long collider could be built in the future to complement physics results obtained at the LHC. CLIC’s accelerating principle is based on a two-beam scheme: a drive beam provides power for the accelerating structures, which accelerate the main beam. This novel technique avoids the use of thousands of radiofrequency power sources. In order to test the accelerating technologies for CLIC, a facility, CTF3, is being built and commissioned in steps by an international collaboration that at present includes 27 institutes. Construction started six years ago, making use of equipment and infrastructure which became available after the end of LEP operation.

The CTF3 consists of a 150 MeV electron linear accelerator, followed by two rings, the delay loop and the combiner ring. This part is a scaled-down version of the complex required to generate the drive beam at CLIC. The role of the two rings is to compress the long bunch train from the linac into a short, high current pulse. The compressed beam is then sent into the CLIC experimental hall (CLEX). Designed to test the two-beam acceleration scheme, this houses a second linac, the Probe Beam linac, where the main beam undergoes a first acceleration, and the so-called Two-Beam Test Stand (TBTS). The TBTS is a unique facility that has the two electron beams running in parallel over 10 meters. The compressed drive beam is decelerated in a specially developed radiofrequency structure. The radiofrequency power generated by this deceleration is used to accelerate the main beam. Operating at a radiofrequency of 12 GHz, the main beam acceleration will be tested with the nominal CLIC accelerating gradient of around 100 MV/m.

The success of these commissioning operations not only proves that the beam lines built by the CTF3 collaboration perform well, but also demonstrates that all the control, cooling, power, vacuum and safety systems worked coherently. Well on schedule, it constitutes a major milestone towards the feasibility demonstration of the novel CLIC technology and a conceptual design, expected by 2010, of a Multi-TeV Linear Collider based on the CLIC technology.

Building on this success, a major effort will now go into commissioning the whole CTF3 complex to reach nominal beam parameters. The programme also foresees bringing the Probe Beam linac into operation and installing and testing a first decelerating structure in the TBTS drive beam line. By next year, after installation of the first accelerating section, it will then be ready to probe the two-beam acceleration.