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Optimized first energy stage for CLIC at 380 GeV

Panagiotis Charitos — Tue, 06 Dec 2016 11:10:59 +0000

Optimized first energy stage for CLIC at 380 GeV
by Daniel Schulte & Philipp Roloff (CERN)

The CTF3 test facility at CERN, which has demonstrated CLIC’s novel two-beam acceleration technology (Image credit: Maximilien Brice)

In the post-LHC era, one of CERN’s potential options for the next flagship accelerator is an electron–positron collider at the high-energy frontier; the Compact Linear Collider (CLIC).

In August 2016 the CLIC collaboration, which consists of 75 institutes, published an updated baseline scenario. This scenario starts with a first energy stage at 380 GeV center-of-mass, followed by a second stage with an energy around 1.5 TeV, and a final step to 3 TeV.

Prior to the discovery of the Higgs boson particle, the CLIC conceptual design report (CDR) focused on the design of the 3 TeV stage and has documented the viability of the technology required for this energy. Lower energy stages have been considered with much less detail.

With the information obtained from the Higgs discovery, the optimum energy choice for the first stage was also studied. The physics programme has been evaluated, including detailed studies of realistic detector configurations. The choice of 380GeV would allow detailed measurements of the Higgs boson and the top quark.

To optimize the CLIC accelerator, a systematic design approach has been developed and used to explore a large range of configurations for the RF structures of the main linac. For each structure design, the luminosity performance, power consumption and total cost of the CLIC complex are calculated.

For the first stage, different accelerating structures operating at a somewhat lower accelerating gradient of 72 MV/m will be used to reach the luminosity goal. The design of this will have a cost and power consumption similar to earlier projects at CERN such as LHC with its injectors, whilst it ensures that the cost of the higher-energy stages is not inflated. The design should also be flexible enough to take advantage of projected improvements in RF technology during the construction and operation of the first stage.

In order to upgrade to higher energies, the structures optimized for 380 GeV will be moved to the beginning of the new linear accelerator and the remaining space filled with structures optimized for 3 TeV operation. The RF pulse length of 244 ns is kept the same at all stages to avoid major modifications to the drive-beam generation scheme.

Data taking at the three energy stages is foreseen to last for a period of seven, five and six years, respectively. The stages are interrupted by two upgrade periods of two years, meaning that the overall three-stage CLIC programme would last for 22 years from the start of operation. The duration of each stage is derived from integrated luminosity targets of 500 fb^–1 at 380 GeV, 1.5 ab^–1 at 1.5 TeV and 3 ab^–1 at 3 TeV.

Overview of the CLIC layout at 3 TeV, showing combiner rings (CR), delay loop, damping ring (DR), pre-damping ring (PDR), bunch compressor (BC) and beam delivery system (BDS). The red and green squares represent beam dumps. (Image Credit: CLIC collaboration).

Further improvements are being pursued via an intense R&D programme. For instance, the CLIC study recently proposed a novel design for klystrons that could increase efficiency significantly. In addition, permanent magnets are also being developed that are tunable enough to replace the normal conducting magnets are also being developed as they could reduce power consumption even further.

The goal is to develop a detailed design of both the accelerator and detector in time for the update of the European Strategy for Particle Physics towards the end of the decade.

*A version of this article appeared in the November 2016 issue of CERN Courier.

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issue 19

Mechanical stabilisation of CLIC quadrupoles to the sub nanometre

Sabrina El Yacoubi — Thu, 27 Nov 2014 11:10:37 +0000

Mechanical stabilisation of CLIC quadrupoles to the sub nanometre
by Kurt Artoos (CERN)

A CLIC Main Beam Quad prototype on two stabilisation actuators.
Image credit: CERN

In order to reach the luminosity of 2.1034 cm-2m-1 in CLIC, the cross section of the colliding particle beams at the interaction point will be in the order of the nanometre. Quadrupole magnets are used as focusing elements to keep the beam size small along the full accelerator length and to focus the beams to the collision point

Mechanical vibrations transmitted to the quadrupoles will however create small dynamic displacements of the magnets, resulting in a gradual increase of the beam size along the accelerator and jitter of the beam at the interaction point.

Vibration stabilisation systems were developed and successfully tested both at CERN and at LAPP Annecy under EuCARD WP9 framework. The level of vibrations of the quadrupoles is decreased by the systems to values smaller than a nanometre. The calculated gain in luminosity obtained by this vibration reduction is significant. The magnets are placed on vibration isolating supports based on piezo-electrical actuators that will reduce the vibrations measured by seismometers placed on the ground and on the magnet. The same actuating support makes it also possible to make very precise adjustments to the magnet. A precision of a quarter of a nanometre was already demonstrated on a prototype.

During 2013, new full scale prototypes will be constructed in order to move from a laboratory set-up to an accelerator component, integrated with other technical systems. Improved vibrations sensors are being developed.

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Phase Control at CLIC

Sabrina El Yacoubi — Thu, 27 Nov 2014 10:34:52 +0000

Phase Control at CLIC
by Fabio Marcellini (INFN)

In a two-beam system, the RF power is provided by the drive beam to the main beam accelerating structure. Drive Beam timing errors must be avoided to maximize the acceleration gradient uniformity in the accelerating structures, and consequently to stabilize the Main Beam energy and optimize the collider luminosity. Image credit: CERN.

Extremely precise beam phase control is required for CLICtwo-beam acceleration technology as well as in Free Electron Lasers (FELs). The development of beam arrival time measurement systems has been carried out within Task 5 of the EuCARD Work Package 9, in collaboration with CERN, INFN/LNF and PSI.

In CLIC the Main Beam must be precisely synchronized with respect to the RF power produced by the Drive Beam. Timing errors would have an impact on the collider performance. The Drive Beam phase errors should be controlled, by means of a feed forward system, within 0.1Рat 12 GHz, corresponding to a timing stability below 23 fs, to avoid a luminosity reduction larger than 2%. A prototype of such a system is being installed in the CLIC Test Facility CTF3 and the performances of the beam phase arrival monitor have been already successfully tested.

FELs also require a tight synchronization of the beam with respect to photo injector lasers, RF and other systems. The beam phase measurement has been pursued at PSI with a different approach based on electro optical modulators. It has the advantage of very high band width, allowing the measurement of individual bunches arrival time with a potential resolution below 10 fs. The system was tested and the performance with beam validated at the PSI FEL test injector.

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Accelerators in the European Strategy for Particle Physics meeting in Cracow

Margarita Synanidi — Thu, 27 Nov 2014 08:56:42 +0000

Accelerators in the European Strategy for Particle Physics meeting in Cracow
by Frank Zimmermann (CERN), Roy Aleksan (CEA)

Open Symposium on the European Strategy for Particle Physics (ESPP2012). Image credit: CERN

From 10 to 12 September 2012 about 500 particle physicists and accelerator experts came together in Cracow, Poland, at an Open Symposium organized by the CERN Council to discuss the future European strategy. The Symposium’s Accelerator Science and Technology Session featured two excellent overview talks, on the energy frontier by Caterina Biscari (INFN-LNF) and on the intensity frontier by Mats Lindroos (ESS, on leave from CERN), which were complemented by a lively discussion.

The smooth operation of the LHC represents a huge success. The measures needed to raise the LHC collision energy up to 13-14 TeV by 2014 are at hand. Work is progressing on the technology for the LHC luminosity upgrade (HL-LHC) around 2020. Increasing further the collision energy up to 26-33 TeV in the LHC tunnel requires substantial R&D for 16-20 T magnets (HE-LHC). A new 80-km tunnel could allow reaching energies of 80-100 TeV in proton-proton collisions.

Great progress in the SRF development for the ILC makes the construction of a high-energy lepton collider possible. CLIC with two-beam technology could be an alternative if 3 TeV is needed but R&D is still required. A lower-energy CLIC based on klystrons is also proposed. A number of new ideas for circular or gamma-gamma colliders, to study a “Higgs” particle at 125 GeV have also emerged. Much higher energy using leptons requires muon colliders, dielectric RF structures or plasma acceleration, with increasing complexity. High-power proton linacs, such as ESS and IFMIF, are under construction. Neutrino beams will be improved worldwide.

Many R&D topics are common for various accelerators, e.g. high-field magnets, RF structures & RF power sources, particle sources, alignment & stabilization. The conference brought together experts from these areas, highlighting the need to promote further collaborations with other fields of science.

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CLIC now entering phase two

Margarita Synanidi — Wed, 26 Nov 2014 13:57:11 +0000

CLIC now entering phase two
by Katarina Anthony (CERN)

NCLinac (WP9 of EuCARD) includes improvements to the CLIC test facility CTF3 at CERN. Image credit: CERN

Building on the success of their feasibility phase, the CLIC test facility, CTF3, has just launched into a five-year project development phase. This will involve detailed performance optimisation studies, marking the project’s transition from pure research and development to prototyping and construction.

CTF3’s second phase will focus on selected performance-related research areas for further investigation. The largest of these involves the construction and testing of several authentic CLIC accelerator modules that are currently being assembled at CERN (see image).

Four of the CLIC modules will undergo mechanical testing in laboratory conditions, where they will have their alignment, stabilization and thermal cycling tested. These tests will be done over the next 2 years outside of the CTF3 facility. The remaining three modules will be installed in CTF3’s experimental area. Two further modules will be added in 2014, and will incorporate results from both the laboratory and CTF3 tests.

Alongside the module testing, the CTF3 team will be working to provide synchronicity between CLIC’s drive beam and its main beam. This is accomplished by compensating for any phase “jitters” by adjusting the path length of the drive beam. Phase monitors and a kicker system (which will adjust the beam path) are currently being installed in the facility, and the first system tests are planned for next summer.

Article originally in CERN Bulletin.
Reproduced with permission.

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