Résumé

EuCARD arrive à bon port

Après plus de quatre ans d’existence, le projet EuCARD de R&D sur les accélérateurs est arrivé à son terme le 31 juillet 2013, ayant réussi à atteindre la plupart de ses objectifs, pourtant ambitieux. Le projet était axé sur la R&D générale et ciblée pour des accélérateurs de pointe dans les domaines de la physique des particules, de la physique nucléaire et des applications de rayonnement synchrotron. Parmi les aspects abordés, des travaux sur les aimants supraconducteurs à champ élevé et des avancées importantes concernant l’assemblage et l’intégration, avec une précision extrême, de modules radiofréquence pour un futur collisionneur linéaire électron-positon. De plus, deux installations d’essai ont été ouvertes à l’" accès transnational " et un réseau scientifique a été constitué sur le sujet de l’accélération laser dans un plasma.

The EuCARD project for accelerator R&D came to an end on 31 July 2013, more than four years after starting on 1 April 2009 (CERN Courier November 2009 p16). The project’s focus has been generic and targeted R&D for frontier accelerators in the fields of particle physics, nuclear physics and synchrotron radiation applications. Many accelerator infrastructures or projects were involved, including the upgrades for the LHC at CERN; the Facility for Antiproton and Ion Research (FAIR); the European free-electron laser project, XFEL, and FLASH at DESY; and the studies for the Compact Linear Collider (CLIC) and International Linear Collider (ILC).

A framework for collaborative R&D finds its justifications in the extreme technological challenges, the synergies between projects or studies and the complementary competences of laboratories, universities and institutes. R&D naturally precedes the design stage but is not confined to it. It continues during the lifetime of the accelerator to allow the large infrastructures to remain at the forefront of research and make the best use of society’s significant investments.

The EuCARD project was initiated by the European Steering Group on Accelerator R&D (ESGARD) as successor to the Coordinated Accelerator Research in Europe (CARE) project, which ran under FP6 from 2004 to 2008. Its total cost was €36 million, with €10 million covered by a European Union Seventh Framework Programme (FP7) grant. The remaining €26 million came through matching funds from the 38 EuCARD partners, who represent most of the European accelerator laboratories, as well as a large number of universities and specialized institutes. CERN provided co-ordination and project management. The project’s work was organized around three poles: scientific networks, open access to facilities and collaborative research activities.

Following CARE, the EuCARD networks have consolidated their positions as recognized platforms for the international exchange of ideas and experts – from Europe, Japan, the US, and beyond. Providing support for accelerator centres, they organized more than 50 topical workshops on diverse themes, from electron-cloud mitigation, through RF test stations, crab cavities and so on, to long-term visions of future developments.

The networks originally included neutrino facilities, accelerators and colliders (performance and RF technologies). Later, another network was launched on laser-plasma acceleration, with the primary goal of federating the many European research teams around a common road map. The ambitious objective was to collaborate on a transition from the demonstration of the plasma-wakefield concept to operational accelerators. The network bridges the gap between accelerator, laser and plasma communities and after a successful start is now funded fully in EuCARD’s successor – EuCARD-2.

A main objective and result of the neutrino networks was to contribute to the update to the European Strategy for Particle Physics by allowing the community to discuss strategies and prepare summary documents, one of which was submitted to the update process. The community acknowledges the conclusions of the updated strategy, which recognizes the need to re-establish an accelerator-based programme at CERN.

A major outcome of the accelerator networks is an ambitious vision for future facilities for high-energy physics, from the LHC luminosity and energy upgrades through unconventional lepton and photon colliders to hadron colliders in the 100 TeV range (figure 1). This effort, which included helping to define key R&D areas for the coming decades, has the potential to guide debates on the future of frontier accelerators at a European level.

Transnational access

Two test facilities were open in EuCARD to transnational access: HiRadMat at CERN’s Super Proton Synchrotron (SPS) and MICE at the Rutherford Appleton Laboratory (RAL). The European Commission funding of these activities was dedicated mostly to the support of visits and research by new users.

HiRadMat – the High Irradiation to Materials facility – was constructed at CERN in 2011 to provide high-intensity pulsed beams to an irradiation area where material samples as well as accelerator components can be tested (figure 2). During the duration of EuCARD, nine user projects and 19 users were supported via transnational access (HiRadMat@SPS). When the SPS restarts in autumn 2014, the facility will be open to transnational access in the framework of EuCARD-2. Several communities have already expressed interest.

The UK’s Science and Technology Facilities Council (STFC) provided transnational access to a specialized precision beamline at the Muon Ionization Cooling Experiment (MICE) at the ISIS facility at RAL. A total of 19 researchers from eight institutes were supported for 131 visits during EuCARD’s lifetime.

Joint research activities had the lion’s share in EuCARD, with 87% of the total budget, about 50 objectives that led to concrete results and as many reports containing scientific results. Many of the developments are described in the EuCARD Final Report, soon to be published as a EuCARD monograph. Here are a few highlights.

Under EuCARD, R&D was initiated in Europe for the first time on high-field Nb3Sn magnets (figure 3) and on high-temperature superconducting (HTS) yttrium barium copper oxide (YBCO) inserts. Together, these initiatives are ushering in the era of magnets with fields in the 20 T range. After overcoming many challenges with these delicate superconductors – such as the high strains, insulation and required resistance to radiation – the work is well advanced, with the final results expected in two years. Success will open the door to a new generation of accelerators at the energy frontier, including the energy upgrade of the LHC. In the nearer future, it will allow the upgrade of CERN’s FRESCA test station for superconducting cables, which is used also by the ITER fusion project, for example. Other possible application areas could be nuclear magnetic resonance and magnetic resonance imaging.

The HTS electrical-link demonstrator at CERN is fully operational. It will allow energy-efficient remote powering of magnets. This will have a positive impact on the LHC upgrade, allowing powering away from radiation areas. The principle, studied in collaboration with industry, may also find applications in the energy domain.

Studies of new robust materials for beam collimation have pointed to metal–diamond or metal–graphite composites that offer promising solutions when increasing the energy or power of accelerator beams. The use of HiRadMat was instrumental in the characterization of these novel, more robust materials. The "smart" LHC collimator and the cryo-catcher for FAIR (figure 4) were designed, built and successfully tested with beams.

EuCARD’s contribution to linear colliders is deeply integrated in the CLIC and ILC studies. Significant progress was made in the ultra-precise assembly and integration of RF modules, thermal stabilization, ultra-precise phase control to 20 fs and beam control. The active mechanical stabilization of magnets to a fraction of a nanometre is especially impressive, as are the highly sophisticated simulations of RF breakdowns, which show new microscopic mechanisms and offer directions for mitigation. The study of an innovative compact crab cavity also gave momentum to this R&D line, going well beyond the original plans with the fabrication of a bulk-niobium superconducting unit. This is now part of the baseline LHC luminosity upgrade project.

In other work on superconducting RF, the strategy for fabrication and processing of cavities for proton linacs should set a new higher standard for accelerating gradients. This is of relevance for all proton linacs, for example for the European Spallation Source and accelerator-driven systems. Progress has been made on the delicate process of sputtering a thin film of niobium onto a copper RF cavity, but full validation remains to be done. Experts believe that this technique – pioneered for phase 2 of CERN’s Large Electron-Positron collider – could reach much higher gradients, well in excess of the performance of bulk niobium, which has reached close to its theoretical limit. High-performance cavities also require higher-performance RF couplers to feed them. The R&D on an automatic cleaning machine is a step forward, needing a demonstrator, and promises to decrease significantly the cost and duration of the processing of couplers for large accelerators.

In the field of diagnostics and control, FLASH is benefiting from an upgraded modular low-level RF, with the novelty that it is based on a commercial telecommunication standard. Already being commissioned, it provides a significant gain in field stability. Such a control system could be used by the XFEL or adapted for the ILC.

EuCARD also set aside about 10% of its budget for joint research studies on unconventional concepts, such as crab-waist crossing, diagnostics for the nonscaling fixed-field alternating gradient machine EMMA at Daresbury Laboratory, and emittance measurements for the widely diverging beams of laser-plasma accelerators. This could lead to interesting contributions to the field.

Making an impact

By co-funding scientific research, the European Union (EU) aims to strengthen the collaboration between European institutes and universities, to implement the well-known adage "union is strength". Therefore each project must evaluate its impact on a progressive integration of effort.

EuCARD’s main impact has probably been to encourage scientists at accelerator centres to adapt to collaborative working methods that involve distributed work and decision making. Challenges are, in a first phase, the minimization of overheads as a result of collaborative working methods requiring more reporting, for example; and in a second phase, to make best use of the added potential of collaborative work. Like CARE and other European projects, EuCARD has provided invaluable hands-on experience in this context to its members – inspired by the organization of the particle-physics community, but adapted to the field of accelerators with its different boundary conditions.

Beyond this qualitative impact, EuCARD’s legacy will include a series of scientific monographs on accelerator sciences. In addition, a quarterly newsletter, Accelerating News, created by EuCARD, was extended to all EU accelerator projects and beyond, and now reaches more than 1100 subscribers. Both will continue serving the community via EuCARD-2 and the TIARA project (CERN Courier June 2011 p28).

Other impact has been at the EU policy level, where accelerator R&D was ranked highly in a survey among EU project co-ordinators. The project has contributed to the birth of other FP7 ventures, such as HiLumi-LHC, and allowed stronger co-operation via networks with laboratories in the US and with KEK in Japan, the latter now being a full member of HiLumi-LHC. EuCARD also established a bridge with the FP7 project ICAN, with its focus on high-power high-repetition-rate lasers potentially suitable for laser acceleration (CERN Courier November 2013 p21).

Experience with EuCARD has enabled the concept for Enhanced European Coordination for Accelerator R&D – EuCARD-2 – to be defined in ESGARD. This next phase of co-ordinated accelerator R&D started on 1 May. It will run for four years with a total budget of €23.4 million and provide a framework for 40 research institutes across the world. EuCARD-2 has networks on innovation, energy efficiency, accelerator applications, extreme beams, low-emittance rings, and novel accelerators. HiRadMat@SPS will continue to provide access for new users, as will the Ionisation Cooling Test Facility – ICTF@RAL. The R&D activities will address the technological limits of current machines with regard to magnetic fields, RF gradients and technologies, and collimator materials. There will also be dedicated activity on plasma-wakefield acceleration as an alternative to current approaches.