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International Linear Collider and High Gradient Superconducting RF-Cavities

Periodic Report Summary 4 - ILC-HIGRADE (International Linear Collider and High Gradient Superconducting RF-Cavities)

Project Context and Objectives:

A linear e+e- collider has long been the next major project in High Energy Physics following the successful start of operations of the Large Hadron Collider (LHC) and the first presentations of physics results. A linear collider has been prominently positioned in the European Strategy for Particle Physics agreed by CERN Council, which served as the basis for ESFRI recommendations for High Energy Physics (HEP) in 2007. The initial physics results from the LHC give confidence that the field will receive more guidance from the LHC by the end of 2012 – when large statistics samples become available – on the detailed design decisions for such a linear collider, in particular the energy reach of such a facility. This impression is particularly spurred by the findings of the two general-purpose detectors at the LHC, which narrowed considerably the mass window for a possible Higgs boson and may have seen first experimental indications of its existence. It is generally believed that by the end of 2012 the mystery of the existence of the Standard Model Higgs boson will be resolved. This finding and additional information from the LHCC bodes well and timely for the update of the European Strategy, which will be released early in the year 2013. A process has been launched in the community to seek input for establishing the proper strategy for the coming five years.
In the energy range from 500 to 1000 GeV a design for such a machine exists: the e+e- International Linear Collider (ILC). It is well understood today that the ILC will constitute the precision tool for the Terascale, the scale of electroweak symmetry breaking. The ILC complements the potential of the LHC, which has been charting this unknown territory in earnest since 2010. – If a much farther leap into the Terascale is suggested by the physics results one will have to revisit the optimisation of the layout and time scales. Today a proven technology for the multi-TeV energy region does not exist. For this reason the R&D on the Compact Linear Collider (CLIC) technology has been identified as a field of intense research in the recommendations of the European Strategy for Particle Physics.
The ILC-HiGrade consortium concentrates on the rapid realisation of the International Linear Collider ILC and brings together the key players in Europe. They constitute a large fraction of the European element of the Global Design Effort (GDE) that has led to the publication of the Reference Design Report (RDR) in 2007. The report forms the basis for the Technical Design Phases I and II of the ILC, which the GDE will complete by mid-2012. The proposal for the ILC will then be presented to the global stakeholders, i.e. governments and funding agencies to seek approval. The technically driven schedule envisages start of construction as early as 2012. Project approval and start of construction is a two-stage process.
Starting in 2008, the ILC-HiGrade Consortium began to address important elements in this two-stage process with siting of the facility as one major ingredient. Currently site proposals for all three regions Japan, US and in Europe exist. Their benefits are being evaluated and the international framework in which the project will be realised will be developed. ILC-HiGrade encompasses the European side in this global endeavour. The participating laboratories and universities contribute their long-standing experience in conceiving large-scale experiments and the organisation of large collaborations to a process that establishes the global framework for an organisation that will support start of construction matching the technical timelines.
The linear accelerator sections of the ILC constitute a major cost-driver. Their design and their cost depend on the achievable accelerating gradient for the ILC. The global gradient development programme of the GDE will establish a realistic operational gradient for the ILC by employing proven preparation techniques, with European laboratories leading the effort. In the course of ILC-HiGrade, the partners are preparing 24 fully dressed cavities, which will initially serve as a technical reference for the decision on the choice of gradient and eventually as the industrialisation of the high-gradient process. While their delivery is pending important steps have been made to prepare the facilities and the instrumentation for analysis and full diagnostics. Particular achievements have been made in the reporting period as detailed below.
The timelines of this 4-year project are well aligned with those of the Global Design Effort, aimed at establishing the technical basis for proposing the ILC by 2012. It thus matches the timelines of the iteration on the European Strategy for the High Energy Physics. If chosen, the ILC construction could commence soon after.
From a European perspective, all crucial elements necessary to produce this outcome, both technical and political are reinforced and explicitly supported in the ILC-HiGrade project.

Project Results:
On a worldwide scale the ILC project is well on track to deliver its Technical Design Report by 2012, which is the target defined for the Global Design Effort. The Technical Design Report will describe the International Linear Collider to a level that is amenable to the detailed engineering design. Major technical hurdles will have been investigated and tested in prototypes so that actual solutions exist. ILC-HiGrade contributes to this worldwide effort by advancing the research on the accelerating fields of the e+e- linacs. The performance of the superconducting cavities is a cost driver of the project and hence a critical component. ILC-HiGrade so far has established methods that identify the limitations in gradient. ILC-HiGrade also contributes to the global development where a significant increase in gradient has been observed over the past few years.
ILC-HiGrade has also investigated governance structures for an international project like the ILC. The bases for this investigation are the existing international projects such as the LHC at CERN and ITER in Cadarache.
The siting of such a facility is driven in part by technical demands and specific site properties such as ground motion. In the end the site for a facility such as the ILC will be decided upon in a political process. ILC-HiGrade has described some of the criteria relevant for this decision process. An interim version of this report is available.

Potential Impact:
The high-gradient research pursued in this project will lead to accelerating structures that are more cost-effective. The benefit for the ILC is immediate: the total length of the facility can be adapted or better even a higher energy for the colliding beams can be achieved. The results are however farther reaching. Superconducting cavities are nowadays used in many areas where intense beams are needed in near continuous wave operation (cw-operation). Their efficiency is largely dependent on the quality of the cavities, the so-called quality factor. The quality of a cavity is directly correlated with the maximum field that can be supported by the cavity. High-gradient cavities thus benefit many fields of accelerator application. Room-temperature copper-based structure cannot sustain the power for an extended period.
The impact of the International Linear Collider as a scientific instrument touches immediately on the fundamental questions of the existence of the universe and of mankind. The desire to understand the formation of the world we live in from its origin in the big bang and the nature of the forces that govern this process originates from a curiosity that is not driven by an immediate technological application but rather has to be seen in the context of accumulating knowledge that serves the well-being of future generations. Fundamental research often has led to surprises and has facilitated “solutions” that were unthinkable before. In the end it is up to society to find the right balance between fundamental and applied research. The motivation for the International Linear Collider is fundamental research; its technological developments are already now seen to have a large impact in applied research.

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