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A heavy-duty crane on the surface will transport the assembled detector slices to the hall below. Graphic: Marco Oriunno

Sometimes big things have to move in the way of small things to find exciting things. The ILC detectors, for example. True to the scientific principle of reproducibility of results, two detectors, ILD and SiD, will one day record what happens when electrons and positrons collide so that one can verify (or not) what the other has observed, using different detection technologies. However, they will never be able to do this simultaneously as there will be only one interaction point. The detectors will have to move into and out of the beam in as short a time as possible for maximum data harvest, and this caused detector designers, machine experts and the guys who know all about shifting rock no end of headache. Now they have found a solution that addresses all problems (at least for an ILC that is not built in a mountainous region).

The final design for the non-mountain hall for the detectors is shaped like a Z. The downstroke, which actually is at right angles to the side bits, is where the beams come in, and the side bits are the garages for the detectors when they are not in use. Though rather compact compared to the LHC’s giant ATLAS detector, both ILD and SiD are heavyweights, and with dimensions up to 16 metres in length and up to 15,000 tonnes on the scales, they are not easily pulled around. The total surface area of the hall, therefore, also measures over 3300 square metres. This allows not only for smooth operation, but also for easier assembly and maintenance.

Assembly is the main argument for the final choice of shafts that are needed for the ILC’s collision point. There will be one big shaft, 18 metres in diameter, right above the central part of the Z for the lowering of the giant detector slices, magnet coils and endcaps. Like the CMS detector at CERN, the two ILC detectors will be assembled on the surface and then lowered underground in complete slices. Two smaller shafts – nine and ten metres in diameter – give access from above to the two garages for detector maintenance, and another two are for people only so that they can get down and up easily and also have an escape route in case of an evacuation.

Spot the Z shape – one detector in parking position, one taking data. The non-mountainous detector hall for the ILC could look like this. Graphic: Marco Oriunno

Now obviously things will not be as easy as they may sound here. “We faced the problem of how to make both detectors fit the space between the two tunnels. And it’s the first time in history that two detectors share one interaction space in a push-pull-configuration,” says Marco Oriunno of SLAC, a member of the common task group on machine-detector interface and responsible for the impressive 3-D graphics of the area.

How do you move a 15,000-tonne object from a garage into the beam and back some 15 times a year? How do you make sure none of the high-tech, mega-precise parts move during the transport? How do you keep the magnets cool? The answer is: concrete slabs that serve as platforms for the detectors and will be moved by either airpads or rollers, and flexible cryogenic lines that move with the moving detector. A set of compressors on the surface makes sure that enough coolant is around while two cold boxes, one for each detector, will be installed underground. The lines extend from the garage to the interaction point. And the detectors adapted their configurations to each other so that both reach the beampipe shielding that sticks out at both sides of the central hall. Both also had to be self-shielding with respect to ionising radiation and magnetic fields for hall safety.

The shielding around the beampipe and the detectors’ self-shielding material are the only protective screens needed for the hall design. Maintenance on one detector will be possible underground while the other is busy taking data. The group also thought about how to organise beam commissioning. Before you start colliding particles, the machine operators have to take a series of important steps to truly understand and control their machine. A stray beam can cause great damage in a sensitive detector, so commissioning will not happen with a detector in place. Instead, walls of shielding blocks will be erected around the beam pipe so that work can continue on both the assembly of the detectors and the commissioning of the accelerator.

All this will be very different if the ILC is built under a mountain range. Shafts will not be vertical, for example, and the transport of the detector parts will be different. The design of the hall for these conditions is still a work in progress. Similarly, a civil engineering company is currently working on detailed studies of what can be expected of the non-mountainous geology when five shafts of different diameters are dug within relatively close distance to each other, and a detailed design of the moving platforms. Stay tuned for future info!

The push-pull concept as illustrated from the CERN ARUP report, considering the scheme for both CLIC and ILC

Since the inception of the ILC design effort, we have been developing the concepts for detectors to do the science as an integral part of our work. The interactions between the accelerator and the detectors are complex and demanding. For that reason, we have a group of accelerator and detector experts working together on machine-detector interface (MDI) issues. The ILC physics programme is based on building two complementary detectors that will share beam time. The value of having two detectors with different designs, technologies, collaborations and emphasis has proven to be a very effective way to exploit the science, as evidenced through three generations of colliders.

The push-pull interaction region layout from the US study, including surface support buildings

In the ILC Reference Design Report (RDR), chapter 8 of the detector volume very effectively outlines the arguments for having two detectors. To quote the introduction to that chapter: “The ILC’s scientific productivity will be optimised with two complementary detectors operated by independent international collaborations, time-sharing the luminosity. This will ensure the greatest yield of science, guarantee that discoveries can be confirmed and precision results can be cross-checked, provide the efficiency of operations, reliability, and insurance against mishap demanded for a project of this magnitude, and enable the broadest support and participation in the ILC’s scientific programme.” The arguments for planning for two detectors are further discussed in the chapter.

However, in carrying out the early design work, it soon became apparent that designing two independent beam lines that alternately share the beam would be an expensive proposition. The problem is that the beam delivery system for the ILC is in itself a long, complex and demanding system and therefore the cost of building two such systems was forbidding. As a result, in the RDR, we proposed using a push-pull concept to cost-effectively share the beam between two detectors. Previous detectors have been built such that they can be moved on and off the beamline for servicing and upgrades, but the demands were far less than for the ILC, where we want to be able to change between the detectors on relatively short time scales and with little down time. At the time of the RDR, we were able to determine that there appeared to be no show stoppers in this scheme for the RDR, but were not able to develop a design that could accommodate the differences between detectors and meet the other ambitious requirements.

A study of the concrete slab deformation under the detectors in the Japanese interaction region study

For the Technical Design Report, we undertook to carry out engineering designs, and for rather different sites. Now we have completed concepts to accommodate two detectors on a common platform, and have defined access and staging areas and to meet the other demanding technical requirements. It is also interesting that the Compact Linear Collider (CLIC) Study has adopted the push-pull system as well, with some specific differences to meet their more severe requirements for the stability of the final focus.

The CERN ARUP (a civil engineering consultant company) study concluded that the displacement limits of plus or minus 2 millimetres can be achieved by moving ILD on a 2.2-metre slab and SiD on a 3.8-metre slab, both with pads or rollers. They recommend future work on the movement system and an evaluation of the slab final positioning systems. Their study of the overall cavern performance under load in the CERN geology is somewhat marginal and depends on the detailed geology, in situ stresses and the construction sequence.

We are now reviewing the facility costs for the ILC push-pull designs, in order to ensure that we maintain the same cost consciousness for these facilities as we are for the rest of the ILC complex. Overall, however, we have established the reality of employing a push-pull system for ILC (and CLIC) and have identified the issues needing further study.

Learn more about the relationship between vacuum and “virtual” particles, the Higgs boson, supersymmetry and dark energy

Vic Kuchler, Fermilab, Americas Conventional Facilities Leader

The fourth Baseline Technical Review, held at CERN on 22 and 23 March, focused on conventional facilities and siting. All significant changes to the 2007 Reference Design Report (RDR) baseline were reviewed and evaluated for impacts on performance, cost and related systems. This was the last of the formal reviews of the Technical Design Report baseline, so the main activity now officially moves to producing the TDR by the end of 2012. Some further changes may still be incorporated as costing information becomes available or because of other new considerations over the coming months. However, we now consider the TDR baseline as established. The main task now is now to produce the report.

John Osborne, European Conventional Facilities Leader

There has been a set of changes to the RDR baseline, many of which have impacts on the conventional facilities. For example, we have changed to a single excavated tunnel for all sites, changing the tunnelling requirements; the electrical and mechanical loads are changed; the damping rings have been reduced in size, reducing the amount of tunnel required; the interaction region configurations and requirements are better defined; and a detector platform and moving system has been defined. Other systems have been refined and the better information is being used for the TDR costing.

Atsushi Enomoto, KEK, Asian Conventional Facilities Leader

One change that became obvious sitting through these conventional facility TDR reviews is how the design and issues have become more refined and the ways in which the detailed solutions are site-dependent. At the time of the RDR, we expected to see differences between sites and, for that reason, we asked and received a sample site from each region (Europe, Asia and the Americas). But in fact, at that time our knowledge of technical details and sites was limited, so we presented one design that would be used in any of the three sites. For the TDR design, many technical features are site-dependent. That means both the technical solutions (for example, distribution of high-level radiofrequency (RF) power), and the tunnelling and other solutions are site-dependent, even the shape of the underground tunnels. This leaves us grappling with the dilemma of how to present the multiple schemes we have studied. I will discuss this issue further, as we decide how to best handle these variations in the design in the TDR.

The conventional facility designs as presented for each region are considerably more detailed, especially regarding the mechanical, electrical and safety systems. A very productive pre-meeting was held on 21 March, reviewing with industrial consultants the detailed electrical and mechanical systems, and taking advantage of the expertise and experience that exists at CERN. Representatives from the Asian region presented mechanical and electrical designs that have been developed using the Asian region high-level RF system that are suitable for a mountain site in Japan. Representatives from the Americas region presented mechanical and electrical designs that have been developed for the klystron cluster RF system for the Americas sample site.

In addition to the changes and refinements discussed above, there is a much better understanding of the interaction region and of how to compatibly incorporate the two detector groups’ “Letters of Intent” in a push-pull scheme to enable alternating which detector is on the beamline. I will address this whole region and the present concept and issues in a separate column.

This week, linear collider researchers meet in Daegu, Korea for KILC12. Among other topics, they discussed the final production stages of the Detailed Baseline Design and Technical Design Report. To top it all off, conference organisers are treating attendees to their choice of excursions through the vibrant city of Daegu.

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Signposts point the way along a narrow track that can be difficult to find. Image: Youhei Morita

When I was a young postdoc, the only roadmaps I was familiar with were useful for planning vacations. In particle physics, we didn’t necessarily know where we were going but we still seemed to reach our goals with the vehicles to hand: PETRA at DESY, to discover the gluon, SppbarS (or SPS) at CERN, to discover the W and Z, LEP at CERN to put the Standard Model on firm footing, the Tevatron at Fermilab, to discover the top quark. I don’t remember if we had a roadmap when we were discussing the Large Hadron Collider (LHC) and the Superconducting Supercollider, but if we did, it surely included a linear electron-positron collider to complement the LHC and investigate the finer details of the hoped-for discoveries.

One thing is however certain: roadmaps like many things in life become outdated and eventually misleading and useless. The only way to avoid this is to update them when it is clear that the landscape has, or is about to, change significantly. In 2005, CERN Council reinvented its role, laid out in the CERN Convention, of leading European developments in particle physics that could go beyond CERN the laboratory in Geneva. After a year of deliberations in 2006, including an open meeting at LAL in Orsay for the community to express its views, the steering group produced a document that set out the European priorities. These were the delivery and exploitation of the LHC, R&D into accelerators, including the Compact Linear Collider (CLIC) Study, support of the ILC as the next likely machine for energy-frontier research and a variety of other measures. By agreement with the European Union, this document was incorporated into the European Strategy Forum for Research Infrastructures’ (ESFRI) own roadmap for large-scale facilities with a substantial European involvement.  This opened up a variety of EU Framework 7 funding opportunities for the cornerstones of the CERN Roadmap, LHC, ILC and CLIC. For the ILC, we have received substantial R&D funding as well as support for investigations into governance for an ILC laboratory from the ILC-HiGrade project, which has just finished its funding. Other EU projects with ILC involvement enabled via the ESFRI roadmap include CRISP, which is in its early stages, and is designed to share best practice and information between a variety of so-called “preparatory phase” projects, such as the ILC.

CERN Council agreed that the European Roadmap should be reviewed and revised every five years. This review was thus put in train last year with a view to producing a new strategy early in 2013, which will then be formally adopted at a meeting in Brussels in May or June 2013. This is planned to coincide with a meeting involving European Research Ministers so that they can be exposed to the new strategy. A call for input both from individuals and interest groups has been issued by the CERN Council Strategy Secretariat, led by Tatsuya Nakada. These inputs should be available in advance of the Open Meeting to be held in Cracow from 10 to 13 September.

I, as European Director of the ILC Global Design Effort (GDE), Steinar Stapnes as Leader of the CERN Linear Collider Study and Juan Fuster as Chair of the European Committee for Future Accelerators (ECFA) Study for the Linear Collider, discussed how best to prepare an input to this process. The first thing we decided was that it made no sense to have a specifically European response on an issue which is of its very nature completely international; the input should be carefully coordinated with our colleagues from other regions. On the other hand, there are particular European issues and perspectives that ought to be reflected in a contribution to a European strategy. This led us to decide to set up a working group that contained experts from all three regions but had a preponderance of Europeans and a European chair.

The charge for the working group is as follows:

The committee is requested to review the physics case for a linear electron-positron collider in the centre-of-mass energy range from around 250 GeV – 3 TeV in the light of LHC results up to mid-2012 and building on previous studies.

The committee should consider the case for a linear collider in terms of the physics reach beyond that of the LHC under the assumptions in the current CERN planning: a) 300 fb^-1 and b) 3000 fb^-1.

It should assume linear collider performance based on the details contained in current documents from ILC and CLIC but without a detailed comparison of the relative performance of the machines. The aim is to make the strongest possible case for a generic linear collider for submission to the European Strategy process.

The committee is requested to submit its draft report to the GDE European Regional Director, the CERN Linear Collider Studies Leader and the Chair of the ECFA Study for the Linear Collider by June 18th 2012.

The final version of the report should be delivered by end July.

We were delighted that Francois Le Diberder, who is also a member of the ILCSC, agreed to chair the working group. In conjunction with him, we invited experts from across the world and were also delighted that we could convince so many to devote considerable time to preparing this input. The final composition of the working group is: Francois Le Diberder (Paris-VII University, LAL, Orsay) (chair); Jim Brau (University of Oregon); Rohini Godbole (Indian Institute of Science, Bangalore); Mark Thomson (University of Cambridge); Harry Weerts (Argonne National Laboratory); Georg Weiglein (DESY); James Wells (CERN) and Hitoshi Yamamoto (Tohoku University). They will work on updating our long-standing physics case for the linear collider in the light of the exciting results already beginning to emanate from the LHC.

The group has already had several meetings and welcomes input from colleagues at any stage. In order to facilitate this input and discuss the issues, the working group has organised an open meeting which will take place in Paris on 16 May. I would like to encourage you all to give the working group your views and if possible to attend this meeting, which is taking place at a time when the physics bedrock is moving under our feet as LHC results continue to flood in. This should guarantee an interesting discussion. It should be possible for most Europeans to fly in early on the morning of the 16^th and catch the last flight back, should they feel able to resist the delights of a longer stay in Paris in the springtime.

Unfortunately I myself and other members of the GDE and Physics Directorates cannot attend as the only possible date that suited the working group clashes with the ILC Program Advisory Committee meeting in Fermilab. The working group will take some time to digest the results on the meeting and the other inputs from the community before producing the first draft of the report. This will be made available for comments from the community before it is input to the CERN strategy process. We hope that, having taken input from the community worldwide, this document will be helpful as the other regions update their own roadmaps. For example, the US is planning its own exercise, which will culminate in the traditional gathering in Snowmass in summer 2013.

Roadmaps are of course useless unless one has a vehicle to get to the destination. In the linear collider community, we are clear that we need two of these vehicles. One is the LHC, which is doing a great job in clarifying the highway we need to drive down. Often, however, the greatest points of interest can only be reached by following a signpost along a narrow track that can be very difficult to find. The ILC can explore such routes and ensure that we can reach the distant horizon from where we all expect that we will be able to see physics much more clearly than today.

No longer a test facility, STF is now an operating accelerator. Image: Nobu Toge

On 13 April at KEK’s superconducting radiofrequency test facility (STF), researchers successfully transported beam to the beam dump. The dump, located in the last part of the accelerator, is designed to absorb the energy of particles within accelerated beam. Now STF is no longer a test facility: it is the STF accelerator.

STF is an important facility for ILC R&D on superconducting RF accelerating systems. Scientists have been conducting an array of R&D and tests towards beam operation of the accelerator for the Quantum Beam Project. The aim of this project is to develop a compact and high-quality X-ray source for use in broad areas such as medicine, life science, information technology, nanotechnology and quantum science.

Full-scale remodeling of the test facility into an accelerator started in 2011. Two superconducting accelerating RF cavities were loaded into a cryostat and installed in the beamline. The photocathode RF electron gun for producing low-emittance beam was placed at the upper stream of the cryostat, and the focus beamline for the compact, high-flux X-ray source was set in place at downstream.

“We worked on the improvement of our electropolishing facility in parallel with accelerator development,” said Hitoshi Hayano, professor at KEK’s accelerator laboratory, who leads the R&D at STF. To realise the high accelerating gradient, it was important to maintain the smoothness and cleanliness of the cavities’ inner surfaces, as well as the purity of the niobium, the cavity material.

“We introduced a new rinsing method, using detergent to get rid of residue, such as niobium oxide or sulfur particles, leftover from electropolishing. We also optimised the subsequent baking process in the cleanroom so that we could prevent the melting of the indium coating on the Helicoflex seal,” said Hayano. As a result of these optimisations, researchers realised the high gradients for two cavities installed in STF accelerator: 40 and 33 megavolts per metre (MV/m), well over the ILC specification of 31.5 MV/m.

On 12 April, scientists finished the final setup of the two nine-cell cavities and started beam operation with the RF electron gun and the cavities. They confirmed the successful acceleration and transportation of the beam to the beam dump the very next day.

Scientists are planning to install an optical cavity for laser beam accumulation during the short shutdown in May. This optical cavity is another critical component for producing high-intensity X-rays. They developed a four-mirror cavity system that circulates and stores the laser pulses. The beam operation with the four-mirror cavity is planned to begin running in June with a goal to demonstrate high-flux X-ray generation using inverse Compton scattering.

“This is a wonderful R&D milestone toward realising the ILC,” said Akira Yamamoto, project manager of the Global Design Effort and head of KEK’s linear collider office.

Cryomodule 2 in the Fermilab Industrial Center Building. Image: Reidar Hahn

Fermilab researchers will soon take a quantum step towards the realisation of an ILC-type cryomodule.

Next week the newly assembled cryomodule RFCA002, familiarly referred to as CM2, will replace CM1 in the Advanced Superconducting Test Accelerator at the laboratory’s NML test facility. The change-out is a rung up on the R&D ladder, and not only because it is the second eight-cavity cryomodule to come out of the laboratory. Far more than the first, CM2 resembles an ILC-type cryomodule in its components and cavity test performance.

“The hope for CM2 is that it will be the first cryomodule to reach the average ILC specification gradient at Fermilab,” said lead engineer Tug Arkan. The so-called S1 goal of the ILC programme is to achieve an average gradient of 31.5 megavolts per metre over eight metre-long cavities. “That’s the goal to demonstrate. We haven’t yet proved it at Fermilab.”

But they came teasingly close to a different goal. Prior to their being installed in CM2, six of its cavities individually reached or exceeded the ILC specification of 35 MV/m in their horizontal tests. Two fell just shy of the mark, achieving 33 MV/m. (One of these did not receive a final horizontal test after it achieved 36 MV/m in a vertical test, a result of additional surface processing conducted after an earlier poor horizontal test.) Practically speaking, CM2 components are up to ILC standards so far.

“That’s the vital thing,” said Elvin Harms, who leads the cryomodule commissioning and testing programme. “This is an ILC cryomodule.”

The high cavity performance brings the S1 goal that much more within reach. And with 15 months of lessons learned from operating CM1, the CM2 team has plenty of accumulated expertise to draw from.

“Running CM1 was a great opportunity to cut our teeth on operating a multi-cavity cryomodule,” Harms said. “The run was satisfying and very instructive for the whole team. We did all the measurements we set out to do, and have done a lot not just with the device itself, but also commissioned all the subsystems that are necessary for safe and reliable operation.”

Although demonstrating its operability and measuring its performance parameters have been the prime goals since CM1 was installed in 2010, Lorentz force detuning compensation has been demonstrated to a level considered by many to be the world standard. And, in a nice case of one R&D programme helping to support another, the team used CM1 to provide proof of principle that the nine-millisecond beam pulse required by the proposed Project X proton accelerator was feasible. Further, as an unscheduled activity, the team even nailed down and fixed a nitrogen leak without having to pull out the cryomodule, which itself proved to be a valuable learning experience.

Once CM1 is uninstalled, the Fermilab team will conduct a post-mortem to identify weak points in its operation. Three of the cavities underperformed, and one of the tuners stopped working almost before it started.

Researchers hope to be able to more readily assess CM2’s performance, as they’ll enjoy the advantage of having all of its data at their fingertips. Unlike CM1, which was assembled from a DESY kit and with the help of DESY and INFN staff, CM2 is home-grown. Though many of its components were purchased from Europe, US personnel put it together. Moreover, all eight of its cavities were processed and tested at Fermilab and Jefferson Lab.

The high-gradient cavities aren’t the only components that nudge CM2 towards being an ILC type. Its tuners, designed by INFN in Italy, will replace the kind used in CM1. They will be moved from the ends of the cavities, where they sat in CM1, to the cavities’ centres.

CM2 will first undergo warm tests. It will then be cooled down, at which point it will be put through cold tests and, with some good fortune, by early 2013, tests with beam.

For the RF systems, beam opens up a whole new dynamic. Beams consume power and the low-level system has to compensate while remaining stable.

“Let’s hope the average gradient of this cryomodule runs at 31.5. Is it a realistic hope?” Arkan asked. “It’s not an easy task, but we’re trying everything in our power to do it. Now we test and see what’s going to happen.”