Skip to main content


Accelerators and detectors

Accelerators and detectors

Disappointment as Japan fails to commit to hosting the International Linear Collider

07 Mar 2019 Michael Banks
Artist's impression of the International Linear Collider
Tunnel vision: the Japanese government has announced that it will now being formal negotiations to host the International Linear Collider. (Courtesy: Rey Hori/KEK)

Particle physicists have expressed their disappointment after the Japanese government today failed to announce its intention to host the ¥800bn ($7.5bn) International Linear Collider (ILC). Officials in Japan said that their government has formally “expressed an interest” in the 20 km-long particle smasher but has not decided whether to host the machine. The final go-ahead will only be given if enough international support and funding can be found to construct the machine and there is a consensus within the Japanese scientific community that the project is worth pursuing.

First mooted over a decade ago, the ILC would accelerate and smash together electrons with positrons to study the Higgs boson and other particles in precise detail. The ILC’s five-volume technical design report was published in June 2013, in which it called for a 30 km-long linear collider that operating at around 500 GeV (see timeline below). The Japanese physics community quickly got behind the project, expressing its desire to host the machine, with a site in the Tōhoku region, about 400 km north of Tokyo, chosen as a potential location.

However, the government has dragged its feet over whether to support the ILC and in 2017 physicists came up with a revised plan to make it more palatable. This involved reducing the ILC’s energy to 250 GeV — an energy aimed to study the 125 GeV Higgs boson — and shortening the length of the tunnel to around 20 km, with the option of later upgrading the collider to energies of around 1 TeV. However, their plans were hit late last year when an independent committee of the Science Council of Japan (SCJ) issued a report that failed to support the ILC’s construction in Japan. The SCJ pointed out that the ILC did not yet have enough international backing, stating that the collider’s importance beyond research was “unclear” and “considered to be limited”.

Setting conditions

Given that European particle physicists are currently updating their future strategy, which is due out by May 2020, officials then gave the government a deadline of March to decide on whether to support the ILC in Japan. Today’s announcement means that government agrees with the Japanese particle physics community that the ILC is worth pursuing and that it will enter negotiations to host the machine. However, it will only give the ILC the final go-ahead if those negotiations are successful and if international support, particularly funding, can be found. It is expected that the government could supply half the $7.5bn with the other half needing to come from international partners such as the US, CERN and Europe as well as Canada.

Timeline: twists and turns of a linear accelerator

2004 An international panel of experts decide that a future linear collider should be based on superconducting technology that has been developed at the DESY laboratory in Germany

2005 Barry Barish of the California Institute of Technology in the US is chosen to lead the effort to build the International Linear Collider (ILC). The ILC’s first tentative design is released calling for a 20 km-long machine that would operate at 500 GeV with a possible future upgrade to 1 TeV that would require extending the tunnel by an additional 18.6 km

2007 Updated “reference design” is released for the ILC calling for two 12 km-long arms to collide electrons with positrons. The estimated cost of the ILC is $6.7bn

2011 The Japanese particle-physics community announces it will bid to host the ILC with possible candidate sites in Kyushu and Iwate

2013 Lyn Evans, who masterminded the Large Hadron Collider’s construction, takes up the reins as linear-collider director, overlooking the design of the ILC. The “technical design report” for the ILC is released calling for a 31 km-long track of superconducting cavities that accelerate electrons to 500 GeV. The ILC community identifies a location in the Iwate prefecture north of Tokyo as a possible site for the ILC

2016 Japan’s High Energy Accelerator Research Organization (KEK) releases a 12-page plan showing that they have measures in place if the Japanese government decides to begin negotiations with other countries to start construction

2017 The International Committee for Future Accelerators, which oversees work on the ILC, endorses plans to reduce the scope of the collider. Estimated to cost $7.5bn, the ILC would be built in a 20 km-long tunnel and with an initial design energy to 250 GeV with the option of further energy upgrades

2018 A report by the influential Science Council of Japan raises several issues about the Japan hosting the ILC and does not support its construction.

Another condition laid out by the government is that the ILC needs to be more widely supported by the Japanese scientific community. That means that it will need to complete the necessary procedures to be included in the next roadmap of large science projects put together by Japan’s Ministry of Education, Culture, Sports, Science and Technology. Physics projects included in MEXT’s 2017 roadmap included the Hyper Kamiokande neutrino detector as well a high luminosity upgrade for the Large Hadron Collider. The government also said that the ILC must be included in the SCJ’s master plan of large-scale projects, which will not reach a conclusion until October this year.

“It is actually extremely positive that the Japanese government says that it has an interest in the ILC project,” Hitoshi Murayama from the Kavli Institute for the Mathematics and Physics of the Universe in Tokyo told Physics World, adding that to make such a statement meant that discussions must have taken place with other government ministries including the finance ministry.

This is a real window of opportunity for Japan, but this window cannot remain open for much longer

Philip Burrows

Speaking at a press conference this morning in Tokyo organised by the International Committee for Future Accelerators (ICFA), which oversees work on both the ILC and a rival design the Compact Linear Collider, ICFA chair Geoffrey Taylor noted that that they have been encouraged by the government’s comments. “It shows us the political and executive environment in Japan is rapidly moving towards the ILC,” he says. “The important step we await now is for the government to commit and declare its interest in becoming the host of the ILC.”

Moving on

Yet particle physicist Brian Foster from the University of Oxford, who was European regional director for the ILC’s Global Design Effort, says that he is “disappointed” by the statement. “It is difficult to be convinced that the Japanese government is serious about this,” says Foster. “Delaying the decision in this way seems like a typical Japanese way of saying ‘no'”. Foster adds that it is especially concerning that the Japanese government has now referred the decision process back to the SCJ, which has not been enthusiastic about the ILC. “How all this will now play out in the European strategy discussions is hard to know”.  At the press conference, it was noted that negotiations on cost sharing will now be carried out by officials from the KEK particle-physics lab.  Yet Foster warns that this is a “waste of time”. “Negotiations needs to take place at a higher level,” he adds.

“It is difficult to be convinced that the Japanese government is serious about this. Delaying the decision in this way seems like a typical Japanese way of saying ‘no’.

Brian Foster

The announcement from the Japanese government is also unlikely to result in linear-collider physicists getting behind the ILC and ditching plans for CLIC, which would offer higher collision energies up to around 3 TeV. “Today’s MEXT statement appears to fall short of a clear positive decision by the Japanese government, and is, frankly, disappointing”, says particle physicist Philip Burrows from the University of Oxford, who is CLIC’s spokesperson. “CLIC represents a serious alternative design for an energy-frontier linear collider and we will make every effort to keep it on the table for consideration pending  greater clarity on ILC from the Japanese government. This is a real window of opportunity for Japan, but this window cannot remain open for much longer – the world must move on, other projects are advancing, and CLIC provides a great opportunity for a linear collider Higgs factory in Europe.

That view is shared by particle theorist John Ellis from King’s College London who told Physics World that the statement is “disappointing” for the community. “For the time being, the European particle physics strategy update will have to continue without assuming that the ILC will go ahead,” he says, adding that there are other projects on the table such as CLIC, China’s Circular Electron Positron Collider and the Future Circular Collider that could “do similar physics and provide ways forward for the community”.

International Linear Collider Q&A

What is the International Linear Collider (ILC)?

The ILC is a 20 km-long particle collider that will accelerate electrons and positrons to energies around 250 GeV. To do so, it will consist of thousands of superconducting radiofrequency accelerator cavities made of niobium. The ILC will then smash these beams together roughly 7000 times a second at an “interaction point”. The ILC will have two all-purpose detectors based around the interaction point — SiD and ILD — that would take turns being in the beam. Interchanging the detectors is estimated to take around a day to complete.

How is this different from CERN’s Large Hadron Collider?

The 27 km-circumference LHC is a circular collider that is made up of more conventional technology such as radiofrequency cavities that accelerate the beam, dipole magnets that bend the particles along a circular path, and quadrupole magnets that focus the beam. The ILC instead uses superconducting cavities to accelerate the beam along a straight path before being focussed by quadrupole magnets. This linear acceleration has the advantage that the electrons do not lose energy via X-rays when travelling along a circular path. The benefit of a circular machine is that it allows for more integration points — four in the LHC’s case, with no need to swap detectors.

Has this accelerator technology been tested before?

Yes. The European X-ray Free Electron Laser (E-XFEL) facility near Hamburg, Germany, uses 768 superconducting niobium cavities to accelerate electrons to 17.5 GeV over 1.7 km. Rather than collide the particles, however, the E-XFEL makes them produce X-rays that are then used for a range of experiments from biophysics to condensed-matter physics. The E-XFEL is considered to some extent as an ILC prototype.

What would the ILC study?

Its main aim would be precision studies of the Higgs boson, which was discovered in 2012 at the LHC. The LHC has managed to measure the properties of the Higgs – notably how it couples to other particles – with a precision of around 20%. Yet the LHC’s proton-proton collisions suffer from a large amount of “debris” that affects the precision of the measurements. As electrons and positrons are fundamental particles, their collisions are much “cleaner” meaning that the ILC would improve this precision to 1% or lower. The ILC could also be later upgraded to higher energies to study the top quark.

Why is this exciting?

Physicists hope that the door to “new physics” could be opened through precision studies of particles such as the Higgs. This would come from deviations from those predicated by the Standard Model of particle physics.

Why has Japan dragged its feet for so long?

Japan has balked at the potential cost of building the ILC, which is one reason why physicists proposed a scaled-down version in 2017 that is both cheaper and would not take as long to build.

So why now?

Particle physicists are feverishly planning the next collider following the LHC and the ILC is the most mature proposal. The time is also right given that Europe will update its particle physics strategy next year. A further reason is using the project as part of the reconstruction efforts following the magnitude-9 earthquake and tsunami that hit the Tōhoku region in 2011.

Are we far from a decision?

Who knows. Negotiations will continue with international partners, but if the Japanese government does not receive sufficient support then the ILC could still not go ahead. The coming years will be crucial for the project.

When could the ILC see the light of day?

If everything goes well, 2035 at the earliest. Negotiations and preparations could take around four years to complete with construction then taking a decade.

Copyright © 2020 by IOP Publishing Ltd and individual contributors