Like a force of nature, it just can’t be helped. Even though the Large Hadron Collider, or LHC, has taken three decades and about $9 billion to build, spans over 17 miles in circumference 570 feet beneath the Franco-Swiss border, and is finally colliding protons at incredible energies never before observed — physicists cannot wait for an upgrade.
“We’re always greedy,” said University of Manchester physicist Roger Jones. “We always want more.”
For the past 23 years, Jones and other top particle physicists representing over 100 institutions from 25 countries have already been planning the next pre-eminent particle colliders. The next generation machines will be larger, come with a new set of challenges, and will most likely cost more than the LHC, a project of the European Organization for Nuclear Research, better known as CERN. The LHC began making its first record-breaking collisions in November 2009, and is tentatively scheduled to begin operating at full blast in 2013.
Yet while physicists hope the LHC will reveal fabric-of-the-universe particles such as the elusive Higgs boson — a particle that would explain the origin of mass — bigger machinery is necessary to make sense of the LHC’s findings, researchers say.
It will be difficult for scientists to understand what they’ve uncovered with the LHC because of the particles it collides — protons. Protons are made of smaller elementary particles called quarks and gluons, and smashing them together gets messy.
“It’s like colliding two Swiss watches together,” said Stephen Holmes, director of particle accelerators at Fermilab near Chicago, Ill., home of the world’s second-largest particle accelerator. “You get a lot of gears that fly out and you somehow have to make sense of what you started with.”
In addition, not all protons are the same. They are made up of different recipes of quarks and gluons, making it even more mind-boggling for physicists to analyze the data that will come out of the LHC.
However, the next class of colliders will slam together electrons and positrons, two of six elementary particles known as leptons.
“With electron-positron collisions, you’re not colliding a collection of different particles,” said Holmes. “It’s like colliding a gear with a gear.”
Since leptons lose energy when making turns — a phenomenon known as synchrotron radiation — these colliders must be linear, unlike the circular LHC, in order to achieve high enough collision energies. Instead of a racing circuit, the next collider will be like two cars accelerating toward each other on a drag strip. Also, to get to high enough energies, it must be massive — up to 30 miles in length.
For now, the most powerful lepton collider is at the Stanford Linear Accelerator Center in California. Physicists there speed up particles along a two mile track and crash them at up to 50 billion electron volts — that’s about 33 billion AA batteries.
The next linear colliders, however, may be up to 60 times more powerful, with collision energies of three trillion electron volts. That’s 2 trillion batteries.
“We have to go to extremes to understand fundamental physics,” said Jones of the University of Manchester.
Despite the years they have already invested in planning them, scientists might have to wait another decade or longer before breaking ground on these machines. There are two designs for lepton colliders currently being considered: the International Linear Collider, or ILC, and the Compact Linear Collider, or CLIC. The ILC is further along in development and could be cheaper than the CLIC, but only a third as powerful.
Physicists will use the results from the LHC to determine which one of these will be built next. “We need to wait to see what energy range is necessary,” said CERN physicist Jean-Pierre Delahaye, who is the CLIC project leader. If the Higgs boson or any other new particle discovered by the LHC can be produced at a low enough energy range, then it’s most likely the smaller ILC will be built. The next machine will most likely reside in Europe at CERN, though physicists say Fermilab in the United States has also voiced a strong desire to house the next big collider.
With price tags likely to top $10 billion, either of the next-generation colliders would require massive international cooperation. Delahaye estimates for materials alone, the ILC will cost about $6.4 billion in 2010 dollars, not including the salaries of an estimated 130,000 full time workers needed to construct the machine. Scientists will release official cost analysis for the CLIC later this year.
Although neither proposal has advanced beyond blueprints and component testing, the United States and United Kingdom have already reduced support to the ILC due to budget cuts, with future prospects unclear. While most of the funding won’t have to be committed until a site is established, researchers recognize one large hurdle will be to convince governments the machine is worth building.
Before physicists can do that, there are technical barriers they must first overcome. For example, Jones explained, the acceleration of leptons produces energy waves known as wakefields. Much like a boat creates a wake in water, sped-up leptons create a wake of energy. The more leptons added, and the faster and closer in distance they travel, the more powerful the wakefield, which has the potential to rip these machines to shreds.
“These machines must be designed very carefully and are highly sensitive to manufacturing errors,” said Jones, who is a lead engineer for both of the proposed next-generation colliders.
According to the engineers, a rigorous testing process is more crucial than ever. Even with close to 30 years of planning, technical mishaps have brought the LHC at least four costly years behind schedule from unleashing its full power. Especially with their costs, these machines won’t be built unless scientists can guarantee their operation will be much smoother. The ILC technology testing is currently underway, while the CLIC testing is set to conclude at the end of this year.
Thus, even under the most optimistic scenario, 2013 would be the earliest the ILC could finish testing and receive approval to begin construction, while the CLIC might have to wait until 2017, said Delahaye. After approval, it would take at least seven years to finish the machines.
Despite the formidable hurdles that remain, these physicists are still moving ahead with their work on the next big physics machine, even as they wait for results from the LHC.
“You have to keep pushing the envelope and think long term,” Jones said. “These linear colliders will explore completely new energies and may show us something we’ve never even dreamed of.”
*Correction (March 26, 2010): This sentence originally read: “The CLIC will likely cost more in materials, however, scientists won’t start official cost analysis until later this year.”
**Correction (March 26, 2010): This sentence originally read: “The ILC technology testing is currently underway, while the CLIC testing is set to begin at the end of this year.”