ONLY A SHORT time after setting up shop in Texas, the Superconducting Super Collider (SSC) seems to be walking into a political shoot out. Increasing costs and technical difficulties are raising political doubts about the project, and giving rise to increasing conflicts within the scientific community.
As a result, proponents of the SSC are preparing for a major struggle with Congress to guarantee future funds for the project. At the same time, physicists involved in other projects remain worried that their funding will be held back to pay for the SSC – despite promises to the contrary from the Bush administration.
The SSC has been planned by its designers as the ultimate circular particle collider; to reach higher energy levels, entirely new accelerator designs are likely to be needed, probably linear rather than circular. The most powerful existing particle collider in the US, the Tevatron at Fermilab near Chicago, is designed to accelerate protons to 1 teraelectron volt (TeV) and smash them together. The SSC is designed to accelerate counter-rotating streams of protons to 20 TeV, and smash them together in a 40 TeV collision. To achieve this, the protons will have to travel through an electromagnetic field created by powerful magnets placed in a ring 83kilometres in circumference.
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European physicists are currently discussing plans to build a similar, but less powerful, proton-proton collider called the Large Hadron Collider (LHC), at the European Laboratory for Particle Physics (CERN) in Geneva. The LHC would require adding a superconducting ring to CERN’s recently opened Large Electron-Positron Collider (LEP). The recent successes of LEP, following other achievements at CERN in the early 1980s, have fuelled the US’s desire to press ahead with constructing the SSC in order to regain its leadership in particle physics.
As recently as two months ago, supporters of the SSC were optimistic that they would receive $390 million for the next stage of the accelerator’s development, sufficient to allow them to start construction. This followed the selection last year of a site at Waxahachie in Texas, chosen from a short-list of seven candidates in different states by the Department of Energy.
Last month, however, two supporters of the SSC in Congress met the project’s contractors, and told them they would have to lobby hard if they were to get even the $318 million that President Bush is asking for in next year’s budget. According to one observer at the meeting, the message delivered by Robert Roe, chairman of the house committee on science, space and technology, was stark: ‘Don’t count on anything you have not fought for your life for’.
Congress’s initial reluctance to commit itself to an eventual bill of $5.9 billion for the collider had earlier been overcome when the Department of Energy promised that this would be ‘the absolute final cost’. Part of the DOE’s promise was based on the assurance that the collider would use proven technology, and that the cost figures had a wide margin of error built in.
Since then, however, problems have begun to appear. At the end of last year, researchers reported that experiments at Fermilab had shown that eddies in the magnetic field created by the SSC’s superconducting magnets would cause so-called ‘persistent currents’. These irregularities would disrupt the protons passing through the fields, and send many of the particles crashing into the walls of the magnets.
Other scientists began running simulations on a supercomputer of the paths that the protons will follow in the collider. By following 60 protons through the 10 million circuits it takes to accelerate them to 20 TeV, the scientists found that the particles are relatively unstable at low energies.
The computer simulations predicted that, when the protons are introduced into the main ring at 1 TeV, many of them will wander into the walls of tube containing the beam. This reduces the luminosity of the beam – the number of proton-proton collisions that occur at full energy – and thus the overall effectiveness of the collider.
¿ìè¶ÌÊÓƵs at the SSC Laboratory in Dallas, Texas, which has recently been set up with funds from the DOE to oversee development of the accelerator, have decided that they will not be able to eliminate the persistent current. They are optimistic that they may be able to increase the homogeneity of the field by increasing the interior diameter of the magnets from four to five centimetres. However, the redesign of the magnets will create an eight-month delay, and will add $390 million to the final cost, according to Roy Schwitters, director of the SSC.
In order to stabilise the beam as the main ring is being filled with protons, the SSC laboratory used an injector that can deliver protons at 2 TeV rather than 1 TeV as originally planned. Some physicists say this could give rise to additional costs and delays, because no one has ever built a 2 TeV accelerator, while a 1 TeV injector could be modelled directly on the Tevatron. However, officials at the SSC laboratory say they are confident that there will not be any problems designing and building a 2 TeV injector.
There is disagreement among physicists on the DOE’s High Energy Physics Advisory Panel (HEPAP) about whether the SSC needs both larger magnets and a more powerful injector. Some physicists on the committee think that a higher injection energy will stabilise the beam sufficiently, and that larger magnets will not be required.
Alexander Chao, chief of accelerator physics for the SSC, says that this may or may not be true – but adds that there are other good reasons for building bigger magnets. For example, the larger magnets will actually be easier to produce, says Chao, and will also provide scope for future increases in luminosity.
The SSC laboratory also wants the field strength of the magnets to be increased by reducing their operating temperature to less than 4.35 K. And it is also suggesting that more focusing magnets be introduced.
The new designs would increase the projected cost of the collider considerably. Last month, Schwitters reported that the SSC would cost ‘about $1 billion more’ than the $5.9 billion previously estimated. Now scientists at the SSC say the additional cost may be even higher, between $1.3 and $1.9 billion.
The DOE is currently analysing all costs to reach a final number. Many members of Congress, however, doubt that even this ‘final number’ will live up to its description. For one thing, all estimates of costs rest on the assumption that the general inflation rate will remain as low as 6 per cent – and that inflation for research and development costs will be even lower, at only 2 per cent.
Many feel these estimates are unrealistically low. In addition, costs are likely to increase when construction begins, according to Philip Webre, an analyst who has prepared a report on the SSC for the Congressional Budget Office.
The present cost increase ‘may not be the only surprise,’ says Webre. He points out that the two recent physics projects that closely resemble the SSC – the Energy Saver and Tevatron I at Fermilab – eventually cost about twice the figure that had been estimated. ‘We don’t want to repeat the experience with Isabelle,’ he says, referring to an abandoned project to build a 400 GeV accelerator project at Brookhaven National Laboratory in New York. The DOE pulled the plug on Isabelle, after tunnelling had been virtually completed, because of problems with the design of the magnets.
One way to lower costs would be to reduce the energy of the collider from 20 TeV to 17, or even 15, TeV. However, after a review by a ‘blue ribbon’ panel of physicists – including five winners of the Nobel prize – the DOE has become convinced that 20 TeV is ‘sacrosanct’, according to James Watkins, the Secretary of Energy. Addressing Congress this week, he said that the SSC should be built at 20 TeV or not at all.
Watkins’ case is based on the conclusion of physicists that it is necessary to go up to this energy level to be relatively confident of finding new phenomena. Even a lack of phenomena at this energy level will be significant. ‘If you go past 20 TeV and don’t find a new particle or force, it begins to make mathematical nonsense,’ says Steven Weinberg of the University of Texas, who won the Nobel prize for physics in 1979.
The question of the appropriate energy levels has an important political consequence. CERN’s proposed LHC would have maximum energy of 8 to 10 TeV in each of the two beams. Many physicists at CERN argue that this could still be sufficient to make major new discoveries, and that, since the LHC would be considerably cheaper than the SSC, it would be a more cost-effective.
Supporters of the SSC challenge this conclusion, however, claiming that there is a high possibility that this energy level would not be high enough to produce sufficiently novel physics. Physicists say they need the combined energy of two 20 TeV protons to create particles of 1 TeV. It is in this energy region that they should be able to find an elusive particle called the Higgs boson; equally significantly, they may not.
Another particle, the massive top quark, is also elusive, but should be spotted at these high energies.
The scientific goal of the SSC is to investigate precisely such phenomena. The DOE’s advisory panel has said substantial reductions in costs, leading to a lower operating energy, would ‘significantly increase the risk’ that none of these particles would be found.
The physicists may find, however, that insisting on the higher price will significantly increase the risk that the SSC is built slowly if at all. ‘We have a real clash of cultures – the physicists don’t want to compromise at all, and Congress is about nothing if not compromise,’ says one Congressional analyst.
Congressional backers of the SSC say they have the committee votes needed to ensure that the DOE’s budget request is met in full. But many members of Congress who voted for the SSC last year, such as Tom Bevill, chairman of the house appropriations subcommittee for energy and water development, are refusing to rule out the possibility that the SSC may be put on hold.
Not all politicians in Washington are happy with this prospect. In particular, the powerful group of Texan lawmakers – President Bush included – are circling their wagons around the collider. Even opponents of the SSC admit that such a powerful political grouping will be difficult to beat. ‘If I was a betting man I would say that it will be funded this year and this thing will play itself out to its very expensive conclusion,’ says Sherwood Boehlert, a Republican Congressman from New York who has long opposed the SSC.
The DOE hopes to avoid the need to apply to Congress for additional funds by involving more foreign countries in the project. The department claims that it can raise one-third of the total cost of the SSC from other countries and the state of Texas.
So far, however, this promise has met widespread scepticism in Congress. A DOE spokesman for the DOE says that negotiations are currently taking place with many countries, including Britain, in the hope that they will be prepared to support some aspects of the SSC. However to date only India has made a firm pledge, of $50 million.
Other physicists in the US are themselves growing increasingly concerned about where the extra money needed to build the SSC is likely to come from. Many are sceptical about the government’s promise that funds will not be taken from other projects to build the SSC. ‘When fiscal reality strikes, some compromises will be made,’ says Mel Shochet, a physicist at Fermilab.
Compromise is already being reached on the SSC’s construction schedule. Even before the most recent predicted cost increases, officials at the SSC laboratory had hoped to receive about $450 million in the financial years beginning 1 October. They argue that the $318 million requested from Congress by the Bush administration will be barely sufficient for the redesign to meet the technical difficulties already encountered, and that this could set the project back considerably.
Schwitters says that he hopes to make up for delays by speeding up construction in later years. But he admits that the construction schedule is already ‘very tight’.
For those with direct experience of the construction of previous accelerators, the experience of SSC is not unusual. Physicists push for their machine to be completed as quickly as possible, budget officials strive to keep costs to a minimum, and the administration tries to forge a year-by-year compromise between the two, as dictated by Washington’s budget procedures.
Many physicists argue, however, that this stop-go approach to funding major projects takes its own toll. ‘Europe has gone full speed ahead in physics over the last decade,’ says physicist Lee Roberts, head of the advanced gradient synchroton users’ group at Brookhaven. ‘The basic reaction in this country, however, is to starve everything and stretch it out over years.’ Some fear the SSC will be no exception.
