What is the Future for Particle Accelerators?

This year all physics eyes are on the Large Hadron Collider as it approaches its promised landmark discovery of the Higgs Boson (or maybe its undiscovery). At the same time some physicists are planning the future for the next generation of colliders. What will they be like?

The answer depends in part on what the LHC finds. Nothing is likely to be built if there is no sign that it will do anything useful, but decisions are overdue and they have to make some choices soon.

Hadron colliders

Accelerators like the LHC that collide protons are at the leading edge of the Energy and Luminosity frontiers because they work with the heaviest stable particles that are available. The downside of colliding protons is that they produce messy showers of hadrons making it difficult to separate the signal from the noise. With the Tevatron and now the LHC, hadron colliders have been transformed into precision experiments using advanced detectors.

One technique is to capture and track nearly all the particles from the collisions making it possible to reconstruct the jets corresponding to interesting high energy particles such as bottom quarks created in the heart of the collision. Missing energy and momentum can also be calculated by subtracting the observed energy of all the particles from the original energy of the protons. This may correspond to neutrinos that cannot be detected or even to new stable uncharged particles that could be candidates for dark matter.

High luminosities have been achieved making it possible to scour the data for rare events and build up a picture of the interactions with high statistics. As luminosity increases further there can be many collision events at once making it difficult to reconstruct everything that happens. The LHC is now moving towards a new method of operation where it looks for rare events producing high energy electrons, muons and photons that escape from the heart of the collision giving precise information about new particles that decayed without producing jets or missing energy. In this way hadron colliders are getting a new lease of life that turns them into precision tools very different from how they have been seen in the past.

So what is the future of hadron colliders? The LHC will go on to increase its energy to the design limit of 14 TeV while pushing its luminosity even higher over the coming years. Its luminosity is currently limited by the capabilities of the injection chain and the cryogenics. These could undergo an upgrade to push luminosities ten times higher so that each year they collect 50 times as much data as they have in 2011. Beyond that a higher energy upgrade is being planned that could push its energy up to 33 TeV. The magnets used in the LHC main ring today are based on superconducting  niobium-titanium coils to generate magnetic fields of 8.5 tesla. Newer magnets could be built using niobium-tin to push the field up to 20 Tesla to more than double the energy. If they could revive the tunnel of the abandoned SSC collider in Texas and use niobium-tin magnets it would be possible to build a 100 TeV collider, but the cost would be enormous. The high-energy upgrade for the LHC is not foreseen before 2030 and anything beyond that is very distant.  Realistically we must look to other methods for earlier advances.

Is the future linear?

The latest linear accelerator built to date is SLAC at Stanford with a centre of mass energy of 90 GeV. As hadron colliders reach their physical limits physicists are returning to the linear design for the next generation of colliders. When accelerating in a straight line there is no advantage in using heavy particles so linear colliders work equally well with electrons and positrons which give much cleaner collisions.

The most advanced proposal is the International Linear Collider which would provide centre of mass energies of at least 500 GeV with 1 TeV also possible. The aim of the ILC would be to study the Higgs boson and top quark with very high precision measurements of their mass, width and other parameters. This may seem like an unambitious goal but if the LHC finds nothing beyond the standard model in the data collected in 2011 this could be the best option. the standard model makes very precise predictions about the quantities that a linear collider could measure. If these can be checked, any deviations could give clues to the existence of new particles at higher energies. Such precision measurements have already been useful in predicting where the mass of the Higgs Boson lies, but once all the parameters of the standard model can be measured the technique will really come into its own. Finding solid evidence for deviations from the standard model would be the requirement to choose and justify the construction of the next collider at the energy frontier.

But there is an alternative. A new innovative design for a compact linear collider (CLIC)  is being studied at CERN and it could push the energy of linear colliders up to 3 TeV or even 5 TeV. The principle behind CLIC is to use a high intensity drive beam of electrons at lower energy to accelerate another lower intensity beam of electrons too much higher energy. Just think of how a simple transformer can be used to convert a high current low voltage source of electricity into a low current high voltage source. CLIC does a similar trick but the coils of wire in the transformer are replaced by resonant cavities. It is a beautiful idea, but is it worth doing?

The answer depends on whether there is anything to be found in the extended energy range. This is being explored by the LHC and so far nothing new has been seen with any level of certainty. There is still plenty of room for discovery but decisions must be made soon so the data collected in 2011 will be what any decision has to be based on.

It is going to be a hard choice. For me it would be swung towards CLIC if it could be the start of a design that could lead to even higher energies. Could the same trick be used a second time to provide even higher energies, or is it limited by the amount of power needed to run it? Do other designs have better prospects, such as a muon collider? Big money and decades of development are at stake so let’s hope that the right decision is made based on physics rather than politics.

Perhaps it is worth a poll. If it was a straight choice, which of these would you prefer to see international funds spent on?


35 Responses to What is the Future for Particle Accelerators?

  1. Cuprate superconductors can stand up to 200T, why isn’t research into this kind of superconductor considered?

    • ondra says:

      Daniel, these materials are usually brittle ceramics which cant be made into flexible wires needed to make sc coils used in colliders.

      • Yeah, but why not make them in the shape of coils?

      • anna v says:

        Daniel De França says:
        November 6, 2011 at 3:41 pm

        “Yeah, but why not make them in the shape of coils?”

        There are kilometers of windings in the LHC superconducting magnets, it seems an insurmountable problem because how many coils can be molded at a time? Do not forget that the problem with superconductors are the number of necessary contacts to bridge the current from one section of wire to another. As was demonstrated at the accident with the LHC which was due to a bad bridge.

      • ” it seems an insurmountable problem because how many coils can be molded at a time”

        Did anyone try?

        A random ability to deform is required for general applications, but couldn’t a collider use a more predictable shape?

      • Philip Gibbs says:

        High Temperature Superconductors are already in use for some connectors and are being considered for the magnets in the High Energy upgrade. A hybrid solution solution could be favoured but it is early days. see http://arxiv.org/abs/1108.1619

  2. JollyJoker says:

    Voted “Nothing yet” since a commitment to any one of these is, IMO, premature. Spending the next five years on doing research and planning for ILC, CLIC and a muon collider is far preferable to picking only one of the options at a time when the LHC within the next few months or years will give us info that makes the choice easier if not completely obvious.

    Some speculation on what the different options for what we know after the 2012 run are and what they mean for the next collider would be interesting.

    • ohwilleke says:

      To say nothing of the fact that the basic scientific research budgetary situation is not looking bright in the near future. Better to lie low and stay off the radar of budget cutters who might slow down the existing LHC run until the Eurozone comes around and the U.S. works through some of its budget angst.

      We need bite sited experiments, not megaprojects right now.

  3. Philip Gibbs says:

    The real choice for now is between the ILC or CLIC. If they find only a Higgs at 140 GeV it may mean that only the standard model is in range of current technology. They could build an ILC with energy up to twice the top mass and that would be enough to study the SM in great detail to see if there are signs of anything more.

    If a Higgs is found at 120 GeV it would be a sign that something more could be in reach and CLIC might be worth going for. Any other evidence of new physics at ~ 1 TeV coming out of the LHC now would also be good news for CLIC.

    The problem is that they don’t really want to wait until end of 2012 before deciding. A compromise solution might be a staged CLIC with a lower initial energy that can be scaled up later.

    This is based on what I have read at the recent “implications” meeting at http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=157244

  4. Nemo says:

    Ts ts, nothing found yet at the LHC, and already thinking about the next collider? This is real hubris.

    I named the LHC the “tunnel of Babylon” in my blog, and that is what it will remain for the next 50 years at least.

    • Philip Gibbs says:

      It is still early days for the LHC so far too early to say it wont find anything. It’s main job is to explore the Higgs sector and it will do that, most probably by finding the Higgs boson.

      If it finds nothing else that is still very important for the advance of science. Negative results are very important for narrowing down the models to study. A good example is the failure to find the decay of the proton that ruled out models such as SU(5) GUT. Not finding the Higgs boson would be even more dramatic because it is a strong prediction.

      If you don’t think building colliders is a justifiable use of money read my previous post and make relevant comments there.

      • ohwilleke says:

        The issue is not “is it a justifiable use of money.” More scientific results, be they new physics or negative results, are always a plus.

        The question in my mind is where out of many options can we get the most bang for our buck? What low hanging fruit have we failed to invest in before we commit ourselves to another very expensive venture? What could we achieve if we took half the current LHC staffing and budget and broke those folks into a dozen separate projects instead? Is there medium budget physics that needs to be done after this high budget round?

        What are the LHC results telling us as Bayseans about the best places to be looking for breakthoughs?

        If we must plan, we also ought to defeat group think by having one planning group explore each of the plausible outcomes of the next few years of LHC research (e.g. one set of planners should be prioritzing based on a no higgs scenario and another should be prioritizing based on a SM Higgs scenario).

  5. Mike says:

    As the decision to build a new collider seems to be linked to the outcome of the Higgs search at the LHC, when will we have an answer on an SM Higgs at 114 – 140 GeV? I hear estimates of December of this year to March of next year but it sounds like we have a high enough luminosity and enough data right now, so are we just waiting on data analysis?

    • Philip Gibbs says:

      The initial analysis for each experiment should be ready for review in December. How long it takes to review will depend on how clear any signal is. If they decide to wait for a full ATLAS+CMS combination before approving it will take longer. March 2012 seems to me like a reasonable estimate for public release but it is impossible to be sure at this stage.

  6. Vladimir says:

    if, no doubt, standard model confirmed

    1-st 1 TeV International Linear Collider http://www.linearcollider.org/
    2-nd Muon Collider http://www.fnal.gov/pub/muon_collider/

  7. Murod says:

    Many people say that NOT finding the Higgs boson is even more exciting. But what exactly does it mean?

    Making the Higgs mechanism more and more complicated? Abandoning the idea of Higgs boson?
    Any new directions in particle physics theory?

    • Philip Gibbs says:

      It would mean exploring a range of possibilities including testing some of the Higgsless models already out there. However a favourite would be that the Higgs is there but is hidden because e.g. it decays to unknown particles that are not easy to detect.

      In any case there are excesses in all the best Higgs channels at 1/fb – 2/fb so at present there is little point in worrying about the possibility that it will not be found.

    • nameab says:

      Have you considered the feasibility of the Bohr
      orbits quantization for multiple electronic

  8. chris says:

    the real question is: will there be a new collider?

    • anna v says:

      Maybe a hiatus on new colliders built by extending old concepts might be good, because there might be money going into new methods of acceleration.

      Back in the 1980′s Tom Ypsilantis was looking into that, trying to use the very high electrical fields in crystals to accelerate muons to very high energies. He did a few exploratory experiments with muons at CERN but in the end the RICH design adopted for DELPHI absorbed all his energies.

      Very little effort and money has gone since then to push research into new accelerator methods/ideas. Now with nano technology growing in leaps and bounds as well as superconductivity, it might be possible that his dream of a table top accelerator may come to pass. Then there would be no need for huge centers and each university could have its own, the way the had van der graaphs when nuclear physics was in vogue.

    • Philip Gibbs says:

      “Very little effort and money has gone since then to push research into new accelerator methods/ideas.”

      That is simply not true. There have been a few prototypes built for Wakefield accelerators of various forms for example (just Google it). These are often touted as “table-top” accelerators because the particles can be accelerated over a very short distance, but in truth if you could scale this up to the luminosities and energies that would make them viable alternatives you would probably need supporting infrastructure on a scale similar to what is required for conventional accelerators.

      A better example is CLIC itself which is also a new and more compact method of acceleration, but one that can be made to work at usable energy and luminosity in our lifetime.

      • anna v says:

        Since I retired in 2000, I guess I am not up to date. My experience was with CERN and there was little effort at the time to attract new students and push new directions.

        CLIC sounds very interesting, but it is being developed on the same logic that accelerators up to now use.

  9. Your picture (of 2 doorknobs?) is a mystery. What is it?

    • JollyJoker says:

      It’s a dystopian future vision of hadron colliders, yet an old post-apocalyptic photograph depicting our present.

      (Hint: File name)

  10. Lawrence B. Crowell says:

    The one problem with accelerator technology is that you have these RF cavities which pump EM radiation in that push protons. These cavities are fairly large, in part because the wavelength of this EM radiation is in the MHz range. What is needed is to reduce the wavelength of this radiation, where ideally this might be optical radiation. Maybe we can push protons with lasers. In that way the size of accelerators do not increase to more geographical dimensions, or as to galactic scales in the case of the Planck energy — not that I think we are going to have Planck scale colliders, at least not soon.

  11. Cliff Harv says:

    I voted for a 33 TeV LHC, but my heart really goes to the 100 TeV SSC, or an equivalent. In the meantime it probably makes sense to do a linear collider, but I don’t see any reason why longer term we shouldn’t plan to do one very big, very high energy hadron collider to explore that regime. I say long term both so that A) we can actually know what we’re dealing with in terms of LHC findings up to 14 TeV and B) we can get a better understanding of the viable models, mostly meaning the relevant stringy compactifications. Based on my own reading, many of these viable models would have clear signatures below 100 TeV, and Im sure our understanding of how generically this condition holds will improve.

    Basically there is no need to rush. It seems to me that it would make more sense to just build a massive collider, financed over a longer period of time, than to make many incremental improvements. If we take our time, and again conditioned on what we find at 14 TeV, I think it will likely make a lot of sense to talk about an ambitious future mega-collider.

    Here in the US we have problems wasting dramatically larger sums of money on adventures that make the world more dangerous.

  12. Karsten says:

    What is to my mind missing in this discussion are the different time scales that are involved in these future projects. While the ILC is basically technically ready to be built, all other options need significant more time to get on the real axis.

    CLIC multi-TeV looks as a nice optional choice for a linear collider, but it needs at least another 15 years to bring it to the “decision ready” state, IMHO….

    Another point that is missing are the power needs of these future machines. While the ILC probably is still in the same ballpark for the power consumption as LHC (say 150-200 MW), a 3-TeV CLIC will need close to 500 MW, not speaking about a 5 TeV option.

  13. nameab says:

    Have you considered the feasibility of the Bohr orbits quantization for multiple electronic

  14. ohwilleke says:

    For my druthers, we’ve put enough money into brute force collider physics with LHC for a while.

    Atmospheric neutrino physics, deep space experiments to confirm terrestrial results where there is much less background noise, microscale tests of gravitational attraction, and precision beta decay studies (that could refine double beta decay limitations), to name a few, would all be money better spent. Some of the most interesting recent results, e.g., muonic hydrogen data or helical photon polarizations (I may not have the terminology of that just right), have not involved simple atom smashing.

    Or, what about an experiment in close solar orbit that would have higher neutrino fluxes, shorter neutrino distances traveled, and would bring more easily measurably relativistic gravitational fields into play. Precision QED experiments in an environment like that would test both relativity and QED.

    If one devoted a big chunk of money (say $500 million) to computational power for the QCD background calculation guys that one could wring a lot of additional power out of existing LHC results. Theoretical prediction uncertainty dramatically increases the amount of inverse fbs required to get results of given significance, especially in some of the most theoretically interesting places and at the highest energies. What’s the poiint of spending multibillions on an experiment that will always confirm the Standard Model because the backgrounds are too fuzzy to distinguish signals in the data?

    Given what we should know at the end of LHC’s run in HEP, that a juiced up version of LEP would be better advised than a bigger LHC. The area just beyond where LEP was when the experiment ended turns out to be the lowest resolution area of LHC. For example, a juiced up LEP, informed by LHC data, could do a lot to confirm or disprove the quark-lepton complementarity hypothesis.

    What we could find from a “neutrino collider” and studies of low energy neutrinos would allow us to back into their masses from studying their Lorentz transforms.

    Similarly, one of the big question marks out there involves “molecules’ of mesons — is there a way to coax these buggers into being rather than smashing everything in sight and hoping that they show up once in a while? In theory, one ought to be able to do proof of concept with pretty plain vanilla mesons.

    And, have we done enough with non-colliding states? It might be interesting to devote more attention to what is happening to exotic products of low energy collisions as we spin them at relativistic speeds without smashing them, refining the precision of our understanding of things like decay timing and hadronization speeds.

    There is also a lot to be said for lying low and deciding what looks interesting once we have more data, and trying to be focused in finding the interesting stuff, rather than brute force approaches. Model dependence has a bad rap, but when the LHC run is done, all models will be highly constrained.

    Wouldn’t it be worth some seriously theoretical effort, informed by LHC data to devise a more efficient and targeted test of R-party violation or baryon number violation for a tenth the cost?

    Aren’t there better ways to hone our understanding of the effective nuclear binding force (e.g. by using a wider variety of isotypes in a lower powered collider)?

    What about more precise measurements of the beta function that governs the running of the three coupling constants of the Standard Model in the low to medium energy range through cleaner experimental designs?

    Lots of the interesting stuff coming out of lattice QCD is in the infrared, but we need some clever ideas about how to test its predictions. Are there more efficient ways to create “glue factories” to test QCD predictions about glueballs?

  15. Dirk Pons says:

    This is great as a discussion as among physicists. But what’s missing are the societal and economic dimensions to the decision-making.

    Europe and USA are in trouble. It is going to take 5 years or more to restore global wealth. There is a risk that donor countries don’t have the appetite for expensive science. Furthermore, there may be more pressing problems by then, e.g. with securing alternative energy generation capability, or addressing global warning.

    Regarding the societal, the mood in some countries has become anti-science. Science has been perceived to have a belligerent attitude towards society, particularly in the area of religious beliefs. Given that taxpayer dollars fund fundamental science, it really does not help to bite the hands that feed us.

    As physicists it is easy, and indeed genuine, to say that negative results from the LHC would still be useful. But that is the assumption of an academic world, and the same premise is not held in in a money-tight world where resources are stretched.

    The way society views these things is like this: ‘You took millions of taxpayer dollars, and built something. You found nothing, and now you want more money to build a bigger machine? What assurance can you give that it you will find something at all?’

    No, my intuition tells me it will be a hard sell to get the funding for a yet-more-expensive collider. Not unless China builds it.

    Let’s face the facts. We can’t even get back to the Moon, and even Mars is too risky. The existing LHC will have to keep going until it wears out. Until the current physics is positively confirmed or the next physics uncovered, what government is going to fund a bigger machine?

    • Dilaton says:

      Yes You are right,

      it is oviously much easier to fund the military by 10^500 times the amount of money needed for a particle accelerator than to build a new machine :-(

      Make war and NOT science; is it this what the tax payers want their money to be used for?

      So may it be then; now and till the end of time

    • ondra says:

      Well i fully agree with with Dirk Pons and Dilaton while CERN can be now talking possible no higgs and nothing found as very exciting, they sold this machine on Higgs. They are actually very lucky and exceptional with members having to pay their contribution else they would end like SSC having canceled their funding in a day.
      But for those not taking part in todays science, science funding is no else than bussiness and very high one in case of CERN so they are of course playng their PR and VIP visits games.
      So if there is no clear result, i agree we will wait for a next big accelerator for a long time and LHC will have to do whatever it can.

  16. Leo Vuyk says:

    The MUON COLLIDER SEEMS TO PRODUCE ALSO TAU LEPTONS WHICH ARE MUCH HEAVIER THAN THE MUON !!
    And as we know Tau leptons decay into Muons.

    It would be great to have a cyclotron with alternating Muons into Tau leptons and back agian over a sector of 180 degrees.
    As a result of the mass differences Tau and Muon the whole system would feel a vacuum based acceleration in the equatorial plane.

    http://bigbang-entanglement.blogspot.com/

  17. [...] de compact linear collider (CLIC), die vergelijkbaar is met de ILC, maar wiens botsingsenergie hoger ligt: tot 3 of zelfs tot 5 TeV. De bedoeling van CLIC is dat met een bundel electronen met hoge intensiteit, maar lager energie een tweede bundel van electronen wordt opgestuwd tot grote energie, resulterend in zeer schone botsingen. Aan beide versnellers zijn uiteraard peperdure prijskaartjes verbonden – $ 6,75 miljard voor de ILC, de kosten van CLIC weet ik even niet, maar dat zal niet voor een grijpstuiver zijn. :bron: Bron: viXra. [...]

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