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'Up-tight' at CERN?

By Hamish Johnston

If you asked me to name an “outspoken” particle physicist, I might choose Tommaso Dorigo of Italy’s University of Padova. Dorigo, you may recall, was embroiled in a controversy last year over the supposed sighting of the Higgs boson by the CDF collaboration at Fermilab.

Dorigo is a CDF member and had discussed preliminary results from the experiment on his blog, where they were picked up by the press and reported as evidence of the elusive Higgs. While these results had been previously reported at a conference, they had not been “approved” by Fermilab for mass consumption.

Needless to say, the CDF data did not provide strong evidence for the Higgs, and Dorigo has been criticized for discussing the results in public.

Now, Dorigo spends most of his time working on the LHC’s CMS experiment — so what does he have to say about the recent setbacks at CERN?

Nothing it seems, and he has even made a point of saying so in a recent blog posting .

Dorigo observes “CERN appears a bit up-tight about the latest events…”, and claims “my blog is targeted as a possible source of leaks”.

As a result, he has chosen to keep quiet: “And if I play fair, maybe I am allowed to survive here, and maybe one day I will stop being threatened every other day, in the name of protecting internal information of the experiments I am part of”.

Strong stuff…so, once burned, is Dorigo making the right choice?

LHC on hold until spring of 2009

The magnet failure last week at the Large Hadron Collider (LHC) means that the accelerator will not be up and running again until early spring of 2009, say officials at CERN.

To keep the project on schedule, the team running the accelerator near Geneva have decided to skip a planned test run at an intermediate energy and re-start the LHC in 2009 at the full beam energy of 7 TeV.

We are not behind schedule for 7 TeV James Gillies, CERN

They are now warming up a sector of the beam line that failed on 19 September to determine exactly what happened when one tonne of liquid helium escaped from the accelerator’s cooling system after a magnet “quench”.

The warming is expected to take three to four weeks and CERN officials say that the subsequent investigation and repair processes will run into the scheduled winter shutdown of the experiment — which will begin at the end of November. As a result, the accelerator is not expected to be running again until March or April 2009.

The failure occurred as the accelerator’s two proton beams were being ramped up for a test run at 5 TeV. CERN had then planned to use the winter shutdown to make final adjustments to the superconducting magnets that guide the beam so that the accelerator could start-up again in the spring at the full energy of 7 TeV.

However, CERN has now decided to cancel the 5 TeV test run and re-start the accelerator at full power in the spring, according to CERN spokesperson James Gillies. “We are not behind schedule for 7 TeV”, he told physicsworld.com.

According to Gillies, many individual components of the accelerator (including the magnets) have already been “trained” to operate at 7 TeV and now it is a matter of getting these components to work in concert.

LHC team confronts first major hitch since ‘switch on’

The team operating the Large Hadron Collider (LHC) at the CERN lab near Geneva is standing firm against its biggest setback in months while admitting that it might be forced to replace several superconducting magnets.

On Friday, physicsworld.com revealed that a huge warm-up or “quench” in one of the eight sectors of magnets caused about one tonne — some 8000 litres — of liquid helium to evaporate rapidly into the LHC’s tunnel. At the time the team had been increasing the energy of the machine from 450 GeV — the energy with which proton bunches are injected from Super Proton Synchrotron, the last in CERN’s accelerator chain — to 5 TeV.

The team now believes that the quench was a side-effect of a faulty electrical connection that melted at high current. Although the quench is not a big issue, the sector containing the fault will have to be warmed up to enable repairs, and then slowly cooled back again to its operating temperature of 1.9 K.

“We may have to exchange more magnets,” LHC project leader Lyn Evans told physicsworld.com in an e-mail. “[But] we have spares.”

“The mood at CERN is not joyful,” he continued. “However, we have had to face up to problems in the past and we will do it again. Teams are being organized to make the repair as quickly as we can.”

The problem now looks likely to set back the commissioning schedule by around two months. “A full investigation is underway, but it is already clear that the sector will have to be warmed up for repairs to take place,” CERN spokesperson James Gillies wrote in a statement over the weekend. “This implies a minimum of two months downtime for LHC operation.”

The rocky road of commissioning

Last week’s electrical fault is the second the LHC has suffered since the highly successful “switch on” on 10 September, when the operations team managed to circulate proton beams in both directions around the 27 km-long tunnel. Late on 12 September — as first revealed on the physicsworld.com blog — a short-circuit demanded the replacement of a mammoth 30 tonne transformer.

The latest problem, aside from being a blow to morale, will probably scupper the plans to have useable data pouring out of the LHC in time for 21 October, when various heads of state will travel to CERN for an official inauguration.

Presently the team still hopes to “train” the magnets to handle beams at the full energy of 7 TeV during the winter, when the LHC is shut down. However, there is a worry that, upon warming the sector, the team could find the problem is worse than they had expected.

LHC loses liquid helium

The Large Hadron Collider (LHC) has lost up to a tonne of liquid helium after some of its superconducting magnets inadvertently heated up this morning, physicsworld.com has learnt.

A log entry written by the current LHC co-ordinator at 11:27 am CET (10:27 am BST) states that there has been a “massive quench” in sector 3–4. Quenches occur when superfluid helium in the magnets rises above its operating temperature of 1.9 K, and can be caused, for example, when a proton beam veers off course.

According to the entry, firefighters were dispatched to that area of the tunnel. It also says that the vacuum in that part of the beam pipe was lost.

A source at CERN, the European lab hosting the accelerator, says that the quench caused one tonne of superfluid helium — about 1% of the LHC’s total — to escape.

An official spokesperson was not available for comment. However, a message on the machine’s website states: “During the commissioning of the final LHC sector (sector 3–4) for 5 TeV operation, an incident occurred at 12:05 [am] today resulting in a large helium leak into the tunnel. Further details are not yet known. Investigations will continue over the weekend and more information will be made available as soon as possible.”

An LHC status report on the same website shows that temperatures are now being brought down, implying that technicians have been able to replace the lost helium.

The problem will be a disappointment to the operations team, who had enjoyed a highly successful media day last week when they circulated beams of protons in both directions around the machine’s 27 km-long ring.

Lasers slim down radiotherapy equipment

Researchers from Italy, France and Germany have shown that a tabletop laser can be used to accelerate a beam of electrons suitable for use in radiotherapy. The group, led by Antonio Giulietti of the Institute for Physical Chemistry Processes in Pisa, believes that such laser-based particle acceleration could considerably reduce the size and simplify the operation of radiotherapy facilities.

In radiotherapy beams of photons, electrons, protons, neutrons or ions are used to destroy tumours by ionizing the atoms within the tumours’ DNA. Usually this involves irradiating the patient from a number of different directions in order to pinpoint the tumour, and in the case of deep tumours, using higher-energy particles. This inevitably leads to some damage of the healthy tissue surrounding the tumour.

Damage limitation

Damage can be limited using a technique known as intraoperatory radiotherapy (IORT), which involves irradiating the patient just once with electrons. This occurs in the operating theatre right after the tumour has been surgically removed. The idea is to destroy tumour cells that the surgery has missed. Because they do not have to penetrate deeply, the electrons can be fewer in number and have a lower energy, which means that the accelerators employed can be smaller.

However, as Giulietti points out, IORT, like ordinary radiotherapy, still uses radiofrequency electric fields to accelerate the electrons, which requires a machine more than two metres high and over half a tonne in weight. The machine must be shielded from the operating theatre and any maintenance requires the shut down of the theatre. “This therefore limits the energy of the electrons that can be used in the technique,” he adds.

Giulietti and colleagues have shown that these problems can be overcome by using a laser rather than radiofrequency electric fields to accelerate the electrons.

At the SLIC laboratory in Saclay, France, the researchers fired ultra-short laser pulses onto a jet of gas, creating a plasma with a fluctuating electron density. The electric field generated by these fluctuations accelerated the free electrons within the plasma such that they had energies and spatial characteristics suitable for use in IORT. By then passing these electrons through a 2 mm–thick piece of tantalum (and therefore decelerating them rapidly) the researchers were able to create gamma–ray photons that could also be used in radiotherapy (Phys. Rev. Lett. 101 105002).

Just a small metal box

Because the laser beam can travel for several tens of metres without any appreciable loss, the laser itself can be located outside the operating theatre. According to Giulietti, the only thing that would need to be in the theatre is a metallic box perhaps 50 by 20 by 20 cm across that would convert the laser beam into the electron beam, and which would contain a roughly 10 cm–long device to generate the gas jet and focusing optics of a similar size.

Giulietti points out that scaling up the facility would allow IORT to be carried out at higher energies than is currently possible, which would render the technique more effective against certain kinds of tumours. He adds that more work is needed to design a laser–based system suitable for actual hospital use, in particular ensuring the stability of both the laser output and the acceleration process within the plasma.

Quantum gas of ultracold polar molecules is a first

The first stable quantum gas of molecules with large electric dipole moments has been made by physicists in the US. Unlike other quantum gases, the molecules interact with each other over relatively large distances. This means that the system could be used to study a wide range of quantum phenomena — and perhaps even be used to create robust quantum bits that could be used to store and process information.

Previous attempts at making such a gas had failed because it proved impossible to cool molecules with large dipole moments to the sub-milliKelvin temperatures needed to create a quantum gas. But now a team led by Deborah Jin and Jun Ye at NIST/JILA in Boulder, Colorado have come up with a laser technique that solves this problem (Sciencexpress 10.1126/science.1163861) .

First created in the mid 1990s, a quantum gas is formed when the constituent atoms or molecules are cooled until they have little energy and are sufficiently close together for the overall behaviour of the gas to be governed by quantum, rather than classical, physics. The forces between the gas atoms tend to be very small and act over very short distances. Physicists have learned how to control these forces using magnetic fields to allow the atoms or molecules to get very close together. This has let physicists use ultracold gases as “quantum simulators” for studying more complicated systems such as electrons in superconductors.

Long-range challenge

What researchers had not been able to do is make a quantum gas from atoms or molecules that interact via long-range forces. This could be very useful for simulating many “real-life” systems which involve long-range interactions between electrons.

The NIST/JILA technique starts with a very cold gas that is simply a mixture of potassium and rubidium atoms. The atoms are confined by a laser beam and are subjected to a magnetic field, which creates a weak attraction between potassium-rubidium pairs that binds them into a polar molecule.

Jun Ye
Jun Ye

At this point the molecules are relatively large and each molecule has a great deal of internal energy — the molecules are both vibrating and rotating. In order to make a dense quantum gas, these molecules must “shrink” in size by losing much of their internal energy. Unfortunately, this expelled energy tends to heat up the gas, making the shrinking process a difficult one.

The team got around this problem by firing near-infrared laser light at two specific wavelengths at the molecules. This causes the molecules to give up their internal energy as photons of red light, which exit the gas without heating it.

Lowest energy states only

This left the majority of the molecules in their lowest vibrational and rotational energy states, resulting in a quantum gas with a temperature of 350 nK and density of 1012 molecules per cubic centimetre.

The team then measured the dipole moment by applying a small electric field to the gas and determining the resultant shift in the molecule’s energy levels using laser spectroscopy. The dipole moment of a molecule in the lowest energy state was 0.566 Debye, which is about one third the dipole moment of a water molecule.

The creation of a stable quantum gas of molecules with large electric dipole moments is of particular interest to physicists who are keen on making quantum bits (or qubits) for quantum computers. This is because qubits made from such molecules would (in principle) be robust to interference from outside influences, but could be manipulated by the simple application of an electric field.

“This is a landmark paper!” said David DeMille — a physicist at Yale University who studies the use of dipolar quantum gases in quantum computing. DeMille told physicsworld.com that the work also opens the door to the study of chemistry at ultracold temperatures as well as new tests of fundamental symmetries in physics.

McCain chips in on science

US presidential candidate John McCain has joined the debate on the future of American science by answering the “14 top science questions facing America” posed by the organization ScienceDebate 2008.

The Democratic party hopeful Barack Obama has already answered the same questions, which were selected from thousands of suggestions sent in by the American public.

Some scientists have accused the current Republican administration of political interference when it comes to climate change and other politically-charged scientific issues. But in response to how he would “balance scientific information with politics and personal beliefs?” McCain — also a Republican — says “Denial of the facts will not solve any of these problems… I believe policy should be based upon sound science”.

Denial of the facts will not solve any of these problems…I believe policy should be based upon sound science John McCain

To do this, McCain promises to recruit at least five science and engineering experts into senior advisory positions with the aim of “restoring the credibility and role of the Office of Science and Technology Policy as an office within the White House.”

McCain says he is “committed to reinvigorating America’s commitment to basic research, and will ensure my administration funds research activities accordingly”. He points out that he has a record of supporting increased funding for science research, adding “I have a broad and cohesive vision for the future of American innovation.” He also says he would encourage the commercialization of new technologies — particularly those created by federally funded research.

To the moon and beyond

Looking to the heavens, McCain says he would “Ensure that space exploration is top priority and that the US remains a leader.” He has committed himself to funding NASA’s Constellation programme, which aims to send astronauts to the Moon by 2020. McCain also promises to complete construction of the ISS National Laboratory — which is the US-funded portion of the International Space Station – and “seek to maximize [its] research capability and commercialization possibilities.

On the subject of climate change, McCain says: “The facts of global warming demand our urgent attention, especially in Washington.” He says he will establish a tax credit equal to 10% of a firm’s wages spent on research and development to encourage the development of environmentally friendly technologies. He also wants to offer a $300m prize for the development of a battery package that would improve significantly performance of electric and hybrid vehicles.

Turning to energy security and sustainability, McCain says he will ensure that 45 new nuclear reactors are built in the US by 2030. However, he supports “letting the market decide” which alternative forms of energy (such as wind and solar) would be ultimately be adopted by the US.

Cash for science teachers

On education, the Republican candidate says he will “Grow public understanding and popularity of mathematics and science by reforming mathematics and science education in schools.” He stresses the importance of ensuring that US primary and secondary schools prepare students for “the rigors of engineering, math, science and technology degrees”. To achieve this, McCain will devote 60% of “Title II” federal education funding to produce pay bonuses for “high performing teachers” in math, science and other key subject areas.

ScienceDebate 2008 was formed towards the end of last year by a group of six people who wanted science policy to be debated by the presidential candidates in the run up to the November election. Since then the organizers have gathered the signatures of some 37,000 supporters including university presidents, the representatives of scientific institutions and Nobel laureates.

While Matthew Chapman, president of Science Debate 2008, is grateful that McCain and Obama have both responded, he remains hopeful that the candidates will also agree to attend a televised debate on science policy, which was the original motive of the organization.

• You can read John MacCain’s’s full responses to the questions posed by ScienceDebate 2008 here.

The LHC, one week later

By Jon Cartwright

Many of you will be wondering how the Large Hadron Collider (LHC) has been getting on since last Wednesday’s celebrated “switch on”. Well, if you are willing to overlook one 30 tonne hitch, commissioning is still going well.

On the switch-on day itself, if for some reason you left the planet, the operations team managed to get proton bunches all the way around the LHC’s 27 km-long ring in both directions. But even though the media had trickled away by early evening, the LHC team didn’t stop ploughing ahead, as I discovered when I went to the control centre the morning after. By then they had already had an anticlockwise bunch endlessly circulating, albeit spread or “de-bunched” around most of the ring. To correct the de-bunching, the team initiated their radio-frequency systems, which by Friday had been successfully tuned in both frequency and phase.

Friday, unfortunately, also brought difficulties. A transformer weighing some 30 tonnes developed a short circuit, forcing the team to replace it. As I hear from Lyn Evans, the LHC project leader, the new transformer has been lifted into place and the electrical systems, which feed the vital cryogenics systems, should soon be back on line.

The good news, however, is that Evans is planning to try some low-energy collisions next week. Hang on to your hats.

Pulsar signal for mobile phones

Mobile phones that get signal even in the remotest parts of the world could soon be a reality if a technology being developed by researchers in the US and UK gets off the ground. John Singleton of the Los Alamos National Laboratory in New Mexico and colleagues say that their “polarization synchrotron”, which they claim mimics the distinctive emission of pulsars, will enable extremely long-range or low-power radio communication.

Singleton’s team built and tested a proof-of-principle version of the device some five years ago. It consisted of a 2 m–long arc of dielectric with a series of electrodes embedded along its length. By applying a sinusoidally varying voltage across each electrode, but offsetting the phase of this voltage very slightly between neighbouring electrodes, they were able to produce a changing pattern of polarization along the dielectric that they say travelled faster than the speed of light (noting that no material object actually exceeds light speed).

Inspired by the Crab pulsar

They were inspired to do so by the work of team member Houshang Ardavan of Cambridge University, who had previously calculated that it was superluminal charge patterns that are responsible for the way in which pulsars — rapidly spinning neutron stars — generate their beams of radio waves that are visible on Earth as pulses. According to Ardavan, the electromagnetic radiation given off by the rotating charge pattern piles up into a tightly focused beam and this beam swings round like that of a lighthouse, a theory that the group says is backed up by recent observations of the Crab pulsar (Mon. Not. R. Astron. Soc. 388 873).

Singleton’s team believes that its polarization synchrotron also produces a tightly focused beam of radio waves in this way, and that the intensity of this radiation falls off as 1/r, rather than the 1/r2 of normal spherically decaying radiation. The group backed up this claim by measuring the output of the device over 3 km of airfield and is now putting the finishing touches to two much smaller, laptop-sized versions that they hope will demonstrate its commercial viability. The first of these, which they say should be finished early next year, will be circular, while the second, planned for later in the year, will be straight.

Patents pending

The group claims that the devices will allow spacecraft to transmit low-powered signals to Earth, or allow mobile phones to communicate directly with satellites, rather than having to rely on base stations. Singleton and colleagues have filed patents on various aspects of the technology and are talking with several interested potential sponsors. However, John Hannay, a theoretical physicist at Bristol University, told physicsworld.com that the group should first test its technology over at least several tens of kilometres.

Jefferson lab upgrade approved

A massive $310m upgrade to the Thomas Jefferson National Accelerator Facility in Virginia has been approved, which will provide physicists with beams of 12 GeV electrons to study the fundamental structure of protons and neutrons. The upgrade will allow scientists to investigate the origins of why quarks — fundamental building blocks of matter — do not exist on their own.

“The upgrade is really a big deal for us. It will also enable us to maintain the 1200 users per year that use our facility from around the world,” Jefferson lab director Hugh Montgomery told physicsworld.com. Construction is expected to start in January with the upgrade ready by 2015.

Researchers at Jefferson currently use beams of 6 GeV electrons produced from the Continuous Electron Beam Accelerator Facility (CEBAF). This is a 1500 m long oval-shaped track built 25 m underground that accelerates electrons by using superconducting radio-frequency (SRF) modules, which are radio frequency cavities coated in a superconducting material.

Inner secrets

The beam smashes into the experimental targets and huge detectors collect the fragments. By studying the speed, direction and energy of the scattered fragments, scientists can unveil the inner secrets of protons and neutrons to test quantum chromodynamics and the Standard Model of particle physics.

The new money, announced yesterday by the US Department of Energy (DOE), will let the lab build ten new SRF modules on top of the 40 currently used now. Higher energy electrons will allow higher momentum transfer — corresponding to smaller distance scales — so that the beams of 12 GeV electrons will enable researchers to produce “exotic” mesons that will provide clues into why quarks do not exist on their own. If these mesons are not found then it could mean that our understanding of the fundamental theory of quantum chromodynamics would have to be revised.

When the electrons are accelerated they are then sent to three separate experimental halls that house spectrometers and detectors. As part of the upgrade, a new experimental hall will also be built, which will use the full 12 GeV energy to perform exotic meson spectroscopy — a new technique at the lab.

‘What’s going on in the nucleon’

The three remaining halls will also be improved to enable researchers to take advantage of 11 GeV electron beams that will allow the exploration of quark-gluon structure of hadrons – particles composed of quarks and gluons — as well as performing tests of the Standard Model of particle physics. “The upgrades to existing experiments will able us to get a full 3D picture of what’s going on in the nucleon,” says Allison Lung, deputy project manager for the upgrade.

The Jefferson lab operates with a budget of $100m per year and is funded by the DOE, which yesterday gave the go-ahead for construction known as critical decision three.

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