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TOPIC: Large Hadron Collider
Blobrana


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Large Hadron Collider
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Researchers building the world's next top particle accelerator, the Large Hadron Collider (LHC) that straddles the Franco-Swiss border, may not get a chance to work out the bugs before they fire up the machine in earnest.
The experiment is still on track to begin hunting for the long sought Higgs boson next March. But a crucial upgrade of 16 superconducting magnets around the accelerator will likely prevent a full test run planned for this December, meaning researchers will have to troubleshoot glitches on the fly.

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The first sector of CERN s Large Hadron Collider (LHC) to be cooled down has reached a temperature of 1.9 K (-271°C), colder than deep outer space.
 Although just one-eighth of the LHC ring, this sector is the worlds largest superconducting installation. The entire 27-kilometre LHC ring needs to be cooled down to this temperature in order for the superconducting magnets that guide and focus the proton beams to remain in a superconductive state. Such a state allows the current to flow without resistance, creating a dense, powerful magnetic field in relatively small magnets. Guiding the two proton beams as they travel at nearly the speed of light, curving around the accelerator ring and focusing them at the collision points is no easy task. A total of 1650 main magnets need to be operated in a superconductive state, which presents a huge technical challenge.

"This is the first major step in the technical validation of a full-scale portion of the LHC"  -  Lyn Evans, LHC project leader.

There are three parts to the cool down process, with many tests and intense checking in between. During the first phase, a sector is cooled down to 80 K, slightly above the temperature of liquid nitrogen. At this temperature the material will have seen 90% of its final thermal contraction, a 3 millimetre per metre shrinkage of the steel structures. Each of the eight sectors is about 3.3 kilometres long, which means shrinkage of 9.9 metres. To deal with this amount of shrinkage, specific places have been designed to compensate, including expansion bellows for piping elements and cabling with some slack. Tests are done to make sure no hardware breaks as the machinery is cooled.
The second phase brings the sector to 4.5 K using enormous refrigerators. Each sector has its own refrigerator and each of the main magnets is filled with liquid helium, the coolant of choice for the LHC because it is the only element to be in a liquid state at such a low temperature.
The final phase requires a sophisticated pumping system to help bring down the pressure on the boiling Helium and cool the magnets to 1.9 K. To achieve a pressure of 15 millibars, the system uses both hydrodynamic centrifugal compressors operating at low temperature and positive-displacement compressors operating at room temperature. Cooling down to 1.9 K provides greater efficiency for the superconducting material and for the heliums cooling capacity. At this low temperature helium becomes superfluid, flowing with virtually no viscosity and allowing greater heat transfer capacity.

"Its exciting because for more than ten years people have been designing, building and testing separately each part of this sector separately and now we have a chance to test it all together for the first time" - Serge Claudet, head of the Cryogenic Operation Team.

Source CERN

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Blobrana


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Will big questions be answered when the Large Hadron Collider (LHC) switches on in 2007?  What will scientists find? Where might the research lead?  
Nima Arkani-Hamed, a noted particle theorist, is a Professor of Physics at Harvard University.  He investigates a number of mysteries and interactions in nature – puzzles that are likely to have experimental consequences in the next few years via particle accelerators, like the LHC, as well as cosmological observations.

Prof.  Nima Arkani-Hamed,  will provide a  Perimeter Institute public lecture in Canada on Wednesday, February 7, 2007, 7:00 pm.

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Blobrana


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ATLAS Barrel Toroid
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The largest superconducting magnet ever built has successfully been powered up to its nominal operating conditions at the first attempt. Called the Barrel Toroid because of its shape, this magnet provides a powerful magnetic field for ATLAS, one of the major particle detectors being prepared to take data at CERN 's Large Hadron Collider (LHC), the new particle accelerator scheduled to turn on in November 2007.
The ATLAS Barrel Toroid consists of eight superconducting coils, each in the shape of a round-cornered rectangle, 5m wide, 25m long and weighing 100 tonnes, all aligned to millimetre precision. It will work together with other magnets in ATLAS to bend the paths of charged particles produced in collisions at the LHC, enabling important properties to be measured. Unlike most particle detectors, the ATLAS detector does not need large quantities of metal to contain the field because the field is contained within a doughnut shape defined by the coils. This increases the precision of the measurements it can make.

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Blobrana


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ATLAS experiment
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University College London scientists involved in the construction of a 16-mile-long tunnel under Geneva this week saw the beginning of ATLAS, the world’s largest scientific experiment.

The tunnel is home to a giant particle accelerator, the flagship facility of CERN, the European Laboratory for Particle Physics. In the ATLAS experiment, particles will be fired towards each other at speeds of more than 600 million miles an hour. Their collisions will be recorded by a semiconductor tracker – essentially an ultra-sensitive digital camera – which can take 40 million pictures in a second and measure particle paths to an accuracy of a tenth of the width of a human hair.
Currently, the tracker is being used to record the paths of ‘cosmic rays’ – particles arriving naturally at the Earth from outer space. However, when the massive machinery starts to work fully, much more complicated images will be taken, and their analysis could be hugely important.
It is hoped that the effects of the collisions of particles will help to track down the Higgs Boson – thought to be the only type of basic particle yet to be discovered. The massive amounts of energy that will be generated by the particle accelerator may also be enough to produce so-called ‘dark matter’, which astronomers believe makes up a large part of the universe and is responsible for the movements and arrangement of stars and galaxies.

University College London has been involved throughout the development of the experiment and the colossal machinery involved in its execution. The High Energy Physics group at University College London Physics & Astronomy was involved in developing the electronics behind the semiconductor tracker, as well as playing a role in the electrical and mechanical engineering required to construct the particle detector.
ATLAS is a collaborative project involving research groups from around the world. There are 1,800 physicists (including 400 students) participating from more than 150 universities and laboratories in 35 countries.

"It is great news that after decades of research and planning, we finally know that the machinery we have helped to develop is working. What is really exciting is that, within a year, when the machinery is fully operational, we will be able to explore the most fundamental constituents of the universe" - Dr Alan Barr, a member of the University College London High Energy Physics group.

UCL High Energy Physics Group
The ATLAS experiment

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Blobrana


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RE: Large Hadron Collider
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The world's largest particle detector is nearing completion following the construction of its 'endcap' at the University of Liverpool.

Its assembly of advanced apparatus, at the University’s Semiconductor Detector Centre, has been a joint effort by physicists, engineers and technicians from the Universities of Liverpool, Glasgow, Lancaster, Manchester and Sheffield as well as CCLRC Daresbury and Rutherford Appleton Laboratories.
The endcap is part of a semiconductor tracker (SCT) based at the heart of ATLAS - a giant particle detector the size of a five-storey building. The SCT will become part of the world’s largest particle accelerator – the Large Hadron Collider (LHC), based at CERN, the European Centre for Particle Physics Research, in Switzerland.

The LHC is being constructed 100 metres underground in a 16-mile long circular tunnel, running under the Franco-Swiss border. Inside the tunnel two particle beams will be accelerated to extremely high energies, and will crash into each other forty million times a second, creating a snapshot of conditions that existed billionths of a second after the ‘Big Bang’. ATLAS, the culmination of 15 years’ work by over 150 European institutions, aims to find the Higgs particle that holds the key to understanding the origin of mass.

"Using the LHC we are aiming to discover the Higgs particle and hoping to find evidence for so-called Super-Symmetric particles, which we believe could offer an explanation for the ‘dark matter’ in the universe. At present the normal matter that we can see in the universe accounts for only 5% of its mass. The origin of the missing mass is unknown, but Super-Symmetric particles may account for some of it. If we discover these particles then we are on our way to explaining why the universe is made the way it is.
At Liverpool we have tested 988 detector modules and assembled them into one of two SCT endcaps. The modules will detect the reactions produced as the accelerator collides billions of protons in the centre of ATLAS. The particles produced in these collisions are recorded as they pass through the endcaps. The collisions will be strong enough to recreate particles and reactions that were present fractions of a second after the Big Bang" - Dr Neil Jackson, from the University’s Department of Physics.

The Big Bang theory is the dominant scientific theory about the origin of the universe. It suggests that the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter in all directions.
The conditions that will be reproduced at LHC will correspond to approximately 1/10,000,000,000 of a second after the ‘Big Bang’ when the temperature was 1,000,000,000,000,000 degrees. Large detectors will electronically register the movement and position of charged particles allowing physicists to analyse the reactions that created them.


The 'endcap'.
Credit University of Liverpool

The endcap will begin its journey to Switzerland later this month.

"We have to be extremely careful that the endcap we have constructed does not become damaged on its journey to Switzerland. We have just completed a trial run of the journey, using a dummy load to represent the endcap. Accelerometers and position-sensitive detectors were positioned on the transport frame to monitor the machine and we tested driving conditions with emergency stops, sleeping policemen, gradients and motorway driving. The results of the test were very encouraging" - Dr Neil Jackson

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Blobrana


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The mysteries of dark matter, multiple dimensions and even the conditions following the Big Bang could be solved with the help of the world's biggest computer grid.

The Large Hadron Collider (LHC) being constructed at CERN near Geneva will be the largest scientific instrument on the planet and will need the hugely powerful computing to process the 15 petabytes of data that it will produce each year.
The LHC will smash protons and ions into head-on collisions to help scientists understand the structure of matter.
Discovering new types of particles can only be done by statistical analysis of the massive amounts of data the experiments will generate, which is where the LHC Computing Grid project comes in.
And although the LHC won't be up and running until 2007, work has already begun on the grid, with the UK being one of the largest contributors.
Of the 150 grid sites around the world, 18 are in the U.K. And much of the U.K. work is being done at the Rutherford Appleton Laboratory (RAL) in Oxfordshire, England.
Because of the scale of processing needed, the grid is the best way to go.

"The computing has been planned for years; we've been looking at distributed computing for a long time. They couldn't afford to do all the computing at CERN so we knew we would have a big distributed computing problem of sifting the data around the world and finding it again. It's the biggest production grid in the world" - John Gordon, deputy director of the Council for the Central Laboratory of the Research Councils e-Science Centre at RAL.

The grid will use a four-tier model; data will be stored on tape at CERN, the 'Tier-0' centre. From there, data will be distributed to Tier-1 sites which have the storage and processing capacity to cope with a chunk of the data. These sites make the data available to the Tier-2s, which are able to run particular tasks. Individual scientists can then access data from Tier-3 sites, which could be local clusters or individual PCs.
RAL hosts the UK's Tier-1 site, with the universities of Lancaster and Edinburgh and Imperial College operating Tier-2 sites.
And while real data won't start flowing until 2007, scientists are already using lots of processing power on simulations.

"They need to know what they are looking for so they do lots of simulations" - John Gordon.

Commodity hardware and open source software are being used to keep costs down.

"Because it's worldwide we are all looking at open source. All the grid stuff is done in open source, that's taken for granted. Grid should use standard protocols, it's across administrative domains" - John Gordon.

Network bandwidth will also be key--at the moment it has a 2Gbps dedicated link to CERN--the same amount of bandwidth RAL uses for all the rest of its internet traffic, and the plan is to build a dedicated fibre-optic network between the sites.

"What we are looking at is setting up a network of private light-paths to Tier-1 sites" - John Gordon.

Managing the huge number of files the experiments will generate is another problem the team is working on.

"You end up with millions of files and the problem comes in handling them and that's where the data management comes in. Data management is key" - John Gordon.

But beyond all the exciting technology, much of the work will be in persuading different organizations to share.

"A lot of it is sociological--you are persuading people that they gain by connecting all their computers together. It's about collaboration; it's not about people sitting in London using computers all over the world, it's about groups of people working on the same problem" - John Gordon.

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The ATLAS Tracker (SCT), the heart of the Large Hadron Collider (LHC), the biggest physics collaboration in the world, has left Oxford today for its new home at the European Particle Physics Laboratory, CERN, near Geneva.



The SCT detector consists of a central region and two end caps. The central region is formed of four concentric barrels, covered with 2112 silicon modules (30 square metres worth).
The modules were produced by collaborators in different countries and sent to Oxford’s Department of Physics for precision assembly.
The SCT will track the positions of charged particles passing through the detector with an accuracy of better than 20 microns (less than the diameter of a human hair) over one metre. The information obtained by the SCT will form a crucial part of the data gathered by the full ATLAS Detector system and will be essential in the task of unravelling the physics in high energy particle collision.

The ATLAS experiment is the world’s largest collaboration in physical sciences, involving more than 1800 scientists from around the world. The detector measures 44 metres long and 22 metres high, as large as a five-story building, and weighs 7000 tons. Yet at its heart, where the SCT will operate, narrow beams of particles will be focussed to collide in an area much less than one square mm.

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