Graham Objects v 4

Emma Sanders June 2011 version 4

CERN Objects for Science Museum LHC exhibition This is the worlds biggest scientific adventure. 27 km long and 100 m below ground, the Large Hadron Collider accelerates the building blocks of matter to almost the speed of light before bringing them into collision, recreating the conditions in the first moments of the universe. 1. The fastest racetrack on the planet 1.1 LEP radio frequency accelerating cavity 4* rating (small doubt due to possible residue radioactivity) My contact for the object: James Gillies LEP superconducting accelerating module, the same technology as used in the LHC . 12m long and 1.2m in diameter. They weigh 8 tonnes. Or we can cut you off a piece!

1.2 Section of LHC cavity 5* rating My contact for the object: Olivier Brunner

Protons in the Large Hadron Collider are accelerated by electromagnetic waves generated by radio


frequency cavities. These whip the protons up to 99.9999991 % of the speed of light and bunch them into packets as the positively-charged protons are attracted to the crests of the waves. The protons will be travelling so fast that, if they were chasing a beam of light towards Alpha Centauri, the nearest star outside our solar system, the light would take about four years to arrive, and the protons would get there a mere few seconds later. The revolution(s) in engineering delivered in order to build the object Applying the thin film of niobium on the surface of the copper, several microns thick, to high precision. this was a first for CERN. The surface of each cavity (about 2 m^2) must be coated uniformly. The cleanliness and smoothness of the surface are crucial and repeated surface chemical etching, chemical polishing and high pressure rinsing are applied to obtain ultra-clean surfaces with an average roughness lower than 0.1 micron. Few lines on the engineering/science associated with the deliver The electric field is created by a current of 170000 Amperes / mm^2 flowing through a thin film of niobium applied to the copper cavities. Such a large current density would inevitably melt the surface, were it not superconducting, so the entire cavities are cooled to -269 C. Synchronisation of cavities is extremely important, both within the LHC as protons speed up, and also on injection to the LHC from the preceding chain of accelerators. The protons must always feel a positive voltage kick when they pass through otherwise theyd not get any faster. 2. The emptiest space in the solar system 2.1 Section of LHC beam-pipe 4* rating This is likely to be only a short section. Diameter 54mm.

If the protons in the LHC collided with an air molecule, they would be stopped.


So that protons are not lost through collisions with air molecules, they travel in a tube that is pumped down to a vacuum that is as empty as interplanetary space. In all, there are 54km of continuous vacuum pipe equivalent in volume to pumping down the nave of a cathedral. Protons are stored for about 10 hours in the LHC. During this time, they make four hundred million revolutions around the machine, travelling a distance equivalent to the diameter of the solar system. The new vacuum techniques that have been invented for the LHC find applications in the future generation of solar panels. In the object proposed, you can see the dual layer beamtube, used in all the cold sections of the LHC. It effectively pumps stray air molecules through the holes and onto the outer surface, because of a temperature difference between the 2 layers.

3. One of the coldest places in the universe / The worlds largest fridge! / The biggest superconducting installation ever With an operating temperature of about -271 degrees Celsius, just 1.9 degrees above absolute zero, the LHC is colder than outer space. This is not the zero of your freezer at home, but -273C. This extreme cooling is needed so that the wires in the LHC superconduct. Without using superconducting technology, we would not reach the magnetic field needed. Associated engineering challenges: When the magnets are cooled, they contract: normally 15 metres long, each magnet shrinks by 4.5 cm on its way down to 1.9 degrees above absolute zero. One side of each 30 000 kg magnet is held stationary, while the other is left free to move. All connections must absorb the contraction. Cooling down or warming up the LHC takes 6 weeks. Over 12 million litres of liquid nitrogen and 800 000 litres of superfluid helium are needed to cool the 36 000 tonnes of equipment to 1.9 degrees above absolute zero. All in all, LHC cryogenics needs 40 000 leak-proof pipe junctions. Object suggestions : Cryostat of liquid nitrogen? You would need to get this loaned from some-one in the UK. Possibly by a sponsor? We could provide the drawings that would allow you to make a mock-up of a section of LHC. Certain real pieces such as the metal bellows that absorb the contraction (3*) and the PIMs


connecting pieces along the beam-tube that absorb the contractions (5*) could be contributed from CERN.

4. The highest precision steering / The worlds biggest string of magnets / Getting beams of protons to collide inside the experiments requires the precision of firing knitting needles from either sides of the Atlantic and getting them to collide in the middle. 4.1 LHC magnet cryostat 5* rating aprox dimensions: 1m diameter tube, about 15 m long (16 m with end caps) aprox mass: 5 tons This piece will be in Paris in November 2011. If it is not needed in 2012 by CERN, maybe you could save on transport and take it on from Paris. To be investigated My contact: Lucio Rossi

This is the cryostat that contains the bending magnets and beamtubes where the LHC protons travel. The difference in temperature between the blue outer surface and the magnets inside is 300 degrees. There are 1 700 such cryostats containing magnets in the LHC. The magnets focus and guide two beams of protons in opposite directions around the 27km ring. The high magnetic fields needed can only be reached using superconductors. The current creating the magnetic field passes through superconducting cables at up to 12 000 amps, about 30 000 times the current flowing in a 100 W light bulb. All this with no energy costs, apart from those for the big fridges which consume 40MW. If non superconducting wires had been chosen, running the magnets would require 900MW a fairly good-sized nuclear power plant. The LHC is the largest superconducting installation in the world. Engineering breakthroughs include : - the accuracy of the coil winding is better than 30 microns and this over the 15 m length of all 1700 large magnets!


- the 2 in 1 magnet design one cryostat containing the magnets for both beams of protons which operate with opposing fields. At full field, the force on 1m of magnet is equivalent to the weight of a jumbo jet. If the wires in the magnet coils move even the slightest amount, that creates friction, which means heat, which means the magnet no longer superconducts. - The magnets contains 7 Mjoule of energy (the energy of as one tonne mass at a height of 7 km ). The energy release that can wipe out superconductivity is less than millijoule: this is equivalent to bringing the complete magnet in its cryostat (35 tonnes) to a 200 m height, where it would have 7 Mjoule of gravitational energy and then needing to control its height to 20 nanometer accuracy! 4.2 high temperatre superconducting current lead rating 3* 50-70kg 1.2m long, 15cm diameter My contact : Lucio Rossi

The high temperature superconducting leads that connect the immense copper cables to the magnets, each bridge a temperature difference of 300 degrees! These leads are currently around a metre in length, however R& D has started on larger leads that would stretch all the way from the underground tunnel to the surface - using cheaper high temperature superconductor material which presents major engineering challenges because of its fragility. In the future, applications of such technologies could have a major impact on our use of energy - long distance superconducting power distribution lines with minimal energy loss open up the possibility of using sustainable energy sources such as solar panels situated in Africa to contribute to Europes energy needs. 4.3 LHC magnet cross-section 4* rating aprox dimensions: 600mm diameter, 10mm thick aprox mass: 15 kg My contact: Lucio Rossi like one of these 2 cross-sections:


4.4 Superconducting wires 5* rating

300 000 km of superconductng niobium titanium wires, containing each 6000 filaments, make up the LHC magnet coils. This is enough high-tech wiring to reach to the sun and back 5 times, with some left over for a few return trips to the moon NB from Lucio Rossi:

Prototypes of new pieces being developed for the next stages of the LHC can also be made available. These are currently under development for the LHC 2013 and 2020 upgrades. Some of these pieces will be built in the UK.

One object he has in mind here is :


We can send a flat coils of Nb3Sn (the new superconductor for High Lumi LHC). It is a prototype small coil for future 13 Tesla magnets (50% stronger than LHC) It is rectangular slice, 30 cm wide and 60 cm long, 2 cm thick, weight about 20 kg.

5. The biggest, fastest camera in the world To sample and record the particles created in up to 600 million proton collisions per second, scientists are building gargantuan devices that measure particles with thousandth of a millimetre precision.

5.1 ATLAS calorimeter mock-up 1* rating (unlikely because ATLAS wishes to reuse the piece to test their detector upgrade) aprox dimensions: 6m diameter, 4-5m long aprox mass: 1 ton My contacts: Claudia Marcelloni / Marzio Nessi


The object is made primarily from wood. It is a 1:1 scale mock-up of part of the barrel of ATLAS that was used to test the tricky process of bringing the cables carrying information out of the very central layers of ATLAS to the computers on the outside on as short a route as possible, all this without disturbing the functioning of the outer layers of detector. The mock-up could not be displayed outside the museum because it would indeed rot. However, in its current state, I have been told by one of the engineers who made it that it would be relatively easy to dismantle into smaller pieces and then reassemble, in, for example, the museum entrance area. The very big caveat here is that it is likely to be needed by ATLAS in 2014/2015 and is therefore very unlikely to be loaned in 2013. However ATLAS did initially propose to add real detector pieces to the wooden structure to make it more authentic. It is very likely that some of these pieces could be loaned to the museum, even if the large support structure is not available. 5.2 ATLAS prototype magnet coil 1* rating (ATLAS may use the piece in an on-site exhibition) aprox dimensions: My contact: Claudia Marcelloni


Major contributions from British Universities to ATLAS: Oxford, Liverpool and RAL were among around 10 UK universities who collaborated on the 2nd layer of ATLAS silicon tracking detectors, the SCT. Pippa Wells is the name James gave you here. Big advances in high speed electronics were made but the ATLAS trigger teams, mainly Birmingham and also RAL. The triggers have the essential job of cherry-picking the few interesting collisions to record from the 600 Million occurring every second. The first level trigger (with strong Brit involvement) reduces the collisions to be analysed by a factor of nearly 10000. Overall, the entire trigger system reduces the data flow by a factor of a million, only discarding uninteresting collision data. To give you an idea of the progress made in reaction time of the electronics, at LEP collisions occurred every 22 micro-seconds. At the LHC they occur every 25 nanoseconds! A factor 1000 improvement needed in the trigger electronics for decision making. The first level trigger has about 2 microseconds to make a decision half of this is cable time for the data to get out from the detector to the trigger electronics. Hence the importance of correct cabling!! (see object 5.1) RAL was also involved in the ATLAS toroid magnets (see object 5.2 above) 5.3 CMS Magnet slice 5* rating aprox dimensions: 2m x 80cm x 60cm aprox mass: 1140 kg My contact: Dave Barney


The CMS magnet is the central device around which the experiment is built, with a 4 Tesla magnetic field that is 100,000 times stronger than the Earths. Its job is to bend the paths of particles emerging from high-energy collisions in the LHC. The more momentum a particle has, the less its path is curved by the magnetic field. Tracing the path gives a measure of momentum. CMS began with the aim of having the strongest magnet possible because a higher strength field bends paths more and, combined with high-precision position measurements in the tracker and muon detectors, this allows accurate measurement of the momentum of even high-energy particles. More coils give a stronger field, a stronger field gives more precise results, and with more precise results we can spot more physics. But whilst getting the best magnetic field possible was the most important consideration in designing the detector, its size was also limited. For the sake of efficiency the magnet was to be built offsite and transported to CMS by road, which meant it physically could not be more than 7 metres in diameter, else it would not fit through the streets on its way to Cessy! The CMS magnet

is the largest superconducting magnet ever built weighs 12,000 tonnes, is cooled to -268.5C, a degree warmer than outer space, is 100,000 times stronger than the Earths magnetic field, stores enough energy to melt 18 tonnes of gold, uses almost twice much iron as the Eiffel Tower.

5.4 CMS Tracker support 5* rating aprox dimensions: 2m diameter, 6m long My contact: Duccio Abbaneo and Jean-Francois Pernot


This is what the mock-up looks like fully wired:

ie far more interesting to look at! Which is why we have been offered a piece of tracker see 5.4 to help recreate the ambiance somehow. 5.5 CMS Tracker segment 5* rating aprox dimensions: 2m x 0.8m aprox mass: 15kg


A smaller piece also exists My contact: Duccio Abbaneo and Stefano Mersi

The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points. The tracker needs to record particle paths accurately yet be lightweight so as to disturb the particle as little as possible. It does this by taking position measurements so accurate that tracks can be reliably reconstructed using just a few measurement points. Each measurement is accurate to 10 thousandths of a millimetre, a fraction of the width of a human hair. It is also the inner most layer of the detector and so receives the highest volume of particles: the construction materials were therefore carefully chosen to resist radiation. The final design consists of a tracker made entirely of silicon: the pixels, at the very core of the detector and dealing with the highest intensity of particles, and the silicon microstrip detectors that surround it. As particles travel through the tracker the pixels and microstrips produce tiny electric signals that are amplified and detected. The tracker employs sensors covering an area the size of a tennis court, with 75 million separate electronic read-out channels: in the pixel detector there are some 6000 connections per square centimetre. In the very first design sketch of CMS, the tracker section was left blank because it was thought that with the intensity of particles experienced in the LHC it would be impossible to make a tracker that could withstand it ! Major contributions from Brit Universities to CMS: The biggest contributions came from RAL and Imperial College.


Jim Virdee, long time spokesperson of CMS is an Imperial physicist and was a major proponent of the crystal technology used by the experiment (and which has interesting applications in medecine). Both Imperial and RAL worked on the extremely complex and fast-reacting front-end electronics for the tracker in addition to the calorimeter. 5.6 LHCb Vertex Detector Module 4* rating (the piece is on show in Microcosm at the moment) aprox dimensions: 0.2m aprox mass: light My contacts: Bolek Pietrzyk & Tara Shears One slice of this:

Like an elaborate trap to catch something so small it has never yet been seen, the VELO measures the distance between the point where protons collide (and where B particles are created) and the point where the B particles decay, spraying out other particles that VELO can detect. The B particles are never measured directly - their presence is inferred from the separation between these two positions. Nevertheless, the VELO can locate the position of B particles to within 10 microns (100th of a millimetre). B particles live for just a millionth of a millionth of a second, during which they travel over one millimetre before decaying into other particles. The revolution delivered by the VELO is that it allows LHCb to select B particles in real time, as they are created in LHC collisions. The combination of lightning fast detector readout, and the particular geometry used by the detectors, allows B particles to be traced and recognised in fractions of a second. This ensures that LHCb collects the data it needs to understand antimatter, and why this differs so slightly to normal matter.


VELO detectors have also found other uses. The Clatterbridge oncology centre near Liverpool treats eye cancer using a beam of protons. To deliver a dose successfully, the position of the beam must be known precisely and continuously monitored. Thanks to their quick response and tolerance to radiation, VELO modules have proved ideally suited to the job. Brit University : Liverpool / Tara Shears 5.7 LHCb Ring Imaging Cherenkov detector mirror 2* rating Unfortunately I have been unable to get dimensions or mass or a photo of the actual object proposed. The image below shows the full detector. You would hopefully be getting 1 of the mirrors and an example of the electronics that translates the light into a signal that is then reconstructed by computers My contact : Carmelo DAmbrosio

This is where particles travel faster than light! (through the particular medium in this detector, of course!) LHCb measures the light version of the sonic boom when particles pass through the RICH detectors. Particles emit a cone of light as they travel. This is then reflected onto an array of sensors using mirrors. The shape of the cone of light depends on the particles velocity, enabling the detector to determine its speed. I am unfortunately missing the engineering challenges for this piece. Brit Universities: Cambridge, Glasgow, Imperial, Oxford, RAL.


5.7 ALICE time of flight module 5* rating aprox dimensions: 1m20 x 1m20 My contact : Despina Hatzifotiadou / Crispin Williams

On the left, a large piece of the time of flight detector, on the right a single detector unit. ALICEs time of flight detector measures, with a precision better than a tenth of a billionth of a second, the time that each particle takes to travel from the collision point. Truly fast electronics and ground breaking detector technology that, again, has applications in medicine. The total surface of this detector is 150m2, divided up into 18 SuperModules, each of which is further divided into 5 modules. The object proposed is one of these modules. The detector technology used is known as Mulitgap Resistive Plate Chambers. There are 1638 of them in total. Their inventor is a Brit : Crispin Williams Notes from Crispin :

Time-of-flight is a technique for measuring the speed of the particle. In general in most particle physics experiments, the momentum of the particle is measured (by measuring the curvature of the particles track in a magnetic field). The momentum, together with the speed, allows the mass of the particle to be determined, and thus the particle type. Up to the year 2000, the most common Time Of Flight technique was to use scintillators read out by photomultiplier tubes. This is very expensive. The photomultipliers have problems with the magnetic field, and there is a problem with segmenting the detector in case of very high multiplicity events. There are also difficulties untangling the results when there is a very high collision rate, like in the LHC.


The revolution in Time Of Flight (TOF) detectors happened in 2000 when the MRPC was adopted by the ALICE collaboration as the detector for a large TOF array. The MRPC is a series of individual parallel plate chambers that have common readout pads or strips where the separation between each device is made with resistive glass; where, almost miraculously they sit at exactly the correct voltage even though they are not connected to a voltage source; they can operate in a strong magnetic field and can be segmented at will.

Examples of the revolution: The STAR experiment at RHIC was built without a TOF detector - but quickly followed the lead of ALICE and have just upgraded the STAR experiment with a full TOF barrel using the MRPC. FOPI at GSI also have implemented a TOF barrel using the MRPC.

There is no Brit university in the group that built this object, but the detector is a good example of international collaboration. It was developed by a collaboration of scientists from the University and INFN of Bologna and the University of Salerno, Italy, the Institute of Theoretical Physics, Moscow, and Kangnung National University, Korea. Otherwise, Birmingham University made significant contributions to ALICE. 6. The hottest spots in the galaxy The silicon detectors listed under point 5 (CMS Tracker or the LHCbs vertex detector) could be used to illustrate how we manage to measure the extremes of LHC collisions. When two beams of protons collide, they generate temperatures 1000 million times hotter than the heart of the sun, but in a minuscule space. 7. The biggest scientific experiment in the world 2 major challenges for the LHC:

civil engineering work excavating the experimental caverns started while the previous LEP machine was still operating. No underground blasting was allowed and innovative solutions had to be found. In the case of ATLAS, the top 10 m of the vast cavern were evacuated first and the 8000 tonne concrete ceiling suspended from 38 cables anchored in access galleries 20 m above. During a 9 month period, the entire roof moved no more than a mm. At the CMS site, 2 underground streams had to be temporarily frozen for access shafts to the cavern to be completed.


John thinks one of the British firms to have worked on the LHC might possibly be able to loan you a rock breaker. they look like this : http://cdsweb.cern.ch/record/842864

Since working on the LHC the firm was renamed LBA (London Bridge Associates) and are currently working on the cross rail project. John could put you in touch if interested (another sponsorship opportunity maybe)

John also mentions a good National Geographic film of the civil engineering challenges. Mega Structures atom smashers 8. Exploring deeper into matter than ever before (A possible section on why we are doing all this)

9. The most extensive computer system in the world

No ideas for objects here, rather a globe showing LHC GRID data transfer in real-time world wide

Documents

Graham Objects v 4