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Tuesday, October 1, 2013

The geekiest place in the world

...was open for visits.

I am not sure a "geek-ness" ranking exists for places, it probably does, but I have no factual data about that.
Still I am pretty sure that most would agree that if this is not the place with the highest score in the world, it actually gets a pretty damn good placement in the ranking.

I am talking about the CERN facilities between Geneva (Switzerland) and France.

From time to time they need to shutdown the machines and perform some maintenance, if you are lucky enough to be around, you get a guided tour of the Physics Disneyland.
I live nearby, so it was an easy one for me.

Turns out that this time they had a two days open to the public, with chances to visit the underground tunnel of the LHC.

Cern personnel (scientists, technicians etc) was acting as guide and showing us around - thanks guys, you are awesome -

While I enjoy physics, I am not good enough to provide in depth explanations, still I thought it was cool to post a few pictures here.

The Large Hadron Collider  (LHC) is "the big one"at the moment, accelerating particles in a 27Km ring placed between 150 and 180 mt below the surface, across Switzerland and France.

A friend of mine and myself started our visit there, at point 4

After getting an helmet and being assigned to a guide together with a small group of visitors, we descended in the underground with an elevator, first thing we met was one of the many rooms with control electronics.

The LHC is a Synchrotron accelerator, meaning it bends the beam so that it runs in a long circle, comes back and gets another "kick" of acceleration.  
Electric fields (in cavities) are used in few points to accelerate the particles and magnetic fields are used to bend the beam.
Additional magnets (quadripoles) are used to focus the beam which would naturally tend to disperse (being composed by charged particles of the same type).

All this requires a lot of energy, in fact the machine consumes about the same energy as the private consumption in the whole Geneva city.

The "compact" dipole magnets are about 15 meters long and produce a 8.4 Tesla magnetic field using a 11.000A current.
The only way to get all that current in a relatively small solenoid, is to use superconductors which are cooled down at 1.9K with Helium.

Machines and equipment are transported to/from the surface using vertical tunnels like this one :

Before getting to the actual LHC ring, you pass by rooms full of machines, mainly for the cryogenic (like the one in the picture) and electric control

Finally the "Ring": 
Once the beams are formed (two beams rotating in the opposite direction, running in separate vacuum pipes, crossed for collisions in 4 points in the ring), they are accelerated in cavities

Electrical energy here is converted from normal conducting to superconducting to feed the magnets that will need to focus and guide the beam (sorry the picture is a bit out of focus)

The huge black cables on the top part bring down the normal electrical energy from the surface, a tiny (superconducting) cable of the section visible in the bottom part (it is there just for demo) transports the same energy to the magnets.

This is the part that caused the incident back in 2008, which resulted in a 4 month unplanned stop of the machine.
Apparently the connectors between those two pipes did not perform according to the specs and started to heat up, slowly transferring heat to the magnets and forcing their conductors to exit the normal superconducting temperature range.
Don't ask me why, but this eventually converted part of the beam energy into kinetic energy, which displaced the magnets (we are talking about "little toys" with the weight of few tons).
In this stage the magnets are used to focus the beam, which is particularly difficult when the beam is "slow", in fact when it reaches relativistic speed, (some "funny" effect of relativity) particles reduce the "hate" they have between them, so it is easier to contain them.

Finally the blue dipoles gradually bend the beam (you can see it is bent on the left) in the tunnel, till the next station which is 3.7Km down this tunnel.
I searched for the Gelmini Tunnel, but it was nowhere to be found.

All this is really cool, I admit I can grasp some of the basic concepts, but that's  pretty much it,  still every single cubic meter there is packed with technology like you would expect in Geek's Heaven.

However, why stop at today's  technology when you can have  a sneak-peek of the technology of tomorrow?
Let's  go see 2030

The Compact Linear Collider (CLIC) does not actually exist now, there is a small prototype used to prove the concept (it worked!).

CLIC is supposed to be a 48Km Linear  collider (one end should arrive pretty close to my house), being linear it does not need dipoles to bend the beam and it is not supposed to use superconducting magnets, even to focus the beam.

But the most interesting feature is how the energy for the acceleration is provided.
In a synchrotron the beam comes back to a given point several times (11K times a second in the LHC) so it can be accelerated in few points.
In a linear machine, you need to keep accelerating the beam all along the path in order to achieve the needed speed in one single run.
Transporting the needed energy all along the 48Km path would be really challenging.
CLIC uses a "drive" beam to provide energy to accelerate the test beam.

The concept is that a "wide" beam (lots of charges) is started together with the test "small" beam then all along the path energy is extracted from the drive beam (by slowing it down) and transferred to the test beam via a 12GHz pulse.

This is the CLIC working prototype,  in the picture above the beams are created.
Magnets based on standard technology solenoids are the used to focus the beams

The researcher who was guiding us explained that there are some studies about these solenoids, obviously not being supercondicting they are not really efficient and pose a few issues, interesting enough they are also exploring the possibility to use huge neodymium permanent magnets and powerful mechanical actuators to modulate the magnetic field with them.

Before entering the acceleration module, part of the test beam is extracted and it's energy (speed) is measured, finally dumping it in a concrete block.
This sets a baseline to verify the acceleration achieved after the acceleration module.

In the image above the acceleration module.
In the front part there is the test beam passing through the cavities, in the back side the drive beam also going through cavities (to slow it down in this case) and the energy is routed in radio frequency via those copper pipes visible in the right part.
A precise piston there allows the regulation of the "accelerating" wave to ensure it is in phase with the test beam.

Finally the beam is measured and dumped in another concrete block (this is just a prototype containing one acceleration module, the real project is supposed to have about 20.000 modules, guess the concrete block at the end will have to be a bit bigger and sturdy :) ).

In the picture above an accelerating element, you will notice the hole for the beam is really small and this is one of the characteristics of CLIC.
Having an extremely compact beam has several advantages, but also poses some big challenges.
Just imagine a pipe 48 Km long, under the ground, where those holes are perfectly aligned all along the path.

For this reason the whole structure is mounted on a gazzilion of extremely precise actuators that manage to dynamically ensure the alignment.

One of the modules (picture above) undergoing mechanical tests in another lab.

And this basically concludes my report of the visit at CERN, I may have made a few mistakes (hopefully not too many) in my description, I cannot claim to be an expert on the subject, I just get excited seeing technology stuff that actually works and since you are reading this blog, you are probably like myself.

Feel free to send comments, corrections and to call me ignorant if you like (I know I am, so I will not take that as an offense :) ).

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