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Can the FCC tunnel(s) become much thinner?

Are you a hardcore theorist who sometimes loves to play the game that he (or she, Ann and Anna) is a game-changing inventor dealing with the practical life issues and construction, nevertheless? I am and I do. ;-)

Electric cars with batteries suck because 1 kg of a battery only stores 2% of what 1 kg of petrol does. Recharging is slow and some of these parameters won't get much better. But why don't we add wires to all our highways and switch to personal trolleybuses everywhere? The electric cars could have batteries just for a few miles of being off the grid. What's your objection, grumpy reader? :-)



Why don't we fill the land with personal trolleybuses? No batteries, no refueling anymore. The Pilsner model above is only designed for speeds up to 65 kph but it could be improved, I guess.

Or why don't we have nuclear-powered aircraft? You can invent such ideas and Google search for them. You will usually find out that it's been discussed and there are some usual problems that are immediately presented as fatal. For example, the nuclear-powered airplanes suck because the people can't be nicely protected against the radiation.



When I saw the proposals to build the next \(100\TeV\) collider at CERN, the FCC, I was impressed how surprisingly cheap the project is claimed to be (although it's not guaranteed that the final price wouldn't be much higher – it often is). Well, \(100\TeV\) is more than 7 times \(13\TeV\) but €21 billion is less than 5 times $5 billion, the price of the LHC, and it does include the new tunnel which the LHC inherited from LEP for free.

And those €21 billion are "cheaper euros" due to some 15 years of inflation – maybe by some 30% – than the "LHC euros". The cost only grows like the square root of the collision energy, it seems! Every person who has at least some relationship to science agrees that even €21 billion is peanuts for the most extreme and far-reaching science experiment that is being built just once in 20 years at the current speed.



However, in the decomposition of the expenses to the basic parts, I was rather annoyed by the expensive tunnels. Well, those €21 billion are composed of:

€5 billion for the 100-kilometer-long tunnel,
€4 billion for the lepton collider magnets etc.,
€12 billion for the later upgrade, hadron collider magnets.
I think it doesn't make sense to be more precise than that because the final numbers can't be estimated too accurately. Great. €5 billion for the tunnels looks like a lot. The percentage of the price that is consumed by the tunnel, the most low-brow part of the project, seems to be going up.

In a calculation in my article about Musk's proposed discount (which is ludicrous because his Boring Company is doing the same as competitors), I saw that by the volume and the proportionality law, using the previous colliders, the new tunnel should only cost €2 billion, not €5 billion. But a part of the increase is explained by inflation. A part may be due to a somewhat thicker tunnel. And the boring costs may grow faster than the general inflation, who knows. Maybe the rocks in the FCC area are less friendly, too.

To get higher collision energies, you need a greater curvature radius of the tunnels to keep the particles in the pipes – well, except for the magnets' getting stronger but the improvements have their limits. That implies that the tunnel has to be long. But it could arguably be thinner and therefore cheaper because the boring costs are almost proportional to the volume of the rock (and therefore to the cross section area, assuming a fixed length of the tunnel).

The cross section of the FCC tunnel is said to be 23.76 square meters. By saying it equals \(\pi d^2/4\), you will get the diameter \(d=5.5\,{\rm meters}\). Wow, that's a pretty thick tunnel, indeed. Is that really needed?

Why wouldn't I ask the people behind the FCC? The key people behind a €21 billion project surely don't have anything better to do than to chat with the laymen on Twitter – and I was right. ;-) So I asked:


The hyperlink goes to the Wikipedia page about "microtunneling".
The answer arrived almost immediately.


I surely did suspect that I would be immediately thrown at some usual excuses why they can't get below 24 square meters. But I think that the FCC folks hopefully do suspect that I won't give up this easily! ;-)


The FCC proponents weren't careless, of course:


And, to make things worse:


We mustn't forget:


Finally:


And some extra niceties with an offer to explain things by the e-mail.

OK, there are clearly some extra "veins" that go through the tunnel, on top of the 1.2-meter-in-diameter cylinder with magnets. But this is a €5 billion tunnel – it might be a good idea to save some of those 23.76 square meters in the cross section, to miniaturize things a little bit, right?

We need the main pipe with the particles and magnets; cryogenic lines with another meter of space in diameter; space through which the magnet is transported during installation (to avoid "LIFO" deconstruction of the whole collider during repairs); cables and cooling pipes plus a space for a person to get there. I omitted the extra comments unrelated to the content of the large intestine.

What do you think my reaction should be?

I did know that there are things on top of the main tube, of course, and one doesn't want to deconstruct the whole collider during repairs. But I think that several thin tunnels could replace the extremely thick one. Let's count the square meters that we really need.

The main cylinder with the magnets and particles in the middle could be 1 square meter. These magnets could be transported there through another thin tunnel which is another 1 square meter, and these tunnels (and all other tunnels in the plan below) could be fully connected e.g. on one hundred 50-meter-long segments each 1 kilometer of the circumference. On each kilometer, all the magnets in the row would be taken out if one of them had to be repaired.

Another 1 square meter is the cryogenic line, another 1 square meter is some wires and extra cooling, and 1 additional square meter is enough for a CERN employee to physically get there. If Elon Musk kindly allowed, the employee would be a British diver who is not a pedo and doesn't suffer from claustrophobia. He could easily climb through a tube of diameter 1 meter. Each 100 meters, there would be some small holes in between all the small tunnels so that he could look or fix the mechanisms that allow things to be moved in between all the tunnels on each 1 kilometer.



Just by eye-balling, don't you agree that at least one-half of the area of the disk-shaped cross section is wasted?

I tried to be tough and reduce the total cross section from 24 to 5 square meters. I am surely gonna be told that it's too ambitious and impossible. Maybe some merger into two tunnels of the diameter of 2 meters could be better. Maybe we could get to 12 square meters in total. But the price of the tunnel – now tunnels – could still drop by one-half or two billion Euros, I think.

Some optimization should be tried. It's a lot of money.

One of the arguments we sometimes quote as the "secondary" benefits of the collider projects is that they encourage the progress in lots of the technologies that are needed to build that huge device. We usually mean the superconducting magnets and other "hi-tech" components. But what about the damn tunnels? They're a century-long technology but some "clever tunnels for the 21st century" which minimize the cross section and allow all things to get to the right places due to some clever enough logistics should be a part of the "secondary progress" ignited by the CERN projects.

The kind FCC folks surely feel uneasy about such proposed revisions. But I do think that they should move their aß and try to do some clever optimization of the tunnels' infrastructure because the thickness of the tunnels looks wasteful – for a 100-kilometer-long tunnel whose space isn't really enjoyed by the human inhabitants – and sort of "outdated", if you appreciate that "miniaturization" is one of the trends of the relatively modern progress. Maybe as soon as they make the lepton collider €3 billion or 30% cheaper, impressed sponsors will immediately approve the project and the serious work may begin.

I also suspect that the dipole magnets themselves and many other things could be thinner than they are as well but I leave this related topic to someone else.

And I must add a medium-term shiny accelerator physics vision: the tunnels need to get longer to achieve higher collision energies but there could be an ongoing miniaturization in the thickness of all the tubes, the cross section could keep on shrinking, and the volume of all the tunnels and magnets and therefore the price could stay fixed as the people build ever stronger colliders!



Off-topic but European and geographically close to the topic: Although Macron has ludicrously declared himself to be one of the Yellow Vests, there had to be some reasons why he didn't like the Italian deputy prime minister's meeting with one of his (Macron's) bosses, leaders of the Yellow Vest movement.

So France has recalled its ambassador to Rome. Clearly, after decades of taking credit for the peace on our continent, the European Union isn't helpful in calming the passions. The video above compares the French and Italian forces in the looming Romance war.

The foes are tied in many respects, in others they are imbalanced and France has a slightly higher number of advantages but the result could be uncertain for a long time, especially because France has a big disadvantage of greater internal disagreements right now, I think.

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