Why do high energy accelerators have to be so large?

[e.bar.goum]

Today is an exciting day, for today will see a new record for the highest energy collisions at the LHC - stable 13 TeV collisions for new physics, signalling the start of the new physics program at the LHC!

There are a few ways you can keep track of progress throughout the day.

The LHC status pages: https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1
https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC3
https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHCCOORD

A webcast due to start at 8:20 Zurich: https://webcast.web.cern.ch/webcast/ (2 minutes from when I write this)

A live blog: http://run2-13tev.web.cern.ch/

And a hashtag - https://twitter.com/hashtag/13tev?src=hash&vertical=default&f=tweets

 

[Orodruin]

Boooooom!

 

[e.bar.goum]

Yeah!

Stable Beams: True.

 

[mfb]

About 70/nb both for ATLAS and CMS. There should have been a few Higgs bosons in those collisions (the expected number is ~7)!
It's just impossible to identify them with such a small dataset.

 

[George Jones]

Particle physicist Adam Falkowksi, aka "Jester", has made an interesting post on his blog "RESONAANCES" about what to expect,

http://resonaances.blogspot.ca/2015/05/how-long-until-its-interesting.html

 

[phion]

Awesome.

 

[Jimster41]

Very cool.

Some acronym translations?

BCT
TED
TDI
BIS
SMP

What indicates a collision in the trend.
I poked around the menu of screens and views. Is there any place to see the detector events?

 

[mfb]

What indicates a collision in the trend.

Which trend?

No idea what the letters stand for:
BCT is related to the transfer lines (for injection).
TED/TDI are related to collimators and other settings for the beam position.
BIS/SMP: Gives an overview over the machine status.

The current collision rate can be seen at LHC operation: "Instantaneous luminosity". The design luminosity in those units is 10000/(μb*s), today we had 3/(μb*s).

Event displays:
ATLAS collisions
CMS collisions
http://lhcbproject.web.cern.ch/lhcbproject/online/comet/Online/
ALICE collisions

 

[Jimster41]

The Intensity, Energy trends in this one

https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1

But now I see this one... which seems more like the one to look at.
[edit] as you pointed outhttps://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC3

What does "BKGD" (Background) indicate.

 

[Jimster41]

Wow, so watching that ALICE view. When it updates and there a collision or collisions, is that live-ish? It updated a moment later and they went away.

yeah, having these on my desktop, a click away, I really needed that...

 

[mfb]

The Intensity, Energy trends in this one

https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1

That page often does not tell you if there are collisions. Well, no beam no collisions obviously, but with beams you don't see it. Sometimes they add the luminosity plot to this page.

What does "BKGD" (Background) indicate.

It is measured somewhere outside the primary collision area, but I don't know where.

The ALICE event display has a time given in the upper left corner. It is now 21:07 CERN time.

 

[Naan-Orientable]

I didn't realize today was the day already. Exciting!

 

[enorbet]

Particle physicist Adam Falkowksi, aka "Jester", has made an interesting post on his blog "RESONAANCES" about what to expect,

http://resonaances.blogspot.ca/2015/05/how-long-until-its-interesting.html

Thank you George. I haven't kept up as much as I'd like and I find this linked blog exceptionally helpful.

 

[Reveille]

What does the teraelectronvolt mean when talking about collisions? Is that how hard the collision is or something?
Very new to this side of physics, very cool though!

 

[mfb]

It is the energy.
1 eV = 1.6*10^-19 J
1 TeV = 10¹² eV = 1.6*10^-7 J, or, as WolframAlpha puts it, "approximate kinetic energy of a flying mosquito"

Tiny in terms of macroscopic objects, huge for particles as small as protons.

 

[Reveille]

I knew it was the energy, I wasn't sure what it meant besides that.
So if I understand correctly, it is the kinetic energy that the particles have before they are smashed into each other? And the higher the value, the more energy they have and therefore get smashed to bits even harder than they did before when using a lower TeV?
Is it similar to when I would smash a wall, for example? The harder I smash it, the more it would crumble. If I were to give it a gentle touch, not much would be happening. If I were to want to knock it out and smash it to crumbles, I would use more force and therefore more kinetic energy. I would have to smash it faster and harder.
Is that kind of how I should see it? A 1 TeV collision would be me giving the wall a gentle touch and the 13 TeV collision would be me smashing it harder and therefore it would crumble to smaller pieces and by that could see the smaller particles comprising of it?
Or am I looking at it the wrong way by that?

 

[mfb]

So if I understand correctly, it is the kinetic energy that the particles have before they are smashed into each other?

6.5 TeV is the energy used currently, yes. As two protons collide, the total energy is 13 TeV.

And the higher the value, the more energy they have and therefore get smashed to bits even harder than they did before when using a lower TeV?

They are not just "smashed to bits", completely new particles get created in those collisions. More energy makes that more frequent and allows the production of heavier particles.

 

[Reveille]

Ahhhh! Like that! I get it now.
Thank you :)

 

[Orodruin]

Just for reference since it was not mentioned in the recent discussion. One eV is the energy an electron (or any other particle of unit charge, so therefore also a proton) gains when accelerating across a potential of 1 V. LHC protons have an energy of 6.5 TeV, i.e., the energy equivalent too having been accelerated across 6500000000000 V.

 

[Nick666]

What limits them to keep increasing the energy ?

 

[e.bar.goum]

What limits them to keep increasing the energy ?

Magnet strength - higher energy beams require stronger magnets to contain the beam. The magnets of the LHC are running a little lower than their designed maximum, but it was deemed that 13 TeV (rather than 14) would be safer - the superconducting magnets risk more frequent quenches (sudden loss of superconductivity) at higher fields. In principle, the LHC could run a bit above 14 TeV.

Any more energy will require stronger magnets, or a larger accelerator.

 

[KylieVegas]

If they have already completed the standard model, what is next for particle physics? This is a lovely news btw!:)

 

[mfb]

If they have already completed the standard model, what is next for particle physics?

Well, all particles have been found. They are still under study to understand their properties in more detail.
The discovery of more particles would be amazing. There are several models that predict additional particles, but none have been found so far.

 

[KylieVegas]

Well, all particles have been found. They are still under study to understand their properties in more detail.
The discovery of more particles would be amazing. There are several models that predict additional particles, but none have been found so far.

That would be really great! I'm so excited to see the future of high energy physics, hopefully next time i'd be able to contribute to it :)

 

[e.bar.goum]

If they have already completed the standard model, what is next for particle physics? This is a lovely news btw!:)

In addition to what mfb said, we have a lot of clues that the standard model is incomplete - gravity, dark matter, dark energy and neutrino masses to name a few. (There are also structural problems with the standard model). The hope is that the LHC will give us hints as to how to incorporate this into a better model of particle physics.

 

[jack476]

What limits them to keep increasing the energy ?

Power and hardware limitations.

First, it requires a massive amount of power to accelerate particles to 13 TeV. That means that the electromagnets need to be kept cool, especially because they use superconducting magnets. That amount of power will cause things to heat up, and they don't have the equipment to eliminate an infinite amount of heat.

Second, limitations of the control systems. Maintaining a magnetic field with sufficient cohesion requires a very sophisticated and fast electronic control system, which can't just be overclocked ad infinitum.

OT: Completely random question, but what would it feel like to be hit by a particle at 13 TeV? I know that's still a small fraction of a single Joule, but just wondering what that would imply if these collisions are supposed to be so energetic.

 

[mfb]

@jack476: nonsense. Getting more power from the grid would be no problem. The acceleration is not done with magnets. The RF cavities for acceleration are a tiny element in the ring, using more of them or using them for a longer time would be trivial. The magnets are superconducting, which means they do not heat up from their current. The control system does not care about the particle energy, it works for all energies.
The limit is the maximal magnetic field strength in the dipole magnets, as e.bar.goum explained. Protons with higher energy would not get bent enough to follow the beam line.

At significantly higher energies (something like 15 TeV instead of 6.5), synchrotron radiation in the dipoles would become a significant issue, and would need more cooling.

OT: Completely random question, but what would it feel like to be hit by a particle at 13 TeV?

You would feel nothing at all. It is possible to see a brief flash of light when a high-energetic particle crosses the eye, astronauts see that frequently .

 

[Mark Harder]

@jack476: ...
Protons with higher energy would not get bent enough to follow the beam line.
At significantly higher energies (something like 15 TeV instead of 6.5), synchrotron radiation in the dipoles would become a significant issue, and would need more cooling.
... .

Is that why high energy accelerators have to be so large? When the radius of curvature expands, the centripetal forces required to accelerate the particles inward are less, and since the acceleration is less, the synchrotron radiation is less intense?
Also, it seems to me that the increase in relativistic mass of the particles as their velocity approaches c demands ever increasing energy inputs in order to accelerate them.

 

[e.bar.goum]

Is that why high energy accelerators have to be so large? When the radius of curvature expands, the centripetal forces required to accelerate the particles inward are less, and since the acceleration is less, the synchrotron radiation is less intense?
Also, it seems to me that the increase in relativistic mass of the particles as their velocity approaches c demands ever increasing energy inputs in order to accelerate them.

Most of the reason high energy accelerators have to be so large is the limitations on magnet technology. There's no reason you couldn't upgrade all the magnets in the LHC and have a higher energy accelerator (this is the plan for HL-LHC) but at some point, it's be cheaper/quicker to just dig a new tunnel and put lower strength magnets in them.

per revolution energy loss due to synchrotron radiation is given by

$P = \frac{2 e^2 c \gamma^4}{3 * 4 \pi \epsilon \rho^2}$

Where $\rho$ is the radius - so synchrotron radiation matters, but since protons are so massive, in machines like the LHC the synchrotron radiation is pretty negligible. (which is one reason the LHC uses protons, and the reasons very high energy electron machines (CLIC/ILC) - the next generation Higgs factories - will be linear colliders)

 

[mfb]

Is that why high energy accelerators have to be so large? When the radius of curvature expands, the centripetal forces required to accelerate the particles inward are less, and since the acceleration is less, the synchrotron radiation is less intense?
Also, it seems to me that the increase in relativistic mass of the particles as their velocity approaches c demands ever increasing energy inputs in order to accelerate them.

Proton synchrotrons are limited by the magnetic field strength, electron synchrotrons are limited by the energy loss from synchrotron radiation.
"Accelerate" is meant in terms of energy. The speed is very close to the speed of light long before the maximal energy of the accelerator is reached.

Most of the reason high energy accelerators have to be so large is the limitations on magnet technology. There's no reason you couldn't upgrade all the magnets in the LHC and have a higher energy accelerator (this is the plan for HL-LHC)

HL-LHC is the high-luminosity LHC with the same energy, the high-energy LHC would be HE-LHC.