Silly Collider Question

[neutrino]

Just read this article on the International Linear Collider

http://physicsweb.org/articles/news/11/2/10/1

Looks like it's going to be a six-and-a-half-billion-dollars, 31 Km long collider that can reach energies of "500 gigaelectronvolts." Also, it seems, that they might consider increasing its length to get to TeV.

Why spend so much when you already have the Tevatron and another collider waiting in the wings, which can, from what I've read, cross the 1 TeV barrier?

 

[ZapperZ]

Because it is a DIFFERENT type of collision and looking at a different sector of the Standard Model "phase space".

The LHC is a hadron collider, meaning they will use ions ranging from protons to medium sized nucleus for collision. the ILC will be colliding electron and positrons. Completely different regime here. In the same idea that LHC is what the Tevatron is, but more powerful and with more capability, the ILC is what LEP was, except bigger and better.

Zz.

 

[neutrino]

Because it is a DIFFERENT type of collision and looking at a different sector of the Standard Model "phase space".

The LHC is a hadron collider, meaning they will use ions ranging from protons to medium sized nucleus for collision. the ILC will be colliding electron and positrons. Completely different regime here. In the same idea that LHC is what the Tevatron is, but more powerful and with more capability, the ILC is what LEP was, except bigger and better.

Zz.

That makes sense. Thanks, Zz.

 

[ziad1985]

Another silly one on the way ,but why they can't use the LHC to collide Electrons and positrons?

 

[humanino]

Another silly one on the way ,but why they can't use the LHC to collide Electrons and positrons?

Because those are too light, mainly. An electron is too light to be bended around a circular orbit at very high energies. You need to accelerate them in a straight line.

 

[humanino]

As for what Zz mentionned, I would like to add a little detail. Electron-positron collisions are somehow "cleaner" than hadronic ones. The strong force mediated collisions produce a lot of particles, at the hadronization stage. This is one of the reasons why one can make precision measurements with electroweak probes.


EDIT
I think I should be more accurate :
one can make precision measurements in hadronic collisions as well, but is much more complicated and difficult.

 

[neutrino]

Because those are too light, mainly. An electron is too light to be bended around a circular orbit at very high energies. You need to accelerate them in a straight line.

Wasn't the LEP circular?

 

[ZapperZ]

Wasn't the LEP circular?

Yes, but it was also colliding electron-positron, just like the ILC will.

Zz.

 

[ZapperZ]

Another silly one on the way ,but why they can't use the LHC to collide Electrons and positrons?

When you design an accelerator, there are precise design issue that takes into account the particle you will be accelerating. RHIC at Brookhaven, for example, will need a complete overhaul if it wants to collider electrons, because it was designed to accelerate protons and heavy nuclei.

The intricate design involved the size of the accelerating structure, the frequency of the RF cavities, the strength of the magnets, the type of detectors, the SIZE of the calorimeter, the positioning of the accelerating structures, etc... etc.

This is where the devil is in the details.

Zz.

 

[humanino]

Wasn't the LEP circular?

It was at lower energy.

You know, if you insist you can in principle accelerate you electrons at the same energy as ILC in a circular collider. It will be much more expensive however, because of the losses due to radiations. The larger the radius of the collider, the less the radiations, but the more the initial cost.

 

[ziad1985]

I do know that energy lost by radiation is more important as the particle is more heavy , but does have that much of an effect in the design of the accelerator?

 

[ZapperZ]

I do know that energy lost by radiation is more important as the particle is more heavy , but does have that much of an effect in the design of the accelerator?

I don't want to be sucked into having to explain the basic detail of an accelerating structure, but I'll give just one basic example.

When you design a series of an iris-loaded cavity, you are using an oscillating RF cavity at some frequency (the ILC parameter is in the L-band, so we'll pick 1.3 GHz, which is the RF that I use at my facility). Now, you have to design this in such a way that the particle you are accelerating are moving in synch with the E-field that is increasing in the right direction as the particles are entering that cavity. As it is exiting that cavity and goes into the next cavity, the same thing has to happen again. All of these cavities are typically powered by a single RF source - a klystron - since a set of these cavities are what we call an accelerating structure. For the ILC, this will be a superconducting structure.

Now, that sounds simple, but it is not. The group velocity of the RF (even though it is really a standing wave structure), must MATCH the particle being accelerated, or else the field will outrun the particles and you have a very inefficient acceleration. This is where you have to design the geometry of the cavity to match the frequency of the RF being used. When you do this, you HAVE to consider the particle that you are accelerating. Electrons are WAY lighter than protons and heavy ions. The design, especially in the SIZE of the structure (such as the width of each of these cavities) are tailor-made for the type of particles. So it is hardwired into the design!

And this is just from the accelerating mechanism alone. We haven't talked about the type of detector that has to be designed for each of the different particle based on what is expected. Note that even when you have the same type of particles, you STILL need different detectors because no one detector can do everything. Tevatron has CDF and D0 that measures different things, but compliments each other. Now think, if one detector can't do everything even when all it looks at is the collision of one type of particles, consider how impossible it is to design a detector that can work with collision of other types of particles having such huge range scale!

We would LOVE to have a flexible accelerator facility that can accelerate everything. Wouldn't that be a terrific sell to build a really expensive facility and be done with? But it is close to a physical impossibility right now, and certainly an engineering impossibility.

Zz.

 

[ziad1985]

When I took Special relativity ,there were 2 chapters talking about relativistic particle moving in an EM field, and then application on particle accelerator , the latter was dropped , so i never knew on how sensitive it is it could be , thank you for the info , I guess i should read more about this..

 

[ZapperZ]

Accelerator physics is a whole sub-field of study under physics/electrical engineering. Even if that section on particle accelerator wasn't dropped, you would have barely even scratched what is contained within this field.

http://www.fieldp.com/cpa/cpa.html

Zz.

 

[ziad1985]

http://www.fieldp.com/cpa/cpa.html

this look good , thank you

Now i have another question , the LEP is circular and the one they are going building now is linear , i know now that for an (e+,e-) it's better for the accelerator to be linear , but does the circular one provide any certain advantages?

 

[jtbell]

Particles go around a circular accelerator many many times, receiving more energy each time around. Particles go through a linear accelerator once. So the accelerating cavities in a linear accelerator have to be much more powerful, unless you want to make the accelerator very very long.