Are there currently working colliders with unequal beam sizes?

[Mikheal]

TL;DR Summary

For coliders of different particles such as RHIC, does the beam sizes of different beams are the same, for example Run-21 where deuterium and Gold ions are colided, what are the the average ratio of beam sizes for such light and heavy particles collision?, if yes, what factors govern this ratio?

I know that for any coliders beams are not exactly the same size but they can be approximated to the same value as the deviation is relatively small, such as LHC. My questions:
1- are there currently working or planned colliders with unequal beam sizes?
2- for coliders of different particles such as RHIC, does the beam sizes of different beams are the same, for example Run-21 where deuterium and Gold ions are colided, what are the the average ratio of beam sizes for such light and heavy particles collision?, if yes, what factors govern this ratio?
3- for e-e+ colliders does vdM scan still used, and does the beams have the same beam sizes?
Please provide me with refreances if it is available.

Thanks

 

[Vanadium 50]

What do you mean by "size"? Length? Width? Emittance? Where do you measure? The radius changes throughout the orbit.

 

[Mikheal]

What do you mean by "size"? Length? Width? Emittance? Where do you measure? The radius changes throughout the orbit.

I mean the rms beam size at the collision point where the two beams are colliding.
Yes, I know that size change along the orbit, thank you

 

[Vanadium 50]

I ask again - length? Width? Emittance?>

 

[Mikheal]

I ask again - length? Width? Emittance?>

Generally in articles they refer to it by rms beam size. I am concerned about the transverse rms beam size, (vertical and horizontal width)
In fact, at the collision point both beams have approximately the same beta function and hence the Emmittance and the width are equivalent.
Thank you

 

[mfb]

Reducing the rms in horizontal or vertical direction is not increasing the luminosity notably if the other beam is wider, but it makes accelerator operation harder and/or reduces the maximal number of particles in the bunch. I would be surprised to find a strong asymmetry anywhere. I found this paper on p-Pb collisions at the LHC where both beams have the same beta* and similar emittance.

Unrelated: In Figure 1 you can see how slow lead ions and protons can't be synchronized, but as the LHC approaches its peak energy their speed gets close enough to synchronize them. The process is surprisingly slow - of the order of minutes.

 

[Mikheal]

I am just curious about the at the collision point where the reaction rates are recorded.
So this mean that both p and Pb have have the same size right? Is there currently working machines with beams with different sizes?

For example, RHIC run 21 Model 3A where d-Au collision with emittance of 1.0 → 1.2 micro for d and of 1.2 → 2.3 micro for Au.

 

[Vanadium 50]

The proton beam has a slightly smaller transverse size than the lead beam. CERN-ATS-Note-2012-094 MD

KEK-B is almost certainly asymmetric, but I couldn't rell you in which direction. Ususally the higher energy beam is smaller and the positron beam is smaller, but these are different beams in KEK-B.

 

[mfb]

In this 2013 design, LER (low energy ring, positrons) has slightly smaller emittance in x and y and smaller beta_y* but slightly larger beta_x* (table 1).
The size is not identical but it's pretty similar.

 

[JonasKK]

Ususally the higher energy beam is smaller and the positron beam is smaller, but these are different beams in KEK-B.

As a small remark: for electron storage rings the equilibrium emittance is determined by the radiative effects and scale as $\epsilon_0 \propto \gamma^2$. So for two identical lattices the high-energy beam will have larger emittance.