# When CERN is done with a beam, what fraction of a typical beam bunch is left having not scattered?

• B
Gold Member
When Cern is done with a particle beam, what fraction of a typical beam bunch is left having not scattered out of the bunch? Is it of order 1/2? A very rough estimate would do.

Edit, I should add that I read an accelerated beam might be used for a day and at the end of the day they dispose of the old beam. What is left of a typical beam bunch at the end of the day.

Thanks!

Last edited:

mfb
Mentor
Which CERN accelerator do you mean?

LHC beams typically get dumped when ~1/2 to 1/3 of the initial protons are left. This is not bound to days, the accelerator operates 24/7. The beam is dumped when refilling (0 collisions for a while but then higher collision rates again) leads to a higher average collision rate than keeping the old beam.

You can watch it live here and here, "intensity" refers to the number of protons in the beams. Often the beams get dumped for safety reasons, that can happen much earlier (as it did yesterday afternoon for example).

vanhees71
Gold Member
Which CERN accelerator do you mean?

I was thinking of our biggest and best, the LHC, right?

With that remaining fraction, call it one half for estimating purposes, should I be able to roughly estimate than the probability that a proton gets scattered from its bunch per interaction with a counter-rotating anti-proton bunch by estimating the total number of collision interactions in say a 24 hour run (about 4X10^9?)?

How many times per orbit around the ring does a bunch interact?

From this image can I infer that number is 4 interactions per orbit?

Thanks!

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mfb
Mentor
The LHC is the largest. The different accelerators all have different purposes, they are all best for their applications.
With that remaining fraction, call it one half for estimating purposes, should I be able to roughly estimate than the probability that a proton gets scattered from its bunch per interaction with a counter-rotating anti-proton bunch by estimating the total number of collision interactions in say a 24 hour run (about 4X10^9?)?
The LHC collides protons with protons. No antiprotons involved.

The LHC starts with close to 2 billion collisions per second in both ATLAS and CMS each, over time that rate goes down. The collision rate in LHCb and ALICE is much smaller. Some of the protons are lost due to other processes.

dlgoff and Spinnor