Where is a good "IP For Dummies" description?

[PsaltyDS]

Rank non-physicist amateurs here, talking about how the beams go from passing each other on parallel tracks, to intersecting at the IPs, and then continue on into their respective pipes.

Where would we find a description of how that is done? The Forum Wiki page for Interaction Point is, uhm... sparse.

TIA



Edit: Typo.

[Xymox]

Yes the wiki is 3 days old... Its a bit sparse on everything right now...

As to your question, I will have to leave that to other more qualified.

Some of the real fun at CERN is poking arourn in the docume server and meetings For info..

I recommend doing a special google search like this. Leave the site:cern.lhc and then google your question

http://www.google.com/#hl=en&ei=whqxS6_ ... d5ffd65a47

[Kasuha]

I guess the IP is where the beams tracks intersect and where particles can collide. Most of the track beams are running through two parallel pipes (one for each beam) without any chance to interact. There are four IPs around the ring and each of them has detector array ("experiment") build around it.

[PsaltyDS]

@kasuha: Yeah, we got that part already.

The question is really about what makes the switch from two separate beams in two separate pipes, to both beams in one pipe on a collision course, then they go off into their respective separate pipes again.

That's the part we don't understand.

[Kasuha]

Pipes are stable, they are always crossing at that point. It's the beam steering and fill pattern what determines if particles collide or not.

Steering: within the tube at IP, one beam may run slightly higher than another, therefore they pass each other without colliding.

Fill pattern: both beams run around at precisely the same speed. Also, beams are not continuous, the full circle is divided into "buckets" and proton bunches are filled into them, one bunch per bucket. At present, most buckets are empty as they are running with just two bunches per beam. A bunch never leaves its bucket unless they turn RF off (which under normal conditions is a reason for immediate beam dump). So if one proton bunch is at IP while other beam's proton bunch is not at the IP at the same time, they will never meet at that IP.

[PsaltyDS]

That was one of the possibilities we discussed, that the beam paths always cross and tweaks to the RF that forms the buckets are responsible for getting them at IP at the same time (or not - when collisions are not desired).

But another possibility is that they NEARLY cross, and the paths are magnetically bent to IP only when collisions are desired. As I write this, it seems the more likely.

Casual spare-time Googling hasn't found an authoritative description yet, but I'm sure we'll come across it soon.

[Kasuha]

Beam pipes always cross in IP. That is, if the B1 pipe was on left before the experiment, it is on the right after it. Bending the beam so that it "touches" in IP would require very strong magnetic field at the place of the experiment and they need detectors there, not bending magnets.

Click for image

[PsaltyDS]

Good diagram.

I don't know, though. Looks like a lot of beam steering going on in this diagram of the IP inside ATLAS: http://lhc-machine-outreach.web.cern.ch ... isions.htm

[tswsl1989]

Courtesy of one of the guys in #lhc today, we have a nice animation showing the process of aligning the beams for collisions at an IP

http://sucs.org/~tswsl1989/Physics/Atlas-CMS-Beams.gif

[PsaltyDS]

Very cool! That shows the beams passing near each other at about 4mm separation (horizontally in the ATLAS and vertically in CMS) then being aligned concentrically.

So they are passing in the same pipe until steering magnets bring them to IP.

Thanks for the link.

[Xymox]

WOW


That was fun !