Current Events Discussion

The place to discuss the LHC. Commissioning, operation, issues, events ....
Kasuha
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Re: Current Events Discussion

Post by Kasuha » Fri Nov 05, 2010 4:59 pm

Second day of ion runs and I can see they already successfully ramped the beam to 3.5 TeV.... wow.

rasalhauge
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Re: Current Events Discussion

Post by rasalhauge » Fri Nov 05, 2010 6:36 pm

Wow, that is quite fantastic. Especially given the estimates they gave at first, or did they set out to reach as high as 3.5TeV initially? I thought it was 2.76TeV or something they were hoping for?

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Fri Nov 05, 2010 10:59 pm

Well in fact it's not really 3.5 TeV, it's just the same current through bending magnets as for 3.5 TeV protons. Per-particle energy is lower because they are accelerating and steering neutrons within these ions, too.

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PhilG
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Re: Current Events Discussion

Post by PhilG » Sun Nov 07, 2010 6:23 pm

It now says the energy is 3.5 Z TeV. Z is the atomic number which is 82 so the energy per beam is 3.5x82 = 287 TeV. Since there are 208 nucleons in the ion, the energy per nucleon is 287/208 = 1.38 TeV and the centre of mass energy per nucleon is 3x1.38 = 2.76 TeV. That was the number they were talking about as their target.

tomey36
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Re: Current Events Discussion

Post by tomey36 » Sat Nov 13, 2010 7:53 am

why dont they need as high luminosity for ion collisions as they do for proton collisisons? aslo what is considered a good luminosity for ion colliosons?

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Sat Nov 13, 2010 3:24 pm

The design luminosity for ions is way higher than what they have now - but don't forget they only started ion collisions a few days ago and are still deep in beam commissioning. They are already running ion collisions with more bunches than they had with proton collisions half a year after start.

rasalhauge
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Re: Current Events Discussion

Post by rasalhauge » Mon Nov 15, 2010 6:21 pm

I just looked at the Live Schedule for LHC and it says that they are going for stable beams to Wed. and thereafter goes over to proton MD. So my possibly quite stupid question is; what do "MD" stand for?

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tswsl1989
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Re: Current Events Discussion

Post by tswsl1989 » Mon Nov 15, 2010 6:52 pm

MD is "Machine Development" if memory serves

rasalhauge
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Re: Current Events Discussion

Post by rasalhauge » Mon Nov 15, 2010 8:13 pm

Ok, but does that mean that they aren't going to continue the heavy ion commissioning during this development? Or are they doing both simultaneously

Kasuha
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Re: Current Events Discussion

Post by Kasuha » Mon Nov 15, 2010 8:44 pm

Wow, I didn't expect them returning to proton physics before christmas break.
Either they got ions working much faster than they anticipated or they are pressed too much by the electron cloud problem. I guess it's a bit of both.
rasalhauge wrote:Ok, but does that mean that they aren't going to continue the heavy ion commissioning during this development? Or are they doing both simultaneously
According to the outline they should return to ions at friday.

rasalhauge
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Re: Current Events Discussion

Post by rasalhauge » Tue Nov 16, 2010 12:09 am

Kasuha wrote:Wow, I didn't expect them returning to proton physics before christmas break.
Either they got ions working much faster than they anticipated or they are pressed too much by the electron cloud problem. I guess it's a bit of both.
rasalhauge wrote:Ok, but does that mean that they aren't going to continue the heavy ion commissioning during this development? Or are they doing both simultaneously
According to the outline they should return to ions at friday.
The electron cloud problem? What is that?

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PhilG
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Re: Current Events Discussion

Post by PhilG » Tue Nov 16, 2010 9:48 am

The reason for going back to proton physics is that the source of lead ions ran dry. It will take a couple of days to fill it so in the meantime they can do a bit more proton MD. They will return to ion physics on Friday but I guess they might run again and get another three days for protons.

PsaltyDS
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Possible flooding in cavern at P4?!

Post by PsaltyDS » Tue Nov 16, 2010 3:11 pm

Current OP VISTARS status says: "Access to P4 and P2 - Access at point 4 for the fire brigade to check a possible flood in the cavern"

Oh noes... hope it's a false alarm.

adam_jeff
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Re: Current Events Discussion

Post by adam_jeff » Thu Nov 18, 2010 3:45 pm

The electron cloud is a lot of electrons which are released from the walls of the beam pipe by the electromagnetic field of the passing bunch. They can then disrupt any following bunches.
It was predicted that this effect would be seen in the LHC due to the high energy of the bunches. It's hard to observe directly but there are pointers that it's happening. For example, the last bunch in a train tends to have worse emittance.
The current Machine Development session aims to investigate the effect by injecting long trains of bunches in different configurations.
The elctron cloud won't stop the machine from running but it increases emittances and will be more important next year as they continue to inject greater numbers of bunches. That's why they want to understand it better.

josch222
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Re: Current Events Discussion

Post by josch222 » Fri Nov 19, 2010 1:31 pm

A whole lot of bunches!

Yesterday they managed to get 680 bunches in both beams, today they
are up to 800, but only in beam 1.

It looks like the scrubbing really helped to keep a better vacuum.

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