LHC portal

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

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?

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.

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.

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?

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.

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?

MD is "Machine Development" if memory serves

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

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.

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?

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.

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.

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.

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.