LHC portal

Indeed, 3 good hours and when this access is completed we should see several more hours of good physics today.

Kasuha wrote:60 Hz is much better than 1-2 Hz last year. But still - I think they'll have to increase number of bunches per beam soon if they want to collect the planned amount of data.

Just wondering... what is the planned rate once everything is fully operational ? Much higher than 60 Hz ? Also what is the expected cumulative "on line time" for physics until they shutdown for the planed "upgrade" to 14Tev ?

Not only the number of bunches per beam (2) is only less than about 1/1000 of the planned maximum (almost 2000 as I remember), but also the concentration of the collission areas (squeez) was not yet done. If everything is setup perfectly and runs with full load the expect up to 1,000,000 collissions per second as far as I remember to have read somewhere.

Expected rate at 'final LHC' is about 600 million collisions per second. That is with:
- full beam energy (7 TeV per beam, now 3.5)
- full number of bunches per beam (2808 bunches per beam, now 4)
- full designed number of protons per bunch (10^11, now 10^10)
- squeezed beams (now unsqueezed)

For comparison, it is estimated that there will be about 19 collisions per bunch crossing while at present there is about one collision per 200 crossings.

What they still have to do is:

- squeeze beams at collision points (in december it improved collision rate by factor of 1.5~2)
- increase number of bunches (they plan to go to about half the projected number which is about 1400 bunches per beam - just this could increase collision rate by factor of 1000)
- increase beam intensity (more protons per bunch - the number could go up by factor of 10 but I don't know how exactly will it affect collision rate)

They are not going to increase beam energy in this run though.

Just when things were looking as if we might see some collisions we get ...

Both beams dumped:

For some reason the tune feedback system for Beam 1 switched back on after it was turned off.

A chromaticity measurement started (presuming the feedback was off) dumped the beam.

Thus we are back to square one this morning ...

Both beems are STABLE NOW and they are taking data!

Kasuha wrote: What they still have to do is:

- squeeze beams at collision points (in december it improved collision rate by factor of 1.5~2)
- increase number of bunches (they plan to go to about half the projected number which is about 1400 bunches per beam - just this could increase collision rate by factor of 1000)
- increase beam intensity (more protons per bunch - the number could go up by factor of 10 but I don't know how exactly will it affect collision rate)

They are not going to increase beam energy in this run though.

I believe they are still injecting only one bunch at a time, any ideas when they will start trying out the multi-bunch injection?
(I assume they have a lot of other things to get working reliably first)

Dave

The current run has 2 bunches per beam as did yesterdays run.

But now that I looked closer at your post ... these 2 bunches were injected separately.

They will always insert bunches one at a time. The source of LHC bunches is SPS accelerator and it is able to accelerate only one bunch at a time.

but this means it will take a long time to inject altogether more than 2000 bunches one by one, I hope they get to higher frequencies like at least one pessecond later on.

Hmm... some description of the injection system is available here. It looks like I was wrong with just one bunch though, it looks like SPS can feed LHC with up to four batches of 72 bunches per fill. That'd speed up the filling significantly.

On the latest slides (Portal, LHC, Progress, CMS, Page 9) it is mentioned that they would like to move to a "3 bunch fill" and keep energy at the 3.5 TeV. This should improve the collision rates.

So if I understand the above posts correctly we are still a long way from having an "useful" amount of collisions ? Is there any schedule for that ?

Regards

Some info is available here (or can be found at other places all over beam commisioning pages). Generally LHC might go up to about 720 bunches per beam at the end of this year with other collision parameter improvements.

I had to laugh when I found this:

First collisions at 3.5 TeV will be a major media event
* And first collisions is first collisions, no Atlas sneaking in there
while we’re commissioning the ramp