Is MD expected to be 25% completed?

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jmc2000
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Is MD expected to be 25% completed?

Post by jmc2000 » Thu Nov 03, 2011 10:01 pm

MD is going through a rough patch at the moment with the cryogenics failing for a day or so, with now the sps now failing. But this isn't unusual and all part of running the LHC with a Hubner factor of around 0.25 meaning that 0.75 percent of the time it's out of action. Nor is this unusual for an accelerator since the Tevatron had a Hubner factor of 0.2.

With all this in mind, it should mean that MD gets 0.25 of its program completed which leads me to ask:

Was it expected that MD would only be 0.25 completed when allocating time for it?

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DCWhitworth
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Re: Is MD expected to be 25% completed?

Post by DCWhitworth » Thu Nov 03, 2011 10:13 pm

I don't know quite what you mean by the Hubner factor. From what I've read it means "Time operating at peak luminosity" not "Time out of action" (i.e. not working). I would also presume that this time includes technical stops etc.

So the simple answer to your question is no, MD would have been planned to get a much higher completion percentage than it has. In fact both the last two MDs have been hit by some pretty heavy time losses. Also the majority of MD doesn't require the machine to be operating at peak power, or in many cases even producing luminosity at all.
DC

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adam_jeff
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Re: Is MD expected to be 25% completed?

Post by adam_jeff » Fri Nov 04, 2011 9:52 am

That's right, the Hubner factor is the ratio of the integrated luminosity actually produced to the thoretically producible maximum. It's much lower than the fraction of time that the machine is running, because it includes time for filling, ramping, squeezing, etc; the effect of the luminosity half-life; and it also subtracts the tech stops and the MDs themselves.
The planning of each MD includes the time necessary to inject and get the machine into the conditions that are needed for that MD, aswell as the time to ramp down and hand over the machine in a reasonable state to the next MD team. Each MD team also plans for the risks of losing the beam: if you cause a dump while testing some new scheme, the time to re-fill etc comes out of your MD, so you have to weigh the risks of each part of the MD.
So no, the MD planning assumes that the LHC will be usable for the whole period, which is split into 8 hour slots with 2 hour 'turn-around' time between which allows a bit of lee-way. But of course the coordinators are aware that it might not work out and they doubtless have a mental 'priority list' of MDs, so that as soon as there's a major delay they can adjust the schedule and lose some MDs. This time, rather a lot of teams will have received the unwanted phonecall from the coordinator.

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