The BIG questions on everyone’s mind are: When will the LHC achieve first collisions, what will be the luminosity (event rate), and what will be the center of mass energy of the first collisions? The LHC Machine Advisory committee met last week at CERN and the representatives of the LHC project gave the current up-to-date answers to those questions. The result? Well, we are all a bit disappointed, but not too much so. We understand that prudence and caution is necessary here as this project is a large extrapolation from present machines. All in all the LHC machine folks have done a great job!
Up to last week, the mantra was that the LHC was turning on (first collisions) on 1 July, 2007 with a center of mass energy of 14 TeV and a significantly lower than design luminosity. We were not concerned about the low luminosity – that is typical when commissioning a new accelerator – and the high energy guaranteed that many Tevatron searches would be eclipsed in just a few weeks of runtime, even at the low luminosity.
Now for the reality check, as presented last week by the LHC project manager Lyn Evans (insert drumroll here): The machine will be closed in August 2007 and first collisions will occur in November 2007 at center of mass energy 1.8 TeV. The same energy as the previous run (known as Run I) at the Tevatron! It seems that this decision is very prudent. In 2007, only a couple sectors of the LHC will be fully commissioned to handle 7 TeV proton beams. The remaining sectors will not be commissioned until early 2008.
Let’s think about this for a moment. Commissioning (starting) new colliders is frought with numerous unintentional aborts of the beam. And when a beam is aborted, it has to go somewhere (it’s called dumping the beam). Hopefully it aborts as planned, otherwise….much energy is dumped somewhere it should not be! At full throttle (7 TeV beams), the energy stored in the LHC beam is 700 MegaJoules, or 10 TeraWatts of power while the beam is dumped. How big is that? Well, 10 TeraWatts is about half of the world’s total instantaneous power output. No wonder the accelerator folks are a bit jittery! They don’t want to dump 10 TeraWatts of beam just anywhere…
Here’s a picture (courtesy of Tom LeCompte) to illustrate this point. The kinetic energy of battleship guns is 300 Megajoules, or just less than half that of the full LHC beam. Now we understand why the machine folks want to be a bit cautious…
The detectors, I am sure, are grateful for this reprieve. They have more time themselves to get ready and need not be quite so concerned about getting their hardware fried during the first collisions. It also provides a neat check in calibrating the detector’s performance given the large amount of literature on hadron collider physics at 1.8 TeV energies. The LHC detectors will be able to amass a good sample of W and Z bosons with which to start their calibration.
The plan is for full commissioning for 7 TeV beams to be completed during the winter 2008 shutdown, with the first physics run at 14 TeV center of mass energy to commence on 1 April 2008. And that’s no joke.
For those interested in the nitty-gritty details, here is the schedule of the magnet installation:
Last beam magnet delivered: October 2006
Last beam magnet tested: December 2006
Last beam magnet installed: March 2007
Machine closed: August 2007
First collisions: November 2007
The full progress of the LHC can be monitored at the LHC Dashboard, which displays the up-to-date status of the delivery and installation of every single machine component. It is great fun to watch! Here is a sample case showing the progress of the dipole cold masses:
We see that they are almost, but not quite, on schedule.
This delay may be frustrating to some, but given how long we have waited for this already it is only a small price to pay (and not at all unusual in commissioning new accelerators). The LHC machine physicists are to be commended in their excellent progress towards bringing this great machine online! The whole world is watching and we can’t wait (but we also don’t want the machine to blow up)!