The Large Hadron Collider is nearly ready to start the last phase of running for proton beam physics during 2010. For the past three weeks they have been commissioning the running parameters necessary for this last stage.
The new settings include a 150ns separation between proton bunches in each beam. Previous runs have been performed with a longer spacing of 1000ns, but to get enough bunches in the ring they now need to packed much closer. The closer packing means that the bunches are more likely to interact with each other as they approach the collision point. This is avoided by increasing the angle at which they cross. To speed up the operations they are also ramping up the beam energy in the LHC more quickly.
All these changes have required a lot of setting up and it has taken about twice as long as expected. This means that they have less time for the next stage during which they hope to gain another factor of 10 in luminosity. At that point the number of collisions seen in each run could be as high as the entire 3.6/pb already collected since the LHC started. This requires them to increase the number of bunches in the ring from 52 to 384, and they have just five weeks left to do it before the LHC is reconfigured for heavy ion collisions.
To achieve this level they will start with 24 bunches some time in the next few days. This will quickly be doubled to 48 if all is well. From then on they will add 48 new bunches at each step until they hit the limit with the current settings at 384 bunches. This will take 7 steps and they will have about 5 weeks in which to do it, meaning they have to step up the number of bunches once every five days. This is faster than previous rates of increase, but it should be possible provided there are no hitches. The only commissioning interruptions will be some work to set up for the heavy ion collisions to come afterwards. To move on to each new step they want at least three good runs with a total of 20 hours of stable beams.
In November they will change mode to perform the heavy ion collisions that will help to understand QCD at high temperatures. That will be followed by a shutdown over the Xmas period and then they will be ready to start serious proton physics data collection during 2011.