LHC Report: First collisions soon

On 16 March beams in the LHC reached the world-record energy of 4 TeV. Stable-beams mode is planned for 3 weeks from now

The LHC equipment teams have now entered the beam commissioning period; the time to make sure their systems – beam instrumentation, radio frequency, beam interlock, feedback on orbit and tune, etc. – work flawlessly.They make detailed measurements of optics and physical apertures to ensure that magnets are correctly set and aligned.

The optics measurements include the beta* of the squeezed beam at the centre of the experiments where the collisions will soon take place. This year the aim is to have a smaller beta* of 60 centimetres for the ATLAS and CMS experiments. Smaller values of beta* mean thinner and more tightly squeezed beams at the collision points. A small beta* requires that, at full energy, the collimators be positioned very close to the beam. The collimation system is carefully set up in different machine modes (injection energy, full energy, full energy with squeezed bunches and with collisions). Operators provoke beam losses and make “loss maps” to make sure the beam is actually lost in the collimation region and not on any other machine elements where it could cause damage.

All these tests are performed with one, or very few, low-intensity bunches. Initially, even with stable beam mode officially achieved, only three bunches in each direction will circulate in the LHC. At this point, the experiments will be switched on to check their detectors work correctly with beam. With lot of hard work and a bit of luck, the first stable beams will be achieved next week.