LHC Report: First collisions soon

On the evening of Friday 16 March beams were accelerated in the LHC at 4 TeV for the first time: a new world record! According to the schedule for the machine restart it will take another three weeks before the stable beams mode – the requirement for the detectors to start taking data – is achieved.


During the beam commissioning period the equipment teams make sure that their systems – beam instrumentation, radio frequency, beam interlock, feedback on orbit and tune, etc. – are working flawlessly with beam. Confidence in the correct functioning of all the magnets, their settings and their alignment is obtained by detailed measurements of the optics and the physical aperture. 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 cm for the ATLAS and CMS experiments. As a reminder, smaller values of beta* mean thinner and more squeezed beams at the collision points.

A lot of time is devoted to guaranteeing the safety of the machine. The 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). By provoking beam losses and making “loss maps”, operators verify that the beam is actually lost in the collimation region and not on any other machine elements where it can cause damage.

All these tests and measurements are being performed with one or very few, often low-intensity bunches. Initially, even with the stable beam mode officially achieved, only three bunches in each direction will circulate in the machine. At this point, the experiments will be switched on to check the correct functioning of their detectors with beam. With a bit of luck, good availability of the machines and a lot of hard work by all the teams involved, the first stable beams will be achieved next week.


by Jan Uythoven for the LHC team