Towards higher intensities

Over the past 2 weeks, commissioning of the machine protection system has advanced significantly, opening up the possibility of higher intensity collisions at 3.5 TeV. The intensity has been increased from 2 bunches of 10¹⁰ protons to 6 bunches of 2x10¹⁰ protons. Luminosities of 6x10²⁸ cm^-2s^-1 have been achieved at the start of fills, a factor of 60 higher than those provided for the first collisions on 30 March.

 

To increase the luminosity further, the commissioning crews are now trying to push up the intensity of the individual proton bunches. After the successful injection of nominal intensity bunches containing 1.1x10¹¹ protons, collisions were subsequently achieved at 450 GeV with these intensities. However, half-way through the first ramping of these nominal intensity bunches to 3.5 TeV on 15 May, a beam instability was observed, leading to partial beam loss. Work is now under way to understand, control and cure this instability by using longer bunches and by powering the special correction magnets (octupoles).

Single bunches of nominal intensity are now being accelerated with very good lifetimes. The collimator set-up is being refined and made more accurate for higher intensity bunches at 3.5 TeV in preparation for higher luminosity collisions in the coming weeks.

by CERN Bulletin