By the end of June the LHC was making good progress towards delivering the first 100 nb–1 of integrated luminosity at an energy of 3.5 TeV per beam. This followed some two weeks devoted to beam commissioning, with the goal of achieving stable collisions at 3.5 TeV with the design intensity of 8 × 1011 protons per bunch. The first days of July saw machine fills for physics with six bunches per beam at this nominal intensity, providing further boosts to the goal of reaching 1 fb–1 before the end of 2011.
The first collisions at 3.5 TeV between bunches at nominal intensity were achieved on 26 May, following earlier tests on ramping the energy with bunches at this intensity. However, to make progress towards further stable running, the accelerator team needed to perform a variety of commissioning studies to establish the appropriate baseline for operating the LHC in these conditions.
These studies involved establishing the optimal reference settings for both ramping the energy and for a “squeeze” to β* of 3.5 m, prior to bringing the beams into collision. (The squeeze reduces the beam size at the interaction points and is described by the parameter β*, which gives the distance from the interaction point to the place where the beam is twice the size.) The settings include the all-important collimator positions, a key part of the machine protection system, and this alone involved 108 setup operations.
The work also involved commissioning the transverse damper – basically, an electrostatic deflector – to subdue instabilities in the nominal bunches as they are ramped to 3.5 TeV.
By 26 June the teams were ready with a new sequence to ramp, squeeze and collapse the separation at the interaction points to bring three bunches per beam at nominal intensity into collision at 3.5 TeV. With a physics run at an instantaneous luminosity of 5 × 1029 cm–2 s–1, the integrated luminosity in the experiments since 30 March already doubled, rising to more than 30 nb–1. A few days later, on 7 July, the machine ran with seven bunches per beam at nominal intensity and achieved a new luminosity record of 1030 cm–2 s–1. This is one more step towards the goal for 2010 of 1032 cm–2 s–1, which will require 800 nominal bunches per beam.
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