FIRST EXPERIMENTAL OBSERVATIONS FROM THE LHC DYNAMIC APERTURE EXPERIMENT

Following intensive numerical simulations to compute the dynamic aperture for the LHC in the design phase, the successful beam commissioning and the ensuing beam operations opened the possibility of performing beam measurements of the dynamic aperture. In this paper the experimental set-up and the first observations based on the few experimentalsessions performed will be presented and discussed in details. DYNAMIC APERTURE MEASUREMENTS The basis of theproposedtest to probethedynamicaperture (DA) is the inverse logarithm scaling law for dynamic aperture [1, 2]. This scaling law, derived from tracking data, hasbeenused recentlyto derivea possiblerelationbetween the intensity evolution and dynamic aperture [3]. So far, no particular lifetime issues were observed at injection, thus indicating that the dynamicapertureshould be comparable to the mechanical one. This suggests that a more effective strategy for measuring the DA consists of reducing it artificially by acting on some of the non-linear circuits present in the ring. In any case, the injected beam needs to be blown-up in order to have enough particles probing high amplitudes and hence experiencing non-lineareffects. This is certainly not the only technique to measure the dynamic aperture and in future also other approaches will be attempted, such as using the aperture kicker to bring the whole bunch to high amplitude. In light of these considerations, the strategy was as follows(consideringthatonlyBeam1wasusedforthesemea