On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ∼−16 V to −20 V during the outburst. A clear sequence

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Simulations of collimation and beam cleaning were so far often performed with simplified computer models. However, the increase in available CPU power has opened the possibility for far more realistic simulations. For large accelerators like LHC it is now possible to track millions of particles, element by element over hundreds of turns. The well established SixTrack code treats the full six-dimensional phase space and considers the non-linear magnet components up to very high order. This code is being used for all LHC tracking simulations and has well developed linear and non-linear error models. SixTrack was extended for tracking of large ensembles of halo particles, taking into account halo interaction with arbitrarily placed collimators. An interface to a program for aperture analysis allows obtaining beam loss maps in the machine aperture. A standardized and portable SixTrack version is now available, providing all functionality of the old SixTrack, as well as the newly added support for halo tracking, collimation and aperture loss maps. EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN -AB Department A NEW VERSION OF SIXTRACK WITH COLLIMATION AND APERTURE INTERFACEG. Robert-Demolaize, R. Assmann, S. Redaelli, F. Schmidt, CERN, Geneva, Switzerland AbstractSimulations of collimation and beam cleaning were so far often performed with simplified computer models. However, the increase in available CPU power has opened the possibility for far more realistic simulations. For large accelerators like LHC it is now possible to track millions of particles, element by element over hundreds of turns.The well established SixTrack code treats the full sixdimensional phase space and considers the non-linear magnet components up to very high order. This code is being used for all LHC tracking simulations and has well developed linear and non-linear error models. SixTrack was extended for tracking of large ensembles of halo particles, taking into account halo interaction with arbitrarily placed collimators.An interface to a program for aperture analysis allows obtaining beam loss maps in the machine aperture. A standardized and portable SixTrack version is now available, providing all functionality of the old SixTrack, as well as the newly added support for halo tracking, collimation and aperture loss maps.

The dynamic aperture experiment at the CERN Super Proton Synchrotron ͑SPS͒ was aimed at finding the relevant effects that limit single-particle stability in hadron storage rings. These effects were studied in the SPS and compared with long-term particle tracking to determine to what extent computer simulations can predict the dynamic aperture under well-known conditions. Such investigations are very important for future hadron colliders such as the Large Hadron Collider as the design of these machines relies heavily on simulations. Besides this practical goal it was of utmost interest to improve the phenomenological understanding of the intricate details of particle motion in phase space. This experiment was carried out by successive teams over a period of ten years. We summarize the techniques, results, and conclusions. ͓S1063-651X͑97͒10602-X͔ PACS number͑s͒: 29.20.Ϫc

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