Operational beams for the LHC

The variety of beams, needed to set-up in the injectors as requested in the LHC, are reviewed, in terms of priority but also performance expectations and reach during 2015. This includes the single bunch beams for machine commissioning and measurements (probe, Indiv) but also the standard physics beams with 50 ns and 25 ns bunch spacing and their high brightness variants using the Bunch Compression Merging and Splitting (BCMS) scheme. The required parameters and target performance of special beams like the doublet for electron cloud enhancement and the more exotic 8b$\oplus$4e beam, compatible with some post-scrubbing scenarios are also described. The progress and plans for the LHC ion production beams during 2014-2015 are detailed. Highlights on the current progress of the setting up of the various beams are finally presented with special emphasis on potential performance issues across the proton and ion injector chain.Comment: Submitted for publication in a CERN Yellow Report (YR

High intensity effects of fixed target beams in the CERN injector complex

The current fixed target (FT) experiments at CERN are a complementary approach to the Large Hadron Collider (LHC) and play a crucial role in the investigation of fundamental questions in particle physics. Within the scope of the LHC Injectors Upgrade (LIU), aiming to improve the LHC beam production, the injector complex will be significantly upgraded during the second Long Shutdown (LS2). All nonLHC beams are expected to benefit from these upgrades. In this paper, we focus on the studies of the transverse instability in the Proton Synchrotron (PS), currently limiting the intensity of Time-Of-Flight (ToF) type beams, as well as the prediction of the impact of envisaged hardware modifications. A first discussion on the effect of space charge on the observed instability is also being presented

Benchmarking headtail with electron cloud instabilities observed in the LHC

After a successful scrubbing run in the beginning of 2011, the LHC can be presently operated with high intensity proton beams with 50 ns bunch spacing. However, strong electron cloud effects were observed during machine studies with the nominal beam with 25 ns bunch spacing. In particular, fast transverse instabilities were observed when attempting to inject trains of 48 bunches into the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data from the transverse damper pick-ups during these injection studies is presented, showing a clear signature of the electron cloud effect. These experimental observations are reproduced using numerical simulations: the electron distribution before each bunch passage is generated with PyECLOUD and used as input for a set of HEADTAIL simulations. This paper describes the simulation method as well as the sensitivity of the results to the initial conditions for the electron build-up. The potential of this type of simulations and their clear limitations on the other hand are discussed.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba, Ital

Micro‐fracture experiments on nanocomposite hard coatings

Physical or chemical vapor deposited nanocomposite thin films evoke much scientific interest due to their unusual combination of mechanical properties, such as high hardness, high elastic recovery, high elastic strain limit, and high tensile strength. One of the most frequently studied film systems in this context is titanium-silicon-nitride (Ti-Si-N). The self-organized nanostructure consists typically of TiN nanocrystals (nc) covered by an amorphous (a) Si3N4 tissue phases. While the exceptional high hardness of Ti-Si-N films and the underlying mechanisms have been studied extensively, less attention has been paid on the fracture toughness. Here we show experimental results of cantilever bending tests, performed on 2 µm thick reactive magnetron sputtered Ti-Si-N films. We found that nc-TiN/a-Si3N4 possesses a significantly higher fracture toughness as TiN, namely KIC values of up to 4.5±0.6 MPa√m in comparison with 1.9±0.4 MPa√m of TiN. This, in combination with a high hardness of 38±2 GPa (TiN: 26±1 GPa), a high fracture strength of up to around 6 GPa, as well as a high elastic recovery and flexibility is an ideal basis for high performance coatings, e.g., used for various industrial applications such as machining. The film nanostructure was carefully studied by independent X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy

Catalysis in Quantum Information Theory

Catalysts open up new reaction pathways which can speed up chemical reactions while not consuming the catalyst. A similar phenomenon has been discovered in quantum information science, where physical transformations become possible by utilizing a (quantum) degree of freedom that remains unchanged throughout the process. In this review, we present a comprehensive overview of the concept of catalysis in quantum information science and discuss its applications in various physical contexts.Comment: Review paper; Comments and suggestions welcome

Detecting chaos in particle accelerators through the frequency map analysis method

The motion of beams in particle accelerators is dominated by a plethora of non-linear effects which can enhance chaotic motion and limit their performance. The application of advanced non-linear dynamics methods for detecting and correcting these effects and thereby increasing the region of beam stability plays an essential role during the accelerator design phase but also their operation. After describing the nature of non-linear effects and their impact on performance parameters of different particle accelerator categories, the theory of non-linear particle motion is outlined. The recent developments on the methods employed for the analysis of chaotic beam motion are detailed. In particular, the ability of the frequency map analysis method to detect chaotic motion and guide the correction of non-linear effects is demonstrated in particle tracking simulations but also experimental data.Comment: Submitted for publication in Chaos, Focus Issue: Chaos Detection Methods and Predictabilit

Annealing effect on the Fracture Toughness of CrN/TiN Superlattice Systems

Coherently grown nanolayered thin films are generally known for their superior mechanical properties, compared to their monolithically grown constituents. Recently, we have shown that CrN/TiN superlattice films exhibit a bilayer period dependent peak in fracture toughness KIC. We propose that a dominating factor influencing these mechanical properties is the interface constitution between the layers. To proof this concept we modified the interfaces of CrN/TiN superlattice thin films with a bilayer period Λ of 9 and 18 nm by vacuum annealing experiments at different temperatures. This treatment promotes interdiffusion between CrN and TiN layers, leading to the formation of “blurred” interfaces and further on to interphases (CrN and TiN form a solid solution), as well as the reduction of coherency strains in the interface region. To calculate the fracture toughness of our hard coatings, we performed in-situ micromechanical cantilever bending tests on the ex-situ vacuum annealed samples. As expected for coatings without an age hardening effect, the hardness H decreases with increasing annealing temperature for both superlattice systems. For Λ = 9 nm the fracture toughness experiences a similar reduction following predictions given by the empirical H/E criteria. However, the coating with Λ = 18 nm does not follow this criteria and exhibits a peak in fracture toughness for an annealing temperature of Ta = 700 °C