Beam-Beam Effects

One of the most severe limitations in high-intensity particle colliders is the beam-beam interaction, i.e. the perturbation of the beams as they cross the opposing beams. This introduction to beam-beam effects concentrates on a description of the phenomena that are present in modern colliding beam facilities.Comment: 29 pages, contribution to the CAS - CERN Accelerator School: Advanced Accelerator Physics Course, Trondheim, Norway, 18-29 Aug 201

Operational considerations on the stability of colliding beams

While well studied in the absence of beam-beam and while colliding head-on, the stability of the LHC beams can be very critical in intermediate steps. During the squeeze, the long-range beam-beam interaction becomes a critical component of the beam's dynamics. Also, while the transverse separation at the interaction points is collapsed, the beam-beam forces change drastically, possibly deteriorating the beam's stability. Finally, during luminosity production, the configuration of the LHC in 2012 included few bunches without head-on collision in any of the interaction points having different stability properties. Stability diagrams are being evaluated numerically in these configurations in an attempt to explain instabilities observed in these phases during the 2012 proton run of the LHC.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201

Ultra-Low-Power Superconductor Logic

We have developed a new superconducting digital technology, Reciprocal Quantum Logic, that uses AC power carried on a transmission line, which also serves as a clock. Using simple experiments we have demonstrated zero static power dissipation, thermally limited dynamic power dissipation, high clock stability, high operating margins and low BER. These features indicate that the technology is scalable to far more complex circuits at a significant level of integration. On the system level, Reciprocal Quantum Logic combines the high speed and low-power signal levels of Single-Flux- Quantum signals with the design methodology of CMOS, including low static power dissipation, low latency combinational logic, and efficient device count.Comment: 7 pages, 5 figure

Stability diagram of colliding beams

The effect of the beam-beam interactions on the stability of impedance mode is discussed. The detuning is evaluated by the means of single particle tracking in arbitrarily complex collision configurations, including lattice non-linearities, and used to numerically evaluate the dispersion integral. This approach also allows the effect of non-Gaussian distributions to be considered. Distributions modified by the action of external noise are discussed.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201

Observations of beam-beam effects at the LHC

This paper introduces a list of observations related to the beam-beam interaction that were collected over the first years of LHC proton physics operation (2010-12). Beam-beam related effects not only have been extensively observed and recorded, but have also shaped the operation of the LHC for high-intensity proton running in a number of ways: the construction of the filling scheme, the choice of luminosity levelling techniques, measures to mitigate instabilities, and the choice of settings for improving performance (e.g. to reduce losses), among others.Comment: Presented at the ICFA Mini-Workshop on Beam-Beam in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 March 201

Models to study multi bunch coupling through head-on and long-range beam-beam interactions

In the LHC almost 6000 bunches will collide in four interaction regions where they experience head-on as well as clustered long range interactions. These lead to a coupling between all bunches and coherent beam-beam effects. For two colliding bunches this is well understood. However, for a larger number of bunches colliding with different collision patterns, it results in a complex spectrum of oscillation frequencieswith consequences for beam measurements and Landau damping. To study the coherent beam-beam modes, three complementary models have been developped and will be described in this report. Two of these methods rely on self-consistent multi-bunch and multi-particle tracking while the third is an analytic model based on a complex matrix algorithms. The three methods together provide useful information about the beambeam coupling of multi bunch beams and together provide a deeper insight into the underlying physics