BNL, Upton, Long Island, New York
CERN, Geneva
Lancaster University, Lancaster
KEK, Ibaraki
SLAC, Menlo Park, California
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
LBNL, Berkeley, California
Fermilab, Batavia
Funding: This work was partially performed under the auspices of the US DOE and the European Community-Research Infrastructure, FP6 programme (CARE, contract number RII3-CT-2003-506395)}
The LHC crab cavity program is advancing rapidly towards a first prototype which is anticipated to be tested during the early stages of the LHC phase I upgrade and commissioning. Some aspects related to crab optics, collimation, aperture constraints, impedances, noise effects, beam transparency and machine protection critical for a safe and robust operation of LHC beams with crab cavities are addressed here.
BNL, Upton, Long Island, New York
CERN, Geneva
Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and the US LHC Accelerator Research Program (LARP).
In the Relativistic Heavy Ion Collider (RHIC) beams collide in the two interaction points IP6 and IP8. An increase of the bunch intensity above 2·1011 in polarized proton operation appears difficult due to the large beam-beam tune spread generated by the two collisions. A low energy electron beam or electron lens has been proposed to mitigate the head on beam-beam effect. In RHIC such a device could be located near IP10. We summarize multi-particle weak-strong beam-beam simulations of head-on beam-beam compensation with an electron lens. The proton beam's lifetime and emittance are calculated and compared for situations with and without an electron lens. Parameters such as the proton bunch intensity, the electron beam intensity and the betatron phase advances between IP8 and IP10 are scanned in the simulations.
BNL, Upton, Long Island, New York
Fermilab, Batavia
Funding: Work supported by U.S. DOE under contract No DE-AC02-98CH1-886
Long-range and head-on beam-beam effects are expected to limit the LHC performance with design parameters. To mitigate long-range effects current carrying wires parallel to the beam were proposed. Two such wires are installed in RHIC where they allow studying the effect of strong long-range beam-beam effects, as well as the compensation of a single long-range interaction. The tests provide benchmark data for simulations and analytical treatments. To reduce the head-on beam-beam effect electron lenses were proposed for both the LHC and RHIC. We present the experimental long-range beam-beam program and report on head-on compensations studies at RHIC, which are primarily based on simulations.
CERN, Geneva
BNL, Upton, Long Island, New York
Graz University of Technology (TUG), Signal Processing and Speech Communication Laboratory (SPSC), Graz
In particle accelerators coaxial cables are commonly used to transmit wideband beam signals covering many decades of frequencies over long distances. Those transmission lines often have a corrugated outer and/or inner conductor. This particular construction exhibits a significant amount of frequency dependent group delay variation. A comparison of simulations based on theoretical models and S11 and S21 network analyzer measurements up to 2.5 GHz is presented. It is shown how the non-linear phase response and varying group delay leads to ringing in the pulse response and subsequent distortion of signals transmitted through such coaxial transmission lines.
CERN, Geneva
BNL, Upton, Long Island, New York
The effect of magnet misalignments in the beam orbit and linear optics functions are reviewed and correction schemes are applied to the negative momentum compaction lattices of PS2. Chromaticity correction schemes are also proposed and tested with respect to off-momentum optics properties. The impact of the correction schemes in the dynamic aperture of the different lattices is finally evaluated.
CERN, Geneva
BNL, Upton, Long Island, New York
In view of the CERN Proton Synchrotron proposed replacement with a new ring (PS2), a detailed optics design as been undertaken following the evaluation of several lattice options. The basic arc module consists of cells providing negative momentum compaction. The straight section is formed with a combination of FODO and quadrupole triplet cells, to accommodate the injection and extraction systems, in particular the H- injection elements. The arc is matched to the straight section with a dispersion suppressor and matching module. Different lattices are compared with respect to their linear optics functions, tuning flexibility and geometrical acceptance properties.
SLAC, Menlo Park, California
LBNL, Berkeley, California
BNL, Upton, Long Island, New York
CERN, Geneva
Funding: Work supported by Department of Energy contract DE–AC03–76SF00515 and the US LARP program.
The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. While the SPS has a coupled-bunch transverse feedback system, control of Ecloud-driven motion requires a much wider control bandwidth capable of sensing and controlling motion within each bunched beam. This paper draws beam dynamics data from the measurements and simulations of this SPS instability, and develops initial performance requirements for a feedback system with 2-4 GS/sec sampling rates to damp Ecloud-driven transverse motion in the SPS at intensities desired for high-current LHC operation. Requirements for pickups, kickers and signal processing architectures are presented. Initial lab measurements of proof-of-principle lab model prototypes are presented for the wideband kicker driver signal functions.
EPFL, Lausanne
CERN, Geneva
BNL, Upton, Long Island, New York
The upgrade of the CERN Large Hadron Collider (LHC) would require a four- to fivefold increase of the single bunch intensity presently obtained in the Super Proton Synchrotron (SPS). Operating at such high single bunch intensities requires a detailed knowledge of the sources of SPS beam coupling impedance, so that longitudinal and transverse impedance reduction campaigns can be planned and performed effectively if needed. In this paper, the transverse impedance of the SPS is studied by injecting a single long bunch into the SPS, and observing its decay without RF. This particular setup enhances the resolution of the frequency analysis of the longitudinal and transverse bunch signals acquired with strip line couplers connected to a fast data acquisition. It also gives access to the frequency content of the transverse impedance. Results from measurements with short and long bunches in the SPS performed in 2008 are compared with simulations and theoretical predictions.
LBNL, Berkeley, California
BNL, Upton, Long Island, New York
SLAC, Menlo Park, California
CERN, Geneva
Funding: Supported by the US-DOE under Contract DE-AC02-05CH11231 and the US-LHC LARP. Used resources of NERSC, supported by the US-DOE under Contract DE-AC02-05CH11231.
Electron clouds impose limitations on current accelerators that may be more severe for future machines, unless adequate measures of mitigation are taken. Recently, it has been proposed to use feedback systems operating at high frequency (in the GHz range) to damp single-bunch transverse coherent oscillations that may otherwise be amplified during the interaction of the beam with ambient electron clouds. We have used the simulation package WARP-POSINST to study the growth rate and frequency patterns in space-time of the electron cloud driven beam breakup instability in the CERN SPS accelerator with, or without, an idealized feedback model for damping the instability. We will present our latest results and discuss their implications for the design of the actual feedback system.