• S.M. White, R. Alemany-Fernandez, H. Burkhardt, M. Lamont
  CERN, Geneva

We discuss luminosity monitoring, optimization and absolute calibration in the LHC. Interaction rates will be continuously monitored both by detectors on the machine side as well as by the four large LHC experiments. Horizontal and vertical separation scans will be used to optimize luminosity and to measure the beam sizes in the interaction region. An application software has been developed for this purpose. We describe the procedures which have been prepared and discuss expected systematic effects which may limit the accuracy of the measurement.

• M.K. Sullivan, K.J. Bertsche, J. Seeman, U. Wienands
  SLAC, Menlo Park, California
• S. Bettoni
  CERN, Geneva
• M.E. Biagini, P. Raimondi
  INFN/LNF, Frascati (Roma)
• E. Paoloni
  University of Pisa and INFN, Pisa

Funding: Work supported by the Department of Energy under contract number DE-AC03-76SF00515.

We present an improved design for a Super-B interaction region. The new design minimizes local bending of the two colliding beams by separating all beam magnetic elements near the Interaction Point (IP). The total crossing angle at the IP is increased from 50 mrad to 60 mrad. The first magnetic element is a six slice Permanent Magnet (PM) quadrupole with an elliptical aperture allowing us to increase the vertical space for the beam. This magnet starts 36 cm from the Interaction Point (IP). This magnet is only seen by the Low-Energy Beam (LEB), the High-Energy Beam (HEB) has a drift space at this location. This allows the preliminary focusing of the LEB which has a smaller beta y* at the IP than the HEB. The rest of the final focusing for both beams is achieved by two super-conducting side-by-side quadrupoles (QD0 and QF1). These sets of magnets are enclosed in a warm bore cryostat located behind the PM quadrupole for the LEB. We describe this new design for the interaction region.

• M.K. Sullivan, K.J. Bertsche, A. Novokhatski, J. Seeman, U. Wienands
  SLAC, Menlo Park, California

Funding: Work supported by the Department of Energy under contract number DE-AC03-76SF00515.

The PEP-II B-Factory was designed and optimized to run at the Upsilon 4S resonance (10.580 GeV with a 9 GeV e^- beam and a 3.1 GeV e⁺ beam). The interaction region (IR) used permanent magnet dipoles to bring the beams into a head-on collision. The first focusing element for both beams was also a permanent magnet. The IR geometry, masking, beam orbits and beam pipe apertures were designed for 4S running. Even though PEP-II was optimized for the 4S, we successfully changed the center-of-mass energy (Ecm) down to the Upsilon 2S resonance and completed an Ecm scan from the 4S resonance up to 11.2 GeV. The luminosity throughout these changes remained near 1x10³⁴ cm^-2s^-1 . The Ecm was changed by moving the energy of the high-energy beam (HEB). The beam energy differed by more than 20% which produced significantly different running conditions for the RF system. The energy loss per turn changed 2.5 times over this range. We describe how the beam energy was changed and discuss some of the consequences for the beam orbit in the interaction region. We also describe some of the RF issues that arose and how we solved them as the high-current HEB energy changed.

• Y.S. Derbenev, S.A. Bogacz, P. Chevtsov
  JLAB, Newport News, Virginia
• A. Afanasev, C.M. Ankenbrandt, V. Ivanov, R.P. Johnson, G.M. Wang
  Muons, Inc, Batavia

Designers of high-luminosity energy-frontier muon colliders must provide strong beam focusing in the interaction regions. However, the construction of a strong, aberration-free beam focus is difficult and space consuming, and long straight sections generate an off-site radiation problem due to muon decay neutrinos that interact as they leave the surface of the earth. Without some way to mitigate the neutrino radiation problem, the maximum c.m. energy of a muon collider will be limited to about 3.5 TeV. A new concept for achromatic low beta design is being developed, in which the interaction region telescope and optical correction elements, are installed in the bending arcs. The concept, formulated analytically, combines space economy, a preventative approach to compensation for aberrations, and a reduction of neutrino flux concentration. An analytical theory for the aberration-free, low beta, spatially compact insertion is being developed.

• J. Beebe-Wang, A.K. Jain
  BNL, Upton, Long Island, New York

Funding: Work performed under the auspices of the US DOE.

The existence of multipolar components in the dipole and quadrupole magnets is one of the factors limiting the beam stability in the RHIC operations. Therefore, the statistical properties of the non-linear fields are crucial for understanding the beam behavior and for achieving the superior performance in RHIC. In an earlier work*, the field quality analysis of the RHIC interaction regions (IR) was presented. Furthermore, a procedure for developing non-linear IR models constructed from measured multipolar data of RHIC IR magnets was described. However, the field quality in the regions outside of the RHIC IR regions had not yet been addressed. In this paper, we present the statistical analysis of multipolar components in the magnetic fields of the RHIC arc regions. The emphasis is on the lower order components, especially the sextupole in the arc dipole and the 12-pole in the quadrupole magnets, since they are shown to have the strongest effects on the beam stability. Finally, the inclusion of the measured multipolar components data of RHIC arc regions and their statistical properties into tracking models is discussed.

*J. Beebe-Wang and A. Jain, “Realistic Non-linear Model and Field Quality Analysis in RHIC Interaction Regions”, proc. of PAC 2007, page 4309-4311 (2007)

• M.J. Bogan, S. Boutet, P. DeCorwin-Martin, D.G. Starodub
  SLAC, Menlo Park, California
• S. Bajt, H. Chapman, J. Schulz
  DESY, Hamburg
• A. Barty, W.H. Benner, M. Frank, S.P. Hau-Riege, B. Woods
  LLNL, Livermore, California
• J. Hajdu, B. Iwan, M.M. Seibert, N. Timneanu
  Uppsala University, Biomedical Centre, Uppsala
• S. Marchesini
  LBNL, Berkeley, California
• U. Rohner
  Tofwerk, Thun

Radiation damage limits the resolution of structural information obtained by X-ray diffraction. We are developing coherent diffractive imaging of biological specimens beyond conventional radiation damage resolution limits. The soft X-ray free-electron-laser (FEL) in Hamburg, FLASH*, was used to generate high-resolution low-noise coherent diffraction patterns from nanostructured nonperiodic objects before they turned into a plasma and exploded during single {10}-30 fs long X-ray pulses**,***. Iterative phase retrieval algorithms were used to reconstruct images of the objects****. Recent single particle diffraction experiments at FLASH, achieved in part due to the bunch train time pattern available from this superconducting linear accelerator, will be described. Data from single nanoparticles, their clusters and single cells will be discussed. Extending this approach to hard X-ray FELs, such as the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory, is anticipated to facilitate near atomic resolution imaging of nm-to-um-sized objects without the need for crystallization*****.

* Ayvazyan et al Eur Phys J D 2006 37 297
** Chapman et al Nat Phys 2006 2 839
*** Bogan et al Nano Lett 2008 8 310
**** Marchesini Rev Sci Instr 2007 78 011301
***** Neutze et al Nature 2000 406 752

• F.W. Jones
  TRIUMF, Vancouver
• W. Herr, T. Pieloni
  CERN, Geneva

The simulation code COMBI has been developed to enable the study of coherent beam-beam effects in the full collision scenario of the LHC, with multiple bunches interacting at multiple crossing points over many turns. The parallel version of COMBI was first implemented using a soft-Gaussian collision model which entails minimal communication between worker processes. Recently we have extended the code to a fully self-consistent collision model using a Grid-Multipole method, which allows worker processes to exchange charge and field information in a compact form which minimizes communication overhead. In this paper we describe the Grid-Multipole technique used and its adaptation to the parallel environment through pre- and post-processing of charge and grid data. Performance measurements in multi-core and Myrinet-cluster environments will be given. We will also present our estimates of the potential for very large-scale simulations on massively-parallel hardware, in which the number of simulated bunches ultimately approaches the actual LHC bunch population.