INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
CERN, Geneva
BINP SB RAS, Novosibirsk
KEK, Ibaraki
University of Pisa and INFN, Pisa
The SuperB project aims at the construction of an asymmetric (4x7 GeV), very high luminosity, B-Factory on the Roma II (Italy) University campus. The luminosity goal of 1036 cm-2 s-1 can be reached with a new collision scheme with large Piwinski angle and the use of “crab” sextupoles. A crab-waist IR has been successfully tested at the DAPHNE Phi-Factory at LNF-Frascati (Italy) in 2008. The crab waist together with very low beta* will allow for operation with relatively low beam currents and reasonable bunch length, comparable to those of PEP-II and KEKB. In the High Energy Ring, two spin rotators permit bringing longitudinally polarized beams into collision at the IP. The lattice has been designed with a very low intrinsic emittance and is quite compact, less than 2 km long. The tight focusing requires a sophisticated Interaction Region with quadrupoles very close to the IP. A Conceptual Design Report was published in March 2007, and beam dynamics and collective effects R&D studies are in progress in order to publish a Technical Design Report by the end of 2010. A status of the design and simulations is presented in this paper.
SLAC, Menlo Park, California
Stanford University, Stanford, California
UCLA, Los Angeles, California
Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
SSRL and SLAC groups are developing a long-range plan to transfer its evolving scientific programs from the SPEAR3 light source to a much higher performing photon source that would be housed in the 2.2-km PEP-II tunnel. While various concepts for the PEP-X light source are under consideration, including ultimate storage ring and ERL configurations, the present baseline design is a very low-emittance storage ring. A hybrid lattice has DBA or QBA cells in two of the six arcs that provide a total ~30 straight sections for ID beam lines extending into two new experimental halls. The remaining arcs contain TME cells. Using ~100 m of damping wigglers the horizontal emittance at 4.5 GeV would be ~0.1 nm-rad with >1 A stored beam. PEP-X will produce photon beams having brightnesses near 1022 at 10 keV. Studies indicate that a ~100-m undulator could have FEL gain and brightness enhancement at soft x-ray wavelengths with the stored beam. Crab cavities or other beam manipulation systems could be used to reduce bunch length or otherwise enhance photon emission properties. The present status of the PEP-X lattice and beam line designs are presented and other implementation options are discussed.
SLAC, Menlo Park, California
BINP SB RAS, Novosibirsk
Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515.
For proper operation of the LCLS x-ray free-electron laser, measurement and control of the electron bunch longitudinal phase space is critical. The LCLS accelerator includes two bunch compressor chicanes to magnify the peak current. These magnetic chicanes can generate significant coherent synchrotron radiation (CSR), which can distort the phase space distribution. We propose a diagnostic scheme by exciting a weak skew quadrupole at an energy-chirped, high dispersion point in the first bunch compressor (BC1) to reconstruct longitudinal phase space on an OTR screen after BC1, allowing a detailed characterization of the CSR effects.
SLAC, Menlo Park, California
Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
The electron beam for the Linac Coherent Light Source (LCLS) at SLAC is accelerated by disk-loaded RF structures over a length of 1 km. The mainly longitudinal field can sometimes exhibit transverse components, which kick the beam in x and/or y. This is normally a stable situation, but when a klystron, which powers some of these structures, has to be switched off and another one switched on, different kicks can lead to quite a different orbit. Some klystrons, configured in an energy and bunch length feedback, caused orbit changes of up to 1 mm, which is about 20 times the σ beam size. The origins and measurements of these kicks and some efforts (orbit bumps) to reduce them will be discussed.
SLAC, Menlo Park, California
INFN/LNF, Frascati (Roma)
Funding: Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515.
The use of normal conducting cavities and an ion-clearing gap will cause a significant RF accelerating voltage gap transient and longitudinal phase shift of the individual bunches along the bunch train in both rings of the SuperB accelerator. Small relative centroid position shifts between bunches of the colliding beams will have a large adverse impact on the luminosity due to the small beta y* at the interaction point (IP). We investigate the possibility of minimizing the relative longitudinal position shift between bunches by reducing the gap transient in each ring and matching the longitudinal bunch positions of the two rings at the IP using feedback/feedforward techniques in the LLRF. The analysis is conducted assuming maximum use of the klystron power installed in the system.
SLAC, Menlo Park, California
CERN, Geneva
INFN/LNF, Frascati (Roma)
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.
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.
SLAC, Menlo Park, California
INFN/LNF, Frascati (Roma)
Funding: Work supported by the Department of Energy under contract number DE-AC03-76SF00515.
We present a possible design for a fast luminosity feedback for the Super-B Interaction Point (IP). The design is an extension of the fast luminosity feedback installed on the PEP-II accelerator. During the last two runs of PEP-II and BaBar (2007-2008), we had an improved luminosity feedback system that was able to maintain peak luminosity with faster correction speed than the previous system. The new system utilized fast dither coils on the High-Energy Beam (HEB) to independently dither the x position, the y position and the y angle at the IP, at roughly 100 Hz. The luminosity signal was then read out with three independent lock-in amplifiers. An overall correction was computed based on the lock-in signal strengths and beam corrections for position in x and y and in the y angle at the IP were simultaneously applied to the HEB. With the 100 times increase in luminosity for the SuperB design, we propose using a similar fast luminosity feedback that can operate at frequencies between DC and 1 kHz, high enough to be able to follow and nullify any vibrational beam motion from the final focusing magnets.