SLAC, Menlo Park, California
For the PEP-II Operation Staff: PEP-II is an asymmetric e+e- collider operating at the Upsilon 4S and has recently set several performance records. The luminosity has reached 1.2x1034/cm2/s and has delivered an integrated luminosity of 910/pb in one day. PEP-II operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 3.0 A of positrons and 1.9 A of electrons in 1732 bunches. The total integrated luminosity since turn on in 1999 has reached over 410/fb. This paper reviews the present performance issues of PEP-II and also the planned increase of luminosity in the near future to over 2 x 1034/cm2/s.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
Submitted for the High Luminosity Study Group for an Asymmetric Super-B-Factory: Parameters are being studied for a high luminosity e+e- collider operating at the Upsilon 4S that would deliver a luminosity of over 1036/cm2/s. This collider would use a novel combination of linear collider and storage ring techniques. In this scheme an electron beam and a positron beam at 4 GeV x 7 GeV are stored in low-emittance damping rings similar to those designed for a Linear Collider (LC). A LC style interaction region is included in the ring to produce sub-millimeter vertical beta functions at the collision point. A large crossing angle (±30 mrad) is used at the collision point to allow beam separation and reduce the hourglass effect. Beam currents of about 3 A x 2 A in 1700 bunches can produce a luminosity of 1036/cm2/s. Design parameters and beam dynamics effects are discussed.
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
Liverpool University, Science Faculty, Liverpool
* P. Raimondi, "New Developments for SuperB Factories", Invited talk, this Conference
SLAC, Menlo Park, California
INFN/LNF, Frascati (Roma)
SLAC, Menlo Park, California
The low energy ring (LER) in PEP-II has a design emittance of 0.5 nm-rad in the vertical, compared to nearly 0.1 nm-rad for the HER ring. This was thought to come from the "vertical step" of about 1 m in the interaction straight, where the LER beam after horizontal separation gets bend vertical so it sits on top of the HER in the rest of the ring. Since the program MAD does not easily reveal the location of the major emittance contribution, a program was written to calculate the coupled "curly H" parameter of mode 2 (mainly vertical) along z. Weighting it with the magnet bending revealed that the weak long bends inside the "vertical step" did less than 20% of the emittance growth. More than 80% comes from the ends of the adjacent arcs with strong bends. This is caused by the coupling cancellation of the solenoid starting already there with the skew quadrupoles SK5 and 6. By introducing additional skews in the straight instead of SK5 and 6 the emittance could be reduced by a factor of ten in simulations, but with very strong skews. Reasonable strong magnets might generate a workable compromise, since a factor of two in emittance promises 50% more luminosity in beam-beam simulations.
SLAC, Menlo Park, California
For optics measurement and modeling of the PEP-II electron (HER) and position (LER) storage rings, we have been doing well with MIA* which requires analyzing turn-by-turn Beam Position Monitor (BPM) data that are resonantly excited at the horizontal, vertical, and longitudinal tunes respectively. However, in anticipating that certain BPM buttons or even pins in the PEP-II IR region will be missing for the next run starting in January 2007, we have been developing a data validation process, hoping to reduce the effect due to the reduced BPM data accuracy on PEP-II optics measurement and modeling. Besides the routine process for ranking BPM noise level through data correlation among BPMs, allowing BPMs to have linear gains and linear cross couplings, we can also check BPM data symplecticity by comparing the invariant ratios. We may also work out nonlinear BPM data correction if needed. Results on PEP-II measurement will be presented.
* Y. T. Yan, et. al. EPAC06 Proceedings, WEPCH062, (2006)
SLAC, Menlo Park, California
Ion induced beam instability is one critical issue for the electron damping ring of the International Linear Collider (ILC) due to its ultra small emittance of 2pm. Bunch train filling pattern is proposed to mitigate the instability and bunch-by-bunch feedback is applied to suppress it. Multi-bunch train fill pattern is introduced in the electron beam to reduce the number of trapped ions. Our study shows that the ion effects can be significantly mitigated by using multiple gaps. However, the beam can still suffer from the beam-ion instability driven by the accumulated ions that cannot escape from the beam during the gaps. The effects of beam fill pattern, emittance, vacuum and various damping mechanism are studied using self-consistent program, which includes the optics of the ring.