| Paper |
Title |
Page |
| MOPLT127 |
Diagnosing the PEP-II Injection System
|
833 |
| |
- F.-J. Decker, M.H. Donald, R.H. Iverson, A. Kulikov, G.C. Pappas, M. Weaver
SLAC, Menlo Park, California
|
|
| |
The injection of beam into the PEP-II B-Factory, especially into the High Energy Ring (HER) has some challenges. A high background level in the BaBar Detector has so far inhibited us from trickling charge into the HER similar to the Low Energy Ring (LER). Analyzing the injection system has revealed many issues which could be improved. The injection bump between two kickers was not closed, mainly because the phase advance wasn't exactly 180 degrees and the two kicker strengths were not balanced. Additionally we found reflections which kick the stored beam after the main kick and cause the average luminosity to drop about 3% for a 10 Hz injection rate. The strength of the overall kick is nearly twice as high than the design, indicating a much bigger effective septum thickness. Compared with single beam the background is worse when the HER beam is colliding with the LER beam. This hints that the beam-beam force and the observed vertical blow-up in the HER pushes the beam and especially the injected beam further out to the edge of the dynamic aperture or beyond.
|
|
| MOPLT128 |
Lattice Effects due to High Currents in PEP-II
|
836 |
| |
- F.-J. Decker, H. Smith, J.L. Turner
SLAC, Menlo Park, California
|
|
| |
The very high beam currents in the PEP-II B-Factory have caused many expected and unexpected effects: Synchrotron light fans move the beam pipe and cause dispersion, higher order modes cause excessive heating, e-clouds around the positron beam blow up its beam size. Here we describe an effect were the measured dispersion of the beam in the Low Energy Ring (LER) is different at high and at low beam currents. The dispersion was iteratively lowered by making anti-symmetric orbit bumps in many sextupole duplets, checking each time with a dispersion measurement where a dispersive kick is generated. This can be done parasitically during collisions. It was a surprise when checking the low current characterization data that there is a change. Subsequent high and low current measurements confirmed the effect. It is located far away from any synchrotron radiation in the middle of a straight (PR12), away from sextupoles and skew quadrupoles and creates a dispersion wave of about 70 mm at high current while at low current it is negligible.
|
|
| MOPLT129 |
Identifying Lattice, Orbit, and BPM Errors in PEP-II
|
839 |
| |
- F.-J. Decker
SLAC, Menlo Park, California
|
|
| |
The PEP-II B-Factory is delivering peak luminosities of up to 7.4·1033 1/cm2 1/s. This is very impressive especially considering our poor understanding of the lattice, absolute orbit and beam position monitor system (BPM). A few simple MATLAB programs were written to get lattice information, like betatron functions in a coupled machine (four all together) and the two dispersions, from the current machine and compare it the design. Big orbit deviations in the Low Energy Ring (LER) could be explained not by bad BPMs (only 3), but by many strong correctors (one corrector to fix four BPMs on average). Additionally these programs helped to uncover a sign error in the third order correction of the BPM system. Further analysis of the current information of the BPMs (sum of all buttons) indicates that there might be still more problematic BPMs.
|
|
| MOPLT130 |
Bunch Pattern with More Bunches in PEP-II
|
842 |
| |
- F.-J. Decker, S. Colocho, A. Novokhatski, M.K. Sullivan, U. Wienands
SLAC, Menlo Park, California
|
|
| |
The number of bunches in the PEP-II B-Factory has increased over the years. The luminosity followed roughly linear that increase or even faster since we also lowered the spot size at the interaction point. The recent steps from 933 in June of 2003 to about 1320 in February 2004 should have been followed by a similar rise in luminosity from 6.5·1033 1/cm2 1/s to 9.2·1033 1/cm2 1/s. This didn't happen so far and a peak luminosity of only 7.3·1033 1/cm2 1/s was achieved. By filling the then partially filled by-3 pattern to a completely filled by-3 pattern (1133 bunches) should even give 7.9·1033 1/cm2 1/s with scaled currents of 1400 mA (HER) and 1900 mA (LER). We are typically running about 1300 mA and 1900 mA with 15% more bunches. The bunch pattern is typically by-2 with trains of 14 bunches out of 18. The parasitic beam crossings or electron cloud effects might play a role in about a 10% luminosity loss. Also the LER x-tune could be pushed further down to the ½ integer in the by-3 pattern. On the other hand we might not push the beam-beam tune shift as hard as in June of 2003 since we started trickle injection and therefore might avoid the highest peak luminosity with a higher background. A mixed pattern with a by2-by3 setup (separation of 2, 3, 2, 3 ?) would give totally filled a slightly higher number of bunches (1360), but near the interaction point there would be only one parasitic crossing per beam lowering the tune shift by two.
|
|
| MOPLT135 |
Damping the High Order Modes in the Pumping Chamber of the PEP-II Low Energy Ring
|
854 |
| |
- A. Novokhatski, S. Debarger, F.-J. Decker, A. Kulikov, J. Langton, M. Petree, J. Seeman, M.K. Sullivan
SLAC, Menlo Park, California
|
|
| |
The Low Energy Ring of the PEP-II B-factory operates with extremely high currents and short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of the High Order Modes. A temperature rise has been found in the vacuum chamber elements in one transition from straight section to arc. The power in the wake fields was high enough to char beyond use the feed-through for the Titanium Sublimation Pump. This pumping section consists of the beam chamber and an ante-chamber. Fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater wires of the TSP come out. A small ceramic tile was placed near the TSP feed-through to absorb these fields. A short wire antenna was also placed there. HOM measurements show a wide spectrum with a maximum in the 2-3 GHz region. A special water cooled HOM absorber was designed and put inside the ante-chamber part of the section. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss is 750 W for a beam current of 2 A. Measurements of the HOM impedance for different bunch patterns, bunch length and transverse beam position will be presented.
|
|
| MOPLT143 |
Results and Plans of the PEP-II B-Factory
|
875 |
| |
- J. Seeman, J. Browne, Y. Cai, S. Colocho, F.-J. Decker, M.H. Donald, S. Ecklund, R.A. Erickson, A.S. Fisher, J.D. Fox, S.A. Heifets, R.H. Iverson, A. Kulikov, A. Novokhatski, M.T.F. Pivi, M.C. Ross, P. Schuh, T.J. Smith, K. Sonnad, M. Stanek, M.K. Sullivan, P. Tenenbaum, D. Teytelman, J.L. Turner, D. Van Winkle, U. Wienands, M. Woodley, Y.T. Yan, G. Yocky
SLAC, Menlo Park, California
- M.E. Biagini
INFN/LNF, Frascati (Roma)
- J.N. Corlett, C. Steier, A. Wolski, M.S. Zisman
LBNL, Berkeley, California
- W. Kozanecki
CEA/DSM/DAPNIA, Gif-sur-Yvette
- G. Wormser
IPN, Orsay
|
|
| |
PEP-II is an e+e- B-Factory Collider located at SLAC operating at the Upsilon 4S resonance. PEP-II has delivered, over the past four years, an integrated luminosity to the BaBar detector of over 175 fb-1 and has reached a luminosity over 7.4x1033/cm2/s. Steady progress is being made in reaching higher luminosity. The goal over the next few years is to reach a luminosity of at least 2x1034/cm2/s. The accelerator physics issues being addressed in PEP-II to reach this goal include the electron cloud instability, beam-beam effects, parasitic beam-beam effects, trickle injection, high RF beam loading, lower beta y*, interaction region operation, and coupling control.
|
|
| MOPLT144 |
Design for a 1036 Super-B-factory at PEP-II
|
878 |
| |
- J. Seeman, Y. Cai, F.-J. Decker, S. Ecklund, A.S. Fisher, J.D. Fox, S.A. Heifets, A. Novokhatski, M.K. Sullivan, D. Teytelman, U. Wienands
SLAC, Menlo Park, California
|
|
| |
Design studies are underway to arrive at a complete parameter set for a very high luminosity e+e- Super B-Factory (SBF) in the luminosity range approaching 1036/cm2/s. The design is based on a collider in the PEP-II tunnel but with an upgraded RF system (higher frequency), magnets, vacuum system, and interaction region. The accelerator physics issues associated with this design are reviewed as well as the site and power constraints. Near term future studies will be discussed.
|
|
| MOPLT146 |
Trickle-charge: a New Operational Mode for PEP-II
|
881 |
| |
- J.L. Turner, S. Colocho, F.-J. Decker, S. Ecklund, A.S. Fisher, R.H. Iverson, C. O'Grady, J. Seeman, M.K. Sullivan, M. Weaver, U. Wienands
SLAC, Menlo Park, California
- W. Kozanecki
CEA/DSM/DAPNIA, Gif-sur-Yvette
|
|
| |
In regular top-up-and-coast operation, PEP-II average luminosity is about 70…75% of the peak luminosity due to detector ramp-down and ramp-up times plus the time it takes to top-up both beams. We recently commissioned a new operational mode where the Low Energy Ring is injected continuously without ramping down the detector. The benefits?increased luminosity lifetime and roughly half the number of top-ups per shift?were expected to give an increase in delivered luminosity of about 15% at the same peak luminosity; this was confirmed in test runs. In routine trickle operation, however, it appears that the increase in delivered luminosity is more than twice that due to an increase in availability credited to the more stable operating conditions during trickle operation. In this paper we will present our operational experience as well as some of the diagnostics we use to monitor and maintain tuning of the machine in order to control injection background and protect the detector. Test runs are planned to extend trickle-charge operation to the High Energy Ring as well.
|
|