| Paper |
Title |
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| MOPP063 |
A New Chicane Experiment in PEP-II to Test Mitigations of the Electron Cloud Effect for Linear Colliders
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688 |
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- M. T.F. Pivi, D. Arnett, F. D. Cooper, D. Kharakh, F. King, R. E. Kirby, B. Kuekan, J. J. Lipari, M. Munro, J. S.T. Ng, J. Olszewski, T. O. Raubenheimer, J. Seeman, B. Smith, C. M. Spencer, L. Wang, W. Wittmer
SLAC, Menlo Park, California
- C. M. Celata, M. A. Furman
LBNL, Berkeley, California
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Beam instability caused by the electron cloud has been observed in positron and proton storage rings and it is expected to be a limiting factor in the performance of the positron Damping Ring (DR) of future Linear Colliders such as ILC and CLIC. Possible remedies for the electron cloud effect include thin-film coatings, surface conditioning, antechamber, clearing electrodes, and chamber with grooves or slots. The effect is expected to be particularly severe in magnetic field regions. To test this and possible mitigation methods, we have installed a new 4-dipole chicane experiment in the PEP-II Low Energy Ring (LER). We have also installed test chambers in straight field free regions. The associated chamber consists of bare aluminum and TiN-coated inner surface sections. Each section is instrumented with arrays of readout electrodes and retarding grids. Installation of a grooved chamber is also planned. In this paper, we describe the ongoing R&D effort at SLAC to reduce the electron cloud effect in linear colliders. We present the design of the chicane, the chambers and diagnostics, as well as the experimental results obtained.
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| WEPP041 |
High-current Effects in the PEP-II Storage Rings
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2611 |
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- U. Wienands, W. X. Cheng, W. S. Colocho, S. DeBarger, F.-J. Decker, S. Ecklund, A. S. Fisher, D. Kharakh, A. Krasnykh, A. Novokhatski, M. K. Sullivan
SLAC, Menlo Park, California
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High beam currents, 2A(HER) & 3A(LER), in PEP-II has been a challenge for the vacuum system. For the ~1 cm long bunches peak currents reach 50 A. Thus modest impedances can give rise to voltage spikes and discharges. A weakness was uncovered during Run 6: rf seals at the "flex flanges" that join the HER arc dipole and quadrupole chambers became a source of an increasing number of HER beam aborts. Vacuum activity was seen and thermal sensors on these flanges saw temperature spikes. Inspection of the seals found arcing and melting, prompting us to replace all of these seals with an improved design using Inconel instead of GlidCop fingers. We believe the GlidCop fingers do not maintain elasticity and hence can not follow chamber motion due to thermal effects. The Run 7 startup confirmed the success of this repair. However, high bunch current in the LER caused breakdown in a LER kicker. This limited the LER bunch current to about 1 mA. Inspection revealed damage to one of the recently added Macor pins that help support the electrodes. Failure analysis revealed heating of the pin & post-facto modeling shows high fields coming from a combination of HOM impedance and high peak currents.
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| THPC007 |
Permanent Magnet Skew Quadrupoles for the Low Emittance LER Lattice of PEP-II
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2987 |
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- F.-J. Decker, S. D. Anderson, D. Kharakh, M. K. Sullivan
SLAC, Menlo Park, California
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The vertical emittance of the low energy ring (LER) in the PEP-II B-Factory was reduced by using skew quadrupoles consisting of permanent magnet material. The advantages over electric quadrupoles or rotating existing normal quadrupoles are discussed. To assure a high field quality a Biot Savart calculation was used to cancel the natural 12-pole component by using different size poles over a few layers. A magnetic measurement confirmed the high quality of the magnets. After installation and adjusting the original 12 skew and 16 normal quadrupoles the emittance contribution from the region close to the interaction point, which was the biggest part in the original design, was considerably reduced.
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| WEPC023 |
Ideas for a Future PEP Light Source
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2031 |
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- R. O. Hettel, K. L.F. Bane, L. D. Bentson, K. J. Bertsche, S. M. Brennan, Y. Cai, A. Chao, S. DeBarger, V. A. Dolgashev, X. Huang, Z. Huang, D. Kharakh, Y. Nosochkov, T. Rabedeau, J. A. Safranek, J. Seeman, J. Stohr, G. V. Stupakov, S. G. Tantawi, L. Wang, M.-H. Wang, U. Wienands
SLAC, Menlo Park, California
- I. Lindau
Stanford University, Stanford, Califormia
- C. Pellegrini
UCLA, Los Angeles, California
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With the termination of operation of the PEP-II storage rings for high energy physics at hand, and with the migration of accelerator operation at SLAC in general to photon science applications, a study of the potential conversion of the PEP-II to a future light source has been initiated. With a circumference of 2.2 km and the capability for high current operation, it is clear that operating a converted ring at medium energy (3-6 GeV) could offer very low emittance and an average brightness of order 1022, limited primarily by the power handling capacity of photon beam line optical components. Higher brightness in the soft X-ray regime might be reached with partial lasing in long undulators if the emittance is sufficiently low, and high peak brightness could be reached with seeded FEL emission. Advanced pulsed rf technology might be used to generate short bunches and fast switched polarization in soft X-ray rf undulators. An overview of the preliminary findings of the PEP Light Source study group will be presented, including lattice, X-ray source and beam line options.
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