03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

A10 Damping Rings

Paper	Title	Page
MOPLS133	Preliminary Studies of Ion Effects in ILC Damping Rings	867
	G.X. Xia, Eckhard. Elsen DESY, Hamburg
	Ion effects are potentially detrimental to the performance of the damping rings for the International Linear Collider (ILC). In this paper, the ion effects in the damping rings of ILC are briefly reviewed. Fast beam-ion instability (FBII) is studied in the linear regime. The growth rates and the beam blowups due to FBII are analytically calculated and compared for two variants of the ILC damping ring designs (OCS and TESLA) and discussed as a function of the vacuum pressure. Finally, some detailed simulation results are also presented.
MOPLS134	Minimizing Emittance for the CLIC Damping Ring	870
	H.-H. Braun, M. Korostelev, D. Schulte, F. Zimmermann CERN, Geneva E.B. Levitchev, P.A. Piminov, S.V. Sinyatkin, P. Vobly, K. Zolotarev BINP SB RAS, Novosibirsk
	The CLIC damping rings aim at unprecedented small normalized equilibrium emittances of 3.3 nm vertical and 550 nm horizontal, for a bunch charge of 2.6 109 particles and an energy of 2.4 GeV. In this parameter regime the dominant emittance growth mechanism is intra-beam scattering. Intense synchrotron radiation damping from wigglers is required to counteract its effect. Here the overall optimization of the wiggler parameters is described, taking into account state-of-the-art wiggler technologies, wiggler effects on dynamic aperture, and problems of wiggler radiation absorption. Two technical solutions, one based on superconducting magnet technology and the other on permanent magnets, are presented. Although dynamic aperture and tolerances of this ring design remain challenging, benefits are obtained from the strong damping. Only bunches for a single machine pulse need to be stored, making injection/extraction particularly simple and limiting the synchrotron-radiation power. With a 360 m circumference, the ring remains comparatively small.
MOPLS135	Correction of Vertical Dispersion and Betatron Coupling for the CLIC Damping Ring	873
	M. Korostelev, F. Zimmermann CERN, Geneva
	The sensitivity of the CLIC damping ring to various kinds of alignment errors have been studied. Without any correction, fairly small vertical misalignments of the quadrupoles and, in particular, the sextupoles, introduce unacceptable distortions of the closed orbit as well as intolerable spurious vertical dispersion and coupling due to the strong focusing optics of the damping ring. A sophisticated beam-based correction scheme has been developed to bring the design target emittances and the dynamic aperture back to the ideal value. The correction using dipolar correctors and several skew quadrupole correctors allows a minimization of the closed-orbit distortion, the cross-talk between vertical and horizontal closed orbits, the residual vertical dispersion and the betatron coupling.
MOPLS136	Ion Effects in the Damping Rings of ILC and CLIC	876
	F. Zimmermann, W. Bruns, D. Schulte CERN, Geneva
	We discuss ion trapping, rise time of the fast beam-ion instability, and ion-induced incoherent tune shift for various incarnations of the ILC damping rings and for CLIC, taking into account the different regions of each ring. Analytical calculations for ion trapping are compared with results from a new simulation code.
MOPLS137	Tracking Studies to Determine the Required Wiggler Aperture for the ILC Damping Rings	879
	I. Reichel LBNL, Berkeley, California A. Wolski Liverpool University, Science Faculty, Liverpool
	The injection efficiency of an ILC damping ring is closely tied to its acceptance. To maximize both, one wants a physical aperture as large as possible in the wiggler magnets, as these are the limiting physical apertures in the ring. On the other hand, a small aperture in the wiggler magnets is needed to achieve the required field profile, a high magnetic field that is very linear over the whole physical aperture of the magnet. Tracking studies were done for all proposed ILC damping ring lattices to determine their required apertures. Although a half-aperture of 8 or 10 mm had been proposed, our studies showed that, for most lattices, a 16 mm half-aperture is required. (For some lattices a 12 mm half aperture might suffice.) We present here the results of our studies, which led to adopting a 16 mm half-aperture in the current ILC damping ring baseline design.
MOPLS138	Space Charge and Equilibrium Emittances in Damping Rings	882
	M. Venturini LBNL, Berkeley, California K. Oide KEK, Ibaraki A. Wolski Liverpool University, Science Faculty, Liverpool
	The unusual combination of small beam size and long ring circumference may cause space charge to have noticeable effects on the beam dynamics of the ILC (International Linear Collider) damping rings. One possible consequence is a modification of the vertical equilibrium emittance resulting from a non-ideal lattice. One simple way to account for this effect is to model space charge in the linear approximation within the framework of Oide's envelope (or Chao's matrix) formalism, whis is commonly used to calculate equilibrium emittances in lepton storage rings. However, this model would likely overestimate the effect as a linear approximation for space charge is accurate only in a small neighborhood of a bunch center. For a more accurate modelling, we propose to make use of Sacherer's envelope equations consisting of a closed set of equations for the second moments of a beam distribution that account for the nonlinear dependence of the space-charge force. Here we will illustrate how Sacherer's equations can be combined with Oide's formalism and apply the result to the ILC damping rings.
MOPLS139	Choosing a Baseline Configuration for the ILC Damping Rings	885
	A. Wolski Liverpool University, Science Faculty, Liverpool J. Gao IHEP Beijing, Beijing S. Guiducci INFN/LNF, Frascati (Roma)
	The damping rings for the International Linear Collider must be capable of accepting large beams from the electron and positron sources, and producing highly damped beams meeting demanding stability specifications, at the machine repetition rate of 5 Hz. Between March and November 2005, a program of studies was undertaken by an international collaboration of 50 researchers to compare a number of configuration options, including ring circumferences between 3 and 17 km. Here, we outline the studies and discuss the principal considerations in the choices of the baseline and alternative damping ring configurations.
MOPLS140	Tuning Algorithms for the ILC Damping Rings	888
	J.K. Jones CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
	Emittance preservation is an important aspect in the design and running of the International Linear Collider with a direct consequence on the luminosity of the machine. One major area of concern is in the damping rings, where the extracted emittances set the effective lower limits for the rest of the machine. Algorithms for tuning this system have been investigated, and simulations have been performed to understand the design and implementation issues. The different algorithms have been applied to the various damping ring designs, and the effectiveness of each algorithm has been assessed. A preliminary recommendation of tuning algorithm, and its effectiveness under various conditions, is given.
MOPLS141	The Proposed Conversion of CESR to an ILC Damping Ring Test Facility	891
	M.A. Palmer, R.W. Helms, D. L. Rubin, D. Sagan, J.T. Urban Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York M. Ehrlichman University of Minnesota, Minneapolis, Minnesota
	In 2008 the Cornell Electron Storage Ring (CESR) will end nearly three decades of providing electron-positron collisions for the CLEO experiment. At that time it will be possible to reconfigure CESR as a damping ring test facility, CesrTF, for the International Linear Collider (ILC) project. With its complement of 12 damping wigglers, CesrTF will offer horizontal emittances in the few nanometer range and, ideally, vertical emittances approaching those specified for the ILC damping rings. An important feature of the CesrTF concept is the ability to operate with positrons or electrons. Positron operation will allow detailed testing of electron cloud issues critical for the operation of the ILC positron damping rings. Other key features include operation with wigglers that meet or exceed all ILC damping ring requirements, the ability to operate from 1.5 to 5.5 GeV beam energies, and the provision of a large insertion region for testing damping ring hardware. We discuss in detail the CesrTF machine parameters, critical conversion issues, and experimental reach for damping ring studies.
MOPLS142	Optimization of CESR-c Superferric Wiggler for the International Linear Collider Damping Rings	894
	J.T. Urban, G. Dugan, M.A. Palmer Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
	We present the results of an optimization of the Cornell Electron Storage Ring (CESR) superferric wiggler for the International Linear Collider (ILC) damping ring. The superferric CESR wiggler has been shown to have excellent beam dynamics properties in the ILC damping ring. We reduced the physical size, and hence cost, of the CESR wiggler with minimal degradation of ILC damping ring beam dynamics. We will provide a description of the optimized superferric wiggler and show the performance of this wiggler in the ILC baseline damping ring.
MOPLS143	Suppression of Secondary Emission in a Magnetic Field using Sawtooth Surface	897
	L. Wang, T.O. Raubenheimer, G.V. Stupakov SLAC, Menlo Park, California
	The effect of surface roughness on the secondary electron emission from a sawtooth surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. Some of the secondary electrons emitted from the sawtooth surface return to the surface within their first few gyrations, resulting in low effective secondary electron yield. A sawtooth surface in magnetic field can significantly reduce the secondary emission yield below the multipacting threshold.
WEYPA02	Damping Rings towards Ultra-low Emittances	1857
	S. Guiducci INFN/LNF, Frascati (Roma)
	The presentation will review the various designs of Damping Rings to achieve ultra-low emittance beams in Linear Colliders (ILC and CLIC) pointing out the major issues both from the beam dynamics and the technological point of vue and comparing the required performances with the one achieved in SLC or FFTB. It will then present the design, beam simulations, benchmarking and performances already achieved in test facilities, especially the ATF1 facility developed and operated at KEK. Finally, it will present future R&D plans and schedule in terms of beam performances, beam stability and technological development as well as the world-wide organization to achieve them.
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