EPAC08 - Classification:03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques/A10 Damping Rings

03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

A10 Damping Rings

Paper	Title	Page
MOPP049	Collective Effects in the CLIC Damping Rings	658
	G. Rumolo, J. B. Jeanneret, Y. Papaphilippou, D. Quatraro CERN, Geneva
	The possible performance limitations coming from collective effects in the CLIC damping rings are the subject of this paper. In particular, the consequences of space charge, due to the very high beam brilliance, and of the resistive wall impedance, due to the locally very small beam pipe, are considered potentially dangerous in spite of the high beam energy. Hence, they have been studied in detail with the HEADTAIL code, which has been modified in order to take into account a finer lattice structure as well as multi-bunch effects of the resistive wall wake field. The study aims at setting the intensity thresholds determined by these phenomena.
MOPP050	Electron Cloud Build Up and Instability in the CLIC Damping Rings	661
	G. Rumolo, Y. Papaphilippou CERN, Geneva W. Bruns WBFB, Berlin
	Electron cloud can be formed in the CLIC positron damping ring and cause intolerable tune shift and beam instability. 2D and 3D build up simulations with the Faktor2 code, developed at CERN, have been done to predict the cloud formation in the arcs and wigglers of the damping rings. HEADTAIL simulations have been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.
MOPP051	Effect of Fill Patterns on Extraction Jitter in Damping Rings	664
	K. M. Hock, A. Wolski Cockcroft Institute, Warrington, Cheshire
	Injection of fresh bunches into a storage ring can induce jitter on stored bunches, as a result of wake field coupling. This transient effect can lead to an undesirable increase in the emittance of stored bunches; in the case of linear collider damping rings, there can also be jitter in the extracted bunches, which can adversely affect performance. We consider how the wake field coupling in a storage ring depends on the fill pattern, and, for the ILC damping rings, present the results of simulations of the transverse dynamics with a resistive wall wake field for a number of different fill patterns. We draw correlations between the extraction jitter and various machine parameters, including the fill pattern.
MOPP055	A Comparison of Tuning Strategies for a Linear Collider Damping Ring	667
	J. K. Jones STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
	Emittance preservation is an important aspect in the design and running of any new Linear Collider design, with a direct consequence on the luminosity of the machine. Damping rings provide the lower limit on achievable emittance, and so are designed to produce as small a vertical emittance as possible, not only for luminosity considerations, but also to relax tolerances in downstream, emittance diluting, systems. Maintaining such small emittances requires that the damping ring emittance is regularly “tuned”. Several methods of damping ring tuning are investigated, and analysed both in terms of their relative effectiveness, under a variety of conditions, and the non-monetary cost involved in implementing and using the various algorithms.
MOPP056	Beam Coupling Impedance in the ILC Damping Rings	670
	M. Korostelev, O. B. Malyshev, A. Wolski Cockcroft Institute, Warrington, Cheshire A. F. Grant, J. Lucas STFC/DL, Daresbury, Warrington, Cheshire
	The ILC damping rings have stringent specifications for beam quality and stability. To avoid instabilities, the various components in the vacuum chamber will need to be carefully designed to minimize the longitudinal and transverse wake fields. We present the results of impedance calculations for various components that are expected to make a significant contribution to the overall machine impedance.
MOPP057	ILC DR Vacuum Design and E-cloud	673
	O. B. Malyshev STFC/DL/ASTeC, Daresbury, Warrington, Cheshire W. Bruns WBFB, Berlin
	An electron cloud parameters and vacuum design are tightly bounded to each other. Input parameters for the e-cloud depend on shape of vacuum chamber and surface property (material, roughthness, coatings, etc.), electron multipacting in the vacuum chamber causes the electron stimulated gas desorption and may require modification of vacuum system to deal with it. This paper describes the e-cloud modelling performed in a way to optimise ILC DR vacuum design in positron ring and to have clear understanding what modification in vacuum chamber are required. Three parameters of e-cloud were varied in turn: photo-electron emission, secondary electron yield and gas pressure. It was found all three parameter should not exceed certain value to keep the e-cloud density to an acceptable level. The energy and intensity of electron bombardment of the vacuum chamber walls and electron stimulated gas desorption were also calculated. It was found that electron stimulated gas desorption is comparable or larger than the photon stimulated desorption and should be considered in vacuum design.
MOPP059	Study for ILC Damping Ring at KEKB	676
	K. Ohmi, J. W. Flanagan, H. Fukuma, K.-I. Kanazawa, H. Koiso, M. Masuzawa, Y. Ohnishi, K. Oide, Y. Suetsugu, M. Tobiyama KEK, Ibaraki M. T.F. Pivi SLAC, Menlo Park, California
	ILC damping ring consists of very low emittance electron and positron storage rings. It is necessary for ILC damping ring to study electron cloud effects in such low emittance positron ring. We propose a low emittance operation of KEKB to study the effects.
MOPP060	Parameter Scan for the CLIC Damping Rings	679
	Y. Papaphilippou, H.-H. Braun, M. Korostelev CERN, Geneva
	Triggered by the RF frequency reduction of the CLIC main linac cavities, the damping ring parameters had to be reevaluated and the rings' performance adapted to the new luminosity requirements. In view of a staged approach for reaching the ultimate energy of the collider, the dependence of the rings output emittances under the influence of Intrabeam Scattering is evaluated with respect to different beam characteristics such as bunch population, beam energy, coupling and longitudinal beam characteristics.
MOPP061	Non Linear Dynamics Study of the CLIC Damping Rings Using Sympletic Integrators	682
	Y. Papaphilippou CERN, Geneva Ch. Skokos IMCCE, Paris
	A class of symplectic integrators with positive steps (SABA₂) is applied to investigate the non-linear dynamics of the CLIC damping rings. The detrimental effect of the chromaticity sextupoles is studied using frequency and diffusion maps and verified with MADX ptc dynamic aperture tracking. The reduction of the dynamic aperture for off-momentum particles is also investigated.
MOPP062	Optics Design Considerations for the CLIC Pre-damping Rings	685
	Y. Papaphilippou CERN, Geneva F. Antoniou National Technical University of Athens, Zografou
	The CLIC pre-damping rings have to accommodate a large emittance beam, coming in particular from the positron source and reduce its size to low enough values for injection into the main damping rings. Linear lattice design options based on an analytical approach for theoretical minimum emittance cells are presented. In particular the parameterisation of the quadrupole strengths and optics functions with respect to the emittance and drift lengths is derived. Complementary considerations regarding constraints imposed by positron stacking and input momentum spread are also considered.
MOPP063	A New Chicane Experiment in PEP-II to Test Mitigations of the Electron Cloud Effect for Linear Colliders	688
	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
	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.
MOPP064	Secondary Electron Yield Measurements and Groove Chambers Update Tests in the PEP-II Beam Line	691
	M. T.F. Pivi, F. King, R. E. Kirby, T. W. Markiewicz, T. O. Raubenheimer, J. Seeman, L. Wang SLAC, Menlo Park, California
	In the Low Energy Ring (LER) of the PEP-II accelerator, we have installed vacuum chambers with rectangular grooves in straight sections to test this possible mitigation technique for the electron cloud effect in the positron damping ring (DR) of the future Linear Colliders such as ILC and CLIC. We have also installed chambers to monitor the secondary electron yield (SEY) of TiN, TiZrV (NEG) and technical accelerator materials under the effect of electron and photon conditioning in situ. Furthermore, we have also installed test chambers in a new 4-magnet chicane. We describe the ongoing R&D effort to mitigate the electron cloud effect in the ILC damping ring, the chambers installation in the PEP-II and latest results.
MOPP065	Microwave Transmission Measurement of the Electron Cloud Density in the Positron Ring of PEP-II	694
	M. T.F. Pivi, A. Krasnykh SLAC, Menlo Park, California J. M. Byrd, S. De Santis, K. G. Sonnad LBNL, Berkeley, California F. Caspers, T. Kroyer, F. Roncarolo CERN, Geneva
	Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.
MOPP066	Recent Experimental Study of Fast Ion Instability in ATF Damping Ring	697
	N. Terunuma, Y. Honda, T. Naito, J. Urakawa KEK, Ibaraki Eckhard. Elsen, G. X. Xia DESY, Hamburg
	The Fast Ion Instability (FII) is one of the very high priorities of the damping ring R&D for the International Linear Collider (ILC). The Accelerator Test Facility (ATF) in KEK can provide an ILC damping ring-like beam. A specific FII study in ATF has been launched to characterize this phenomenon for the ILC damping ring. A new gas inlet system has been installed recently in the ATF damping ring to control the ion effect. After N2 gas injection into the vacuum chamber in south straight section of the ring, FII has been observed for elevated gas pressures. Beam size blow-up and emittance growth for various fill patterns are presented in this paper and attributed to FII. Comparison between experimental data and simulation results are given as well.
MOPP067	Coupling Correction Simulations for the ILC Damping Rings	700
	K. G. Panagiotidis, A. Wolski Cockcroft Institute, Warrington, Cheshire
	The ILC damping rings are specified to operate with a vertical emittance of 2 pm. To achieve this challenging goal, an effective diagnostic and correction system will be needed; however, BPMs add impedance to the ring, and diagnostics and correctors add complexity and cost. It is therefore desirable to understand how the final achievable emittance depends on the numbers, locations, and performance of the BPMs and correctors, and to determine the minimum number of these components required. We present the results of simulations for the damping rings, indicating the effectiveness of coupling correction for different design scenarios of the diagnostics and correction systems.
MOPP068	Simulation Study of Fast Ion Instability in the ILC Damping Ring	703
	G. X. Xia, Eckhard. Elsen DESY, Hamburg
	The so-called fast ion instability potentially constitutes a performance limitation for the damping ring of the International Linear Collider (ILC). Based on the latest baseline lattice of the ILC damping ring the fast ion instability is simulated using a weak-strong code. Various fill patterns are examined to mitigate the onset of the instability. Feedback mechanisms are explored. The growth time of the fast ion instability is estimated for various vacuum pressures on the basis of the simulated results.