• S. Appel, T. Weiland
  TEMF, TU Darmstadt, Darmstadt
• O. Boine-Frankenheim
  GSI, Darmstadt

For the future operation as an injector for the FAIR project the SIS18 synchrotron has to deliver intense and high quality ion bunches with high repetition rate. One requirement is that the initial momentum spread of the injected coasting beam should not exceed the limit set by the SIS18 rf bucket area. Also the Schottky spectrum should be used to routinely measure the momentum spread and revolution frequency directly after injection. During the transverse multi-turn injection the SIS18 is filled withμbunches from the UNILAC linac at 36 MHz. For low beam intensities theμbunches debunch within a few turns and form a coasting beam with a Gaussian-like momentum spread distribution. With increasing intensity we observe persistent current fluctuations and an accompanying pseudo-Schottky spectrum. We will explain that the multi-stream instability of theμbunch filaments is responsible for the turbulent current spectrum that can be observed a few 100 turns after injection. The current spectrum observed in the SIS18 and the results from a longitudinal simulation code will compared to an analytical model of the multi-stream instability induced by the space charge impedance.

• F.B. Petrov, T. Weiland
  TEMF, TU Darmstadt, Darmstadt
• O. Boine-Frankenheim
  GSI, Darmstadt

Electron clouds generated by residual gas ionization pose a potential threat to the stability of the circulating heavy ion beams in the existing SIS-18 synchrotron and in the projected SIS-100. The electrons can potentially accumulate in the space charge potential of the long bunches. As an extreme case we study the accumulation of electrons in a coasting beam under conditions relevant in the SIS-18. Previous studies of electron clouds in coasting beams used Particle-In-Cell (PIC) codes to describe the generation of the cloud and the interaction with the ion beam. PIC beams exhibit much larger fluctuation amplitudes than real beams. The fluctuations heat the electrons. Therefore the obtained neutralization degree is strongly reduced, relative to a real beam. In our simulation model we add a Langevin term to the electron equation of motion in order to account for the heating process. The effect of natural beam fluctuations on the neutralization degree is studied. The modification of the beam response function as well as the stability limits in the presence of the electrons is discussed. Finally we will also address the electron accumulation in long bunches.

• W.M. Daqa
  IAP, Frankfurt am Main
• O. Boine-Frankenheim, I. Hofmann, V. Kornilov, J. Struckmeier
  GSI, Darmstadt

For high current synchrotrons and for the SIS18 operation as booster of the projected SIS100 it is important to improve the multi-turn injection efficiency. This can be achieved by coupling the transverse planes with skew quadrupoles, which can move the particles away from the septum. Linear betatron coupling by skew quadrupole components in SIS18 including space charge effect was studied in an experiment using different diagnostic methods during the crossing of the difference coupling resonance. The beam loss was measured using a fast current transformer, the transverse emittance exchange was observed using a residual gas monitor and the coupled tunes were obtained from the Schottky noise spectrum. We compared the experimental results with simulation using PARMTRA which is a code developed at GSI.

• M. Klein, N. Hiller, P.F. Tavares
  KIT, Karlsruhe
• A.-S. Müller, K.G. Sonnad
  FZK, Karlsruhe

The ANKA light source is regularly operated with a low momentum compaction factor lattice where short bunches are created for the generation of coherent synchrotron radiation (CSR). Short bunches with high electron density can generate strong self fields which act back on the bunch. This can lead to bunch shape deformation and a microbunching instability which were studied theoretically for the ANKA low alpha parameters (Klein et al. PAC 09). We extended these studies to a comparison of calculated electron distributions and bunch profiles measured with a streak camera. The Haissinski equation was solved for the CSR impedance to obtain a prediction for the distortion of the bunches for different bunch lengths and bunch currents. The comparison shows that the theory predicts a much stronger deformation caused by CSR than the streak camera observes. However, high frequency components of measured FTIR spectra show a clear indication for strong deformation or small

• A. Markoviḱ, G. Pöplau, U. van Rienen
  Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock

The electron cloud, which is initially presumed as a homogeneous distribution of static electrons, changes its transverse centroid position very fast during the passage of even a single bunch. This is due to the strong focusing transverse field of the highly relativistic positron bunch. As the density of the electrons near the beam axis grows, its impact on the beam becomes stronger. The interaction of the electron cloud with the bunch results with the shift of the betatron tune of the coherent dipole motion of the beam. In this paper we simulated the dipole tune shift of the beam interacting with the electron cloud by taking also in to account the own space-charge forces of the electrons which strongly affect the motion of the electrons during the passage of the bunch. We computed the tune shift for different transverse size and density of the electron cloud.

• T. Ieiri
  KEK, Ibaraki

KEKB, an asymmetric electron/positron double-ring collider, utilizes the crab cavity to perform the head-on collision at the interaction point. We observed peculiar phenomena at the transition from the collision to non-collision, where the bunch length slightly changed, even though the beam current and the RF related parameters were almost constant. We also observed that the transverse beam size of both beams changed at the transition. An experimental study was carried out to investigate whether the bunch length would change or not, when the vertical beam size was intentionally changed. The bunch length was measured using a monitor based on the beam spectrum with a resolution of 0.01 mm. We found that the bunch length slightly changed together with the vertical beam size under non-colliding condition. We expect that the change in the bunch length is not caused by the colliding effects, but is related to the longitudinal space charge transformed from the transverse plane. Since the longitudinal space charge effect is negligible for the relativistic beams, some tilting effect of a bunch is suspected.

• T. Ieiri, J.W. Flanagan, H. Fukuma, Y. Ohnishi, M. Tobiyama
  KEK, Ibaraki

Electron cloud instabilities are a great concern for the KEKB, an electron/positron collider. In order to study wakefield effects of electron cloud, a test bunch was injected behind a bunch train with the solenoid fields off, where cloud density rapidly decayed. A current-dependent tune shift and the tune spread of a test bunch were measured as a function of the bunch current while varying the bucket position of a test bunch. The vertical tune shift indicated a strong defocusing force together with widened tune spread in a region of relatively low cloud density and low bunch current. However, the vertical tune shift changed to a focusing force at high cloud density and high bunch current. On the other hand, the horizontal and vertical tune spreads tended to approach a constant value as increasing the bunch current. The turning current is approximately equal to the threshold current of the vertical size blow-up.

• A.Y. Molodozhentsev, T. Koseki, M.J. Shirakata, M. Tomizawa
  KEK, Ibaraki
• A. Ando, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken

During the early J-PARC Main Ring commissioning and the machine operation with the moderate beam power the 'fast extraction' bare working point has been chosen to provide the machine operation in the safe regime. We discuss main experimental results obtained so far and compare with the results of the computational model of the machine, including the first experimental approach to minimize the effect of the 'sum' linear coupling resonance. The strategy to increase the beam power without changing the operational working point is presented by keeping the moderate space-charge detuning. The advantage of the second harmonic MR RF cavity, including the estimation of the beam losses during the injection and acceleration processes, is discussed.

• M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, F. Tamura
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, M. Tada, A. Takagi, K. Takata, M. Yoshii
  KEK, Ibaraki

The Longitudinal emittance in J-PARC RCS should be controlled to accelerate a high intensity proton beam with minimal beam loss. In order to study and minimize the beam loss during acceleration, the optimized way to add the 2nd higher harmonic rf has been calculated by a particle tracking code. Furthermore, the bunch shape at RCS extraction should be controlled and optimized for the MR injection. For this purpose, the optimum RCS acceleration pattern has been calculated. We describe the simulation results and the comparison with the beam test.

• P.-CH. Yu, J. Wei
  TUB, Beijing
• Z.Q. He
  Tsinghua University, Beijing
• H. Okamoto
  HU/AdSM, Higashi-Hiroshima
• A. Sessler
  LBNL, Berkeley, California
• Y. Yuri
  JAEA/TARRI, Gunma-ken

During the beam crystallization process, the main heating source is Intra-beam scattering (IBS), in which the Coulomb collisions among particles lead to a growth in the 6D phase space volume of the beam. The results of molecular dynamics (MD) simulation have shown an increase of heating rate as the temperature is increased from absolute zero, but then a peak in the heating rate, and subsequent decrease with ever increasing temperature*. This phenomenon has been carefully studied by Y. Yuri, H. Okamoto, and H. Sugimoto**. On the other hand, in the traditional IBS theory valid at high temperatures, heating rate is monotonically increasing as the temperature becomes lower***. In this paper we attempt to understand the "matching" at low temperatures between the MD results and traditional IBS theory, by including many body effects in the traditional IBS theory. In particular the Debye shielding is included. We shall present how the traditional theory is modified by shielding, and show how this effect improves the "matching" with the results from MD.

* J. Wei, H. Okamoto, and A. Sessler, Phys. Rev. Lett. 80, 2606
** Y.Yuri, H. Okamoto, and H. Sugimoto, J. Phys. Soc. Jpn. 78, 124501
***A. Piwinski, Lect. Notes Phys. 296, 297 (1988)

• L.J. Mao, G.H. Li, J. Li, J.W. Xia, J.C. Yang, X.D. Yang, Y.J. Yuan
  IMP, Lanzhou

Two electron cooling devices have been used at HIRFL-CSR in order to provide high quality heavy ion beams for nuclear and atomic research. The momentum spread is one of the most important characteristics of the beam quality. At HIRFL-CSR, the momentum spread is measured directly with the aid of longitudinal Schottky spectra system. In this paper, the measurements for various ion species are presented. At relatively high intensity, longitudinal Schottky spectra is double peak due to collective phenomena and the momentum spread can be obtained by fitting the spectra. The dependence of momentum spread on stored particle number is proportional to N**a. Moreover, the heating factor was investigated after switching off the electron cooling. The residual gas scattering, the intrabeam scattering and instabilities are studied according to the measured data.

• C. Carli, M. Chanel, B. Goddard, M. Martini, D. Quatraro, M. Scholz
  CERN, Geneva
• M. Aiba
  PSI, Villigen

The performance of the CERN PS Booster (PSB) synchrotron is believed to be limited mainly by direct space charge effects at low energy. The main motivation to construct Linac4 is to raise the PSB injection energy to mitigate direct space charge effects. At present, simulation of the injection and the ow energy part of the cycle aim at defining Investigations on the influence of parameters of the injected beam on the performance of the PSB are described.

• A.I. Papash
  MPI-K, Heidelberg
• O.E. Gorda
  GSI, Darmstadt
• A.I. Papash
  JINR, Dubna, Moscow Region
• C.P. Welsch
  Cockcroft Institute, Warrington, Cheshire

Electrostatic storage rings have proven to be invaluable tools for atomic and molecular physics. Due to the mass independence of the electrostatic rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged bio-molecules. However, earlier measurements showed strong space charge limitations; probably linked to non-linear fields that cannot be completely avoided in such machines. The nature of these effects is not fully understood. In this contribution, we present the results from simulating an electrostatic storage ring under consideration of non-linear fields as well as space charge effects using the computer code SCALA.

• P. Lebrun, P. Spentzouris
  Fermilab, Batavia
• J.R. Cary
  CIPS, Boulder, Colorado
• P. Stolz, S.A. Veitzer
  Tech-X, Boulder, Colorado

Precision simulations of the electron cloud at the Fermilab Main Injector have been studied using the plasma simulation code VORPAL. Fully 3D and self consistent solutions that includes Yee-type E.M. field maps generated by the cloud and the proton bunches have been obtained, as well detailed distributions of the 6D phase space occupied by the electrons. We plan to include such maps in the ongoing simulation of the space charge effects in the Main Injector. Simulations of the response of retarded field analyzers and microwave transmission experiments are ongoing.

• M.A. Furman
  LBNL, Berkeley, California
• R. De Maria, Y. Papaphilippou, G. Rumolo
  CERN, Geneva

A replacement for the PS storage ring is being considered, in the context of the future LHC accelerator complex upgrade, that would likely place the new machine (the PS2) in a regime where the electron-cloud (EC) effect might be an operational limitation. We report here our present understanding of the ECE build-up based on simulations. We focus our attention on the bending magnets and the field-free regions, and consider both proposed bunch spacings of 25 and 50 ns. The primary model parameters exercised are the peak secondary emission yield (SEY) δ_max, and the electron-wall impact energy at which SEY peaks, E_max. By choosing reasonable values for such quantities, and exploring variations around them, we estimate the range for the EC density n_e to be expected in nominal operation. We present most of our results as a function of bunch intensity N_b, and we provide a tentative explanation for a curious non-monotonic behavior of n_e as a function of N_b. We explore the sensitivity of n_e to other variables such as the beam pipe radius in the field-free regions.

• G. Penn, J.-L. Vay
  LBNL, Berkeley, California

The propagation of TE waves is sensitive to the presence of an electron cloud primarily through phase shifts generated by the altered dielectric function, but can also lead to polarization changes and other effects, especially in the presence of magnetic fields. These effects are studied theoretically and also through simulations using WARP-POSINST. Full electromagnetic simulations are performed for CesrTA parameters, and used as a benchmark for simplified phase shift estimates that are also implemented in WARP/POSINST. Nonlinear effects such as electron heating are also examined.

• J. Qiang, R.D. Ryne
  LBNL, Berkeley, California
• R. De Maria
  BNL, Upton, Long Island, New York
• A. Macridin, P. Spentzouris
  Fermilab, Batavia
• Y. Papaphilippou
  CERN, Geneva
• U. Wienands
  SLAC, Menlo Park, California

A new proton synchrotron, the PS2, is under design study to replace the the current proton synchrotron at CERN for the LHC upgrade. Nonlinear space charge effects could cause significant beam emittance growth and particle losses and limit the performance of the PS2. In this paper, we report on studies of the potential space-charge effects at the PS2 using three-dimensional self-consistent macroparticle tracking codes, IMPACT, MaryLie/IMPACT, and Synergia. We will present initial benchmark results among these codes. Effects of space-charge on the emittance growth, especially due to synchrotron coupling, and the aperture sizes will also be discussed.

• E.W. Nissen, B. Erdelyi
  Northern Illinois University, DeKalb, Illinois
• S.L. Manikonda
  ANL, Argonne

This research involves a method for combining the intricate diagnostic tools for calculating quantities of interest such as tunes, dispersion and resonances from the single particle map of the system, with an accurate approximation of space charge effects on the beam. The space charge calculation involves a novel method of potential integration which allows for rapid Taylor expansion around singularities. This will allow for an accurate computation of space charge induced tune shifts and resonances, as well as allowing for experimental setups to discriminate between space charge caused issues, and lattice caused issues. The code used was COSY Infinity 9.0 which uses Differential Algebras to determine numerical derivatives to arbitrary order, and Normal Form methods to extract information from the map. The effects of space charge are added to the map using Strang splitting. External confounding factors such as the earths magnetic field are also addressed.

• J.R. Calvey, J.A. Crittenden, G. Dugan, S. Greenwald, Z. Leong, J.A. Livezey, M.A. Palmer
  CLASSE, Ithaca, New York
• C.M. Celata
  Cornell University, Ithaca, New York
• M.A. Furman, M. Venturini
  LBNL, Berkeley, California
• K.C. Harkay
  ANL, Argonne

Retarding field analyzers (RFAs) provide an effective measure of the local electron cloud density and energy distribution. Proper interpretation of RFA data can yield information about the behavior of the cloud, as well as the surface properties of the instrumented vacuum chamber. However, due to the complex interaction of the cloud with the RFA, particularly in regions of high magnetic field, understanding these measurements can be nontrivial. This paper will examine different methods for interpreting RFA data via cloud simulation programs. Possible techniques include postprocessing the output of a simulation code to predict the RFA response, and incorporating an RFA model into the program itself.

• J.R. Calvey, Y. Li, J.A. Livezey, J. Makita, R.E. Meller, M.A. Palmer, R.M. Schwartz, C.R. Strohman
  CLASSE, Ithaca, New York
• S. Calatroni, G. Rumolo
  CERN, Geneva
• K.C. Harkay
  ANL, Argonne
• K. Kanazawa, Y. Suetsugu
  KEK, Ibaraki
• M.T.F. Pivi, L. Wang
  SLAC, Menlo Park, California

Over the course of the CesrTA program, the Cornell Electron Storage Ring (CESR) has been instrumented with several retarding field analyzers (RFAs), which measure the local density and energy distribution of the electron cloud. These RFAs have been installed in drifts, dipoles, quadrupoles, and wigglers; and data have been taken in a variety of beam conditions and bunch configurations. This paper will provide an overview of these results, and give a preliminary evaluation of the efficacy of cloud mitigation techniques implemented in the instrumented vacuum chambers.

• J.A. Crittenden, J.R. Calvey, G. Dugan, D.L. Kreinick, Z. Leong, J.A. Livezey, M.A. Palmer, D. L. Rubin, D. Sagan
  CLASSE, Ithaca, New York
• M.A. Furman, G. Penn, M. Venturini
  LBNL, Berkeley, California
• K.C. Harkay
  ANL, Argonne
• R. Holtzapple
  CalPoly, San Luis Obispo, CA
• M.T.F. Pivi, L. Wang
  SLAC, Menlo Park, California

The Cornell Electron Storage Ring Test Accelerator (CesrTA) program has included extensive measurements of coherent tune shifts for a variety of electron and positron beam energies, bunch current levels, and bunch train configurations. The tune shifts have been shown to result primarily from the interaction of the beam with the space-charge field of the beam-induced low-energy electron cloud in the vacuum chamber. Comparison to several advanced electron cloud simulation program packages has allowed determination of the sensitivity of these measurements to physical parameters such as the synchrotron radiation flux, its interaction with the vacuum chamber wall, the beam emittance and lattice optics, as well as to those of the various contributions to the electron secondary yield model. We report on progress in understanding the cloud buildup and decay mechanisms in magnetic fields and in field-free regions, addressing quantitatively the precise determination of the physical parameters of the modelling. Validation of these models will serve as essential input in the design of damping rings for future high-energy linear colliders.

• R.T. Dowd, M.J. Boland, G. LeBlanc, Y.E. Tan
  ASCo, Clayton, Victoria
• D.J. Peake
  Melbourne

The Australian Synchrotron storage ring must maintain a stable electron beam for user operations. The impedance characteristics of the storage ring can give rise to instabilities that adversely affect the beam quality and need to be well understood. Collective effects driven by the resistive wall impedance are particularly relevant at the Australian synchrotron and their strengths are enhanced by small gap insertion devices, such as IVUs. This study will explore the impedance issues identified in the Australian Synchrotron storage ring and current mitigation techniques.

• P.F. Tavares
  Karlsruhe Institute of Technology (KIT), Karlsruhe
• M. Fitterer, N. Hiller, A. Hofmann, V. Judin, M. Klein, S. Marsching, N.J. Smale, K.G. Sonnad
  KIT, Karlsruhe
• E. Huttel, A.-S. Müller
  FZK, Karlsruhe
• P.F. Tavares
  LNLS, Campinas

We present results of a series of measurements aimed at characterizing the beam coupling impedances in the ANKA electron storage ring. The measurements include transverse coherent tune shifts, bunch lengthening and synchronous phase shift as a function of single bunch current. These were performed under a variety of conditions in the ANKA ring, including injection energy (500 MeV), nominal operating energy (2.5 GeV) as well as at 1.3 GeV and in the low alpha mode and are part of a longer term effort to understand the ANKA impedance over a wide frequency range.

• R. Nagaoka, L. Cassinari, M.D. Diop, M.-P. Level, C. Mariette, R. Sreedharan
  SOLEIL, Gif-sur-Yvette

Ever since the commissioning times, transverse instabilities, which now have been identified as the so called Fast Beam-Ion Instability (FBII), have existed in the SOLEIL storage ring. Though along with the improvement of the vacuum level with increasing beam dose its relative importance has decreased to a large extent as compared to the classical instabilities due to the coupling impedance, the FBII still exists persistently at high current, making it difficult to attain a stable beam at the final goal of 500 mA. In particular, sudden beam losses are frequently encountered after keeping the beam stable over a certain time with transverse feedback at the final current, which raised a question as to whether the observed phenomena are compatible with the saturating effect of the FBII. Experimental analysis using the bunch by bunch feedback diagnostics as well as theoretical and numerical analysis using multibunch tracking have been carried out to understand the instability quantitatively and to elucidate the mechanism of the beam losses.

• V. Kornilov, O. Boine-Frankenheim
  GSI, Darmstadt
• V.V. Kapin
  ITEP, Moscow

Octupole magnets can be used as a passive cure against transverse collective instabilities. The octupole field creates a betatron frequency spread due to amplitude-dependent tune shift and thus enhances Landau damping. The drawback is the reduction of the dynamic aperture (DA). Ultimately, a balance between collective damping and DA must be found. Here we analyse the transverse coherent instability thresholds in SIS100 with octupoles and nonlinear space-charge taken into account. As the major impedance sources at low frequencies, the resistive wall and the kickers are considered. A coasting beam is assumed, which results in a conservative stability estimation. On the other hand, we simulate the DA of the SIS100 lattice using the MADX code, with systematic multipole errors, random multipole errors, and closed-orbit errors taken into account.

• G.X. Xia
  MPI-P, München
• B.C. Jiang
  SINAP, Shanghai
• L.G. Liu
  SSRF, Shanghai

Fast ion instability has been observed in the early commissioning and operation of the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. In this paper, a weak-strong code is used to simulate the fast ion instability in SSRF storage ring. Various fill patterns and gas pressures are investigated. The results show that the mini-train fill patterns are very effective to suppress the growth of the fast ion instability. By employing a fast feedback system, it is possible to damp the growth of beam oscillation amplitude below the beam size.

• L. Schächter
  Technion, Haifa

Electron cloud confined to move in the vertical direction by either the wiggler field or a dipole field has been investigated extensively. We present results of an analysis demonstrating that electrons may be trapped in the region of zero vertical field of a wiggler. Their characteristic frequency and life-time are established and some of the implications are discussed.

• M.M. El-Ashmawy, G. D'Auria
  ELETTRA, Basovizza
• M.M. Dehler, J.-Y. Raguin
  PSI, Villigen
• G. Riddone, R. Zennaro
  CERN, Geneva

FERMI@ELETTRA and PSI-XFEL are 4th Generation Light Sources that require high quality electron beam at the entrance of the undulator chains. In this context, a specially developed X-band structure with integrated alignment monitors will be used to mitigate the nonlinearities in the longitudinal phase space due to the second order RF time curvature and the second order momentum compaction term of chicane compressor. The knowledge of the transverse and longitudinal short range wakefields in the X-band structure is essential to evaluate the beam quality in terms of longitudinal energy spread and transverse kick spread. We have used the ABCI code to numerically evaluate the transverse and longitudinal wake potentials for short bunches in this structure.

• M.M. El-Ashmawy, G. D'Auria
  ELETTRA, Basovizza

FERMI@ELETTRA is a single pass FEL Facility in construction at the ELETTRA Laboratory in Trieste. To linearize the beam longitudinal phase space, it is planned to use a short X-band accelerating structure installed before the first bunch compressor. Since both the end tubes of the structure have a reduced radius of 5.0 mm, much smaller than the 13.5 mm radius of the beam pipes before and after the structure, a transition, either stepped or tapered, will be necessary between the two components. Using the ABCI code, we have investigated the short range wake fields at the step-out and taper-out transitions and we have compared them with some conventional analytical models. We have developed specific ABCI-based analytical models that simulate accurately the short range wake field for a wide range of rms bunch lengths (σ: 100 - 1000μm).

• M.M. El-Ashmawy, G. D'Auria
  ELETTRA, Basovizza

In most of the Linac based 4th Generation Light Sources now under development (e.g. FERMI@ELETTRA [1]), a short accelerating structure operating at higher harmonics (i.e. X-band, 12 GHz), is adopted to linearize the beam's longitudinal phase space [2]. This structure could be either travelling wave (TW) or standing wave (SW) type. As it is well known, each one of such structures has its own advantages and drawbacks in terms of RF properties but there is a lack of information about the wake fields of each type compared to the other. In this paper an overall comparison, from the wakefields point of view, of two different X-band structures will be carried out. The purpose is to evaluate quantitatively the longitudinal and transverse wake functions of the structures, determining their relevant wake integrals, such as the average value of energy loss, rms energy spread, kick factor and kick spread.

• M.M. El-Ashmawy, G. D'Auria
  ELETTRA, Basovizza

Step-out transition is one of the most frequent component, commonly used on the new generation light source facilities where very short and dense electron bunches are considered. The numerical calculation of the short-range wake at this type of transition requires a spatial mesh size equal to a fraction of bunch length. This calculation becomes for a very short bunch, e.g. σ = 25μm, very time consuming due to the large number of mesh points required. On the other hand, the available analytical models that calculate the transverse wake field are applicable only on a narrow range of bunch lengths. We developed an ABCI-based analytical model that can calculate accurately the kick factor. The advantage of this model is quick, accurate and covers wide range of rms bunch lengths (up to σ = 1000μm). The model also covers a wide range of beam pipe ratio b/a.

• T. Demma
  INFN/LNF, Frascati (Roma)
• S. Petracca, A. Stabile
  U. Sannio, Benevento

The bunch-to-bunch evolution of the electron cloud density can be modeled using a cubic map. The map approach has been proved reliable for RHIC* and LHC**. The coefficients that parameterize the map may be obtained by fitting from time consuming numerical simulations. In this communication we derive a simple approximate formula for the quadratic coefficient, which determines the saturation of the cloud due to space charge, in the electron cloud density map, under the assumptions of round chambers and free-field motion of the elctrons in the cloud. Results are compared with simulations for a wide range of parameters governing the evolution of the elctron cloud.

* U.Iriso, S.Peggs, Phys. Rev.STAB 8, 024403, 2005.
** T.Demma, S.Petracca, G.Rumolo, F.Ruggiero, F.Zimmermann, Phys. Rev.STAB 10, 114401, 2007.

• T. Demma
  INFN/LNF, Frascati (Roma)
• M.T.F. Pivi
  SLAC, Menlo Park, California

Some collective effects have been studied for the SuperB* high luminosity collider. Estimates of the effect of Intra Beam Scattering on the emittance and energy spread growths have been carried up for both the High Energy (HER, positrons) and the Low Energy (LER, electrons) rings. Electron cloud build up simulations for HER were performed with the ECLOUD code, developed at CERN**, to predict the cloud formation in the arcs, taking into account possible remediation techniques such as clearing electrodes. The new code CMAD, developed at SLAC***, has 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.

* M. E. Biagini, proceedings of PAC'09.
** F. Zimmermann, CERN, LHC-Project-Report-95, 1997.
*** M. Pivi, proceedings of PAC'09.

• K. Kanazawa, H. Fukuma
  KEK, Ibaraki

The near beam electron cloud density in a magnetic field was estimated with a simple electron current detector at KEKB LER. The estimation is based on the assumption that high energy electrons which hit a chamber wall come directly from the region around the beam after the interaction with a circulating bunch. The first successful application of this idea for a drift space was reported at PAC05 by the authors. In a solenoid field of 50 G, the near beam cloud density is reduced by about four orders of magnitude compared to the no field case. In a quadruple magnet, the density around the beam is by two orders of magnitude lower than the density in a typical drift space, as most simulations show.

• K. Shibata, K. Kanazawa
  KEK, Ibaraki

As part of the design works of the interaction region (IR) of SuperKEKB (the upgrade of KEKB B-factory (KEKB)), the loss factor and impedance of beam ducts for the interaction point (IP duct) were calculated by GdfiedL. The IP duct is round and connected to beam ducts for electron and positron beams with a diameter of 20 mm via Y-shaped crotch ducts at both ends. The lengths of the straight section and crotch section are about 200 mm, respectively. The beam crossing angle is 83 mrad. Calculations for two types of IP duct were performed. Both ducts are almost same in design except for the diameter of the straight section (20 mm and 30 mm). The loss factors were about 0.001 V/pC in both cases when the bunch length was 6 mm. The longitudinal impedances showed that there were no modes trapped longitudinally in IP duct. However, from the results of the transverse impedance and eigenmode calculation, it was found that many TE modes can be trapped at the crotch section if the beam is off-center of the beam duct. For comparison, the loss factor and impedance of the IR beam duct of KEKB are also being calculated now. Full details of the calculation results will be provided in this report.

• Y. Suetsugu, H. Fukuma, K. Shibata
  KEK, Ibaraki
• M.T.F. Pivi, L. Wang
  SLAC, Menlo Park, California

Grooved surfaces are effective to suppress the secondary electron emission, and can be a possible technique to mitigate the electron cloud instability (ECI) in positron/proton storage rings. Various types of triangular grooved surfaces have been studied in a laboratory, and also using an intense positron beam of the KEKB B-factory. The grooves have vertex angles of 20 ~ 30 degrees, and depths of 2.5 mm. In the laboratory, the secondary electron yield (SEY) of sample pieces were measured using an electron beam in a magnetic-free condition. The maximum SEY well below 1.0 was obtained after some extent of electron bombardment for most of grooved surfaces. To test he groove efficacy in magnetic field regions of particle accelerators, insertions with several types of grooved surfaces were installed into a test chamber in a wiggler magnet of KEKB positron ring. In a dipole-like chamber wit magnetic field (0.78 T), the reduction in the electron density around the beam was observed for a grooved section when compared to the case of a flat surface with TiN coating. An R&D effort is underway to optimize and manufacture the grooved surface in accelerator beam pipes for practical use.

• Y. Shobuda, J. Kamiya, M. Watanabe
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• T. Toyama
  J-PARC, KEK & JAEA, Ibaraki-ken

There is the famous formula of the horizontal impedance for the matched-traveling wave kicker. However, the real and the imaginary parts of the impedance do not satisfy the Hilbert transformations. On the other hand, the impedance measured by a loop method does not directly give the beam impedance. In this paper we theoretically derive the beam impedance and reproduce the impedance by using the estimated inductances of the kicker by the loop measurement.

• D. Quatraro, G. Rumolo
  CERN, Geneva

The effects of direct space charge forces on the Transverse Mode Coupling Instability (TMCI) are studied using numerical techniques. We have implemented a third order symplectic integrator for the equation of motion, taking into account non linear space charge forces coming from a Gaussian shaped bunch. We performed numerical simulation for the Super Proton Synchrotron (SPS) bunch at 26 GeV of kinetic energy, using either resistive wall or broad band transverse wake fields. In both cases the result of applying direct space charge, leads to an intensity threshold increase by almost 20% before the TMCI appears. Far above the TMCI intensity threshold, the growth rate is almost 10% higher if no space charge forces are applied.

• D. Quatraro, A. Findlay, B. Mikulec, G. Rumolo
  CERN, Geneva

Since many years the Proton Synchrotron Booster (PSB) high intensity beams have shown head-tail instabilities in all of the four rings at around 100 ms after the injection. In this paper we present the latest observations together with the evaluation of the instability rise time and its dependence on the bunch intensity. The acquired head-tail modes and the growth rates are compared with HEADTAIL numerical simulations, which together with the Sacherer theory points at the resistive wall impedance as a possible source of the instability.

• C. Yin Vallgren, G. Arduini, J. Bauche, S. Calatroni, P. Chiggiato, K. Cornelis, P. Costa Pinto, E. Métral, G. Rumolo, E.N. Shaposhnikova, M. Taborelli, G. Vandoni
  CERN, Geneva

Amorphous carbon coatings with low secondary electron yield have been applied to the liners in the electron cloud monitors and to vacuum chambers of three dipole magnets in the SPS. The electron cloud is completely suppressed for LHC type beams in these monitors even after 3 months air venting and no performance deterioration is observed after more than one year of SPS operation. Upon variation of the magnetic field in the monitors the electron cloud current maintains its intensity down to weak fields of some 40 Gauss, where fast conditioning is observed. This is in agreement with dark traces observed on the RF shields between dipoles. The dynamic pressure rise has been used to monitor the behavior of the magnets. It is found to be about the same for coated and uncoated magnets, apart from a weak improvement in the carbon coated ones under conditions of intense electron cloud. Inspection of the coated magnet is foreseen in order to detect potential differences with respect to the coated monitors. Measurements of the stray fields outside the dipoles show that they are sufficiently strong to induce electron cloud in these regions.

• S. Aumon
  EPFL, Lausanne
• S. Aumon, M. Delrieux, P. Freyermuth, S.S. Gilardoni, E. Métral, G. Rumolo, B. Salvant, R.R. Steerenberg
  CERN, Geneva

Transition crossing in the CERN PS is critical for the stability of high intensity beams, even with the use of a second order gamma jump scheme. The intense single bunch beam used for the neutron Time-of-Flight facility (n-ToF) needs a controlled longitudinal emittance blowup at flat bottom to prevent a fast single-bunch vertical instability from developing near transition. This instability is believed to be of Transverse Mode Coupling (TMCI) type. A series of measurements taken throughout 2008 and 2009 aim at using this TMCI observed on the ToF beam at transition, as a tool for estimating the transverse global impedance of the PS. For this purpose, we compare the measurement results with the predictions of the HEADTAIL code and find the matching parameters. This procedure also allows a better understanding of the different mechanisms involved and can suggest how to improve the gamma jump scheme for a possible intensity upgrade of the n-ToF beam.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

Using B. Zotter's formalism, we present here a novel, efficient and exact matrix method for the field matching determination of the electromagnetic field components created by an offset point charge travelling at any speed in an infinitely long circular multilayer beam pipe. This method improves by a factor of more than one hundred the computational time with three layers and allows the computation for more layers than three. We also generalize our analysis to any azimuthal mode and finally perform the summation on all such modes in the impedance formulae. In particular the exact multimode direct space-charge impedances (both longitudinal and transverse) are given, as well as the wall impedances to any order of precision.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

The exact formalism from B. Zotter to compute beam coupling impedances has been fully developed only in the case of an infinitely long circular beam pipe. For other two dimensional geometries, some form factors are known only in the ultrarelativistic case and under certain assumptions of conductivity and frequency of the pipe material. We present here a new and exact formalism to compute the beam coupling impedances in the case of a collimator-like geometry where the jaws are made of two infinite plates of any linear material. It is shown that the impedances can be computed theoretically without any assumptions on the beam speed, material conductivity or frequency range. The final formula involves coefficients in the form of integrals that can be calculated numerically. This way we obtain new generalized form factors between the circular and the flat chamber cases, which eventually reduce to the so-called Yokoya factors under certain conditions.

• C. Zannini, N. Mounet, E. Métral, G. Rumolo
  CERN, Geneva
• B. Salvant, C. Zannini
  EPFL, Lausanne

The kickers are major contributors to the CERN SPS beam coupling impedance. As such, they may represent a limitation to increasing the SPS bunch current in the frame of an intensity upgrade of the LHC. In this paper, CST Particle Studio time domain electromagnetic simulations are performed to obtain the longitudinal and transverse impedances/wake potentials of simplified models of ferrite loaded kickers. The simulation results have been successfully compared with some existing analytical expressions. In the transverse plane, the dipolar and quadrupolar contributions to the wake potentials have been estimated from the results of these simulations. For some cases, simulations have also been benchmarked against measurements on PS kickers. It turns out that the large simulated quadrupolar contributions of these kickers could explain both the negative total (dipolar+quadrupolar) horizontal impedance observed in bench measurements and the positive horizontal tune shift measured with the SPS beam.

• N. Mounet
  EPFL, Lausanne
• N. Mounet, E. Métral
  CERN, Geneva

In this study B. Zotter's formalism is applied to a circular infinitely long beam pipe made of a conductor of infinite thickness where an offset point-charge travels at any given speed. Simple formulae are found for the impedances and electromagnetic fields both at intermediate frequencies (recovering Chao's results) and in the low frequency regime where the usual classic thick wall impedance formula does not apply anymore due to the large skin depth compared to the pipe radius.

• R. Mutzner, N. Mounet
  EPFL, Lausanne
• T. Pieloni
  PSI, Villigen
• G. Rumolo, R. Tomás
  CERN, Geneva

Wake fields in the CLIC Beam Delivery System (BDS) can cause severe single or multi-bunch effects leading to luminosity loss. The main contributors in the BDS are geometric and resistive wall wake fields of the collimators and resistive wall wakes of the beam pipe. The present work focuses only on the multi-bunch effects from resistive wall. Using particle tracking with wake fields through the BDS, we have established the aperture radius, above which the effect of the wake fields becomes negligible. Our simulations were later extended to include a realistic aperture model along the BDS as well as the collimators. The two cases of 3TeV and 500GeV have been examined in this paper.

• B. Salvant
  EPFL, Lausanne
• N. Mounet, E. Métral, G. Rumolo, B. Salvant, C. Zannini
  CERN, Geneva

The SPS kickers are major contributors to the SPS transverse beam coupling impedance. The current "flat chamber" impedance model for a kicker is obtained by applying form factors to the theoretical impedance of an axisymmetric ferrite beam pipe. This model was believed to be acceptable for the vertical dipolar impedance, as two-wire measurements on SPS kickers revealed a satisfactory agreement. However, one-wire measurements on PS kickers suggested that this model underestimates the kickers' transverse quadrupolar (detuning) impedance. The longitudinal and transverse dipolar impedances of another kicker model that accounts for the metallic plates on each side of the ferrite were derived in the past by H. Tsutsui. The same formalism is used in this paper to derive the quadrupolar impedance. These formulae were then successfully benchmarked to electromagnetic simulations. Finally, simulating the interaction of an SPS bunch with the improved kickers' model results in a positive horizontal tune shift, which is very close to the tune shift measured with the SPS beam.

• B. Salvant
  EPFL, Lausanne
• G. Arduini, O.E. Berrig, F. Caspers, A. Grudiev, N. Mounet, E. Métral, G. Rumolo, B. Salvant, E.N. Shaposhnikova, C. Zannini
  CERN, Geneva
• M. Migliorati, B. Spataro
  INFN/LNF, Frascati (Roma)
• B. Zotter
  Honorary CERN Staff Member, Grand-Saconnex

The beam coupling impedance of the CERN SPS is expected to be one of the limitations to an intensity upgrade of the LHC complex. In order to be able to reduce the SPS impedance, its main contributors need to be identified. An impedance model for the SPS has been gathered from theoretical calculations, electromagnetic simulations and bench measurements of single SPS elements. The current model accounts for the longitudinal and transverse impedance of the kickers, the horizontal and vertical electrostatic beam position monitors, the RF cavities and the 6.7 km beam pipe. In order to assess the validity of this model, macroparticle simulations of a bunch interacting with this updated SPS impedance model are compared to measurements performed with the SPS beam.

• A. Rusanov
  NSRRC, Hsinchu

Taiwan Photon Source (TPS) is a new third generation synchrotron storage ring which will be built at the present site of the NSRRC. The paper summarizes results of the impedance studies of the storage ring vacuum components for the TPS project. The main goal of this work was to support the design of the vacuum chamber and, at the same time, to get a detailed model of the machine impedance, which can be used later for detail studies of collective effects. Wake potentials and impedances for each component of the storage ring have been simulated with a 3D electromagnetic code GdfidL. Numerically obtained data have been compared to analytical results for simplified geometries of the vacuum chamber components.

• A. Rusanov, P.J. Chou
  NSRRC, Hsinchu

Taiwan Photon Source (TPS) is a new third generation synchrotron storage ring which will be built at the present site of the NSRRC. Collective effects in the TPS storage ring have been simulated with tracking code ELEGANT. Quasi-Green's function for the entire ring and coherent synchrotron radiation (CSR) have been taken into account in the simulations. Thresholds of the longitudinal microwave instability and the CSR induced instability have been estimated. Time-dependent sawtooth oscillations of the bunch length at high bunch currents have been analyzed and compared to the bunch length oscillations observed at the SLC damping ring.

• R.J. Barlow, R. Appleby, J. Molson, H.L. Owen, A.M. Toader
  UMAN, Manchester

The collimation system of the LHC will be critical to its success, as the halo of high energy (7 TeV) particles must be removed in such a way that they do not deposit energy in the superconducting magnets which would quench them, or showers in the experiments. We study the properties of the LHC collimation system as predicted by the Merlin and Sixtrack/K2 simulation packages, and compare their predictions for efficiency and halo production, and the pattern of beam losses. The sophisticated system includes many collimators, serving different purposes. Both programs include energy loss and multiple Coulomb scattering as well as losses through nuclear scattering. The MERLIN code also includes the effects of wakefields. We compare the results and draw conclusions on the performance that can be achieved.

• J. Rowland, R.T. Fielder
  Diamond, Oxfordshire
• R. Bartolini
  JAI, Oxford
• R. Nagaoka
  SOLEIL, Gif-sur-Yvette

Within the common programme on the analysis of collective instabilities at Diamond and SOLEIL, the numerical codes mbtrack and sbtrack have been extended to include a full description of the nonlinearities in the storage rings by means of the nonlinear one-turn map. We present the details of the map implementation and the recent results on the analysis of the effects of the nonlinear terms of the map on the characteristics of the collective instabilities at the two machines.

• H.J. Kim, T. Sen
  Fermilab, Batavia
• W. Fischer
  BNL, Upton, Long Island, New York

In order to avoid the effects of long-range beam-beam interactions which produce beam blow-up and deteriorate beam life time, a compensation scheme with current carrying wires has been proposed. Two long-range beam-beam compensators were installed in RHIC rings in 2006. The effects of the compensators have been experimentally investigated. An indication was observed that the compensators are beneficial to beam life time in measurements performed in RHIC during 2009. In this paper, we report the effects of wire compensator on beam loss and emittance for proton-proton beams at collision energy.

• H.J. Kim, T. Sen
  Fermilab, Batavia

Increasing the luminosity requires higher beam intensity and often focusing the beam to smaller sizes at the interaction points. The effects of head-on interactions become even more significant. The head-on interaction introduces a tune spread due to a difference of tune shifts between small and large amplitude particles. A low energy electron beam so called electron lens is expected to improve intensity lifetime and luminosity of the colliding beams by reducing the betatron tune shift and spread. In this paper we discuss the results of beam simulations with the electron lens in RHIC.

• T. Sen, C.M. Bhat, H.J. Kim, J.-F. Ostiguy
  Fermilab, Batavia

We investigate the dynamics of longitudinally flat bunches created with a second harmonic cavity in a high energy collider. We study Landau damping in a second harmonic cavity with analytical and numerical methods. The latter include particle tracking and evolution of the phase space density. The results are interpreted in the context of possible application to the LHC.

• A. Valishev
  Fermilab, Batavia

Electron lenses are proposed as a way to mitigate head-on beam-beam effects for the LHC upgrade. An extensive effort was put together within the US LARP in order to develop numerical simulations of beam-beam effects in the presence of electron lenses. In this report the results of beam-beam simulations for RHIC and LHC are presented. The effect of electron lenses is demonstrated and sensitivity of beam-beam compensation to imperfections is discussed.

• A. Valishev, G.F. Kuznetsov, V.D. Shiltsev, G. Stancari, X. Zhang
  Fermilab, Batavia
• A.L. Romanov
  BINP SB RAS, Novosibirsk

Tevatron electron lenses have been successfully used to mitigate bunch-to-bunch differences caused by long-range beam-beam interactions. For this purpose the electron beam with uniform transverse density distribution was used. Another planned application of the electron lens is the suppression of tune spread due to head-on beam-beam collisions. For this purpose, the transverse distribution of e-beam must be matched to that of the antiproton beam. In 2009, the gaussian profile electron gun was installed in one of the Tevatron electron lenses. We report on the first experiments with non-linear beam-beam compensation. Discussed topics include measurement and control of the betatron tune spread, importance of the beam alignment and stability, and effect of the electron lens on the proton and antiproton beam lifetime.

• M. Venturini, M.A. Furman, G. Penn, R. Secondo, J.-L. Vay
  LBNL, Berkeley, California
• R. De Maria, Y. Papaphilippou, G. Rumolo
  CERN, Geneva

One of the options under consideration for a future upgrade of the LHC injector complex includes the replacement of PS with PS2 (a longer circumference and higher energy ring). Efforts are currently underway to design the new machine and characterize the beam dynamics. Electron cloud effects represent a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities or significant degradation of the beam emittance. We present selected results obtained in the more familiar quasi-static approximation and/or in the Lorentz-boosted frame.

• Z. Liu
  IUCF, Bloomington, Indiana
• S.M. Cousineau, V.V. Danilov, J. Galambos, J.A. Holmes, M.A. Plum
  ORNL, Oak Ridge, Tennessee

The instability caused by the electron cloud effect (ECE) may set an upper limit to beam intensity in proton storage rings. This instability is potentially a major obstacle to the full intensity operation, at 1.5·10¹⁴ protons per pulse, of the Spallation Neutron Source (SNS). High intensity experiments have been done with different sets of parameters that affect the electron-proton (e-p) instability, of which bunch intensity and bunch shape are considered as two main factors. In the experiment, the phase and amplitude of the second harmonic RF cavity are used to modify the bunch shape. Simulation with the beam dynamics code ORBIT has been carried out to compare with experimental results and to understand the impact of bunch shape on electron cloud build-up and beam stability. We have also attempted to benchmark the e-p model to predict the frequency spectrum and the RF buncher voltage threshold values against experimental results. Details and discussion will be reported in this conference.

* M.T.F. Pivi and M.A. Furman, PRSTAB 6, 034201 (2003)
** V. Danilov et. al, 39th ICFA Advanced Beam Dynamics Workshop, 2006
*** B. Macek et. al, PAC 2003

• C.R. Prokop, P. Piot
  Northern Illinois University, DeKalb, Illinois
• M.C. Lin, P. Stoltz
  Tech-X, Boulder, Colorado

Terahertz (THz) radiation has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiations. The generation of copious amounts of narrow-band THz radiation using a Smith-Purcell FEL operating as a backward wave oscillator is being pursued by several groups. In this paper we present start-to-end simulations of a Smith-Purcell FEL operating in the superradiant regime. Our concept incorporates a double grating configuration to efficiently bunch the electron beam, followed by a single grating to produce Smith-Purcell radiation. We demonstrate the capabilities and performances of the device, including initial beam properties (emittance and energy spread), with the help of numerical simulations using the conformal finite-difference time-domain electromagnetic solver VORPAL.

• K.L.F. Bane, Y. Cai, G.V. Stupakov
  SLAC, Menlo Park, California

In accelerator design, there is often a need to evaluate the threshold to the (longitudinal) microwave instability for a bunched beam in a storage ring. Several computational tools are available that allow us, once given a wakefield, to numerically find the threshold current and to simulate the development of the instability. In this work, we present the results of computer simulations with codes recently developed at the SLAC National Accelerator Laboratory. Our simulations include the cases of the resonator broadband impedance, the resistive wall impedance and the coherent synchrotron radiation impedance. We compare the accuracy of the threshold prediction and discuss the capabilities and limitations of the codes.

• K.L.F. Bane, L. Lee, C.-K. Ng, G.V. Stupakov, L. Wang, L. Xiao
  SLAC, Menlo Park, California

PEP-X, a next generation, ring-based light source is designed to run with beams of high current and low emittance. Important parameters are: energy 4.5 GeV, circumference 2.2 km, beam current 1.5 A, and horizontal and vertical emittances, 150 pm by 8 pm. In such a machine it is important that impedance driven instabilities not degrade the beam quality. In this report we study the strength of the impedance and its effects in PEP-X. For the present, lacking a detailed knowledge of the vacuum chamber shape, we create a straw man design comprising important vacuum chamber objects to be found in the ring, for which we then compute the wake functions. From the wake functions we generate an impedance budget and a pseudo-Green function wake representing the entire ring, which we, in turn, use for performing instability calculations. In this report we consider in PEP-X the microwave, transverse mode-coupling, multi-bunch transverse, and beam-ion instabilities.

• G.V. Stupakov
  SLAC, Menlo Park, California
• B. Podobedov
  BNL, Upton, Long Island, New York

Collimators and other similar accelerator structures usually include small-angle tapering to lower the wakefields generated by the beam. While the low-frequency impedance is well described by Yokoya's formula (for axisymmetric geometry), much less is known about the behavior of the impedance in the high frequency limit. In this paper we develop an analytical approach to the high-frequency regime for round collimators and tapers. Our analytical results are compared with computer simulations using the code ECHO.

• S.P. Weathersby, A. Novokhatski
  SLAC, Menlo Park, California

The geometry of storage ring collider interaction regions present an impedance to beam fields resulting in the generation of additional electromagnetic fields (higher order modes or wake fields) which affect the beam energy and trajectory. These affects are computed for the Super B interaction region by evaluating longitudinal loss factors and averaged transverse kicks for short range wake fields. Results indicate at least a factor of 2 lower wake field power generation in comparison with the interaction region geometry of the PEP-II B-factory collider. Wake field reduction is a consideration in the Super B design. Transverse kicks are consistent with an attractive potential from the crotch nearest the beam trajectory. The longitudinal loss factor scales as the -2.5 power of the bunch length. A factor of 60 loss factor reduction is possible with crotch geometry based on an intersecting tubes model.

• A. Blednykh, W.X. Cheng, R.P. Fliller, Y. Kawashima, J. Rose, T.V. Shaftan, L.-H. Yu
  BNL, Upton, Long Island, New York

In this paper, we present an overview of the impact of collective effects upon the performance of the NSLS-II booster.

• M.K. Fukuda, S. Araki, A.S. Aryshev, Y. Honda, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• A. Deshpande
  Sokendai, Ibaraki
• K. Sakaue, M. Washio
  RISE, Tokyo
• N. Sasao
  Okayama University, Okayama

We have developed a compact X-ray source based on inverse Compton scattering of an electron beam and a laser pulse, which is stacked in an optical super-cavity, at LUCX accelerator in KEK. The accelerator consists of a photo-cathode rf-gun and an S-band accelerating tube and produces the multi-bunch electron beam with 100 bunches, 0.5nC bunch charge and 40MeV beam energy. It is planned to upgrade the accelerator and the super-cavity in order to increase the number of X-rays. A new RF gun with high mode separation and high Q value and a new klystron for the gun will be installed to provide good compensation with a high-intensity multi-bunch electron beam. A new optical super-cavity consisting of 4 mirrors is also being developed to increase the stacking power in the cavity and to reduce the laser size at the focal point. The first targets are to produce a multi-bunch electron beam with 1000 bunches, 0.5 nC bunch charge and 5 MeV beam energy in low energy mode and 100bunches, 2 nC and 40 MeV in high energy mode to generate X-rays by inverse Compton scattering. In this paper, the status and future plan of the accelerator will be reported.

• F. Furugohri, H. Hioka, S. Someya
  SUT, Noda-shi, Chiba
• M. Yoshida
  KEK, Ibaraki

New terahertz(THz) generator using the non-relativistic electron beam was developed based on the beam optics and the RF deflector. The conventional THz generators using the electron beam are almost based on the relativistic beam to utilize the lorentz factor as FELs or the strong magnet to make high electron density like gyrotrons or BWOs. Thus it causes that the total equipment becomes large. New THz generator uses the non-relativistic electron beam. And it consists of the beam optics which makes the sliced beam by using a anode slit to focus at second slit as the THz radiation plane. In this configuration, the RF deflector works to move for the transverse direction matched with the phase velocity of the radiated electromagnetic field. The moving sliced beam separates into a number of bunches through the second slit and the bunches makes the THz coherent radiation in zero time interval. In this new THz generator, no strong magnet is required and the large diameter beam can be utilized to generate the high power THz electromagnetic wave. In this paper,　the design of new THz generator and its experimental results are reported.

• Y. Taira, M. Hosaka, K. Soda, Y. Takashima, N. Yamamoto
  Nagoya University, Nagoya
• M. Adachi, M. Katoh, H. Zen
  UVSOR, Okazaki
• T. Tanikawa
  Sokendai - Okazaki, Okazaki, Aichi

We are developing an ultra-short gamma ray pulse source based on laser Compton scattering technology at the 750 MeV electron storage ring UVSOR-II. Ultra-short gamma ray pulses can be generated by injecting femtosecond laser pulses into the electron beam circulating in an electron storage ring from the direction perpendicular to the orbital plane. The energy, intensity, and pulse width of the gamma rays have been estimated to be 6.6 MeV, 2.4× 10⁶ photons s^-1, and 150 fs, respectively, for the case of UVSOR-II with a commercially available femtosecond laser. These parameters can be tuned by changing the incident angle of the laser to the electron beam, electron energy, and the size of the laser. A preliminary head-on collision experiment was carried out. The measured spectral shape agreed well with simulation including the detector response calculated by the EGS5 code*, which implied the generation of gamma rays by laser Compton scattering and the validity of the estimation of the gamma ray intensity in the case of 90-degree collisions.

* H. Hirayama et al., SLAC-R-730, (2005).

• C. Feng, Z.T. Zhao
  SINAP, Shanghai

A novel approach to producing coherent hard x-ray based on the echo-enabled staged harmonic generation (EESHG) scheme is proposed. This scheme is not a simple cascaded EEHG, but consists of an EEHG, a beam shifter and a conventional HGHG like configuration, which also works in the EEHG principle. In the first stage, all over the whole electron beam is energy modulated by a laser beam in the first modulator and then converts into separate energy bands by a very strong dispersion section. In the second modulator, the seed laser is adjusted so that only the tail half part of the e-beam is energy modulated, then this beam is sent through the second dispersion section which converts the energy modulated part into a density modulation. The radiation from the first stage serves as the seed laser of the second stage, the beam shifter is so tuned that the head part of the electron beam can exactly interact with the radiation from the first stage in the modulator of the second stage, so the total harmonic number will be hundreds. It is possible to do the proof-of-principle experiment of EESHG on the SDUV-FEL.

• E.V. Bulyak, P. Gladkikh
  NSC/KIPT, Kharkov
• T. Omori, J. Urakawa
  KEK, Ibaraki
• L. Rinolfi
  CERN, Geneva

Compton sources are capable to produce intense beams of gamma-rays necessary for numerous applications, e.g. production of polarized positrons for ILC/CLIC projects, nuclear waste monitoring. These sources need high current of electron beams of GeV energy. Storage rings are able to accumulate a high average current and keep it circulating for a long time. The dynamics of circulating bunches is affected by large recoils due to emission of energetic photons. We report results of both an analytical study and a simulation on the dynamics of electron bunches circulating in storage rings and interacting with the laser pulses. The steady-state transverse emittances and energy spread, and dependence of these parameters on the laser pulse power and dimensions at the collision point were derived analytically and simulated. It is shown that the transverse and longitudinal dimensions of bunches are dependent on the power of laser pulses and on their dimensions as well. Conditions of the laser cooling were found, under which the electron bunches shrink due to scattering off the laser pulses. The beam behavior in rings with the longitudinal strong focusing lattices is discussed.

• M. Shverdin, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, M. Betts, T.S. Chu, C.A. Ebbers, D.J. Gibson, F.V. Hartemann, R.A. Marsh, D.P. McNabb, M. J. Messerly, H.H. Phan, M.A. Prantil, C. Siders, S.S.Q. Wu
  LLNL, Livermore, California

Generation of mono-energetic, high brightness gamma-rays requires state of the art lasers to both produce a low emittance electron beam in the linac and high intensity, narrow linewidth laser photons for scattering with the relativistic electrons. Here, we overview the laser systems for the 3rd generation Monoenergetic Gamma-ray Source (MEGa-ray) currently under construction at Lawrence Livermore National Lab. We also describe a method for increasing the efficiency of laser Compton scattering through laser pulse recirculation. The fiber-based photoinjector laser will produce 50 uJ temporally and spatially shaped UV pulses at 120 Hz to generate a low emmittance electron beam in the X-band RF photoinjector. The interaction laser generates high intensity photons that focus into the interaction region and scatter off the accelerated electrons. This system utilizes chirped pulse amplification and commercial diode pumped solid state Nd:YAG amplifiers to produce 0.5 J, 10 ps, 120 Hz pulses at 10⁶⁴ nm and up to 0.2 J after frequency doubling. A single passively mode-locked Ytterbium fiber oscillator seeds both laser systems and provides a timing synch with the linac.

• F.V. Hartemann, F. Albert, S.G. Anderson, C.P.J. Barty, A.J. Bayramian, T.S. Chu, R.R. Cross, C.A. Ebbers, D.J. Gibson, R.A. Marsh, D.P. McNabb, M. J. Messerly, M. Shverdin, C. Siders
  LLNL, Livermore, California
• E.N. Jongewaard, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks
  SLAC, Menlo Park, California
• V. A. Semenov
  UCB, Berkeley, California

Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable Mono-Energetic Gamma-ray (MEGa-ray) source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linac designed in collaboration with SLAC will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable γ-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. This MEGa-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented, along with important applications, including nuclear resonance fluorescence, photo-fission, and medical imaging.

• J. Smedley, I. Ben-Zvi, X. Chang, P.D. Johnson, J. Rameau, T. Rao, Q. Wu
  BNL, Upton, Long Island, New York
• J. Bohon
  Case Western Reserve University, Center for Synchrotron Biosciences, Upton, New York
• E.M. Muller
  Stony Brook University, Stony Brook

The diamond amplified photocathode has the potential to dramatically increase the average current available from photoinjectors, perhaps to the amphere-class performance necessary for flux-competitive fourth-generation light sources. Electron emission from a diamond amplifier has been observed from hydrogen-terminated diamond, using both photons and electrons to generate carriers. The diamond electron amplifier has been demonstrated, with an emission gain of 40. Very high average current densities (>10 A/cm²) have been transported through the diamond using x-ray generated carriers. The device relies on high-purity intrinsic diamond with low crystalline defect density, as well as a negative electron affinity achieved by hydrogen termination. The effects of diamond purity and crystalline defects on charge transport in the material, and emission from the diamond surface have been studied using a number of techniques and the process is now well understood. The electron affinity of diamond has been measured to be -1.1 eV; the fraction of the electrons produced in the material which are emitted from the surface has also been measured.

• M. Abo-Bakr, B.C. Kuske, A.N. Matveenko
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin

The Helmholtz Zentrum Berlin (HZB) is proposing to build an Energy Recovery Linac Prototype, called BERLinPro, at its site in Berlin Adlershof. A gun test stand for a superconducting RF gun is already under construction at HoBiCaT. In this paper we concentrate on the recirculator part of the ERL and discuss the ERL requirements to the magnet optics. The current design of the magnet lattice will be described and main parameters and simulation results introduced. Since BERLinPro aims to demonstrate high current operation at short pulses according optics aspects will be also discussed. The focus here will be on longitudinal phase space manipulations and lattice layout options, suppressing the BBU instability and increasing its threshold currents.

• B.C. Kuske, M. Abo-Bakr, A.N. Matveenko
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin

The Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB) proposes to construct an ERL test facility. To provide different operational modes for different scientific applications is one of the advantages of these new, linac-driven radiation sources. In contrast to the linear machine layouts of FELs, new challenges arise from incorporating the linac into a circular machine. One of them is the so called merger, a magnetic chicane that threads the low energy, low emittance, but high current bunch from the gun into the recirculator. The preservation of the ambitious gun parameters, the optimal collimation of dark current and flexibility to suit all user demands are the dominant design goals. Different design criteria and possible layouts are discussed and a preliminary merger design is proposed.

• I. Ito, N. Nakamura
  ISSP/SRL, Chiba
• Y. Honda
  KEK, Ibaraki
• Y. Kobayashi, K. Torizuka, D. Yoshitomi
  AIST, Tsukuba

We are developing an Yb fiber laser system that drives an ERL photocathode gun. An Yb fiber laser is expected to have both high stability and high output power required for the drive laser of an ERL photocathode gun. First we started to develop an Yb fiber laser oscillator with a high repetition rate up to 1.3 GHz that is the RF frequency of a superconducting accelerating cavity and then a 30W preamplifier using an Yb doped photonic crystal fiber. We report our recent progress in this development.