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Paper Title Other Keywords Page
MOPC006 Simulations and Experiments of Beam-Beam Effects in e+e- Storage Rings simulation, luminosity, electron, damping 520
  • Y. Cai, J. Seeman
    SLAC, Menlo Park, California
  • W. Kozanecki
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • K. Ohmi, M. Tawada
    KEK, Ibaraki
  Funding: Work partially supported by the Department of Energy under Contract No. DE-AC02-76SF00515.

Over the past decade, extensive simulations of beam-beam effects in positron-electron collliders, based on the particle-in-cell method, were developed to explain many complex experimental observations. Recently, such simulations were used to predict the future luminosity performance of e+e- colliders. Some predictions have been proven to be correct in the existing accelerators. In this paper, many effects such as dynamic beta, beam-beam limit, crossing angle, parasitic collisions, betatron spectrum, and beam-beam lifetime, will be reviewed from the viewpoints of both simulation and experiment. Whenever possible, direct comparisons between the predictions of the simulation and the corresponding experimental results will be provided.

MOPC008 Dynamic Beam-Beam Effects Measured at KEKB emittance, electron, beam-beam-effects, luminosity 606
  • T. Ieiri, Y. Funakoshi, T. Kawamoto, M. Masuzawa, M. Tobiyama
    KEK, Ibaraki
  Funding: This work is partially supported by Grant-in-Aid Scientific Research (16540271) from Japan Society for the Promotion of Science and Technology.

KEKB is a multi-bunch, high-current, electron/positron collider for B meson physics. The two beams collide at one interaction point (IP) with a finite horizontal crossing angle and with a bunch-space of 6 to 8 ns. The luminosity achieved at KEKB is the best in the world. The betatron tunes are set close to a half integer, to expect the dynamic beam-beam effects that change the beta function around the rings and the emittance as a function of the beam-beam parameter. In order to investigate such attractive beam-beam effects, the beam-beam kick and the beam-beam tune-shift were obtained by comparing the beam parameters between a colliding bunch and a non-colliding one. The horizontal beam size at the IP estimated from a beam-beam kick curve was slightly less than a calculated value without the dynamic effect. The horizontal emittance estimated from the beam-beam tune shift was somewhat larger than a calculated natural emittance. These experimental results reflect the dynamic beam-beam effects.

MPPE057 Measurement of the Vertical Emittance and Beta Function at the PEP-II Interaction Point Using the BaBar Detector emittance, luminosity, storage-ring, factory 3387
  • J.M. Thompson, A. Roodman
    SLAC, Menlo Park, California
  • W. Kozanecki
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  Funding: U.S. Department of Energy.

We present measurements of the effective vertical emittance and IP beta function in the PEP-II Asymmetric B Factory. These beam parameters are extracted from fits to the longitudinal dependence of the luminosity and of the vertical luminous size, measured using e+ e- –> mu+ mu- events recorded in the Babar detector. The results are compared, for different sets of machine conditions, to accelerator-based measurements of the optical functions of the two beams.

MPPP024 Recent Observations on a Horizontal Instability in the DAFNE Positron Ring feedback, electron, damping, impedance 1841
  • A. Drago, M. Zobov
    INFN/LNF, Frascati (Roma)
  • D. Teytelman
    SLAC, Menlo Park, California
  A strong horizontal instability limits the maximum positron current storable in the DAFNE Phi-Factory. A powerful feedback system makes it possible to store and collide up to 1250 mA of positron current in 105 bunches. Nevertheless, a much higher current (> 2.4A) has been successfully stored in the twin electron ring. Measurements have been carried out to understand the positron current limit and to characterize the behavior of the horizontal instability at high current with different bunch patterns. Grow/damp turn-by-turn data obtained by turning off the horizontal feedback have been acquired and analyzed. Spectral analysis and grow rates of the instability are shown. In particular, the -1 mode has strong evidence and fast grow rate. Its grow rate behavior is analyzed at different beam currents and bunch patterns.  
MPPP028 The Code MBIM1 for the Calculation of the Multibunch Beams Coherent Oscillations Stability (in Approach of Short Bunches) synchrotron, multipole, electron, storage-ring 2009
  • N. Mityanina
    BINP SB RAS, Novosibirsk
  The code MBIM1 for the calculation of the coherent oscillations stability for multibunch beams in storage rings is presented. The multibunch beams with arbitrary charges of bunches are considered, including counterrotating bunches (in approach of short bunches in comparison with minimal wavelength of considered environment RF spectrum), with the account of beams coupling with the environment (i.e. RF cavities or/and smooth vacuum chamber with walls of finite conductivity). The code uses the approach of small shifts of coherent frequencies, when different multipole types of synchrotron oscillations can be treated as independent from each other.  
MPPT033 Development of a Superconducting Helical Undulator for a Polarised Positron Source undulator, electron, linear-collider, collider 2295
  • Y. Ivanyushenkov, F.S. Carr
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  • D.P. Barber
    DESY, Hamburg
  • E. Baynham, T.W. Bradshaw, J. Rochford
    CCLRC/RAL, Chilton, Didcot, Oxon
  • J.A. Clarke, O.B. Malyshev, D.J. Scott, B.J.A. Shepherd
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • P. Cooke, J.B. Dainton, T. Greenshaw
    Liverpool University, Science Faculty, Liverpool
  • G.A. Moortgat-Pick
    Durham University, Durham
  A method of producing a polarised positron beam from e+e- pair production in a target by circularly polarised ?-radiation is being investigated. Polarised photons are to be generated by the passage of a high energy electron beam (250 GeV as anticipated in the International Linear Collider - ILC) through a helical undulator. For production of 20 MeV photons, an undulator with a period of 14 mm, a bore of approximately 4 mm and magnetic field on axis of 0.75 T is required. First prototypes have been constructed using both superconducting and permanent magnet technologies which are capable of producing the necessary magnetic field configuration in the undulator. This paper details the design, construction techniques and field measurement results of the first superconducting prototype and compares the results with simulation.  
MPPT063 Optimized Analyzing Magnet for Measurements of Polarization of Gamma-Quants at 10 MeV polarization, electron, target, scattering 3582
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We described here calculations and test of magnet for measurement of polarization of gammas by its helicity-dependent attenuation in magnetized iron. Magnet is a compact device which size is ~ten times smaller, than world wide analogues.  
MPPT066 Pulsed Undulator for Polarized Positron Production undulator, power-supply, alignment, photon 3676
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We represent here elements of design and results of testing for helical undulator with ~2.5-mm period, manufactured in Cornell LEPP for polarized positron production at SLAC. At 2.3 kA undulator reaches K~0.2 and operated up 30 Hz.  
TPAT077 Beam-Beam Study on the Upgrade of Beijing Electron Positron Collider luminosity, simulation, collider, injection 4000
  • S. Wang
    IHEP Beijing, Beijing
  • Y. Cai
    SLAC, Menlo Park, California
  It is an important issue to study the beam-beam interaction in the design and performance of such a high luminosity collider as BEPCII, the upgrade of Beijing Electron Positron Collider. The weak-strong simulation is generally used during the design of a collider. For performance a large scale tune scan, the weak-strong simulation studies on beam-beam interaction were done, and the geometry effects were taken into account The strong-strong simulation studies were done for investigating the luminosity goal and the dependence of the luminosity on the beam parameters.  
TPAT085 Development of a Beam-Beam Simulation Code for e+e- Colliders simulation, luminosity, synchrotron, beam-beam-effects 4176
  • Y. Zhang
    IHEP Beijing, Beijing
  • K. Ohmi
    KEK, Ibaraki
  Funding: Chinese National Foundation of Natural Sciences, contract 10275079 JSPS Core University Program

BEPC will be upgraded into BEPCII, and the luminosity will be about 100 times higher. We developed a three dimensional strong-strong PIC code to study the beam-beam effects in BEPCII. The transportation through the arc is the same as that in Hirata's weak-strong code. The beam-beam force is computed directly by solving the Poisson equation using the FACR method, and the boundary potential is computed by circular convolution. The finite bunch length effect is included by longitudinal slices. An interpolation scheme is used to reduce the required slice number in simulations. The standard message passing interface (MPI) is used to parallelize the code. The computing time increases linearly with (n+1), where n is the slice number. The calculated luminosity of BEPCII at the design operating point is less than the design value. The best area in the tune space is near (0.505,0.57) according to the survey, where the degradation of luminosity can be improved.

TPAT087 The Effect of Magnetic Field Errors on Dynamical Friction in Electron Coolers electron, simulation, ion, luminosity 4206
  • D.L. Bruhwiler, D.T. Abell, R. Busby, S.A. Veitzer
    Tech-X, Boulder, Colorado
  • A.V. Fedotov, V. Litvinenko
    BNL, Upton, Long Island, New York
  Funding: Work supported by US DOE grants DE-FG03-01ER83313 and DE-FG03-95ER40926.

A proposed luminosity upgrade to the Relativistic Heavy Ion Collider (RHIC) includes a novel electron cooling section,* which would use ~55 MeV electrons to cool fully-ionized 100 GeV/nucleon gold ions. A strong (1-5 T) solenoidal field will be used to magnetize the electrons and thus enhance the dynamical friction force on the ions. The physics of magnetized friction is being simulated for RHIC parameters, using the VORPAL code.** Most theoretical treatments for magnetized dynamical friction do not consider the effect of magnetic field errors, except in a parametric fashion.*** However, field errors can in some cases dramatically reduce the velocity drag and corresponding cooling rate. We present a simple analytical model for the magnetic field errors, which must be Lorentz transformed into the beam frame for use in our simulations. The simulated dynamical friction for the case of a perfect solenoidal field will be compared with results from this new model, for parameters relevant to RHIC.

*Fedotov et al., Proc. 33rd ICFA Adv. Beam Dynamics Workshop (2004). **Nieter & Cary, J. Comp. Phys. 196 (2004). ***Parkhomchuk, Nucl. Instr. Meth. Phys. Res. A 441 (2000).

TPPE036 Progress of the BEPCII Linac Upgrade electron, linac, gun, target 2416
  • G. Pei
    IHEP Beijing, Beijing
  BEPCII-an upgrade project of the BEPC is a factory type of e+e- collider. It requires its injector linac to have a higher beam energy (1.89 GeV) for on-energy injection and a higher beam current (40 mA e+ beam) for a higher injection rate (=50 mA/min.). The low beam emittance (1.6pmm-mrad for e+ beam, and 0.2pmm-mrad for 300 mA e- beam) and low beam energy spread (±0.5%) are also required to meet the storage ring acceptance. Hence we need a new electron gun system, a new positron source, a much higher power and more stable RF system with its phasing loops, and a new beam tuning system with orbit correction. Up to date, all system design and fabrication work have been completed. And in five months from May 1st of 2004, the positron production system–from the electron gun to the positron source, has been installed into the tunnel. In this paper, we will introduce major upgrades of each system, and present the recent beam commissioning.  
TPPE053 Design Issues for the ILC Positron Source target, electron, photon, undulator 3230
  • V. Bharadwaj, Y.K. Batygin, R. Pitthan, D.C. Schultz, J. Sheppard, H. Vincke, J.W. Wang
    SLAC, Menlo Park, California
  • J.G. Gronberg, W. Stein
    LLNL, Livermore, California
  Funding: Work supported by Department of Energy contract DE-AC02-76SF00515.

A positron source for the ILC can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major issues are: the drive beam, choice of target material, the design of the target station, the capture section, the target vault, and beam transport to the damping ring. In this paper, positron source parameters for the various schemes are outlined and the advantages and disadvantages of each scheme are discussed.

TPPP001 Design of Damping Ring for SuperKEKB emittance, dynamic-aperture, damping, linac 773
  • M. Kikuchi
    KEK, Ibaraki
  In the SuperKEKB, a plan upgrading the KEKB to higher luminosity of (2.5-5) x1035 cm2/sec, the beam currents are 9.4 A for the LER (3.5 GeV-electrons) and 4.1 A for the HER (8 GeV-positrons). In order to supply the HER with the positron beam, which is currently injected to the LER, the field gradient of the injector linac has to be increased. To meet this requirement, the S-band accelerating structures placed at the beam energy greater than 1 GeV, after the positron target, are replaced with C-band structures. A damping ring (DR) is indispensable since the aperture of the C-band structure is much smaller than the beam emittance. In this paper, we describe on the design of DR. We adopt a new cell structure for DR; FODO cell with alternating bends, where one of two bends in a cell is reversed. One of advantages of the proposed ring is that very small, even negative, momentum compaction factor is easily achieved by properly choosing the bend-angle ratio of the reverse bend to the main bend. Tracking simulation for the proposed DR has shown that it has very large dynamic aperture in both transverse and longitudinal phase space, for very wide tune space.  
TPPP011 Investigations of Injection Orbits at CESR Based on Turn-By-Turn BPM Measurements injection, electron, betatron, optics 1228
  • M.G. Billing, J.A. Crittenden, M.A. Palmer
    Cornell University, Department of Physics, Ithaca, New York
  Funding: National Science Foundation.

Development of a data acquisition permitting turn-by-turn orbit measurements has been employed at CESR to study the optics of the injected electron beam. An optimization algorithm uses these measurements to determine the effective lattice functions describing the behavior of the injected electrons. We present comparisons of these measurements to tracking calculations of injection acceptance envelopes which account for the parasitic beam-beam interactions with the stored positron beam.

TPPP012 A Study of the Effect of Beam-Beam Interactions on CESR Optics electron, quadrupole, lattice, betatron 1275
  • J.A. Crittenden, M.G. Billing
    Cornell University, Department of Physics, Ithaca, New York
  • D. L. Rubin
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Funding: National Science Foundation.

The CESR storage ring facility has begun operation in an energy region which allows high-statistics investigation of charm-quark bound states. Experience during the first year has shown that the effects of parasitic crossings in the pretzel orbits present an important factor in injection efficiency, in the beam lifetime and stored current limits. We compare the results of beam dynamics and tracking calculations which quantify the effects of these parasitic crossings on optics and dynamic aperture for the injected and stored trajectories to observations of beam behavior.

TPPP019 Collective Effects in Lepton Ring of eRHIC electron, lepton, impedance, ion 1628
  • D. Wang, M. Farkhondeh, C. Tschalaer, F. Wang, A. Zolfaghari, T. Zwart, J. van der Laan
    MIT, Middleton, Massachusetts
  • M. Blaskiewicz, Y. Luo, L. Wang
    BNL, Upton, Long Island, New York
  Funding: Department of Energy.

The eRHIC is a new generation lepton-hadron collider undergoing design studies by a collaboration of BNL, MIT, DESY and BINP. The collider complex will consist of a hadron machine that is mainly the existing RHIC with necessary upgrades, and a new lepton machine that can provide intense, highly polarized electron and positron beams at energy of 5-10 GeV. The ring-ring option of eRHIC is to build a 5-10 GeV electron ring with a injector chain. In this paper the beam lifetime of lepton beams is calculated.

TPPP026 Bunch-Length Measurements in PEP-II single-bunch, synchrotron, electron, luminosity 1934
  • A.S. Fisher, A. Novokhatski, J.L. Turner, U. Wienands, G. Yocky
    SLAC, Menlo Park, California
  • R. Holtzapple
    Alfred University, Alfred, New York
  Funding: Supported by U.S. Department of Energy contract DE-AC03-76SF00515.

We measured the lengths of colliding e+e- bunches in the PEP-II B Factory at SLAC using various techniques. First, at several RF voltages and with both single-bunch and multibunch beams, a synchroscan streak camera measured synchrotron emission through a narrow blue filter. With 3.8 MV of RF, the length of a single positron bunch was 12 mm at low current, rising to 13 mm at 1.5 mA and 14.8 mm at 3 mA. The electrons measured 12.2 mm with little current dependence. Both are longer than the expected low-current value of 10 mm (e+) and 11 mm (e-), derived from the energy spread and the measured synchrotron tune. We also determined the length from measurements between 2 and 13 GHz of the bunch spectrum on a BPM button. After correcting for the frequency dependence of cable attenuation, we then fit the measured spectrum to that of a Gaussian bunch. With 3.8 MV, the positrons measurement gave 13.2 mm at 1.5 mA/bunch in a full ring, in agreement with the streak camera, but we found 11.4 mm for the electrons at 16.7 MV and 1 mA/bunch, lower than the streak measurement.

TPPP027 Single-Bunch Tune and Beam Size Measurements Along Bunch Trains in PEP-II luminosity, single-bunch, electron, feedback 2006
  • R. Holtzapple
    Alfred University, Alfred, New York
  • D.D. Dujmic, A.S. Fisher
    SLAC, Menlo Park, California
  By scanning a gated camera and a gated tune monitor across the bunch pattern during normal colliding-bunch operation of PEP-II, the single-bunch tunes and beam sizes were measured simultaneously in the high and low energy storage rings of PEP-II. The measurements were made with 1561 colliding bunches in PEP-II, arranged in trains of 66 bunches, with each bunch in the train separated by 4.2 ns. The tune and beam size measurements were correlated with the current, luminosity, and specific luminosity of the bunch. The results show a vertical tune shift at the start and end of the mini-trains, a luminosity droop along the mini-train, and specific luminosity drop in the first and last bunches of the train, since they experience a different parasitic crossing on either side of the IP.  
TPPP030 Damping Higher Order Modes in the PEP-II B-Factory Vertex Bellows damping, vacuum, higher-order-mode, impedance 2131
  • S.P. Weathersby, J. Langton, A. Novokhatski, J. Seeman
    SLAC, Menlo Park, California
  Funding: Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515.

Higher stored currents and shorter bunch lengths are requirements for increasing luminosity in colliding storage rings. As a result, more HOM power is generated in the IP region. This HOM power propagates to sensitive components causing undesirable heating, thus becoming a limiting issue for the PEP-II B-factory. HOM field penetration through RF shielding fingers has been shown to cause heating in bellows structures. To overcome these limitations, a proposal to incorporate ceramic absorbers within the bellows cavity to damp these modes is presented. Results show that the majority of modes of interest are damped, the effectiveness depending on geometrical considerations. An optimal configuration is presented for the PEP-II B-factory IR bellows component utilizing commercial grade ceramics with consideration for heat transfer requirements.

TPPP035 Performance of the PEP-II B-Factory Collider at SLAC luminosity, injection, beam-beam-effects, electron 2369
  • J. Seeman, J. Browne, Y. Cai, S. Colocho, F.-J. Decker, M.H. Donald, S. Ecklund, R.A. Erickson, A.S. Fisher, J.D. Fox, S.A. Heifets, R.H. Iverson, A. Kulikov, N. Li, A. Novokhatski, M.C. Ross, P. Schuh, T.J. Smith, K.G. Sonnad, M. Stanek, M.K. Sullivan, P. Tenenbaum, D. Teytelman, J.L. Turner, D. Van Winkle, M. Weaver, U. Wienands, M. Woodley, Y.T. Yan, G. Yocky
    SLAC, Menlo Park, California
  • M.E. Biagini
    INFN/LNF, Frascati (Roma)
  • W. Kozanecki
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • C. Steier, A. Wolski
    LBNL, Berkeley, California
  • G. Wormser
    IPN, Orsay
  Funding: Work supported by DOE contract DE-AC02-76SF00515.

For the PEP-II Operation Staff: PEP-II is an asymmetric e+e- collider operating at the Upsilon 4S and has recently set several performance records. The luminosity has reached 9.2 x 1033/cm2/s. PEP-II has delivered an integrated luminosity of 710/pb in one day. It operates in continuous injection mode for both beams boosting the integrated luminosity. The peak positron current has reached 2.55 A in 1588 bunches. The total integrated luminosity since turn on in 1999 has reached 256/fb. This paper reviews the present performance issues of PEP-II and also the planned increase of luminosity in the near future to over 2 x 1034/cm2/s. Upgrade details and plans are discussed.

TPPT011 R&D Status of C-Band Accelerating Section for SuperKEKB linac, klystron, luminosity, coupling 1233
  • T. Kamitani, N. Delerue, M. Ikeda, K. Kakihara, S. Ohsawa, T. Oogoe, T. Sugimura, T. T. Takatomi, S. Yamaguchi, K. Yokoyama
    KEK, Ibaraki
  • Y. Hozumi
    GUAS/AS, Ibaraki
  For future energy upgrade of the KEKB injector linac, C-band accelerating section has been developed. First prototype 1-m long section has been installed in the linac and has achieved the accelerating field gradient of 42 MV/m. Developments of second prototype which has thicker coupler iris and third prototype which has smooth surface of the iris are in progress for less frequent breakdown. This paper reports on the recent R and D status of these C-band accelerating sections.  
TPPT012 High Power Testing of Input Couplers for SuperKEKB vacuum, coupling, electron, monitoring 1294
  • H. Sakai, T. Abe, T. Kageyama, Y. Takeuchi
    KEK, Ibaraki
  In KEKB, 32 ARES cavities have been successfully operated to stably accelerate high-current electron and positron beams. Currently, each ARES cavity is fed with RF power (frequency = 509 MHz) of about 300 kW through an input coupler, which has a ceramic disk window at the coaxial line section following the doorknob transformer section with a capacitive iris at the rectangular waveguide entrance. For SuperKEKB, which is a challenging project to boost the luminosity frontier beyond 1035 cm-2 s-1, the power capability of the input coupler needs to be upgraded to more than 900 kW, while the design power capability for KEKB is 400 kW. Recently, we have constructed a new test stand in order to simulate the actual operating condition for the input coupler to drive the ARES cavity with the maximum beam loading of 9.4 A expected for the SuperKEKB LER. In this article, the key features of the new test stand are described together with the recent results of high-power tests.  
TPPT038 Development of C-Band Accelerator Structure with Smooth Shape Couplers simulation, target, linac, acceleration 2530
  • T. Sugimura, M. Ikeda, K. Kakihara, T. Kamitani, S. Ohsawa, T. T. Takatomi, K. Yokoyama
    KEK, Ibaraki
  The first C-band accelerator structure for the SuperKEKB injector linac has been operated in the beam line of e+/e- injector linac for KEKB/PF/PF-AR since September, 2003. A new accelerator structure will locate upstream of the first structure. The upstream structure is exposed to higher RF field than that of downstream structure. For the case of first structure, most of an RF breakdown occurs in an input coupler. In order to reduce a frequency of the breakdown, improvement of a coupler is required. In order to suppress a thermionic emission around the coupler iris, thick and smooth iris is adopted for the upstream structure. The development status of this type of upstream structure is described.  
TOPD002 BEPCII -The Second Phase Construction of the Beijing Electron-Positron Collider luminosity, electron, vacuum, linac 131
  • C. Zhang, G. Pei
    IHEP Beijing, Beijing
  The Beijing Electron-Positron Collider (BEPC) was constructed for both high energy physics and synchrotron radiation researches. The peak luminosity of the BEPC has reached its design goal of 5*1030 cm-2s-1 at J/sai energy of 1.55 GeV and 1*1031 cm-2s-1 at 2 GeV respectively. As the second phase construction of the BEPC, the BEPCII has been approved with total budget of 640 million RMB. The construction was started in the beginning of 2004 and is scheduled to be completed by the end of 2007. The BEPCII is a double ring machine with its luminosity goal of 1*1033 cm-2s-1 at 1.89 GeV, two orders of magnitude higher than present BEPC. The upgrading of the collider should also provide an improved SR performance with higher beam energy and intensity. The beam currents will be increased to 250 mA at E=2.5 GeV for the dedicated synchrotron radiation operation of the BEPCII. Some key technologies, such as superconducting RF system, low impedance vacuum devices, superconducting micro-beta quadrupoles and etc., are being developed in order to achieve the target of the BEPCII.*

*Submitted on behalf of the BEPCII Team.

WOAA001 The International Linear Collider (ILC) Organization and Plans collider, linear-collider, linac, damping 94
  • M. Tigner
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  A discussion of the current organization and Central Team functions will be given. A plan for evolution of the organization towards governance by the funding agencies will be presented. The work plan for the first year will be described and today’s ideas of a possible timeline laid out.  
WOAA003 Progress and Plans for R&D and the Conceptual Design of the ILC Injector Systems emittance, electron, damping, undulator 315
  • S. Guiducci
    INFN/LNF, Frascati (Roma)
  The International Linear Collider Injector is a complex of different subsystems that are strictly correlated: positron source, polarized electron source, damping rings, bunch compressor and spin rotator. The choice of parameters of each subsystem has a strong influence on the others. A description of the critical items requiring further R&D in order to finalize the choice of the parameters needed for the Conceptual Design is given. The status and plans of the R&D in progress on these items at a global level are reported.  
WPAE030 Thermal Analysis of the Al Window for a New CESR-c Luminosity Monitor photon, luminosity, vacuum, simulation 2137
  • Y. He, D.H. Rice
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • Y. Li, M.A. Palmer
    Cornell University, Department of Physics, Ithaca, New York
  Funding: Work supported by the U.S. National Science Foundation.

A luminosity monitor using photons from radiative bhabha events at the CLEO interaction point (IP) has been installed in the Cornell Electron Storage Ring (CESR). A key vacuum and detector component is the photon window/converter whose uniformity and thickness are critical for determining the resolution of the total energy deposited in the segmented luminosity monitor. The window design must accommodate the operational requirements of the new monitor at CLEO-c beam energies of 1.5-2.5 GeV and also provide sufficient safety margin for operation at 5.3 GeV beam energies for Cornell High Energy Synchrotron Source (CHESS) running. During 5.3 GeV operation, intense stripes of synchrotron radiation from the interaction region superconducting quadrupole magnets as well as nearby bending magnets strike the window. During the course of window development, several materials and designs were evaluated. Thermal stresses were calculated using the finite element code ANSYS for various beam conditions to guide the cooling design. A window using aluminum alloy (6061-T6) was ultimately chosen to provide optimal performance for both CLEO-c and CHESS running conditions. The window has been in successful operation since September 2004.

WPAP034 Positron Emulator for Commissioning ILC Positron Source electron, target, damping, linac 2321
  • H. Wang, W. Gai, K.-J. Kim, W. Liu
    ANL, Argonne, Illinois
  Funding: U.S. DOE.

It is apparent that the gamma-ray based positron source components including positron linac and damping rings for ILC can not be easily commissioned until the electron beam is fully conditioned at high energies (> 150 GeV). In this paper, we discuss a scheme that could use a short and energetic electron beam scattered through a set of carefully selected targets to simulate certain behaviors of the positron beam, such as beam emittance and energy spread. The basic idea is to make the phase space distribution of the scattered electron beam to reflect certain aspects of the positron beam distributions. Subsequently, the positron source elements such as capture optics, linacs and even damping ring could be effectively commissioned before ILC colliding electron beam is ready. The simulation results using EGS4 for beam scattering and PARMELA for beam dynamics are presented.

RPAE019 Positron Source from Betatron X-Rays Emitted in a Plasma Wiggler electron, plasma, radiation, wiggler 1625
  • D.K. Johnson, C.E. Clayton, C. Huang, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, M. Zhou
    UCLA, Los Angeles, California
  • C.D. Barnes, F.-J. Decker, M.J. Hogan, R.H. Iverson, P. Krejcik, C.L. O'Connell, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • S. Deng, T.C. Katsouleas, P. Muggli, E. Oz
    USC, Los Angeles, California
  In the E-167 plasma wakefield accelerator (PWFA) experiments in the Final Focus Test Beam (FFTB) at the Stanford Linear Accelerator Center (SLAC), an ultra-short, 28.5 GeV electron beam field ionizes a neutral column of Lithium vapor. In the underdense regime, all plasma electrons are expelled creating an ion column. The beam electrons undergo multiple betatron oscillations leading to a large flux of broadband synchrotron radiation. With a plasma density of 3x1017 cm-3, the effective focusing gradient is near 9 MT/m with critical photon energies exceeding 50 MeV for on-axis radiation. A positron source is the initial application being explored for these X-rays, as photo-production of positrons eliminates many of the thermal stress and shock wave issues associated with traditional Bremsstrahlung sources. Photo-production of positrons has been well-studied; however, the brightness of plasma X-ray sources provides certain advantages. In this paper, we present results of the simulated radiation spectra for the E-167 experiments, and compute the expected positron yield.  
RPAP047 DAQ System of BPM and BCT for the BEPCII Linac linac, pick-up, monitoring, electron 2980
  • J. Cao, Q. Ye
    IHEP Beijing, Beijing
  Following the BEPCII upgrade, total about 19 BPM and 12 BCT have been newly installed in the BEPCII Linac. Also, a set of distributed control system based on EPICS architecture has been built, and the BPM and BCT system are merged into the new control system for the data acquisition. In order to reduce the effects of RF noise, a special gated integrator was used to measure the beam current. In this paper we will describe the DAQ system of BPM and BCT including calibrations in detail.  
RPAT051 Measurement of Dynamic Beam-Beam Effects on Horizontal Beam Size at KEKB Using SR Interferometer Equipped with Retrofocus Optics optics, emittance, simulation, beam-beam-effects 3150
  • J.W. Flanagan, H. Fukuma, S. Hiramatsu, T. Mitsuhashi
    KEK, Ibaraki
  Transverse beam-size enlargement due to dynamic beta and beam-beam effects has been observed in the KEKB Low Energy Ring (LER) and High Energy Ring (HER). In order to observe these effects, a retrofocus optics system has been developed and installed in the horizontal SR interferometers at the HER and LER. This system allows us to vary the apparent beam size to match the dynamic range of the interferometer. We report on the retrofocus optics system and measurement results, and compare the measured effects with those expected from dynamic beta simulations.  
RPAT052 Vertical Beam Size Measurement by Streak Camera under Colliding and Single Beam Conditions in KEKB luminosity, electron, beam-beam-effects, feedback 3194
  • H. Ikeda, J.W. Flanagan, H. Fukuma, Y. Funakoshi, S. Hiramatsu, T. Mitsuhashi, K. Ohmi, S. Uehara
    KEK, Ibaraki
  Beam behavior of KEKB was studied by measurement of the beam size using a streak camera. Effect of the electron-cloud and the parasitic collision on the vertical beam size was examined in beam collision. We intentionally injected a test bunch of positrons after 2 rf buckets of a bunch to enhance the electron cloud effect and changed electron beam conditions to see the beam-beam effect. The beam size was also measured with a single positron beam and compared with that during collision. The result of the measurement is reported in this paper.  
RPAT062 Design and Operation of a Radiative Bhabha Luminosity Monitor for CESR-c luminosity, photon, vacuum, monitoring 3564
  • M.A. Palmer, D. L. Rubin, J.C. Smith
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • M. Cravey, J. Napalitano
    RPI, Troy, New York
  • V. Crede
    Cornell University, Department of Physics, Ithaca, New York
  • K.L. Dooley
    Vassar, Poughkeepsie, New York
  • H. Vogel
    CMU, Pittsburgh, Pennsylvania
  Funding: Work supported by the National Science Foundation.

The CLEO-c experiment at the Cornell Electron Storage Ring (CESR) is presently embarking on a multi-year exploration of charm and QCD physics in the 3-5 GeV center-of-mass energy range. In order to facilitate rapid optimization of machine parameters over this energy range, a luminosity monitor based on the measurement of radiative-bhabha photons coming from the CLEO-c interaction point (IP) has been designed and installed in the CESR ring. Key design criteria of the device include: better than 1% statistical measurements of the luminosity with a 1 Hz update rate over the full range of CESR-c operating conditions; bunch-by-bunch measurement capability; a large horizontal aperture to enable measurements under conditions ranging from single-bunch head-on collisions to multi-bunch collisions with a horizontal crossing angle of up to 4~mrad; and, a segmented readout to provide direct information on beam characteristics at the IP. We review the design and performance of this device and discuss its application to machine tuning and performance studies.

RPAT063 A Bunch-By-Bunch and Turn-By-Turn Instrumentation Hardware Upgrade for CESR-c luminosity, electron, synchrotron, instrumentation 3597
  • M.A. Palmer, J. Dobbins, C.R. Strohman, E. Tanke
    CESR-LEPP, Ithaca, New York
  Funding: Work supported by the National Science Foundation.

A key factor in the colliding beam performance of the Cornell Electron Storage Ring (CESR) is the impact of parasitic beam-beam interactions between bunches in the two beams as they follow their electrostatically separated orbits in a single vacuum chamber. In order to better investigate the differential performance of bunches in CESR, instrumentation electronics has been developed to allow acquisition of turn-by-turn data from multiple bunches simultaneously. The electronics consists of a standardized digital board centered around an Analog Devices TigerSHARC family digital signal processor, a communications interface, and an interface to the CESR Precision Timing System. Mated to these components is an analog front end and digitizer board which is customized for the particular diagnostic device of interest. Front ends have been developed for beam position monitor, luminosity monitor, and beam profile monitor applications. We describe the design and characterization of this new hardware.

RPAT088 Energy-Spread-Feedback System for the KEKB Injector Linac feedback, linac, electron, target 4212
  • M. Satoh, K.  Furukawa, T. Suwada
    KEK, Ibaraki
  New energy-spread feedback system using nondestructive energy-spread monitors have been developed in order to control and stabilize the energy spreads of single-bunch electron and positron beams in the KEKB injector linac. The well-controlled feedback systems of the injector linac are successfully working in dairy operation not only for keeping the injection rate higher along with the beam-orbit and energy feedback systems but also for reducing a background level to the high-energy B-factory experiment. The energy spreads of the injection beams are well stabilized within 0.2%, 0.5% and 0.3% for the electron beam, the positron beam, and the high-current primary electron beam for positron production, respectively, through the energy-spread feedback system under the nominal operation condition. In this paper, we will report in detail the energy-spread feedback system using the nondestructive energy-spread monitors with multi-strip-line electrodes and their performance in the KEKB operation.  
ROPB009 Betatron Sidebands Due to Electron Clouds Under Colliding Beam Conditions luminosity, electron, betatron, feedback 680
  • J.W. Flanagan, H. Fukuma, Y. Funakoshi, S. Hiramatsu, H. Ikeda, K. Ohmi, M. Tobiyama, S. Uehara, S. Uno
    KEK, Ibaraki
  • E. Perevedentsev
    BINP SB RAS, Novosibirsk
  Recently, we have observed vertical betatron sidebands in the transverse beam spectra of positron bunches at the KEKB LER which are associated with the presence of electron clouds. When the LER is operating in single-beam mode (no colliding bunches in the HER), these sidebands are sharply peaked. When the bunches are in collision for physics running, the sidebands are still present but are found to be smeared out. The bunch-by-bunch specific luminosity is lower for bunches with sidebands than for those without sidebands. In this paper, the behavior of the sidebands in collision and the effects on luminosity are discussed.  
RPPE052 Application of Comb-Type RF-Shield to Bellows Chambers and Gate Valves vacuum, impedance, injection, electron 3203
  • Y. Suetsugu, K.-I. Kanazawa, N. Ohuchi, K. Shibata, M. Shirai
    KEK, Ibaraki
  A comb-type RF-shield, which was recently proposed for high current accelerators, was experimentally applied to bellows chambers and gate valves. The comb-type RF-shield has a structure of nested comb teeth, and has higher thermal strength and lower impedance than usual finger-type RF shields. The shield is suitable for future high intensity accelerators, such as particle factories aiming a luminosity of 1·1035 - 36 /cm2 /s. Seven bellows chambers with a circular or a racetrack cross section had been installed in the KEKB (KEK B-factory) positron ring since 2003 in series. Some bellows chambers are forced to bend up to 20 mrad during the beam operation. No significant problem had been found with a stored beam current up to 1.6 A (1.25 mA/bunch). On the other hand, a circular-type gate valve with the comb-type RF shield will be installed in the ring in January, 2005. Structures, properties and results of the beam test of the bellows chamber and the gate valve are discussed.  
RPPE053 R&D Status of Vacuum Components for the Upgrade of KEKB electron, vacuum, impedance, photon 3256
  • Y. Suetsugu, H. Hisamatsu, K.-I. Kanazawa, N. Ohuchi, K. Shibata, M. Shirai
    KEK, Ibaraki
  An upgrade plan of the KEK B-factory (KEKB), Super KEKB, aiming a luminosity over 1·1035 /cm2 /s has been discussed in KEK. To achieve the high luminosity, the stored beam currents are 4.2 - 9.4 A and the bunch length is 3 mm. In designing the vacuum system of the Super KEKB, therefore, the main issues are how to manage the resultant highly intense synchrotron radiation (SR) power, and how to reduce the beam impedance. The R&Ds for basic vacuum components, such as a beam duct, a bellows chamber, a connection flange, a collimator, a high-capacity pump and so on, are now undergoing to deal with the problems. For examples, a copper beam duct with an antechamber was manufactured to reduce the power density of SR, and to suppress the electrons around the beam for the positron ring. The test chamber was installed in the positron ring of KEKB and tested with a beam. Bellows chambers with a newly developed RF-shield were also installed in the ring and the property was investigated. A special connection flange with little step or gap inside was developed and examined in a test bench. The designs of these components and the results of tests are presented and discussed.  
RPPP006 The PITZ Booster Cavity–A Prototype for the ILC Positron Injector Cavities booster, linac, coupling, emittance 1030
  • V.V. Paramonov, L.V. Kravchuk
    RAS/INR, Moscow
  • K. Floettmann
    DESY, Hamburg
  • M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen
  A critical issue of the design of the Positron Pre-Accelerator (PPA) for the future International Linear Collider (ILC) is the operational reliability of the normal conducting, high accelerating gradient L-band cavities. Now a booster cavity, intended for increasing the beam energy at the Photo Injector Test Facility in Zeuthen (PITZ), and developed by a joined INR-DESY group, is under construction at DESY, Hamburg. With the PITZ requirements (accelerating gradient up to 14 MV/m, rf pulse length up to 900 mks, repetition rate up to 5 Hz) this cavity, which is based on the Cut Disk Structure (CDS), is a full scale, high rf power prototype of the cavities proposed for the PPA. The booster cavity operation will allow us to confirm the main design ideas for the high gradient PPA cavities. A detailed technical study was performed during the booster cavity design, resulting in some modifications for the PPA cavities, which are described in this paper. We also propose a program of rf experiments with the PITZ booster cavity for further improvements of the PPA structures.  
RPPP011 Different Options for Dispersion Free Steering in the CLIC Main Linac linac, emittance, electron, quadrupole 1251
  • D. Schulte
    CERN, Geneva
  Funding: We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT-2003-506395).

Sophisticated beam-based alignment is essential in future linear colliders to preserve the beam emittance during the transport through the main linac. One such method is dispersion free steering. In this paper different options to implement this method are discussed, based on the use of different accelerating gradients, RF phases and bunch particle types during a beam pulse.

RPPP020 Linear Damping Systems for the International Linear Collider damping, wiggler, emittance, radiation 1689
  • G. Dugan
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Funding: Supported by the National Science Foundation

The International Linear Collider requires very low transverse emittance beams in order to realize the specified high luminosity. These beams are conventionally produced using radiation damping in specially designed damping rings. A linear damping system, consisting of alternating wigglers and accelerating structures arranged in a straight line, can be considered to replace, or to augment, conventional damping rings. In this paper, the basic features, feasibility, advantages, and disadvantages, of such systems, as applied to the International Linear Collider, will be discussed.

RPPP029 Analysis of Positron Collection in Linear Collider target, electron, damping, emittance 2101
  • Y.K. Batygin
    SLAC, Menlo Park, California
  Funding: Work is supported by Department of Energy Contract No. DE-AC02-76SF00515

In the Linear Collider, the positron capture system includes a positron production target, a flux concentrator, and a linac to accelerate positrons up to the injection energy of the positron damping ring. Two schemes for positron production have been studied: (i) a conventional approach with an electron beam interacting with a high-Z target and (ii) polarized positron production using polarized photons generated in a helical undulator by electron beam which then interact with a positron production target. Efficiency of positron collector is defined by positron yield which is a ratio of positrons accepted into damping ring to the number of incident electrons or photons. The capture system has been optimized to insure high positron yield into the 6-dimensional acceptance of the damping ring keeping the high value of positron polarization. Various parameters affecting the positron capture are analyzed.

RPPP038 Electron-Cloud Effects in Transport Lines of a Normal Conducting Linear Collider electron, focusing, vacuum, resonance 2527
  • J. Wu, M.T.F. Pivi, T.O. Raubenheimer, A. Seryi
    SLAC, Menlo Park, California
  Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.

In the transport lines of a normal conducting linear collider, the long positron bunch train can generate an electron cloud which can then amplify intra-train offsets. This is a transient effect which is similar to but different from the electron-cloud driven coupled bunch instabilities in a positron storage ring. In this paper, we study this phenomenon both analytically and via numerical simulation. Some criterion on the critical cloud density with respect to given collider parameters is discussed.

RPPP039 Heat Deposition in Positron Sources for ILC target, photon, electron, shielding 2574
  • V. Bharadwaj, R. Pitthan, J. Sheppard, H. Vincke, J.W. Wang
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE-AC02-76SF00515.

In an ILC positron source, multi-GeV electrons or multi-MeV photons impinge on a metal target. In either case, the incoming beam power is hundreds of kilowatts. Various computer programs - such as FLUKA or MARS – can calculate how the incoming beam showers in the target and can track the particle showers through the positron source system. The incoming energy ends up as heat in the various positron source elements. This paper presents results from such calculations and their impact on the design of a positron source for the ILC.

RPPP044 Studies of Room Temperature Accelerator Structures for the ILC Positron Source acceleration, impedance, coupling, linear-collider 2827
  • J.W. Wang, C. Adolphsen, V. Bharadwaj, G.B. Bowden, V.A. Dolgashev, R.M. Jones, E.N. Jongewaard, J.R. Lewandowski, Z. Li, R.H. Miller
    SLAC, Menlo Park, California
  Funding: Work supported by U.S. Department of Energy, contract DE-AC02-76F00515.

There are many challenges in the design of the normal-conducting portion of ILC positron injector system such as achieving adequate cooling with the high rf and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. The proposed design for the positron injector contains both standing-wave and traveling-wave L-band accelerator structures for high RF efficiency, low cost and ease of fabrication. This paper presents results from studies of particle energy deposition for both undulator based and conventional positron sources, cooling system design, accelerator structure optimization, RF pulse heating, cavity frequency stabilization, and RF feed system design.

RPPP049 Bunching for Shorter Damping Rings for the ILC damping, extraction, kicker, linac 3052
  • D.V. Neuffer
    Fermilab, Batavia, Illinois
  A variant rearrangement of the bunch trains for the ILC that enables much shorter damping rings is presented. In a particular example the ~2280 bunches are regrouped into ~450 subtrains of five adjacent bunches. These subtrains are extracted from the damping rings at ~2.2 ms intervals, obtaining the 1ms macrobunch length of the baseline TESLA collider scenario. If the baseline damping rf frequency is 325 MHz and the kicker rise and fall times are ~20 ns, a ring circumference of ~4.5km is required. Variations of the scheme could easily reduce the circumference to ~3km, and faster kickers could reduce it even further.  
FPAP001 Electron Cloud Build-Up Study for DAFNE electron, vacuum, simulation, wiggler 779
  • C. Vaccarezza, R. Cimino, A. Drago, M. Zobov
    INFN/LNF, Frascati (Roma)
  • G. Bellodi
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  • K. Ohmi
    KEK, Ibaraki
  • M.T.F. Pivi
    SLAC, Menlo Park, California
  • G. Rumolo
    GSI, Darmstadt
  • D. Schulte, F. Zimmermann
    CERN, Geneva
  After the first experimental observations compatible with the presence of the electron cloud effect in the DAFNE positron ring, a more systematic study has been performed regarding the e-cloud build-up and related instability. The measured field map of the magnetic field has been taken into account in the simulation for elements present in the four 10 m long bending sections, representing 40% of the whole positron ring. The simulation results obtained with different codes are presented and compared with the recent experimental observations performed on the beam instabilities and the vacuum behavior of the positron ring.  
FPAP003 Simulation Study of the Electron Cloud Instability in SuperKEKB electron, simulation, vacuum, synchrotron 868
  • H. Fukuma
    KEK, Ibaraki
  • L. Wang
    BNL, Upton, Long Island, New York
  The electron-cloud instability (ECI), especially a beam blowup caused by the single-bunch instability, is one of the most important issues faced at existing B factories. In SuperKEKB which is an upgrade plan of the KEK B factory, a positron beam will be stored in the high energy ring after LINAC upgrade to mitigate the ECI and ante-chambers will be effective to reduce the number of electrons. Nevertheless the ECI might be an issue of SuperKEKB because a large beam current of 4.1A will be stored with a short bunch spacing of 2ns. We performed a simulation of the cloud buildup by a program CLOUDLAND. The average electron density and the electron density at the center of a chamber were calculated both in drift space and in various magnetic fields. The result shows that a solenoid field is very effective for reducing the electron density. The simulated electron density will be compared with a threshold electron density of the strong head-tail instability.  
FPAP005 Coupled Bunch Instability Caused by Electron Cloud electron, simulation, feedback, betatron 943
  • M. Tobiyama, J.W. Flanagan, H. Fukuma, S.-I. Kurokawa, K. Ohmi, S.S. Win
    KEK, Ibaraki
  Coupled bunch instability caused by electron cloud has been observed in some positron storage ring. We discuss the mode spectrum of the coupled bunch instability due to electrons moving in drift space, weak solenoid field and strong bending field. The mode spectrum of the instability is reflected by the electron motion: that is, we understand global characteristics of elecron motion from the mode spectrum.  
FPAP007 Measurement of the Electron Cloud Density Around the Beam electron, simulation, storage-ring, vacuum 1054
  • K.-I. Kanazawa, H. Fukuma, H. Hisamatsu, Y. Suetsugu
    KEK, Ibaraki
  Under the present operating condition of KEKB LER, most high energy electrons in the electron cloud that hit the chamber wall are produced near the circulating bunch by the single kick. By separating the high energy component of the electron current monitored at a pump port of a vacuum chamber, the density of the electron cloud near the beam is estimated. The estimated density is close to the order of magnitude expected from simulation. At present there still remains an ambiguity that comes from the detector efficiency in the measurement and the assumed secondary electron yield in the simulation.  
FPAP017 Luminosity Optimization With Offset, Crossing Angle, and Distortion luminosity, electron, linear-collider, simulation 1541
  • J. Wu, T.O. Raubenheimer
    SLAC, Menlo Park, California
  Funding: Work is supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.

In a linear collider, sources of beam jitter due to kicker noise, quadrupole vibration and long-range transverse wakefields will lead to beam offsets and tilts at the Intersection Point (IP). In addition, sources of emittance dilution such as short-range transverse wakefields or dispersive errors will lead to internal beam distortions. When the IP disruption parameter is large, these beam imperfections will be amplified by a single bunch kink instability which will lead to luminosity loss. In this paper, we study the luminosity loss and then the optimization required to cancel the luminosity loss first analytically and then with simulation.

FOAA003 HOM Effects in Vacuum System with Short Bunches vacuum, resonance, luminosity, synchrotron 289
  • A. Novokhatski
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE–AC02–76SF00515.

High luminosity in electron-positron factories requires high beam currents of very short bunches. SLAC PEP-II and KEKB B-factories are progressively increasing currents and gaining more and more luminosity. Because of this the interaction of high currents and vacuum chamber elements becomes more important for the operation of the rings. High Order Modes (HOM) excited by short intense bunches propagate along the vacuum chamber, penetrating and dissipating inside vital vacuum elements like shielded bellows, vacuum valves and vacuum pumps. As a result these elements can heat up or have temperature oscillations. Often HOM heating has a resonance character. HOM heating of vacuum pumps can lead to vacuum pressure increases. High frequency modes excited by short bunches “check” the quality of the vacuum chamber by detecting small gaps, weak RF screens or weak feed-through. At these high currents even smooth tapers and smooth collimators become a source of HOM production. We will discuss the physical nature of these very interesting HOM effects.