• Y. Alexahin
  Fermilab, Batavia, Illinois

• M. Giovannozzi, R. Cappi, S.S. Gilardoni, M. Martini, E. Métral, R.R. Steerenberg
  CERN, Geneva
• A.-S. Müller
  FZK, Karlsruhe

• I. Hofmann, G. Franchetti
  GSI, Darmstadt
• J.F. Amundson, P. Spentzouris
  Fermilab, Batavia, Illinois
• S.M. Cousineau, J.A. Holmes
  ORNL, Oak Ridge, Tennessee
• M. Giovannozzi, E. Métral
  CERN, Geneva
• F.W. Jones
  TRIUMF, Vancouver
• A.U. Luccio
  BNL, Upton, Long Island, New York
• S. Machida
  KEK, Ibaraki
• J. Qiang, R.D. Ryne
  LBNL, Berkeley, California

• F. Zimmermann, J.-P. Koutchouk, F. Roncarolo, J. Wenninger
  CERN, Geneva
• Y. Papaphilippou
  ESRF, Grenoble
• T. Sen, V.D. Shiltsev
  Fermilab, Batavia, Illinois

• H. Hotchi, F. Noda, N. Tani
  JAERI/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• J. Kishiro, S. Machida, A.Y. Molodojentsev
  KEK, Ibaraki

• A.Y. Molodojentsev, E. Forest, S. Machida
  KEK, Ibaraki
• H. Hotchi, F. Noda, M.J. Shirakata, Y. Shobuda, H. Suzuki, K. Yamamoto
  JAERI/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• Y. Ishi
  Mitsubishi Electric Corp, Energy & Public Infrastructure Systems Center, Kobe

• R. Bartolini, A.I. Baldwin, M. Belgroune, I.P.S. Martin, J.H. Rowland, B. Singh
  Diamond, Oxfordshire
• J.K. Jones
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

• R. Bartolini
  Diamond, Oxfordshire
• F. Schmidt
  CERN, Geneva

• Y. Cai, Y. Nosochkov
  SLAC, Menlo Park, California

The leading Lie generators, including the chromatic effects, due to hard edge fringe field of single multipole and solenoid are derived from the vector potentials within a Halmitonian system. These nonlinear generators are applied to the interaction region of PEP-II to analyze the linear errors due to the feed-down from the off-centered quadrupoles and solenoid. The nonlinear effects of tune shifts at large amplitude, the synchro-betatron sidebands near half integer and their impacts on the dynamic aperture are studied in the paper.

• J.F. Cardona
  UNAL, Bogota D.C
• R. Tomas
  BNL, Upton, Long Island, New York

Recently, an "action and phase" analysis of SPS orbits measurements proved to be sensitive to sextupole components intentionally activated at specific locations in the ring. In this paper we attempt to determine the strenght of such sextupoles from the measured orbits and compare them with the set values. Action and phase analysis of orbit trayectories generated by RHIC models with non linearities will also be presented and compare with RHIC experiments.

• Y. Luo, F.C. Pilat, V. Ptitsyn, D. Trbojevic, J. Wei
  BNL, Upton, Long Island, New York

The interaction region bump (IR bump) nonlinear correction method has been used for the sextupole and octupole field error on-line corrections in the Relativistic Heavy Ion Collider (RHIC). Some differences were found for the sextupole and octupole corrector strengths between the on-line IR bump correction and the predictions from the action-angle kick minimization. In this report we compare the corrector strengths from these two methods based on the RHIC Blue ring lattice with the IR nonlinear modeling. The comparison confirms the differences between resulting corrector strengths. And the reason for the differences is found and discussed. It is followed by a further discussion of the operational IR bump applications to the octupole, and skew sextupole and skew quadrupole field error corrections.

• M. Takao, M. Masaki, J. Schimizu, K. Soutome, S. Takano, H. Tanaka
  JASRI/SPring-8, Hyogo

• F. Meot
  CEA/DSM/DAPNIA, Gif-sur-Yvette
• F. Lemuet
  CERN, Geneva
• G. Rees
  CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon

Numerical ray-tracing tools for 6-D tracking in FFAG accelerators have been developed. They are applied to the simulation of muon acceleration in the newly introduced isochronous type of FFAG ring designed for 16-turn, 8 to 20~GeV muon acceleration in the Neutrino Factory.

• Y.T. Yan, Y. Cai
  SLAC, Menlo Park, California

Eigen-mode coupling ellipses' tilt angles and axis ratios can be precisely measured with a Model-Independent Analysis (MIA) of the turn-by-turn BPM data from resonance excitation of the betatron motion. For each BPM location one can measure 4 parameters from the two resonance excitation, which completely describe the linear coupling of the location. Results from application to PEP-II storage rings are presented.

• V. Sajaev, L. Emery
  ANL, Argonne, Illinois

Over past few years, the optics of the Advanced Photon Source storage ring was optimized to provide lower natural emittance. Presently, APS operates at 2.5 nm-rad emittance. The optimization was done at the expense of stronger sextupoles and shorter lifetime. Here we present our work on measurement and understanding the dynamic aperture of APS in low-emittance mode. We found good agreement between the dynamic aperture measurements and that of the model derived from the response matrix analysis. Based on the model, we were able to increase the lifetime significantly by optimizing sextupoles, correcting optics, moving working point, and adjusting rf voltage. The higher lifetime allowed us to decrease operating coupling from 2.5% to 1%.

• V.A. Shchepunov
  ORAU, Oak Ridge, Tennessee
• H. Wollnik
  JIHIR, Oak Ridge, Tennessee

A multi-pass time-of-flight (MTOF) mass separator is under development by the UNIRIB collaboration. The MTOF consists of two coaxial electrostatic mirrors, focusing lenses and auxiliary injection, extraction and separation elements. The injected ions having almost the same energy but different masses undergo hundreds or thousands of reflections between the mirrors. In the course of this periodic motion, the ions of different masses and hence velocities are spatially separated in longitudinal direction. The periodic motion in the MTOF has been investigated with a recently developed ray tracing program utilizing the canonical integration technique. Results of the performed numerical simulations are discussed. The simulations displayed nonlinear character of the ion’s behavior both in transverse and longitudinal phase spaces. The ion’s transverse stability and longitudinal isochronicity were the matters of primary attention. It is shown in particular that at transverse tunes of around q=0.75 the system can be adjusted to be isochronous up to at least the 3rd order of the ToF optical aberrations.

• J. Wu, A. Chao, B. Nash
  SLAC, Menlo Park, California

In accelerator systems, it is very common that the motion of the horizontal plane is coupled to that of the vertical plane. Such coupling will induce tune shifts and can cause instabilities. The damping and diffusion rates are also changed, which in turn will lead to a change in the equilibrium invariants. Following the perturbative approach which we developed for synchrobetatron coupling,* we study the x-y coupled case in this paper. Starting from the one turn map, we give explicit formulae for the tune shifts, damping and diffusion rates, and the equilibrium invariants. We focus on the cases where the system is near the integer or half integer, and sum or difference resonances where small coupling can cause a large change in the beam distribution.

*B. Nash, J. Wu, and A. Chao, work in progress.

• V.H. Ranjbar
  Fermilab, Batavia, Illinois

A feed back orbit stabilization system has been developed using a set of BPMS and existing Tevatron corrector magnets to stabilize beam motion up to 50 microns below 25 Hz. The construction of this system is described and the stability limits and magnitude of beam motion reduction is explored.

• N.P. Abreu, N.P. Abreu
  UNICAMP, Campinas, São Paulo
• R.H.A. Farias, P.F. Tavares
  LNLS, Campinas

In the Brazilian Electron Storage Ring, we observed that modulating the phase of accelerating fields at twice the synchrotron frequency suppressed remarkably well a longitudinal coupled-bunch mode of the beam driven by one of the RF cavities. We present results of a set of systematic measurements, in single and multi-bunch mode, aimed at characterizing the effects of the modulation on the beam. We also compare those experiments with the results of tracking simulations.

• T. Kroyer, T. Kroyer
  TU Vienna, Vienna
• F. Caspers, E. Mahner
  CERN, Geneva

In the CERN SPS microwave transmission measurements through beampipe sections with a length of 30 m and 7 m meter respectively have been carried out in the frequency range 2-4 GHz since spring 2003. Here we report on new results obtained with improved measurement techniques during the 2004 run. Observation techniques include a fast real time scope, spectrum analyser IF and video output signal registration and baseband signal observation using a PC soundcard. The unexpected beam induced amplitude modulation has been confirmed on all kinds of available beams including single bunches. It was found that there is a correlation between the amount of beam induced signal attenuation and the beam losses registered by external scintillators. Potential theoretical models are discussed.

• A. Blednykh, J.-M. Wang
  BNL, Upton, Long Island, New York

• S.-Y. Lee, S. Breitzmann
  IUCF, Bloomington, Indiana
• K.Y. Ng
  Fermilab, Batavia, Illinois

Passive ferrite inserts were used to compensate the space charge impedance in high intensity space charge dominated accelerators. We study the narrowband longitudinal impedance of these ferrite inserts. We find that the shunt impedance and the quality factor for ferrite inserts are inversely proportional to the imaginary part of the permeability of ferrite materials. We also provide a receipe for truly passive space charge impedance compensation and, at the same time, avoiding the narrowband microwave instabilities.

• S.C. Gottschalk, K.W. Kangas, D.J. Taylor, W.J. Thayer
  STI, Washington

• E. Willen, M. Anerella, J. Escallier, G. Ganetis, A. Ghosh, R.C. Gupta, M. Harrison, A.K. Jain, A.U. Luccio, W.W. MacKay, A. Marone, J.F. Muratore, S.R. Plate, T. Roser, N. Tsoupas, P. Wanderer
  BNL, Upton, Long Island, New York
• M. Okamura
  RIKEN, Saitama

A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that the magnet can operate in the AGS cooled by several cryocoolers. The design, construction and performance of this unique magnet will be summarized.

• I.N. Onishchenko, N. Onishchenko, G. Sotnikov
  NSC/KIPT, Kharkov
• T.C. Marshall
  Yale University, Physics Department, New Haven, CT

The dielectric wake field accelerator is based on particle acceleration by wake fields excited in a dielectric waveguide by a regular sequence of electron bunches. Enhancement of the accelerating field can be achieved using two phenomena: coherent excitation by many bunches (multibunch effect) and constructive interference of many excited eigenmodes (multimode effect). It was believed that the latter is possible only for planar slab geometry in which the excited modes are equally spaced in frequency. By analysis and simulation, in this presentation the effect of wake field superposition to high amplitude is demonstrated for arbitrary rectangular geometry that is more realizable in experiment. We find this result using simultaneous multibunch and multimode operation providing the repetition frequency of the bunch sequence is equal to the frequency difference between selected modes, whereupon resonant oscillation takes place. Moreover, it is shown that for an appropriate choice of selected modes and bunch repetition frequency a "quasimonopolar” peaked wake field can be excited.

• R. Siemann, A. Chao
  SLAC, Menlo Park, California

Dielectric laser driven accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effect on the short range wakefield is calculated.

• C.M.S. Sears, E.R. Colby, B.M. Cowan, R. Siemann, J.E. Spencer
  SLAC, Menlo Park, California
• R.L. Byer, T. Plettner
  Stanford University, Stanford, Califormia

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and used as a short wavelength modulator forμbunching of beams for laser acceleration experiments*,**. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.25 mJ/pulse laser at 800 nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. We will also discuss diagnostics for obtaining beam overlap and statistical techniques used to account for machine drifts and analyze the data.

*W. D. Kimura, et. al., Phys. Rev. S.T. Acc. & Beams 4 101301 (2001). ** P. Musumeci, et. al., AAC 2004 Proceedings. Pg 170.

• P. Schoessow
  Tech-X, Boulder, Colorado
• A. Kanareykin
  Euclid TechLabs, LLC, Solon, Ohio

• M.S. Hur, G.-H. Kim, H. Suk
  KERI, Changwon
• A.E. Charman, R.R. Lindberg, J.S. Wurtele
  LBNL, Berkeley, California

We present analysis and simulations of kinetic effects in the Raman pulse amplification in plasma. An ultraintense and ultrashort laser pulse is a very essential part in an advanced acceleration scheme using laser and plasma. To make strong pulses, a noble scheme of using Raman backscatter in plasma was proposed and has been studied intensively.* The Raman amplification in plasma does not have a restriction in material damage threshold. However, for the new amplifier to be a promising alternative of the CPA technique, more extensive studies on various issues are required. One of the fundamental issues is the electron kinetic effect such as particle trapping or wavebreaking. We present a theoretical analysis of the kinetic effect; a new kinetic term is derived to be added to the fluid model and the effect of the new term is verified by averaged-PIC (aPIC)** simulations. Various one dimensional and semi-two dimensional aPIC simulations of pulse amplification are presented. We discuss the future application of the Raman scheme to upgrading the laser pulse of the Center of Advanced Accelerator in KERI, which are currently 2 TW and 700 fs, into a few more TW and less than 100 fs.

*V. M. Malkin, G. Shvets, and N. J. Fisch, Phys. Rev. Lett. vol. 82, 4448 (1999).**M. S. Hur, G. Penn, J. S. Wurtele, and R. Lindberg, Phys. Plasmas vol. 11, 5204 (2004).

• A. Kanareykin
  Euclid TechLabs, LLC, Solon, Ohio
• W. Gai, J.G. Power
  ANL, Argonne, Illinois
• S.F. Karmanenko, A. Semenov
  Eltech University, St. Petersburg
• E. Nenasheva
  Ceramics Ltd., St. Petersburg
• P. Schoessow
  Tech-X, Boulder, Colorado

Experimental study of a new scheme to tune the resonant frequency for dielectric based accelerating structure (driven either by the wakefield of a beam or an external rf source) is underway. The structure consists of a single layer of conventional dielectric surrounded by a very thin layer of ferroelectric material situated on the outside. Carefully designed electrodes are attached to a thin layer of ferroelectric material. A DC bias can be applied to the electrodes to change the permittivity of the ferroelectric layer and therefore, the dielectric overall resonant frequency can be tuned. In this paper, we present the test results for an 11.424 GHz rectangular DLA prototype structure that the ferroelectric material's dielectric constant of 500 and show that a frequency tuning range of 2% can be achieved. If successful, this scheme would compensate for structure errors caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity.

• A.E. Charman, R.R. Lindberg, J.S. Wurtele
  UCB, Berkeley, California
• L. Friedland
  The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem

A modified version of the Plasma Beat-Wave Accelerator scheme is introduced and analyzed, which is based on autoresonant phase-locking of the nonlinear Langmuir wave to the slowly chirped beat frequency of the driving lasers via adiabatic passage through resonance. This new scheme is designed to overcome some of the limitations of previous approaches, namely relativistic detuning and nonlinear modulations in the driven Langmuir wave amplitude, and sensitivity to frequency mismatch from density fluctuations. As in previous schemes, instabilities of the ionic background ultimately limit the useful interaction time, but nevertheless peak electric fields approaching the wave-breaking limit seem readily attainable. Compared to traditional approaches, the autoresonant scheme achieves larger accelerating electric fields for given laser intensity; the plasma wave excitation is more robust to variations in plasma density; it is largely insensitive to the choice of chirp rate, provided that chirping is sufficiently slow; and the quality and uniformity of the resulting plasma wave and its suitability for accelerator applications may be superior.

• M. Bai, H. Huang, W. Mac Kay, V. Ptitsyn, T. Roser, S. Tepikian
  BNL, Upton, Long Island, New York
• S.-Y. Lee, F. Lin
  IUCF, Bloomington, Indiana

Siberian snakes now become essential in the polarized proton acceleration. With proper configuration of Siberian snakes, the spin precession tune of the beam becomes $\frac{1}{2}$ which avoids all the spin depolarizing resonance. However, the enhancement of the perturbations on the spin motion can still occur when the betatron tune is near some low order fractional numbers, called snake resonances, and the beam can be depolarized when passing through the resonance. The snake resonances have been confirmed in the spin tracking calculations, and observed in RHIC with polarized proton beam. Equipped with two full Siberian snakes in each ring, RHIC provides us a perfect facility for snake resonance studies. This paper presents latest experimental results. New insights are also discussed.

• R. Tomas
  CELLS, Bellaterra (Cerdanyola del Vallès)
• W. Fischer
  BNL, Upton, Long Island, New York

We consider the scenario of having two identical Interaction Points (IPs) in the Relativistic Heavy Ion Collider (RHIC). The strengths of beam-beam resonances strongly depend on the phase advance between these two IPs and therefore certain phase advances could improve beam lifetime and luminosity. We compute the dynamic aperture as function of the phase advance between these IPs to find the optimum settings. The beam-beam interaction is treated in the weak-strong approximation and a complete non-linear model of the lattice is used. For the current RHIC proton working point (0.69,0.685) the design lattice is found to have the optimum phase advance. However this is not the case for other working points.

• C. Montag
  BNL, Upton, Long Island, New York

To study collisions between polarized electrons and heavy ions or polarized protons at high energy, adding a 10 GeV electron storage ring to the existing RHIC facility is currently under consideration. To achieve high luminosities, vertical beam-beam tuneshift parameters of 0.08 are required for the electron beam. Simulation studies are being performed to study the feasibility of these high tuneshift parameters and to explore the potential for even higher tuneshifts. Recent results of these studies are presented.

• M. Giovannozzi, J. Morel
  CERN, Geneva

• B. Podobedov, S. Krinsky
  BNL, Upton, Long Island, New York

The geometric impedance of small-gap undulator chambers is of paramount importance for modern light sources because it may drive transverse single bunch instabilities. Analytical expressions are derived for the transverse impedance assuming a slowly tapered vacuum chamber with a confocal elliptical cross-section. The analytical results are confirmed by numerical simulations with the GdfidL Electromagnetic Field simulator and they yield the correct asymptotic limits for both round and flat chambers.

• K.Y. Ng
  Fermilab, Batavia, Illinois

• N.E. Vasyukhin, Y. Senichev, R. Tölle
  FZJ, Jülich

One of the most important problems for space charge dominated beam in the low energy part of superconducting linac is halo creation. Many authors show one of the key effects in halo creatiation is parametric resonance due to the mismatched beta-function oscillation (between core and particle). To estimate parametric resonance conditions the nonlinear tune shift for binomial distributed beam is described theoretically in this article. Simultaneously the beam dynamics simulation 3D PIC code was developed. The transverse oscillation frequencies compared with parametric resonance criteria. As a result the recommendation for space charge shift is concluded to minimize halo creation.

• J.F. Amundson, P. Spentzouris
  Fermilab, Batavia, Illinois

We have studied space charge effects in the Fermilab Booster. Our studies include investigation of coherent and incoherent tune shifts and halo formation. We compare experimental results with simulations using the 3-D space charge package Synergia.

• G. Franchetti, I. Hofmann, A. Orzhekovskaya, P.J. Spiller
  GSI, Darmstadt

• J. Wei
  BNL, Upton, Long Island, New York
• H. Enokizono, H. Okamoto, Y. Yuri
  HU/AdSM, Higashi-Hiroshima
• X.-P. Li
  Skyworks Solutions, Inc., Newbury Park. California
• A. Sessler
  LBNL, Berkeley, California

Previously it has been shown that the maintenance condition for a crystalline beam requires that there not be a resonance between the crystal phonon frequencies and the frequency associated with a beam moving through a lattice of N periods. This resonance can be avoided provided the phonon frequencies are all below half of the lattice frequency. Here we make a detailed study of the phonon modes of a crystalline beam. Analytic results obtained in a “smooth approximation” using the ground-state crystalline beam structure is compared with numerical evaluation employing Fourier transform of Molecular Dynamic (MD) modes. The MD also determines when a crystalline beam is stable. The maintenance condition, when combined with either the simple analytic theory or the numerical evaluation of phonon modes, is shown to be in excellent agreement with the MD calculations of crystal stability.

[1] X-P. Li, A. M. Sessler, J. Wei, EPAC (1994) p. 1379 - 1381. ‘Necessary Conditions for Attaining a Crystalline Beam''}[2] J. Wei, H. Okamoto, A.M. Sessler, Phys. Rev. Lett., Vol. 80, p. 2606-2609 (1998).

• A. Bogomyagkov, V.E. Blinov, V.P. Cherepanov, V. Kiselev, E. Levichev, S.I. Mishnev, N.Yu. Muchnoi, S.A. Nikitin, I.B. Nikolaev, D.M. Nikolenko, A.G. Shamov, E. Shubin, A.N. Skrinsky, Yu.A. Tikhonov, D.K. Toporkov, G.M. Tumaikin
  BINP SB RAS, Novosibirsk

• K. Beard, S.A. Bogacz, Y.S. Derbenev
  Jefferson Lab, Newport News, Virginia
• R.P. Johnson, K. Paul, T.J. Roberts
  Muons, Inc, Batavia
• K. Yonehara
  Illinois Institute of Technology, Chicago, Illinois

The technique of using a parametric resonance to allow better ionization cooling is being developed to create small beams so that high collider luminosity can be achieved with fewer muons. In the linear channel that is studied in this effort, a half integer resonance is induced such that the normal elliptical motion of particles in x-x' phase space becomes hyperbolic, with particles moving to smaller x and larger x' as they pass down the channel. Thin absorbers placed at the focal points of the channel then cool the angular divergence of the beam by the usual ionization cooling mechanism where each absorber is followed by RF cavities. Thus the phase space of the beam is compressed in transverse position by the dynamics of the resonance and its angular divergence is compressed by the ionization cooling mechanism. We report the first results of simulations of this process, including comparisons to theoretical cooling rates and studies of sensitivity to variations in absorber thickness and initial beam conditions.

• Y.S. Derbenev
  Jefferson Lab, Newport News, Virginia
• R.P. Johnson
  Muons, Inc, Batavia

Muon collider luminosity depends on the number of muons in the storage ring and on the transverse size of the beams in collision. Ionization cooling as it is presently envisioned will not cool the beam sizes sufficiently well to provide adequate luminosity without large muon intensities. A new idea to combine ionization cooling with parametric resonances has been developed that will lead to beams with much smaller sizes so that high luminosity in a muon collider can be achieved with fewer muons. In the linear channel described here, a half integer resonance is induced such that the normal elliptical motion of particles in x-x' phase space becomes hyperbolic, with particles moving to smaller x and larger x' as they pass down the channel. Thin absorbers placed at the focal points of the channel then cool the angular divergence of the beam by the usual ionization cooling mechanism where each absorber is followed by RF cavities. We discuss the theory of Parametric-resonance Ionization Cooling, including the sensitivity to aberrations and the need to start with a beam that has already been cooled adequately.

• J. Shi, L. Jin
  KU, Lawrence, Kansas
• D. Wang, F. Wang
  MIT, Middleton, Massachusetts

The eRHIC is a proposed electron ring at the RHIC that will provide collisions between a polarized 5-10 GeV electron beam and an ion beam from one of the RHIC rings. In order to achieve proposed high luminosity, large bunch current and small beta-functions at the IP has to be employed. Such measures result in large beam-beam parameters, 0.029 and 0.08 for the electron beam and 0.0065 and 0.0033 for the proton beam in the horizontal and vertical plane, respectively, in the current ZDR design. The beam-beam effect especially the coherent beam-beam effect is therefore one of important issues to the eRHIC. Moreover, the proposed configuration of unequal circumferences of the electron and proton rings could further enhance the coherent beam-beam effect. The beam-beam effect of eRHIC has therefore been studied with a self-consistent beam-beam simulation by using the particle-in-cell method. Beam-beam limits of the electron and proton beam were examined as thresholds of the onset of coherent beam-beam instability. For the proposed luminosity, the electron and proton bunch currents optimized with the consideration of the beam-beam effect will be discussed.

• P.M. Hanlet, M. Alsharo'a, R.P. Johnson, M. Kuchnir, K. Paul
  Muons, Inc, Batavia
• C.M. Ankenbrandt, A. Moretti, M. Popovic, V. Yarba
  Fermilab, Batavia, Illinois
• D.M. Kaplan, K. Yonehara
  Illinois Institute of Technology, Chicago, Illinois

A study of RF breakdown of metals in gases has begun as part of a program to develop RF cavities filled with dense hydrogen gas to be used for muon ionization cooling. A pressurized 800 MHz test cell has been used at Fermilab to compare the conditioning and breakdown behavior of copper, molybdenum, chromium, and beryllium electrodes as functions of hydrogen and helium gas density. These results are compared to the predicted or known RF breakdown behavior of these metals in vacuum.

• T. Abe, T. Kageyama
  KEK, Ibaraki
• Z. Kabeya, T. Kawasumi
  MHI, Nagoya
• T. Nakamura, K. Tsujimoto
  Asahi Kinzoku Co., Ltd., Gifu
• K. Tajiri
  Churyo Engineering Co., Ltd., Nagoya

• K. Yokoyama, M. Ikeda, K. Kakihara, T. Kamitani, S. Ohsawa, T. Sugimura, T. T. Takatomi
  KEK, Ibaraki

• D. Horan, E.E. Cherbak
  ANL, Argonne, Illinois

A 352-MHz fast-ferrite rf cavity tuner, manufactured by Advanced Ferrite Technology, was high-power tested on a single-cell copper rf cavity at the Advanced Photon Source. These tests measured the fast-ferrite tuner performance in terms of power handling capability, tuning bandwidth, tuning speed, stability, and rf losses. The test system comprises a single-cell copper rf cavity fitted with two identical coupling loops, one for input rf power and the other for coupling the fast-ferrite tuner to the cavity fields. The fast-ferrite tuner rf circuit consists of a cavity coupling loop, a 6-1/8” EIA coaxial line system with directional couplers, and an adjustable 360° mechanical phase shifter in series with the fast-ferrite tuner. A bipolar DC bias supply, controlled by a low-level rf cavity tuning loop consisting of an rf phase detector and a PID amplifier, is used to provide a variable bias current to the tuner ferrite material to maintain the test cavity at resonance. Losses in the fast-ferrite tuner are calculated from cooling water calorimetry. Test data will be presented.

• Y.W. Kang, A.V. Aleksandrov, D.E. Anderson, M.M. Champion, M. Champion, M.T. Crofford, C. Deibele, G.W. Dodson, R.E. Fuja, P.E. Gibson, P.A. Gurd, T.W. Hardek, G.A. Johnson, P. Ladd, H. Ma, M.P. McCarthy, M.F. Piller, J.Y. Tang, A.V. Vassioutchenko, D.C. Williams
  ORNL, Oak Ridge, Tennessee
• J.A. Billen, J.T. Bradley, D. Rees, W. Roybal, J. Stovall, K.A. Young, L.M. Young
  LANL, Los Alamos, New Mexico

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

• R.J. England, B. O'Shea, J.B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California
• D. Alesini
  INFN/LNF, Frascati (Roma)

We report progress on the design and construction of a nine-cell dipole (TM 110 mode) cavity for use as a temporal diagnostic of the 14 MeV 300 pC electron bunches generated at the UCLA Neptune Laboratory linear accelerator, with an anticipated temporal resolution of 150 fs at a peak input power of 50 kW. The cavity is a center-fed standing-wave pi-mode structure, operating at 9.6 GHz, and incorporating a knife-edge and gasket assembly which minimizes the need for brazing or welding. Results of initial RF tests are discussed and compared with simulation results obtained using the commercial code HFSS.

• C.-F. Wu, S. Dong, S. Hongbing, D. Jia, H. Lin, L. Wang
  USTC/NSRL, Hefei, Anhui

Mafia code has been used to calculate the RF properties versus the geometric parameters and dielectric permittivity for the X-band (f=9.37GHz) hybrid dielectric-iris-loaded traveling accelerating structure. The simulation results show that when the range of the permittivity is about 5-9, the new structure may have lower ratio (about 1) of peak surface electric field at the iris to axial accelerating electric field by optimizing the geometric parameters, while r, Q, r/Q of the new structure being comparable to iris-loaded accelerating structure. The experimental investigations of the permittivity of the ceramics have been made at the X-band by using the cavity perturbation technique. The measured results are in good agreement with the simulation results of Microwave Studio. Furthermore, the stability of the ceramics is examined. A number of experimental results show that the certain ceramic with permittivity of 5.78 is applied to the design of the new accelerating structure.

• H. Podlech, H. Deitinghoff, H. Klein, H. Liebermann, U. Ratzinger, A.C. Sauer, R. Tiede
  IAP, Frankfurt-am-Main

The Crossbar-H-type CH-structure is a new H-mode drift tube-structure operating in the H11-mode. Due to its mechanical rigidity room temperature as well as superconducting cavities can be realized. The superconducting CH-structure has been developed at the IAP in Frankfurt, Germany. To prove the promising results obtained by simulations a 19-cell, 352 MHz (beta=0.1) prototype cavity has been designed and built. This is the first superconducting low energy multi-cell cavity. We present the first cold tests of the cavity which have been performed in the cryogenic laboratory in Frankfurt.

• J. Rank, I. Ben-Zvi, M. Blaskiewicz, H. Hahn, G.T. McIntyre
  BNL, Upton, Long Island, New York

The ECX Project, Brookhaven Lab's predecessor to the RHIC e-Cooler, includes a prototype RF tuner mechanism capable of both coarse and fine tuning of the superconducting RF cavity. This tuner is adapted originally from a DESY design concept but with a longer stroke and significantly higher loads due to our very stiff cavity shape. Structural design, kinematics, controls, thermal and RF issues are discussed and certain improvements are proposed.

• N. Solyak, T.T. Arkan, P. Bauer, L. Bellantoni, C. Boffo, E. Borissov, H. Carter, H. Edwards, M. Foley, I.G. Gonin, T.K. Khabiboulline, S.C. Mishra, D.V. Mitchell, V. Poloubotko, A.M. Rowe, I. Terechkine
  Fermilab, Batavia, Illinois

A superconducting third harmonic accelerating cavity (3.9 GHz) was proposed to improve beam quality in the TTF-like photoinjector. Fermilab has developed, built and tested several prototypes, including two copper 9-cell cavities, and niobium 3-cell and 9-cell cavities. The helium vessel and frequency tuner for the 9-cell cavity was built and tested as well. In cold tests, we achieved a peak surface magnetic field of ~120mT, well above the 70mT specification. The accelerating gradient was limited by thermal breakdown. Studies of the higher order modes in the cavity revealed that the existing cavity design with two HOM couplers will provide sufficient damping of these modes. In this paper we discuss the cavity design, results of the studies and plans for further development.

• A.S. Hofler, J.R. Delayen
  Jefferson Lab, Newport News, Virginia

Electronic damping of microphonic vibrations in superconducting rf cavities involves an active modulation of the cavity field amplitude in order to induce ponderomotive forces that counteract the effect of ambient vibrations on the cavity frequency. In lightly beam loaded cavities, a reduction of the microphonics-induced frequency excursions leads directly to a reduction of the rf power required for phase and amplitude stabilization. Jefferson Lab is investigating such an electronic damping scheme that could be applied to the JLab 12 GeV upgrade, the RIA driver, and possibly to energy-recovering superconducting linacs. This paper discusses a model and presents simulation results for electronic damping of microphonic vibrations.

• H. Wang, R.A. Rimmer, G. Wu
  Jefferson Lab, Newport News, Virginia

A normal design process for a superconducting cavity shape is to maximize the R/Q (shunt impedance/intrinsic quality factor) and geometry factor G for a given RF field limit of Bpeak/Eacc or Epeak/Eacc. For the application of an Ampere-class, high current energy recovery linac or storage ring, heavy HOM damping is required. This paper reports on a survey of single cell shapes developed for multi-cell cavities for different projects. Using a set of normalized parameters, we compare the designs for different frequencies and ß structures for the fundamental mode. Using dispersion curve (frequency verse phase advance) calculated by MAFIA for a single cell, we explore further how to optimize the cavity shape to avoid a light cone line crossing at the dangerous resonance frequencies determined by the beam bunch structure or the dangerous (trapped or high R/Q) modes with a low group velocity. We expect such a formulation to inform our development of a 5-cell, optimized cavity shape, with good real estate accelerating gradient and strong HOM damping waveguide structure for the JLab 1MW ERL-FEL project.

• C. Nieter, J.R. Cary, P. Stoltz
  Tech-X, Boulder, Colorado
• G.R. Werner
  CIPS, Boulder, Colorado

*C. Nieter and J.R. Cary, J. Comp. Phys. 196 (2004), p. 448. **P.H. Stoltz, ICFA electron cloud work shop, Napa, CA (2004).

• P.E. Gibson, A.V. Aleksandrov, M.M. Champion, G.W. Dodson, J.P. Schubert, J.Y. Tang
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. The warm linac portion, designed by Los Alamos, has been installed and commissioned. The warm linac is comprised of six Drift Tube Linac (DTL) tanks and four Coupled Cavity Linac (CCL) modules. For commissioning purposes the accelerating systems have been operated at less than the design 6% duty factor. During lower power operation there is less RF cavity heating. This decrease in heat load causes operational stability issues for the associated Resonance Control Cooling Systems (RCCSs) which were designed for full duty factor operation. To understand this effect operational results have been analyzed and tests have been performed. External system factors have been explored and the resulting impacts defined. Dynamic modeling of the systems has been done via a collaboration with the Institute for Nuclear Research (INR), Moscow, Russia. New RCCS operation code has been implemented. Increases in system performance achieved and solutions employed will be presented.

• M. Ebert, F.-R. Ullrich
  DESY, Hamburg

• I.H. Yu, Y.J. Han, H.-S. Kang, D.T. Kim, S.-C. Kim, I.-S. Park, J.C. Yoon
  PAL, Pohang, Kyungbuk
• Y.-S. Cho, H.-J. Kwon, K.T. Seol
  KAERI, Daejon

The 100 MeV Proton linear accelerator (Linac) for the PEFP (Proton Engineering Frontier Project) will include 1 RFQ and 1 DTL1 at 350 MHz as well as 7 DTL2 cavities at 700 MHz. The low level RF system with the digital feedback RF control provides the field control to accelerate a 20mA proton beam from 50 keV to 20 MeV with a RFQ and a DTL1 at 350M Hz. The FPGA-based digital feedback RF control system has been built and is used to control cavity field amplitude within ± 1% and relative phase within ± 1°. The fast digital processing is networked to the EPICS-based control system with an embedded processor (Blackfin). In this paper, the detailed description of the digital feedback RF control system will be described with the performance test results.

• M.M. Paoluzzi, R. Garoby, M. Haase, P. Maesen, C. Rossi
  CERN, Geneva
• C. Ohmori
  KEK, Ibaraki

• V.P. Yakovlev, O.A. Nezhevenko
  Omega-P, Inc., New Haven, Connecticut
• J.L. Hirshfield
  Yale University, Physics Department, New Haven, CT

High-power ultra-fast, electrically-controlled switches based on ferroelectric elements for accelerator applications in the centimeter and millimeter wavelength ranges are discussed. Examples of fast switches and phase shifters for pulse compression and power distribution systems at X– and Ka- band are presented. It is shown that such proposed switch designs based on modern ferroelectric materials allow the generation of pulsed power of hundreds of MW’s in both the centimeter and millimeter wave ranges.

• M.J. Wissmann, AA. Guerra, C. Hovater, T. Plawski
  Jefferson Lab, Newport News, Virginia

The CEBAF energy upgrade from 6 GeV to 12GeV will increase the range of beam energies available to the experimental halls. RF deflection cavities (separators) are used to direct the electron beam to the three experimental halls. Consequently with the increase in RF separator cavity gradient needed for the higher energies, RF power will also increase requiring the cavities to have active resonance control. At the 6 GeV energy, the cavities are tuned mechanically and then stabilized with Low Conductivity Water (LCW), which is maintained at constant temperature of 95o Fahrenheit. This is no longer feasible and an active resonance control system, that controls both water temperature and flow has been built. The system uses a commercial PLC with embedded PID controls to control water temperature and flow to the cavities. The system allows the operator to remotely adjust temperature/flow and consequently cavity resonance for the full range of beam energies. Ultimately closed loop control will be maintained by monitoring the cavities reflected power. This paper describes this system.

• S.A. Belomestnykh, R.P.K. Kaplan, J.J.R. Reilly, V. Veshcherevich
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York

An instability of the active RF cavity field control loop was observed during experiments with beam-driven (passive) superconducting cavities in CESR when the cavity external Q factor was raised to a value above 1x10⁷. A computer model was developed and further experiments have been performed to study this instability and find a way to cure it. The results of simulations are presented alongside the experimental results.

• M. Liepe, S.A. Belomestnykh, J. Dobbins, R.P.K. Kaplan, C.R. Strohman, B.K. Stuhl
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
• C. Hovater, T. Plawski
  Jefferson Lab, Newport News, Virginia

The superconducting cavities in an Energy-Recovery-Linac will be operated with a high loaded Q of several 1E7, possible up to 1E8. Not only has no prior control system ever stabilized the RF field in a linac cavity with such high loaded Q, but also highest field stability in amplitude and phase is required at this high loaded Q. Because of a resulting bandwidth of the cavity of only a few Hz, this presents a significant challenge: the field in the cavity extremely sensitive to any perturbation of the cavity resonance frequency due to microphonics and Lorentz force detuning. To prove that the RF field in a high loaded Q cavity can be stabilized, and that Cornell's newly developed digital control system is able to achieve this, the system was connected to a high loaded Q cavity at the JLab IR-FEL. Excellent cw field stability – about 2·10^-4 rms in relative amplitude and 0.03 deg rms in phase - was achieved at a loaded Q of 2.1·10⁷ and 1.4E8, setting a new record in high loaded Q operation of a linac cavity. Piezo tuner based cavity frequency control proved to be very effective in keeping the cavity on resonance and allowed reliable to ramp up to high gradients in less than 1 second.

• I. Terechkine, G.W. Foster, I.G. Gonin, T.K. Khabiboulline, A. Makarov, N. Solyak, D. Wildman
  Fermilab, Batavia, Illinois

• D.E. Anderson, J. Hicks, D. E. Hurst, E.R. Tapp, M. Wezensky
  ORNL, Oak Ridge, Tennessee
• D. Baca, W. Reass
  LANL, Los Alamos, New Mexico
• V.V. Peplov
  RAS/INR, Moscow

The first-generation high frequency switching megawatt-class high voltage converter modulators (HVCM) developed by Los Alamos National Laboratory for the Spallation Neutron Source at Oak Ridge National Laboratory have been installed and are now operational. Each unit is capable of delivering pulses up to 11 MW peak, 1 MW average power at voltages up to 140 kV to drive klystron(s) rated up to 5 MW. To date, three variations of the basic design have been installed, each optimized to deliver power to a specific klystron load configuration. Design improvements, with the primary intention of improving system reliability and availability, have been under development since the initial installation of the HVCM units. This paper will examine HVCM reliability studies, reliability operational data, and modifications and improvements performed to increase the overall system availability. We will also discuss system enhancements aimed at improving the ease of operation and providing for additional equipment protection features.

• C. Pasotti, A. Fabris, M. Svandrlik
  ELETTRA, Basovizza, Trieste

• M.L. Langlois, J.P. Buge, G. Peillex-Delphe
  TED, Vélizy Cedex

• M.J. Bland, J. Clare, P. W. Wheeler
  University of Nottingham, Nottingham
• J.S. Przybyla
  EEV, Chelmsford, Essex

Accelerators used for experiments in high-energy physics require very high power radio frequency sources to provide the energy needed to accelerate the particles. The RF power needs to be stable and predictable such that any variation in the supplied RF power has a limited and acceptable impact on the accelerated beam quality. The output load specifications for high voltage DC power systems are becoming increasingly more demanding. In addition, the impact of such systems on the electricity source is becoming more tightly regulated through power quality directives. These regulations set limits, for example, on the allowable individual harmonic current amplitudes and on "flicker" caused by transient load demands - the latter is particularly important for "long-pulse" modulators. The requirements above have to be met while still providing higher reliability to a higher specification at lower cost. A situation has now been reached where modulators based on existing approaches cannot meet these specifications and stay within acceptable cost and size limits. This demands that new approaches be taken to provide the power supplies needed for such applications. The research proposed here addresses this need.

• H. Matsumoto, S. Kazakov, K. Saito
  KEK, Ibaraki

An attractive structure using capacitive coupling has been found for the input coupler for the 45 MV/m versions of the International Linear Collider (ILC) project. The coupler supports an electrical field gradient of ~1 kV/m around the rf window ceramic with 500 kW through power, a VSWR of 1.1 and a frequency bandwidth of 460 MHz. No unwanted resonances were found in the rf window near the first and second harmonics of the operation frequency.

• S. An
  ORNL, Oak Ridge, Tennessee

Frequency and electromagnetic field distribution sensitivity of a superconducting RF (SRF) cavity due to cavity’s small deformation are the fundamental phyical paramethers in cavity and tuner design. At low temperature, the frequency sensitivity can be obtained by measuring prototype cavity, but it is not easy to test the filed distribution sensitivity. This paper presents and describes a simulation method combining ANSYS and SUPERFISH to calculate the cavity frequency and field distribution variation due to cavity’s small deformation caused by mechanical force, radiation force, thermal expansion etc.. As an example, the simulation results of the frequency and field flatness sensitivity on the SNS cavities were confirmed by their test results.

sun_ancn@yahoo.com

• C.D. Nantista, V.A. Dolgashev, R. Siemann, S.G. Tantawi, J. Weisend
  SLAC, Menlo Park, California
• I.E. Campisi
  ORNL, Oak Ridge, Tennessee

Superconducting rf cavities are increasingly used in accelerators. Gradient is a parameter of particular importance for the ILC. Much progress in gradient has been made over the past decade, overcoming problems of multipacting, field emission, and breakdown triggered by surface impurities. However, the quenching limit of the surface magnetic field for niobium remains a hard limitation on cavity fields sustainable with this technology. Further exploration of materials and preparation may offer a path to surpassing the current limit. For this purpose, we have designed a resonant test cavity. One wall of the cavity is formed by a flat sample of superconducting material; the rest of the cavity is copper or niobium. The H field on the sample wall is 74% higher than on any other surface. Multipacting is avoided by use of a mode with no surface electric field. The cavity will be resonated through a coupling iris with high-power rf at superconducting temperature until the sample wall quenches, as detected by a change in the quality factor. This experiment will allow us to measure critical magnetic fields up to well above that of niobium with minimal cost and effort.

• A. Kanareykin
  Euclid TechLabs, LLC, Solon, Ohio
• A. Dedyk, S.F. Karmanenko
  Eltech University, St. Petersburg
• E. Nenasheva
  Ceramics Ltd., St. Petersburg
• V.P. Yakovlev
  Omega-P, Inc., New Haven, Connecticut

Ferroelectric ceramics have an electric field-dependent dielectric permittivity that can be altered by applying a bias voltage. Ferroelectrics have unique intrinsic properties that makes them attractive for high-energy accelerator applications: very small response time of ~ 10^-11 sec, considerably high breakdown limit of more than 100 kV/cm, good vacuum properties. Because of these features, bulk ferroelectrics may be used as active elements of tunable accelerator structures,* or in fast, electrically - controlled switches and phase shifters in pulse compressors or power distribution circuits of future linear colliders.** One of the most critical requirements for ferroelectric ceramic in these applications is the dielectric loss factor. In this paper, the new bulk ferroelectric ceramic is presented. The new composition shows a loss tangent of 4× 10^-3 at 35 GHz. The ceramics have high tunability factor: the bias voltage of 50 kV/cm was enough to reduce the permittivity from 500 to 400. The material chemical compound, features of the technology process, and mechanical and electrical properties are discussed. The ways of BST ferrolectric parameters further improvement are discussed as well.

*A. Kanareykin, W. Gai, J. Power, E. Sheinman, and A. Altmark, AIP Conf. Proc. 647, Melville, N.Y., 2002, p. 565. **V.P. Yakovlev, O.A. Nezhevenko, J.L. Hirshfield, and A.D. Kanareykin, AIP Conf. Proc. 691, Melville, N.Y., 2003, p.187.

• Y.E. Tan, M.J. Boland, G. LeBlanc
  ASP, Clayton, Victoria

• F.C. Pilat, Y. Luo, N. Malitsky, V. Ptitsyn
  BNL, Upton, Long Island, New York

A method has been developed to measure and correct operationally the non-linear effects of the final focusing magnets in colliders, which gives access to the effects of multi-pole errors by applying closed orbit bumps, and analyzing the resulting tune and orbit shifts. This technique has been tested and used during 3 years of RHIC (the Relativistic Heavy Ion Collider at BNL) operations. I will discuss here the theoretical basis of the method, the experimental set-up, the correction results, the present understanding of the machine model, the potential and limitations of the method itself as compared with other non linear correction techniques.

• C. Steier, D. Robin
  LBNL, Berkeley, California
• W. Decking
  DESY, Hamburg
• J. Laskar
  IMCCE, Paris
• L.S.N. Nadolski
  SOLEIL, Gif-sur-Yvette
• Y.K. Wu
  DU/FEL, Durham, North Carolina

The momentum aperture of a storage ring is a very important parameter that strongly influences the performance, especially the beam lifetime. For the special case of synchrotron light sources with small emittance like the Advanced Light Source (ALS), the momentum aperture depends strongly on the transverse dynamics. It is very sensitive to machine conditions such as the tunes, chromaticities, lattice symmetry, and spurious coupling, since depending on those conditions the Touschek scattered particles explore different resonance regions in the phase space. In light sources, the momentum aperture usually also depends strongly on the vertical physical aperture. Applying frequency analysis techniques in simulations and for turn-by-turn orbit measurement data provides a very powerful tool to measure and understand limitations of the dynamic momentum aperture. The techniques presented are applicable to other light sources, as well as damping rings and many types of colliders.

• A. Temnykh
  Cornell University, Department of Physics, Ithaca, New York

CESR-c operates now as a Wiggler-Dominated Storage Ring extending the lowest operating energy to 1.5GeV/beam. To improve beam stability at low energy, 12 super-ferric wiggler magnets with total length of 15m and 2.1T maximum field were installed in the ring. They cause ~90% of total beam radiation lost and increase radiation damping rate by factor 10 from ~3 to 40 Hz. However, the field of the wiggler magnets not only initiates the radiation, but potentially affects beam dynamics. The latter was an issue of a great concern from the planning the CESR-c project. In this paper we describe general performance of CESR-c and report the results of an experimental study on some aspects of beam dynamics. Comparisons are made between the experimental data and the model prediction. We find that all parameters, which are critically dependent on wigglers, such as beam properties and ring nonlinearity, are in good agreement with those calculated from the model. This validates the ring and wiggler models and justifies our design and production technique of the magnets. The experience we obtained will be extremely useful in future work on linear collider damping rings.

• R.P. Johnson, M. Alsharo'a, P.M. Hanlet, R. E. Hartline, M. Kuchnir, K. Paul, T.J. Roberts
  Muons, Inc, Batavia
• C.M. Ankenbrandt, E. Barzi, L. DelFrate, I.G. Gonin, A. Moretti, D.V. Neuffer, M. Popovic, G. Romanov, D. Turrioni, V. Yarba
  Fermilab, Batavia, Illinois
• K. Beard, S.A. Bogacz, Y.S. Derbenev
  Jefferson Lab, Newport News, Virginia
• D.M. Kaplan, K. Yonehara
  Illinois Institute of Technology, Chicago, Illinois

A six-dimensional(6D)cooling channel based on helical magnets surrounding RF cavities filled with dense hydrogen gas* is used to achieve the small transverse emittances demanded by a high-luminosity muon collider. This helical cooling channel**(HCC) has solenoidal, helical dipole, and helical quadrupole magnetic fields to generate emittance exchange. Simulations verify the analytic predictions and have shown a 6D emittance reduction of over 3 orders of magnitude in a 100 m HCC segment. Using three such sequential HCC segments, where the RF frequencies are increased and transverse dimensions reduced as the beams become cooler, implies a 6D emittance reduction of almost six orders of magnitude. After this, two new post-cooling ideas can be employed to reduce transverse emittances to one or two mm-mr, which allows high luminosity with fewer muons than previously imagined. In this report we discuss the status of and the plans for the HCC simulation and engineering efforts. We also describe the new post-cooling ideas and comment on the prospects for a Higgs factory or energy frontier muon collider using existing laboratory infrastructure.

*R. P. Johnson et al. LINAC2004, www.muonsinc.com/TU203.pdf. **Y. Derbenev and R.P. Johnson, Submitted to PRSTAB, http://www-mucool.fnal.gov/mcnotes/public/pdf/muc0284/muc0284.pdf.

• A.S. Kesar, S.E. Korbly, R.J. Temkin
  MIT/PSFC, Cambridge, Massachusetts
• M. Hess
  IUCF, Bloomington, Indiana

Smith-Purcell radiation (SPR), emitted when a bunch is passing above a periodic structure, is characterized by a broadband radiation spectrum in which the wavelength depends on the observation angle. While various theoretical models agree on this dependence, a significant difference is introduced for the calculated radiated energy by the different approaches. We present two theoretical calculations of the SPR from a 2D bunch of relativistic electrons passing above a finite length grating. The first one uses the finite-difference time-domain approach and the second one uses an electric-field integral equation (EFIE) method. Good agreement is obtained between these two calculations. The results of these calculations are then compared with a formalism based on an infinite length grating in which a periodic boundary condition is rigorously applied. For gratings with less than approximately 50 periods, a significant error in the strength of the radiated field is introduced by the infinite grating approximation. This error disappears asymptotically as the number of periods increases. We are currently working on extending the EFIE model to the case of a three dimensional bunch moving above a finite-length grating.

• E. Huttel, A. Ben Kalefa, I. Birkel, A.-S. Müller, P. Wesolowski
  FZK, Karlsruhe
• M. Giovannozzi
  CERN, Geneva
• M. Pont, F. Pérez
  CELLS, Bellaterra (Cerdanyola del Vallès)

• E. Keil
  CERN, Geneva
• A. Sessler
  LBNL, Berkeley, California
• D. Trbojevic
  BNL, Upton, Long Island, New York

Cancer accelerator therapy continues to be ever more prevalent with new facilities being constructed at a rapid rate. Some of these facilities are synchrotrons, but many are cyclotrons and, of these, a number are FFAG cyclotrons. The therapy method of "spot scanning” requires many pulses per second (typically 200 Hz), which can be accomplished with a cyclotron (in contrast with a synchrotron). We briefly review commercial scaling FFAG machines and then discuss recent work on non-scaling FFAGs, which may offer the possibility of reduced physical aperture and a large dynamic aperture. However, a variation of tune with energy implies the crossing of resonances during the acceleration process. A design can be developed such as to avoid intrinsic resonances, although imperfection resonances must still be crossed. Parameters of two machines are presented; a 250 MeV proton therapy accelerator and a 400 MeV carbon therapy machine.

• J. Ning, C.-Y. Tan
  Fermilab, Batavia, Illinois

We build an electronical instrument to get the frequency response close to the pattern of transverse beam frequency response. The method is to apply 1)a time delay circuit with ADC, FIFO RAM and DAC; 2)a phase shift circuit which is an all pass filter with adjustable phase shift in the frequency range of 25kHz to 30kHz; in a feedback loop of 3)a commutating filter which is a high Q band pass filter. We can dynamically adjust the center frequency, the side band distance during the testing. With this instrument, some beam instruments can be tested without using the real beam.

• S. Casalbuoni, H. Schlarb, B. Schmidt, B. Steffen
  DESY, Hamburg
• P. Schmüser, A. Winter
  Uni HH, Hamburg

• A. Winter
  Uni HH, Hamburg
• N. Ignashin, A. Simonov, S. Sytov
  IHEP Protvino, Protvino, Moscow Region
• E.-A. Knabbe, S. Simrock, B. Steffen
  DESY, Hamburg

• S. Tunyan, G.A. Amatuni, B. Grigoryan
  CANDLE, Yerevan

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

In the Linac Coherent Light Source (LCLS), a short, intense bunch (rms length 20 microns, bunch charge 1 nC) will pass through a small, long undulator beam pipe (radius 2.5 mm, length 130 m). The wakefields in the undulator, particularly the resistive wall wake of the beam pipe, will induce an energy variation along the bunch, a variation that needs to be kept to within a few times the Pierce parameter for all beam particles to continue to lase. Earlier calculations included the short-range resistive wall wake, but did not include the frequency dependence of conductivity (ac conductivity) of the beam pipe walls. We show that for copper and for the LCLS bunch structure, including the ac conductivity results in a very large effect. We show that the effect can be ameliorated by choosing aluminum and also by taking a flat, rather than round, beam pipe chamber (if the vertical aperture is fixed). The effect of the (high frequency) anomalous skin effect is also considered.

• V.D. Shemelin, H. Padamsee
  Cornell University, Ithaca, New York
• M. Liepe
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York

In high current storage rings with superconducting cavities strong broadband HOM damping has been achieved by using beam-pipe ferrite loads, located at room temperature. Adopting the same damping concept for the ERL with RF absorbers between the cavities in a cavity string will require operating the absorbers at a temperature of about 80 K. This temperature is high enough to intercept HOM power with good cryogenic efficiency, and is low enough to simplify the thermal transition to the cavities at 2 K. However the electromagetic properties of possible absorber materials were not well known at cryogenic temperatures. We performed a measurement program at Cornell to find possible absorbers for HOMs in the ERL. Measurements were done for 10 different materials in the range from 1 to 40 GHz.

• M. A. Drury, E. Daly, G.K. Davis, J.R. Delayen, C. Grenoble, W.R. Hicks, K. King, T. Plawski, T. Powers, J.P. Preble, H. Wang, M. Wiseman
  Jefferson Lab, Newport News, Virginia

Thomas Jefferson National Accelerating Facility (Jefferson Lab) has completed production of 24 Superconducting Radio Frequency (SRF) cryomodules for the Spallation Neutron Source (SNS) superconducting linac. This includes one medium-beta (0.61) prototype, eleven medium-beta and twelve high-beta (0.81) production cryomodules. Ten medium-beta cryomodules as well as two high beta cryomodules have undergone complete operational performance testing in the Cryomodule Test Facility at Jefferson Lab. The set of tests includes measurements of maximum gradient, unloaded Q (Q0), microphonics, and response to Lorentz forces. The Qext’s of the various couplers are measured and the behavior of the higher order mode couplers is examined. The mechanical and piezo tuners are also characterized. The results of these performance tests will be discussed in this paper.

• J. Wu, M.T.F. Pivi, T.O. Raubenheimer, A. Seryi
  SLAC, Menlo Park, California

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.

• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Bacci
  INFN/LASA, Segrate (MI)
• A. Falone, M.  Migliorati, A. Mostacci, F. Palpini, L. Palumbo
  Rome University La Sapienza, Roma

• A. Winter
  Uni HH, Hamburg
• J. Chen, F J. Grawert, F.O. Ilday, F.X. Kaertner, J. Kim
  MIT, Cambridge, Massachusetts
• H. Schlarb, B. Schmidt
  DESY, Hamburg

• S.R. Koscielniak
  TRIUMF, Vancouver
• C. Johnstone
  Fermilab, Batavia, Illinois

A fixed-field alternating-gradient accelerator (FFAG) that employs only linear-field elements ushers in a new regime in accelerator design and dynamics. The linear-field machine has the ability to compact an unprecedented range in momenta within a small component aperture. With a tune variation which results from the natural chromaticity, the beam crosses many strong, uncorrec-table, betatron resonances during acceleration. Further, relativistic particles in this machine exhibit a quasi-parabolic time-of-flight that cannot be addressed with a fixed-frequency rf system. This leads to a new concept of bucketless acceleration within a rotation manifold. With a large energy jump per cell, there is possibly strong synchro-betatron coupling. A few-MeV electron model has been proposed to demonstrate the feasibility of these untested acceleration features and to investigate them at length under a wide range of operating conditions. This paper presents a lattice optimized for a 1.3 GHz rf, initial technology choices for the machine, and describes the range of experiments needed to characterize beam dynamics along with proposed instrumentation.

• S.R. Koscielniak, A. Baartman
  TRIUMF, Vancouver

The reduction of transverse and longitudinal cooling requirements, the increased number of beam circulations, and the reduce cost, as compared to RLAs, are arguments to adopt the linear-field FFAG as the acceleration stage of a Neutrino Factory. Because of the large range of central momenta, pm 50% delta p/p, and negative uncorrected chromaticity, the non-scaling FFAG will cross many integer and half-integer betatron resonances during the 10^-20 turns acceleration. There is the expectation that if driving terms are small enough and crossing is fast enough, then there is insufficient time for the betatron amplitudes to grow. The conventional theory of resonance crossing is applied to slow acceleration, over 100s or 1000s of turns. This paper examines whether the rapid parameter changes encountered in the multi-GeV FFAGs, or few-MeV electron model, are compatible with simple theory.

• M.K. Craddock
  UBC & TRIUMF, Vancouver, British Columbia

• T.H. Uesugi, T. Furukawa, K. Noda, S. Shibuya
  NIRS, Chiba-shi

• J. Takano, M. Okamura
  RIKEN, Saitama
• L. Ahrens, M. Bai, K.A. Brown, C.J. Gardner, J. Glenn, H. Huang, A.U. Luccio, W.W. MacKay, T. Roser, S. Tepikian, N. Tsoupas
  BNL, Upton, Long Island, New York
• T. Hattori
  RLNR, Tokyo

A normal conducting helical dipole partial Siberian snake (Warm Snake) has been installed in the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL) for overcoming all of imperfection depolarizing resonances and reducing the transverse coupling resonances caused by the solenoidal Siberian snake which had been operated in AGS before the last polarized run. The polarized proton beam has been accelerated successfully with the warm snake and the polarization at extraction of the AGS was increased to 50% as opposed to 40% with the solenoidal snake. The magnetic field and beam trajectory in the warm snake was calculated by using the OPERA-3D/TOSCA software. We present optimization of the warm snake with beam during RUN5.

• H. Huang, L. Ahrens, M. Bai, A. Bravar, K.A. Brown, G. Bunce, E.D. Courant, C.J. Gardner, J. Glenn, R.C. Gupta, A.U. Luccio, W.W. MacKay, V. Ptitsyn, T. Roser, S. Tepikian, N. Tsoupas, E. Willen, A. Zelenski, K. Zeno
  BNL, Upton, Long Island, New York
• F. Lin
  IUCF, Bloomington, Indiana
• M. Okamura
  RIKEN/RARF/CC, Saitama
• J. Takano
  RIKEN, Saitama
• D.G. Underwood
  ANL, Argonne, Illinois
• J. Wood
  UCLA, Los Angeles, California

The RHIC spin program requires 2*10¹¹ proton/bunch with 70% polarization. As the injector to RHIC, AGS is the bottleneck for preserving polarization: there is not enough space in the ring to install a full snake to overcome the numerous depolarizing resonances. An ac dipole and a partial Siberian snake have been used to preserve beam polarization in the past. The correction with this scheme is not 100% since not all depolarizing resonances can be overcome. Recently, two helical snakes with double pitch design have been built and installed in the AGS. With careful setup of optics at injection and along the ramp, this combination can eliminate all depolarizing resonances encountered during acceleration. This paper presents the accelerator setup and preliminary results.

• H.-S. Kim, Y.-S. Cho, Y.-H. Kim, H.-J. Kwon, K.T. Seol
  KAERI, Daejon
• Y.-S. Hwang
  SNU, Seoul

A 100MeV proton accelerator is under development for the Proton Engineering Frontier Project (PEFP). The goal of the first stage of the project is to develop a 20MeV accelerator and the initial test of the 20MeV accelerator will be made. The DTL of 20 MeV accelerator consists of four tanks and will be driven with single klystron, which gives rise to some unique problems with regard to the way of independent resonance control for each tank. Some changes made in the LLRF for reducing phase or amplitude error of cavities affect all of four tanks simultaneously, for which it is not possible to use LLRF for individual control of phase and amplitude of each tank. For independent control of each tank, we are going to use the temperature control of the drift tubes as a frequency tuner. During the initial test of the DTL, the phase of each tank will be synchronized with the first tank phase, and beam based test will be performed as if all of tanks were single unit. The detailed description of the test scheme and the analysis results will be given in this paper.

• S. Henderson, I.E. Campisi, J. Galambos, D.-O. Jeon, Y. Zhang
  ORNL, Oak Ridge, Tennessee

We describe the techniques which will be employed for establishing RF and quadrupole setpoints in the SNS superconducting linac. The longitudinal tuneup will be accomplished using phase-scan methods, as well as a technique that makes use of the beam induced field in the unpowered cavity.* The scheme for managing the RF and quadrupole setpoints to achieve a given energy profile will be described.

*L. Young, Proc. PAC 2001, p. 572.

• V.V. Mytrochenko, M.I. Ayzatskiy, V.N. Boriskin, A. Dovbnya, I.V. Khodak, V.A. Kushnir, A. Opanasenko, S.A. Perezhogin, A.N. Savchenko, D.L. Stepin, V.I. Tatanov, Z.V. Zhiglo
  NSC/KIPT, Kharkov

• Y. Golub
  MRTI RAS, Moscow

*Yu.Ya. Golub, N.E.Rozanov, Nuclear Instruments and Methods in Physics Research, A358 (1995) 479. **Yu.Ya. Golub, Proceedings of EPAC 2002, Paris, France, p. 1497.

• J. Wu, A. Chao, T.O. Raubenheimer, A. Seryi
  SLAC, Menlo Park, California
• C.K. Sramek
  Rice University, Houston, Texas

In a linear collider, sources of emittance dilution such as transverse wakefields or dispersive errors will couple the vertical phase space to the longitudinal position within the beam (the so-called ‘banana effect'). When the Intersection Point (IP) disruption parameter is large, these beam distortions will be amplified by a single bunch kink instability which will lead to luminosity loss. We study this phenomena both analytically using linear theory and via numerical simulation. In particular, we examine the dependence of the luminosity loss on the wavelength of the beam distortions and the disruption parameter. This analysis may prove useful when optimizing the vertical disruption parameter for luminosity operation with given beam distortions.

• S.M. Lund
  LLNL, Livermore, California
• S. R. Chawla
  UCB, Berkeley, California

It has been observed in both experiment and particle in cell simulations that space-charge-dominated beams suffer strong emittance growth in alternating gradient quadrupole transport channels when the undepressed phase advance σ0 increases beyond about 80 degrees per lattice period. Transport systems have long been designed to respect this phase advance limit but no theory has been proposed to date to explain the the cause of the limit. Here we propose a mechanism to parametrically explain the transport limit as being due to classes of halo particle orbits moving close to the beam edge in phase-space when σ0 increases beyond 80 degrees. A finite beam edge and/or perturbation acting on an edge particle can then act to move edge particles to large amplitude and lead to large increases in beam phase space area, lost particles, and degraded transport. A core particle model for a uniform density elliptical beam in a periodic focusing lattice was written and is applied to parametrically analyze this process for both periodic alternating gradient quadrupole and solenoidal transport lattices. Self-consistent particle in cell simulations are also carried out to support results.

• J. Beebe-Wang
  BNL, Upton, Long Island, New York

Coupling correction is essential for the operational performance of RHIC. The independence of the transverse degrees of freedom makes diagnostics and tune control easier, and it is advantageous to operate an accelerator close to the coupling resonance to minimize nearby nonlinear sidebands. An automated decoupling application has been developed at RHIC for coupling correction during routine operations. The application decouples RHIC globally by minimizing the tune separation through finding the optimal settings of two orthogonal skew quadrupole families. The program provides options of automatic, semi-automatic and manual decoupling operations. It accesses tune information from all RHIC tune measurement systems: the PLL (Phase Lock Loop), the high frequency Schottky system, and the tune meter. It also supplies tune and skew quadrupole scans, finding the minimum tune separation, display the real time results and interface with the RHIC control system. We summarize the capabilities of the decoupling application, and discuss the operational protections incorporated in the program. We also report the decoupling performances with the application during the RHIC 2005 run.

• Y.-J. Chen, J.F. McCarrick, S.D. Nelson
  LLNL, Livermore, California

Using the dielectric wall accelerator technology, we are developing of a compact induction accelerator system primarily intended for pulsed radiography. Unlike the typical induction accelerator cell that is long comparing with its accelerating gap width, the proposed dielectric wall induction accelerator cell is short and its accelerating gap width is comparable with the cell length. In this geometry, the rf modes may be coupled from one cell to the next. We will present recent results of rf modeling of the cells and prediction of transverse beam instability on a 2-kA, 8-MeV beam.

• V.P. Suller
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
• M.G. Fedurin, P. Jines, D.J. Launey
  LSU/CAMD, Baton Rouge, Louisiana

• J.Y. Tang, A.V. Aleksandrov, M.M. Champion, P.E. Gibson, J.P. Schubert
  ORNL, Oak Ridge, Tennessee
• A. Feschenko, Y. Kiselev, A.S. Kovalishin, L.V. Kravchuk, A.I. Kvasha
  RAS/INR, Moscow

The Resonance Control Cooling System (RCCS) for the warm linac of the Spallation Neutron Source was designed by Los Alamos National Laboratory. The primary design focus was on water cooling of individual component contributions. The sizing the RCCS water skid was accomplished by means of a specially created SINDA/FLUINT model tailored to these system requirements. A new model was developed in Matlab Simulink and incorporates actual operational values and control valve interactions. Included is the dependence of RF input power on system operation, cavity detuning values during transients, time delays that result from water flows through the heat exchanger, the dynamic process of water warm-up in the cooling system due to dissipated RF power on the cavity surface, differing contributions on the cavity detuning due to drift tube and wall heating, and a dynamic model of the heat exchanger with characteristics in close agreement to the real unit. Because of the Matlab Simulink model, investigation of a wide range of operating issues during both transient and steady state operation is now possible. Results of the DTL RCCS modeling are presented

• A. Novokhatski
  SLAC, Menlo Park, California

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.

• S. Simrock
  DESY, Hamburg

• H. Okamoto
  HU/AdSM, Higashi-Hiroshima