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dipole

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MOP14 Development of Intense Beam Proton Linac in China rfq, linac, proton, vacuum 63
 
  • S. Fu, S.X. Fang, H. Ouyang, S. Zhao
    IHEP Beijing, Beijing
  • B. Cui, X. Guan
    CIAE, Beijing
  • J. Fang, Z.Y. Guo
    PKU/IHIP, Beijing
  Study on intense beam proton linac was started about four years ago in a national program for the basic research on ADS in China. This ADS program is meant for the future development of the clean nuclear power generation. Another important application of HPPA for Chinese Spallation Neutron Source was also proposed recently in China, and it is financially supported by Chinese Academy of Sciences. In this paper, the research progress on intense beam proton linac in these two application fields will be outlined. It involves the test result of an high-current ECR proton source, construction status of a 3.5 MeV RFQ accelerator and the design of a DTL linac.  
 
MOP16 The TRASCO-SPES RFQ rfq, vacuum, quadrupole, coupling 69
 
  • A. Pisent, M. Comunian, J. Esposito, A. Palmieri
    INFN/LNL, Legnaro, Padova
  • E. Fagotti
    INFN Milano, Milano
  • G. Lamanna
    CINEL, Vigonza (PD)
  • M. S. Mathot
    CERN, Geneva
  A high intensity RFQ is under construction at LNL. Developed within TRASCO research program, the Italian feasibility study an ADS (Accelerator Driven System), it will be employed as the first accelerating element of SPES facility, the ISOL project of LNL. The RFQ operates at the frequency of 352 MHz in CW mode, is able to deliver a proton current up to 30 mA and consists of six brazed segments whose length is 1.2 m. In this article the results obtained from the construction of a 20 cm “technological model”, aimed at testing the construction procedure of the final structure, will be discussed. Finally we will report about the machining and the outcomes obtained after RF testing of the first two segments built up to now.  
 
MOP28 A Study of Higher-Band Dipole Wakefields in X-Band Accelerating Structures for the G/NLC emittance, linac, simulation, impedance 99
 
  • R.M. Jones
    SLAC/ARDA, Menlo Park, California
  The X-band linacs for the GLC/NLC (Global Linear Collider/Next Linear Collider) have evolved from the DDS (Damped Detuned Structure) series [1,2]. The present series of accelerating structures are each 60 cm in length and incorporate both damping and detuning of the dipole modes which comprise the wakefield. In order to adequately damp the wakefield the dipole frequencies of adjacent structures are interleaved. The properties of the first dipole band have been extensively studied. However, limited analysis has been done on the higher order dipole bands. Here, we calculate the contribution of the higher order bands of the interleaved structures to the wakefield using a mode matching computer code [3]. Beam dynamics issues are also studied by tracking the beam through the complete linac using the particle beam tracking code LIAR [4].

[1] R.M Jones et al,1996,Proc. EPAC96 (also SLAC-PUB-7187) [2] J.W. Wang et al, 2000, Proc. LINAC2000 (also SLAC-PUB-8583) [3] V.A. Dolgashev, Ph.D. thesis, Budker INP, Novosibirsk, 2002.[4] R. Assman et al, LIAR, SLAC-PUB AP-103

 
 
MOP36 Preliminary Study on HOM-Based Beam Alignment in the TESLA Test Facility polarization, alignment, gun, higher-order-mode 117
 
  • N. Baboi, G. Kreps, M. Wendt
    DESY, Hamburg
  • G. Devanz, R. Paparella
    CEA/DAPNIA-SACM, Gif-sur-Yvette Cedex
  • O. Napoly
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  The interaction of the beam with the higher order modes (HOM) in the TESLA cavities has been studied in the past at the TESLA Test Facility (TTF) in order to determine whether the modes with the highest loss factor are sufficiently damped. The same modes can be used actively for beam alignment. At TTF the beam alignment based on the HOM signals is planned to be studied in the first cryo-module, containing 8 accelerating cavities. One of several modes with higher loss factor will be used. Its polarization has to be determined. The options to use single bunches or bunch trains will be analyzed. The results will be discussed in this paper.  
 
MOP41 Emittance-Imposed Alignment and Frequency Tolerances for the TESLA Linear Collider emittance, linac, collider, luminosity 132
 
  • N. Baboi
    DESY, Hamburg
  • R.M. Jones
    SLAC/ARDA, Menlo Park, California
  One option in building a future 500 GeV c.m. collider is to use superconducting 1.3 GHz 9-cell cavities. Wakefields excited by the bunch train in the TESLA linac can resonantly drive the beam into unstable operation such that a BBU (Beam Break Up) mode results or at the very least significant emittance dilution occurs. The largest kick factors (proportional to the transverse fields which transversely kick the beam off axis) are found in the first three dipole bands and hence multi-bunch emittance growth is mainly determined from these bands. These higher order dipole modes are damped by carefully orientating higher order mode couplers at the downstream end of the cavities. We investigate the dilution in the emittance of a beam injected with an initial offset from the axis of the cavities. The dependence of beam emittance on systematic errors in the cell frequencies is investigated. We also vary the bunch spacing in order to simulate a systematic frequency error. While scanning the bunch spacing over a wide range, the emittance presents sharp peaks since only few modes contribute effectively to emittance growth. The locations of these peaks sets the frequency tolerances on the structures.  
 
MOP42 Linac Alignment and Frequency Tolerances from the Perspective of Contained Emittances for the G/NLC emittance, alignment, simulation, linac 135
 
  • R.M. Jones
    SLAC/ARDA, Menlo Park, California
  We maintain the stable progress of a beam consisting of a train of bunched charges, by a careful design of the geometry of the structures [1]. In practice, the next generation of linear colliders will consist of several tens of thousands of X-band accelerating structures and this will entail inevitable errors in the dimensions and alignments of cells -and groups thereof. These errors result in a dilution of the beam emittance and consequently a loss in overall luminosity of the collider. For this reason it is important to understand the alignment tolerances and frequency tolerances that are imposed for a specified emittance budget. Here we specify an emittance dilution of no more than 10% of the initial value and we track the progress of the beam down the linac whilst accelerating structures (and sub-groups thereof) are misaligned in a random manner and at the same time random frequency are incorporated with structures. This results in tolerances in both frequency errors and sets of alignment errors to be imposed on the structures for a specified emittance dilution.

[1] R.M. Jones, 1997, SLAC NLC-Note 24.

 
 
MOP64 Wire Measurement of Impedance of an X-Band Accelerating Structure impedance, linear-collider, collider, resonance 165
 
  • N. Baboi
    DESY, Hamburg
  • G. Bowden, V.A. Dolgashev, R.M. Jones, J. Lewandowski, S.G. Tantawi, J. Wang
    SLAC/ARDA, Menlo Park, California
  Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures.

[1] R.M. Jones et al, 2003, Proc. PAC2003 (also SLAC-PUB 9871)

 
 
MOP66 Calculation of RF Properties of the Third Harmonic Cavity scattering, coupling, higher-order-mode, quadrupole 171
 
  • K. Rothemund, D. Hecht, U. van Rienen
    Rostock University, Faculty of Engineering, Rostock
  Recently a third harmonic structure has been proposed for the injector of the TTF-FEL to avoid nonlinear distortions in the longitudinal phase space. This structure, consists of four nine cell TESLA-like cavities. For the use of this structure in combination with the TTF-FEL it might be interesting to investigate higher order modes (HOM) in the structure and their effect on the beam dynamics. The complexity of the structure, four nine cell cavities assembled with four input couplers and eight HOM-couplers, results in an extremely high numerical effort for full 3D modelling. Therefor Coupled S-Parameter Calculation (CSC) [1] has been applied. This method is based on the scattering parameter description of the rf components found with field solving codes or analytically for components of special symmetry. This paper presents the results of the calculation of rf properties (e.g. scattering parameters, Q-values) of the complete four times nine cell structure equipped with all input- and HOM-couplers.

[1] H.-W. Glock, K. Rothemund, U. van Rienen, CSC - A Procedure for Coupled S-Parameter Calculations, IEEE Trans. Magnetics, vol. 38, pp. 1173 - 1176, March 2002

 
 
TUP50 Cumulative Beam Breakup with Time-Dependent Parameters focusing, coupling, injection, linear-collider 384
 
  • J. R. Delayen
    Jefferson Lab, Newport News, Virginia
  A general analytical formalism developed recently for cumulative beam breakup (BBU) in linear accelerators with arbitrary beam current profile and misalignments [1] is extended to include time-dependent parameters such as energy chirp or rf focusing in order to reduce BBU-induced instabilities and emittance growth. Analytical results are presented and applied to practical accelerator configurations.

[1] J. R. Delayen, Phys. Rev. ST Accel. Beams 6, 084402 (2003)

 
 
TUP95 Evaluation of Magnetic Field Enhancement Along a Boundary linac, linear-collider, simulation, collider 501
 
  • Y. Iwashita
    Kyoto ICR, Kyoto
  • T. Higo
    KEK, Ibaraki
  Generally, a cavity has convex corners on its inner surface, where the surface field becomes higher than the average accelerating gradient. This effect has been paid attention not to exceed a criterion only on surfaces that have high electric field gradient. A high magnetic field area, however, sometimes seems harmful on a stable operation too. Such enhancement factors are evaluated in a 2D model to show a feasible crossing angle limit on a convex angle of two surfaces.  
 
THP31 A Four-Cell Periodically HOM-Damped RF Cavity for High Current Accelerators damping, coupling, acceleration, impedance 669
 
  • G. Wu, R.A. Rimmer, H. Wang
    Jefferson Lab, Newport News, Virginia
  • J. Sekutowicz
    DESY, Hamburg
  • A. Sun
    ORNL/SNS, Oak Ridge, Tennessee
  A periodically Higher Order Mode (HOM) damped RF cavity is a weakly coupled multi-cell RF cavity with HOM couplers periodically mounted between the cells. It was studied as an alternative RF structure between the single cell cavity and superstructure cavity in high beam current application requiring strong damping of the HOMs. The acceleration mode in this design is the lowest frequency mode (Zero Mode) in the pass band, in contrast to the traditional “π” acceleration mode. The acceleration mode of a four-cell Zero Mode cavity has been studied along with the monopole and dipole HOMs. Some HOMs have been modeled in HFSS with waveguide HOM couplers, which were subsequently verified by MAFIA time domain analysis. To understand the tuning challenge for the weakly coupled cavity, ANSYS and SUPERFISH codes were used to simulate the cavity frequency sensitivity and field flatness change within proper tuning range, which will influence the design of the tuner structure. This paper presents this novel accelerating structure that may be used for variety of accelerator applications.  
 
THP33 Progress toward NLC/GLC Prototype Accelerator Structures simulation, impedance, pick-up, linac 675
 
  • J. Wang, G. Bowden, V.A. Dolgashev, R.M. Jones, J. Lewandowski, C.D. Nantista, S.G. Tantawi
    SLAC/ARDA, Menlo Park, California
  • C. Adolphsen, D.L. Burke, J.Q. Chan, J. Cornuelle, S. Döbert
    SLAC/NLC, Menlo Park, California
  • T. Arkan, C. Boffo, H. Carter, N. Khabiboulline
    FNAL, Batavia, Illinois
  • N. Baboi
    DESY, Hamburg
  • D. Finley, I. Gonin, S. Mishra, G. Romanov, N. Solyak
    Fermilab, Batavia, Illinois
  • Y. Higashi, T. Higo, T. Kumi, Y. Morozumi, N. Toge, K. Ueno
    KEK, Ibaraki
  • Z. Li, R. Miller, C. Pearson, R.D. Ruth, P.B. Wilson, L. Xiao
    SLAC, Menlo Park, California
  The accelerator structure groups for NLC (Next Linear Collider) and GLC (Global Linear Colliders) have successfully collaborated on the research and development of a major series of advanced accelerator structures based on room-temperature technology at X-band frequency. The progress in design, simulation, microwave measurement and high gradient tests are summarized in this paper. The recent effort in design and fabrication of the accelerator structure prototype for the main linac is presented in detail including HOM (High Order Mode) suppression and couplers, fundamental mode couplers, optimized accelerator cavities as well as plans for future structures. We emphasize techniques to reduce the field on the surface of the copper structures (in order to achieve high accelerating gradients), limit the dipole wakefields (to relax alignment tolerance and prevent a beam break up instability) and improve shunt impedance (to reduce the RF power required).  
 
THP54 Moscow Meson Factory DTL RF System Upgrade rfq, vacuum, coupling, impedance 733
 
  • A.I. Kvasha
    RAS/INR, Moscow
  The last paper devoted to description of the first part (DTL) RF system of Moscow Meson Factory upgrade was published in the Proceedings of PAC95 Conference in Dallas. Since then some new works directed at improvement of reliability and efficiency of the RF system were carried out. Among them there are a new powerful pulse triode “Katran” installed in the output RF power amplifiers (PA) of three channels, modifications of the anode modulator control circuit and crow-bar system, a new additional RF channel for RF supply of RFQ and some alterations in placing of the anode modulator equipment decreasing a level of interference’s at crow-bar circuits. Some new checked at MMF RF channels ideas concerning of PA tuning are of interest for people working in this sphere of activity.  
 
THP72 A Newly Designed and Optimized CLIC Main Linac Accelerating Structure damping, luminosity, linac, vacuum 779
 
  • A. Grudiev, W. Wuensch
    CERN, Geneva
  A new CLIC main-linac accelerating-structure design, HDS (Hybrid Damped Structure), with improved high-gradient performance, efficiency and simplicity of fabrication is presented. The gains are achieved in part through a new cell design which includes fully-profiled rf surfaces optimized to minimize surface fields and hybrid damping using both iris slots and radial waveguides. The slotted irises allow a simple structure fabrication in quadrants with no rf currents across joints. Further gains are achieved through a new structure optimization procedure, which simultaneously balances surface fields, power flow, short and long-range transverse wakefields, rf-to-beam efficiency and the ratio of luminosity to input power. The optimization of a 30 GHz structure with a loaded accelerating gradient of 150 MV/m results in a bunch spacing of eight rf cycles and 29% rf-to-beam efficiency. The dependencies of performance on operating frequency, accelerating gradient, and phase advance per cell are shown.  
 
THP83 Measurements of High Order Modes in High Phase Advance Damped Detuned Accelerating Structure for NLC linear-collider, collider, coupling, controls 791
 
  • N. Khabiboulline, T. Arkan, H. Carter
    FNAL, Batavia, Illinois
  • G. Linder
    University of Illinois at Urbana-Champaign, Urbana, Illinois
  • G. Romanov
    Fermilab, Batavia, Illinois
  The RF Technology Development group at Fermilab is working together with the NLC and JLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We have built several series of structures for high gradient tests. We have also built 150° phase advance per cell, 60 cm long, damped and detuned structures (HDDS or FXC series). Some of these structures will be used for the 8-pack test at SLAC by the end of 2004, as part of the JLC/NLC effort to demonstrate the readiness of room temperature RF technology for a linear collider. HDSS structures are very close to the final design for the linear collider, and it was very interesting to study the properties of high order modes in the structures produced by semi-industrial methods. In this study advanced RF technique and methods developed at Fermilab for structure low power testing and tuning have been used. The results of these measurements are presented in this paper.