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MOPB011 Axial RF Power Input in Photocathode Electron Guns cathode, gun, emittance, electron 743
  • D. Janssen
    FZR, Dresden
  • H. Bluem, A.M.M. Todd
    AES, Princeton, New Jersey
  • V. Volkov
    BINP SB RAS, Novosibirsk
  We discuss the coaxial power input in normal and superconducting RF (SRF)photoinjector cavities. Upstream coaxial power input has been previously used at the PITZ facility where the output beam tube is an intrinsic part of the coaxial transmission line into the gun. In this paper, we describe coaxial coupling from the cathode side of the gun. For normal conducting RF guns, in addition to the advantage from symmetric coupling, an emittance compensation solenoid can now be positioned close to the gun cavity to deliver optimal transverse emittance. Beam dynamics calculations demonstrate 0.8 mm-mrad at 1 nC in X-band. For an SRF gun, we present a design for coaxial input around the cathode using a superconducting coupling cell. This cell matches the external quality factor of the gun for different beam powers and there is no RF loss associated with the axial gap of the cathode. The heat input into the coaxial feed and the surface field of the coupler are discussed. For a 1.3 GHz half-cell gun cavity with stored energy of 6.6 J, a 2.5 MeV electron beam can be delivered with a peak accelerating field of 50 MV/m. At 10 mA,the external Q is 2.1 x 106 and the coaxial line power loss that must be cooled is 28 W.  
TPPE061 RF Design and Operating Performance of the BNL/AES 1.3 GHz Single Cell Superconducting RF Photocathode Electron Gun gun, coupling, cathode, electron 3514
  • M.D. Cole
    AES, Medford, NY
  • I. Ben-Zvi, A. Burrill, H. Hahn, T. Rao, Y. Zhao
    BNL, Upton, Long Island, New York
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  Over the past several years Advanced Energy Systems and BNL have been collaborating on the development and testing of a fully superconducting photocathode electron gun. Over the past year we have begun to realize significant results which have been published elsewhere.* This paper will review the RF design of the gun under test and present results of its performance under various operating conditions. Results for cavity quality factor will be presented for various operating temperatures and cavity field gradients. We will discuss various methods of determining the cavity fields and the extent of agreement between them. We will also discuss future plans for testing using this gun.

*Photoemission studies on BNL/AES all niobium, Superconducting RF injector, T. Rao, these proceedings.

TPPT059 Improvement of the Blade Tuner Design for Superconducting RF Cavities linac, linear-collider, collider, proton 3456
  • C. Pagani, A. Bosotti, P. Michelato, N. Panzeri, P. Pierini
    INFN/LASA, Segrate (MI)
  Funding: This work is partially supported by the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT-2003-506395).

As of today, no complete technological solution exists for a cold tuning system fulfilling the requirements envisaged for the International Linear Collider, based on the superconducting RF technology. We present here the design improvements for the blade tuner, a coaxial device, which can provide both the slow structure tuning and the fast tuning capabilities needed for Lorentz Force Detuning (LFD) compensation and microphonics stabilitization (by means of the integration with a piezoelectric system). The system has been originally built by INFN and installed and tested at DESY on the superstructures, since it is located around the cavity helium vessel and does not require longitudinal clearance. Its design here is parametrically reviewed in terms of the requirements for higher accelerating fields and of the mechanical integration with a piezoelectric based system for the LFD and microphonics compensation.

TPPT071 Preliminary Results on the Simultaneous Excitation of the TM010 and TE011 Modes in a Single Cell Niobium Cavity focusing, coupling, emittance, pick-up 3844
  • G. Ciovati, P. Kneisel
    Jefferson Lab, Newport News, Virginia
  Funding: Work supported by the U.S. DOE Contract No DE-AC05-84ER40150.

Simultaneous excitation of both TM010 and TE011 modes has been proposed recently for superconducting photoinjector applications to take advantage of the accelerating field of the TM mode, combined with the focusing magnetic field of the TE mode. Simultaneous excitation of both modes has been carried out on a CEBAF single cell cavity. The cavity has two beam pipe side-ports for each mode for input and pick-up couplers. Coupling to the TE011 mode is done by magnetic loop couplers while for the TM010 mode coaxial antennas are used. The TE011 mode has the property of having zero surface electric field, surface magnetic field orthogonal to the one in the TM010 mode and concentrated in the iris/wall regions of the cavity. The presence of both modes in the cavity at the same time can also be used to investigate the so-called high field Q-drop in the TM010 mode. This paper will present some preliminary result on the test of the single cell cavity at 2K.

TPPT088 Power Dependence of the RF Surface Resistance of MgB2 Superconductor laser, superconductivity, target, vacuum 4215
  • T. Tajima, A. Findikoglu, A.J. Jason, F.L. Krawczyk, F. M. Mueller, A. H. Shapiro
    LANL, Los Alamos, New Mexico
  • R.L. Geng, H. Padamsee, A.S. Romanenko
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • B. Moeckly
    STI, Santa Barbara, California
  MgB2 is a superconducting material that has a transition temperature (Tc) of ~40 K. Recently, it has been shown at 4 K, liquid helium temperature, that the surface RF resistance can be lower than Nb that has the Tc of 9.2 K and has been used for most superconducting RF cavities in the past decades. One of the problems with other high-Tc materials such as YBCO was its rapid increase in RF surface resistance with higher surface magnetic fields. Recently, we have shown that MgB2 shows little increase up to about 120 Oe, equivalent of an accelerating field of about 3 MV/m. The highest field tested was limited by available power. This result is encouraging and has made us consider fabricating a cavity coated with MgB2 and test it. Also, there might be a potential that this material has a higher critical magnetic field that enables the cavity to run at a higher gradient than Nb cavities.  
TPPT089 Commissioning and Operations Results of the Industry-Produced CESR-Type SRF Cryomodules storage-ring, synchrotron, vacuum, klystron 4233
  • S.A. Belomestnykh, R.P.K. Kaplan, H. Padamsee, P. Quigley, J.J.R. Reilly, J. Sears, V. Veshcherevich
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • S. Bauer, M. Pekeler, H. Vogel
    ACCEL, Bergisch Gladbach
  • L.-H. Chang, C.-T. Chen, F.-Z. Hsiao, M.-C. Lin, G.-H. Luo, C. Wang, T.-T. Yang, M.-S. Yeh
    NSRRC, Hsinchu
  • E. Matias, J. Stampe, M.S. de Jong
    CLS, Saskatoon, Saskatchewan
  Funding: Work is partially supported by the National Science Foundation.

Upon signing a technology transfer agreement with Cornell University, ACCEL began producing turn-key 500 MHz superconducting cavity systems. Four such cryomodules have been delivered, commissioned and installed in accelerators for operation to date. Two more cryomodules are scheduled for testing in early 2005. One of them will be put in operation at Canadian Light Source (CLS); the other will serve as a spare at Taiwan Light Source (TLS). The commissioning results and operational experience with the cryomodules in CESR, CLS and TLS are presented.

WPAE002 Safety Management for the Cryogenic System of Superconducting RF System controls, vacuum, storage-ring, synchrotron 832
  • S.-P. Kao, C.R. Chen, F.-Z. Hsiao, J.P. Wang
    NSRRC, Hsinchu
  The installation of the helium cryogenic system for the superconducting RF cavity and magnet were finished in the National Synchrotron Radiation Research Center (NSRRC) at the end of October 2002. The first phase of this program will be commissioned at the end of 2004. This was the first large scale cryogenic system in Taiwan. The major hazards to personnel are cryogenic burn and oxygen deficient. To avoid the injury of the operators and meet the requirements of local laws and regulations, some safety measures must be adopted. This paper will illustrate the methods of risk evaluation and the safety control programs taken at NSRRC to avoid and reduce the hazards from the cryogenic system of the superconducting RF cavity and magnet system.  
WPAT038 Instability of the RF Control Loop in the Presence of a High-Q Passive Superconducting Cavity feedback, resonance, simulation, luminosity 2553
  • S.A. Belomestnykh, R.P.K. Kaplan, J.J.R. Reilly, V. Veshcherevich
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Funding: Work is supported by the National Science Foundation.

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.

WPAT086 Superconducting RF Cavity Frequency and Field Distribution Sensitivity Simulation simulation, SNS, radiation, resonance 4194
  • S. An
    ORNL, Oak Ridge, Tennessee
  Funding: Under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

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.


WPAT089 Test Bed for Superconducting Materials coupling, superconductivity, vacuum, resonance 4227
  • C.D. Nantista, V.A. Dolgashev, R. Siemann, S.G. Tantawi, J. Weisend
    SLAC, Menlo Park, California
  • I.E. Campisi
    ORNL, Oak Ridge, Tennessee
  Funding: Work supported by the U.S. Department of Energy under contract DE-AC03-76SF00515.

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.

ROAC008 Atom Probe Tomography Studies of RF Materials ion, target, vacuum, instrumentation 612
  • J. Norem
    ANL, Argonne, Illinois
  • P. Bauer
    Fermilab, Batavia, Illinois
  • J. Sebastian, D.N. Seidman
    NU, Evanston
  Funding: DOE

We are constructing a facility which combines an atom probe field ion microscope with a multi-element, in-situ deposition and surface modification capability. This system is dedicated to rf studies and the initial goal will be to understand the properties of evaporative coatings: field emission, bonding interdiffusion etc, to suppress breakdown and dark currents in normal cavities. We also hope to use this system to look more generally at interactions of surface structure and high rf fields. We will present preliminary data on structures relevant to normal and superconducting rf systems.

RPPE061 SRF Accelerator Technology Transfer Experience from the Achievement of the SNS Cryomodule Production Run SNS, vacuum, linear-collider, collider 3517
  • J. Hogan, T.C. Cannella, E. Daly, M. A. Drury, J.F. Fischer, T. Hiatt, P. Kneisel, J. Mammosser, J.P. Preble, T.E. Whitlatch, K. Wilson, M. Wiseman
    Jefferson Lab, Newport News, Virginia
  This paper will discuss the technology transfer aspect of superconducting RF expertise, as it pertains to cryomodule production, beginning with the original design requirements through testing and concluding with product delivery to the end user. The success of future industrialization, of accelerator systems, is dependent upon a focused effort on accelerator technology transfer. Over the past twenty years the Thomas Jefferson National Accelerator Facility (Jefferson Lab) has worked with industry to successfully design, manufacture, test and commission more superconducting RF cryomodules than any other entity in the United States. The most recent accomplishment of Jefferson Lab has been the successful production of twenty-four cryomodules designed for the Spallation Neutron Source (SNS). Jefferson Lab was chosen, by the United States Department of Energy, to provide the superconducting portion of the SNS linac due to its reputation as a primary resource for SRF expertise. The successful partnering with, and development of, industrial resources to support the fabrication of the superconducting RF cryomodules for SNS by Jefferson Lab will be the focus of this paper.