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Cheng, G.

Paper Title Page
WEPMS055 SQUID-based Nondestructive Testing Instrument of Dished Niobium Sheets for SRF Cavities 2469
  • Q. S. Shu, G. Cheng, I. M. Phipps, J. T. Susta
    AMAC, Newport News, Virginia
  • I. Ben-Zvi
    BNL, Upton, Long Island, New York
  • P. Kneisel, G. Myneni
    Jefferson Lab, Newport News, Virginia
  • J. Mast, R. Selim
    CNU, Newport News
  Funding: Acknowledgment: This work is supported by DOE grant DE-FG02-05ER84241

Currently available technology can only inspect flat sheets and allow the elimination of defective flat sheets before the expensive forming and machining of the SRF cavity half-cells, but it does not eliminate the problem of remaining or uncovered surface impurities after partial chemical etching of the half-cells, nor does it detect any defects that may have been added during the fabrication of the half-cells. AMAC has developed a SQUID scanning system based on eddy current technique that allows the scanning of curved Nb samples that are welded to make superconducting RF cavity half-cells. AMAC SQUID scanning system successfully located the defects (Ta macro particles about 100 mm diameter) in a flat Nb sample (top side) and was able to also locate the defects in a cylindrical surface sample (top side). It is more significant that the system successfully located the defects on the backside of the flat sample and curved sample or 3-mm from the top surface. The 3-D SQUID-based Nondestructive instrument will be further optimized and improved in making SRF cavities and allow inspection and detection during cavity manufacturing for achieving highest accelarating fields.

MOPAS075 RF-Thermal-Structural Analysis of a Waveguide Higher Order Mode Absorber 605
  • G. Cheng, E. Daly, R. A. Rimmer, M. Stirbet, L. Vogel, H. Wang, K. Wilson
    Jefferson Lab, Newport News, Virginia
  Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177, and by The Office of Naval Research under contract to the Dept. of Energy.

For an ongoing high current cryomodule project, a total of 5 higher order mode (HOM) absorbers are required per cavity. The load is designed to absorb RF heat induced by HOMs in a 748.5MHz cavity. Each load is targeted at a 4 kW dissipation capability. Embedded cooling channels are employed to remove the heat generated in ceramic tiles and by surface losses on the waveguide walls. A sequentially coupled RF-thermal-structural analysis was developed in ANSYS to optimize the HOM load design. Frequency dependent dielectric material properties measured from samples and RF power spectrum calculated by the beam-cavity interaction codes were considered. The coupled field analysis capability of ANSYS avoided mapping of results between separate RF and thermal/structural simulation codes. For verification purposes, RF results obtained from ANSYS were compared to those from MAFIA, HFSS, and Microwave Studio. Good agreement was reached and this confirms that multiple-field coupled analysis is a desirable choice in analysis of HOM loads. Similar analysis could be performed on other particle accelerator components where distributed RF heating and surface current induced losses are inevitable.

WEPMS068 JLab High-Current CW Cryomodules for ERL and FEL Applications 2493
  • R. A. Rimmer, R. Bundy, G. Cheng, G. Ciovati, E. Daly, R. Getz, J. Henry, W. R. Hicks, P. Kneisel, S. Manning, R. Manus, K. Smith, M. Stirbet, L. Turlington, L. Vogel, H. Wang, K. Wilson
    Jefferson Lab, Newport News, Virginia
  • F. Marhauser
    JLAB, Newport News, Virginia
  Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177, and by The Office of Naval Research under contract to the Dept. of Energy.

We describe the developments underway at JLab to develop new CW cryomodules capable of transporting up to Ampere-levels of beam currents for use in ERLs and FELs. Goals include an efficient cell shape, high packing factor for efficient real-estate gradient and very strong HOM damping to push BBU thresholds up by two or more orders of magnitude compared to existing designs. Cavity shape, HOM damping and ancillary components are optimized for this application. Designs are being developed for low-frequency (750 MHz), Ampere-class compact FELs and for high-frequency (1.5 GHz), 100 mA configurations. These designs and concepts can easily be scaled to other frequencies. We present the results of conceptual design studies, simulations and prototype measurements. These modules are being developed for the next generation ERL based high power FELs but may be useful for other applications such as high energy light sources, electron cooling, electron-ion colliders, industrial processing etc.