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Kang, Y.W.

Paper Title Page
THP045 Twisted Structures and Their Application as Accelerating Structures 888
  • J.L. Wilson, Y.W. Kang
    ORNL, Oak Ridge, Tennessee
  • A.E. Fathy
    University of Tennessee, Knoxville, Tennessee

Funding: This work has been sponsored by ORNL-SNS. The Spallation Neutron Source is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
Normally, reactive loading is employed to construct accelerating cavities in order to slow the phase velocity of the electromagnetic wave. However, due to their non-uniform cross section, they tend to be difficult to machine, requiring complicated welding or brazing processes which increase the total cost. Although empty straight waveguides can only support faster-than-light propagation, empty twisted waveguides can support propagation at or below c. Because twisted structures have a uniform cross section in the transverse plane, they offer several potential advantages over dielectric loaded structures or other types of periodic structures. Of particular interest are twisted structures whose longitudinal cross section has been selected to resemble well-known accelerating structures, such as the iris-loaded accelerating structure and the TESLA type elliptical cavity. Comparisons are drawn between these conventional cavities and their twisted counterparts. Specifically, the phase velocity and dispersion relationship are discussed, the accelerating mode is found and analyzed, and R/Q is calculated. Design guidelines for the design of twisted structures are given.

THP098 RF Vector Control for Efficient Fan-Out Power Distribution 1018
  • Y.W. Kang
    ORNL, Oak Ridge, Tennessee

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
An algorithm for direct high power rf vector control of fan-out rf distribution using reactive circuit elements is presented. In this approach, rf control is performed for the entire fan-out system with many cavities as one system to maximize the rf power efficiency. Control parameters for a set of required rf voltage vectors in the accelerating cavities are determined and maintained for the whole system. Maximizing rf power efficiency with fan-out power distribution can be valuable for large scale SRF accelerators since construction and operation costs can be saved significantly. If a fan-out system employs a fixed power splitter with high power vector modulators in cavity inputs, the optimum power efficiency especially for a SRF system can not be provided since certain rf power headroom is needed for the vector control at each cavity. In the new fan-out vector control approach, a set of required cavity rf voltages is delivered by adjusting the phase delays between the cavities and the reactive loadings at the cavity inputs. The phase shifts and the reactive loadings are realized with high power rf phase shifters.