Author: Marshall, T.C.
Paper Title Page
WEPPP004 A Reciprocity Principle for Wakefields in a Two-Channel Coaxial Dielectric Structure 2726
 
  • G.V. Sotnikov
    NSC/KIPT, Kharkov, Ukraine
  • J.L. Hirshfield, T.C. Marshall, G.V. Sotnikov
    Omega-P, Inc., New Haven, USA
  • S.V. Shchelkunov
    Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
 
  Funding: Research is supported by U.S. Department of Energy, Office of High Energy Physics.
The reciprocity principle* is often used in applications of classical electromagnetism. We have employed this principle for testing wakefields set up by an electron bunch in a two-channel coaxial dielectric structure (CDWA)**. For numerical studies we take a ~1-THz fused silica structure which we plan to test at FACET/SLAC; it has dimensions: outer shell, OD=800 μm, ID=500 μm; inner shell OD=181 μm, ID=50 μm. The structure is energized by a 23-GeV, 3-nC bunch having axial RMS size=25 μm. FACET has no drive bunch of annular shape as required for a CDWA; nevertheless, our analytical studies and simulations prove that for the axial wakefield, an annular drive bunch can be replaced by a pencil-like bunch of the same charge traveling in the annular vacuum channel. The longitudinal electric field along the accelerator channel axis (as recorded by a witness bunch) set up by this pencil-like bunch is the same as in the conventional structure of the CDWA. Moreover, if we interchange the drive bunch and the witness bunch, the witness bunch will register the same axial wakefield. However, the stability of the annular bunch is far superior to that of the pencil bunch.
*L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media (Addison-Wesley: Reading, MA, 1960).
**G. Sotnikov et al., PRST-AB, 061302 (2009).
 
 
WEPPP012 High-Gradient THz-Scale Two-Channel Coaxial Dielectric-Lined Wakefield Accelerator 2747
 
  • S.V. Shchelkunov, M.A. LaPointe
    Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
  • J.L. Hirshfield, T.C. Marshall
    Omega-P, Inc., New Haven, USA
  • G.V. Sotnikov
    NSC/KIPT, Kharkov, Ukraine
 
  Funding: Research is supported by U.S. Department of Energy, Office of High Energy Physics.
A mm-scale THz Coaxial Dielectric Wakefield Accelerator structure is currently under study by Yale University Beam Physics Lab and collaborators for its performance with annular drive bunches. With our recent successful experiments with the cm-scale GHz rectangular module at AWA/Argonne (USA) and planned activity there with yet another cm-scale GHz coaxial structure, the program of new research has two objectives. The first is to design a structure to produce acceleration gradients approaching 0.35 GeV/m per each nC of drive charge when excited by an annular-like bunch; has an attractive feature that the drive and accelerated bunches both have good focusing and stability properties; and also exhibits a large transformer ratio. The second goal is to build and test the structure at FACET/SLAC (USA). At FACET the structure can be excited only with the available pencil-like drive bunch, but the reciprocity principle allows one to observe some of the properties that would be seen if the excitation were to be by an annular drive bunch. This presentation shows our latest findings, discusses related issues, and discusses our plans for experiments.