Modeling large heterogeneous RF structures Page: 4 of 9
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Modeling Large Heterogeneous RF
Zenghai Li, Kwok Ko, Vinay Srinivas and Toshiyasu Higot
SLAC, Stanford University, Stanford, CA 94309
t KEK, Tsukuka, Ibaraki, 305 Japan
Large heterogeneous structures are difficult to model on a numerical grid
because of the limitations on computing resources, so that alternate approaches
such as equivalent circuits and mode-matching have been developed to treat
this problem. This paper will describe the three methods and will analyze a
structure representative of the SLAC and JLC detuned structures to compare
the efficacy of each approach.
Large heterogeneous structures have been in use for many years in accel-
erator systems such as the Stanford Linear Collider (SLC) which employs 3-m
long 86-cell tapered disk-loaded waveguides (DLWGs) to provide constant ac-
celeration. The SLC experienced beam breakup due to cumulative deflection
of the bunch by transverse wakefields in the linac. In the TeV scale linear col-
liders proposed by SLAC and KEK, wakefield effects will be important since
multi-bunch operation (versus single bunch in the SLC) is required to reach
desired luminosity. A primary goal of the accelerator structure design has been
the suppression of wakefields to preserve the low-emittance of the long bunch
trains (90 bunches) during their delivery to the interaction point.
2. Detuned Structure
A promising candidate being considered for SLAC's Next Linear Collider
(NLC)  and KEK's Japan Linear Collider (JLC)  is the detuned structure
whereby the cell dimensions are varied by design to detune the most dangerous
dipole modes in a Gaussian manner. This detuning decoheres the dipole modes
so that the aggregate wakefield is reduced to a safe level (a factor of 100
from peak) over the length of the bunch train. SLAC has fabricated and
tested a detuned structure to confirm the wakefield reduction . Meanwhile,
considerable effort has been devoted to the analysis of wakefields to assess the
effectiveness of this suppression mechanism.
'This work was supported by the U.S. Department of Energy, under contract No. DE-
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Li, Zenghai; Ko, Kwok; Srinivas, V. & Higo, Toshiyasu. Modeling large heterogeneous RF structures, article, November 1, 1996; Menlo Park, California. (digital.library.unt.edu/ark:/67531/metadc677143/m1/4/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.