Abstracts Brochure - CERN

THPCH193
THPCH194
THPCH195
29-Jun-06 16:00 - 18:00 THPCH — Poster Session
Systematic Studies of Cu- Metal Cathodes Using a Hydrogen Ion Beam
Understanding the quantum efficiency (qe)
D. Dowell, F. King, R.E. Kirby, J.F. Schmerge (SLAC)
of a metal photocathode in an s-band RF gun
is important to limit the drive laser energy
requirement and provide the best quality electron beam. Systematic measurements of the qe vs. wavelength for
varying surface contamination have been performed on copper samples using x-ray photoelectron spectroscopy
(XPS). The sample is first cleaned to the theoretical limit of qe using a 1 keV hydrogen ion beam. The H-ion beam
cleans an area approximately 1cm in diameter and has no effect on the surface roughness while removing essentially
all contaminants and lowering the work function to 4.3eV. The sample is then exposed to atmospheric contaminants
(nitrogen and oxygen) and measured again with XPS to determine the degree of contamination and the effect on the
qe. The goal is to determine the best procedure for transferring and installing cathodes in an s-band gun. These
results and comparison with theory are presented.
Investigation of Using Ferroelectric Materials in High Power Fast RF Phase Shifters for RF
Vector Modulation
A fast ferroelectric phase shifter controlled
J.L. Wilson, Y.W. Kang (ORNL) A.E. Fathy (University of Tennessee) by an electric field bias is being investigated
for high-power RF phase shifters in vector
modulation. Such a device could be used in charged particle accelerators, allowing vector control of the RF power
delivered to accelerating RF cavities. Bulk ferroelectric materials, particularly those based on barium-strontium
titanate (BST) compounds, have shown promise in high-power applications because of their low loss tangent and
high dielectric strength. Such materials have already been investigated for use in fast phase shifters at X-Band
frequencies*. Several different compositions of BST compounds are investigated in phase shifter prototypes at 402.5
MHz and 805 MHz that could be easily adapted for future large-scale accelerator projects. The ratio of barium
versus strontium in the composition is varied from sample to sample. This allows an investigation of the tradeoffs
involved between dielectric strength, loss tangent, tunability, and relative permittivity. Since ferroelectrics are by
nature nonlinear dielectric compounds, preliminary study on the nonlinear propagation effects is conducted through
computer simulation.
*V. P. Yakovlev et al. Fast X-Band Phase Shifter, Advanced Accelerator Concepts: Eleventh Workshop, 2004.
New Developments on Low-loss Ferroelectrics for Accelerator Applications
A. Kanareykin (Euclid TechLabs, LLC) A. Dedyk, S.F. Karmanenko
(Eltech University) E. Nenasheva (Ceramics Ltd.) V.P. Yakovlev
(Omega-P, Inc.)
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Recent results on development of BST (barium
strontium titanium oxide composition)
ferroelectric materials are presented to be
used as the basis for new advanced technology
components suitable for high-gradient
accelerators. Ferroelectric materials offer significant benefits for linear collider applications, in particular, for switching
and control elements where a very short response time of 10 ns can be potentially achieved. The applications
include: fast active X-band and Ka-band high-power ferroelectric switches, high-power X-band, and L-band ferroelectric-based
phase-shifters. The recently developed large diameter (11 cm) BST-based ferroelectric rings will be
used at high pulse power (tens of megawatts) for the X-band components as well as at high average power (in the
range of a few kilowatts) for the L-band phase-shifters, which are suitable for ILC applications.