  In the frame of a R\&D effort conducted by CEA toward the design and the
qualification of a 5 GHz LHCD system for the ITER tokamak, two 5 GHz 500 kW/5 s
windows have been designed, manufactured and tested at high power in
collaboration with the National Fusion Research Institute (NFRI). The window
design rely on a symmetrical pill-box concept with a cylindrical beryllium
oxide ceramic brazed on an actively water cooled copper skirt. The ceramic RF
properties have been measured on a test sample to get realistic values for
guiding the design. Low power measurements of the manufactured windows show
return losses below-32 dB and insertion losses between-0.01 dB and-0.05 dB,
with an optimum frequency shifted toward lower frequencies. High power tests
conducted at NFRI show unexpected total power loss for both windows. The
ceramic temperature during RF pulses has been found to reach unexpected high
temperature, preventing these windows to be used under CW conditions. A
post-mortem RF analysis of samples taken from one window shows that the
dielectric properties of the ceramic were not the ones measured on the
manufacturer sample, which partly explain the differences with the reference
modelling.
