Development of an S-band RF window for linear colliders

We report on our research and development of an S-band (2856 MHz) alumina RF window for a high power transmission which exceeds 100 MW. We have studied the mechanism of RF breakdowns of alumina disks experimentally with a test facility based on a resonant ring. At a higher power transmission (>50 MW), impurities within alumina due to sintering binder materials and internal voids were shown to be mostly responsible. An experiment at a resonant ring has shown that the new RF window by using high-purity (99.9%) and low porosity (0.5%) alumina disks can successfully withstand a maximum peak transmission-power of 310 MW with a pulse width 2.5 μs at 10 Hz repetition rate, and a maximum average transmission-power of 300 MW with pulse width 2.5 μs at 50 Hz