High power coupler issues in normal conducting and superconducting accelerator applications

The ceramic material (Al/sub 2/O/sub 3/) commonly used for the klystron output coupler in normal conducting, and for an input coupler to superconducting cavities is one of the most troublesome parts in accelerator applications. But the performance can be improved very much by starting with high purity (>99.9%) alumina powder of controlled grain-size (0.1/spl sim/0.5-/spl mu/m), and reducing the magnesium (Mg) sintering-binder to lower the dielectric loss to the order of 10/sup -4/ at S-band frequencies. It has been confirmed that the new ceramic can stand a peak S-band frequency RF power of up to 300 MW and 2.5 /spl mu/sec pulse width.