High power coupler issues in normal conducting and superconducting accelerator applications

Abstract

The ceramic material (Al 2 O 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 grainsize (0.1~0.5-µm), and reducing the magnesium (Mg) sintering-binder to lower the dielectric loss to the order of 10 -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 µsec pulse width.

Design of a capacitive main power coupler for RF superconducting accelerators

“…To avoid the damage to the window should be the primary consideration while choosing the material. Specifically [5,6] , one should reduce the loss tangent, reduce the inner heat source and prevent it from multipacting (MP).…”

“…We have to pay attention to the contradiction between the sintering binder and the voids. For this purpose, it is helpful to use high purity (>99.9%), ultra fine (diameter<0.5 μm) alumina powders, apply Hot Isostatic Processing (HIP) [5] , or apply a two-step sintering [7] .…”

Design of RF power coupler for superconducting cavities

“…RF input power couplers to normal conducting cavities perform two main functions: provide the effective coupling from the RF power source to the load and serve as a vacuum barrier between the gas-filled transmission line and the vacuum cavity. In addition to these functions, RF couplers to SC cavities have to satisfy to the following requirements (see, for example, [3,4]):…”