4-Port Circulators in SCRF Applications

The use of high power ferrite devices is critical to the operation of accelerator systems to protect the HPA systems from reflected power and to also maintain an appropriate load condition to the HPA to ensure efficient and stable operation. There are two choices of device which can be employed for this purpose, the 3-port junction circulator or the 4-port differential phase shift circulator. These devices differ considerably in their mode of operation and present differing properties to the accelerator design engineer.
In an SCRF (Super-conducting RF Cavity) the materials used are required to be operated at very low temperature, typically around 4 Kelvin. This is achieved by the use of large volumes of liquid Helium in complex cooling structures, the complete assemblies are usually termed cryomodules.Super conducting materials still exhibit a finite conductivity, but the levels are 5-6 orders of magnitude lower than that of NCRF systems. The dissipated power in the cavity walls is much reduced and a large portion of the applied RF energy is constantly reflected by the cavity during operation, the level of which can approach a full reflection in certain situations.This puts a much larger stress on the performance of the circulator employed in these systems.