Improved Field Stability in RFQ Structures with Vane Coupling Rings

The small apertures common in many RFQ linac designs lead to tuning difficulties, primarily because asymmetries in the quadrant fields can arise as a result of small non-uniformities in the vane to vane capacitances. Sensitivity to such capacitance or other tuning variation in the quadrants is greatly reduced by the introduction of pairs of vane coupling rings that provide periodic electrical connections between diametrically opposite vanes. Results of measurements on a cold model RFQ structure with and without vane coupling rings are presented. The number of rings required for field stabilization and the effect of rings on mode frequencies are discussed.