Vane Coupling Rings: A Simple Technique for Stabilizing a Four-Vane Radiofrequency Quadrupole Structure

The benefits of stabilized accelerating structures, with regard to the manufacture and operation, have been well documented. The four-vane radiofrequency quadrupoles (RFQ) presently being designed and constructed in many laboratories are not stabilized because of the weak electromagnetic coupling between the quadrant resonators. This paper presents a simple technique developed at the Lawrence Berkeley Laboratory using vane coupling rings (VCR's) which azimuthally stabilize the RFQ structure and greatly enhance its use as a practical accelerator. In particular, the VCR's: º Completely eliminate the dipole modes in the frequency range of interest; º Provide adequate quadrant balance with an initial precision mechanical alignment of the vanes; º Enhance axial balance and simplify end tuners. Experimental verification tests on a scale model will be discussed.