| The RF design of a RFQ should satisfy several conditions, namely: voltage profile required by beam dynamics, a tunable structure, RF stability and reasonable sensitivity to possible perturbations induced by power operation. RF stability requires sufficient separation between accelerating quadrupole mode and adjacent quadrupole and dipole modes. Quadrupole modes separation is directly related to RFQ length, and can be increased if necessary via segmentation; position of dipole modes spectrum with respect to quadrupole spectrum may be adjusted using rod stabilizers inserted at RFQ ends and on either side of coupling circuits. We present a thorough comparison of a single-segment (RFQ1) vs. a 3-segment (RFQ3), 6-meter long structure at 352 MHz. Both have been assembled using the modular IPHI cold model, and tuned. |
