Abstract
The 3-MeV High Intensity Proton Injector (IPHI) RFQ is the assembly of three 2-m long coupled-segments. The tuning of the end regions of such accelerator with respect to the quadrupole mode, is generally made by machining the thickness of the end plates or increase of the notch in the vanes (LEDA). The dipolar modes are adjusted around the accelerator quadrupolar mode by adding dipole rods on the end plates and adjusting their length. In the case of the last IPHI RFQ segment, the achievable tuning range obtained with the possible plate thickness was not sufficient to adjust the frequency at 352 Mhz without modifying the notch depth, leading to serious engineering problem for the cooling, new thermo-mechanical simulations and drawings. To avoid these difficulties, a new way has been investigated. The end plate thickness adjustment is replaced by a “quadrupole rod” –as opposed to the \"dipole rod\" - length adjustment. These rods are situated between the beam axis and the dipole rods, and the tuning range is largely increased. The paper will describe this method applied to the IPHI RFQ and some experimental results obtained on the cold model.
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