The Radio Frequency Quadrupole (RFQ)
The 4-vane Radio Frequency Quadrupole (RFQ) under development by INFN, will pre-bunch the DC beam from the ion source and will accelerate the beam from 0.1 to 5 MeV. The 9.8 m long 175 MHz cavity is composed of 18 x 0.54 m long modules flanged together and aligned within 0.3 mm tolerance. The RFQ is the world’s longest. The peak surface electric field is limited to a maximum value of x1.8 Kilpatrick’s criterion.
The RF tuning of the RFQ is ensured by 22 slug tuners per quadrant. An aluminium full scale RFQ model was built to validate the tuning procedures and the mode stabilization by means of bead-pull measurements.
After manufacturing, leak tests and dimensional checks of prototype modules to develop the machining and brazing procedures, the RFQ module production has started. Three modules (plus the RF plug) have been completed before the end of 2012 for high power tests, following planned at the beginning of 2013 at INFN-Legnaro.
The RF power (about 1300 kW) is injected by 8 loop couplers, using 6 1/8” RF windows. High power tests have been performed with a high-Q load circuit at JAEA-Tokai. Final acceptance tests and RF conditioning in TW mode of two complete couplers (waveguide, window and tip modules) will be performed at INFN-Legnaro on a specific test bench including a coupling cavity. The manufacturing of the other couplers will start just after approval of the acceptance tests.
The completion of the delivery of RFQ in Rokkasho is expected July 2015.