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In the Linac4 (a part of CERN accelerator complex upgrade), a 3 MeV, 3-meter long, 352 MHz RFQ accelerates a 70 mA H− ion beam from source to DTL input energy. RF design and tuning both rely on the same 4-wire transmission model (TLM), which ensures a consistent control of all RF parameters. 3D simulations are used to determine electrical parameters of TLM in the design process. RFQ end-circuits are designed to minimize sensitivity of RFQ voltage profile to perturbations that might occur during operation, and are tuned with quadrupole rods. Slug tuners size and distribution take into account fabrication tolerances and bead-pull measurement constraints. The three 1-meter long RFQ sections are machined and brazed in CERN. RF bead-pull measurements used to estimate RFQ electrical parameters throughout fabrication steps have not revealed any significant departure from expected values. Vacuum ports position is also adjusted prior to braze using RF measurements. Electrical parameters of end-circuits are derived from sets of five linearly independent bead-pull measurements. Slugs are tuned using a closed-loop algorithm, where "command" quantities are tuner positions, "control" quantities are measured fields, and RFQ inverse transfer function is based on the TLM. Tuning convergence and final accuracy will be presented.
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