THE LINAC4 POWER COUPLER

Linac4 is employing three types of accelerating structures after the RFQ: a Drift Tube Linac (DTL), a CellCoupled DTL (CCDTL), and a Pi-Mode Structure (PIMS) to accelerate the beam up to 160MeV at 352.2MHz. The structures are designed for a peak power of approximately 1MW per power coupler, which is transported via rectangular waveguides from the klystron gallery to the RF cavities. The coupler itself consists of two parts: a ceramic window, which separates the cavity vacuum from the air in the waveguides, and a Tuner-adjustablewaveguideCoupler (TaCo), which couples the RF power through an iris to the cavity. In the frame of the Linac4 R&D both devices have beensignificantlyimprovedwith respecttotheircommonly used design. On the coupler side, the waveguide short circuit with its matched length has been replaced by a fixedlength λ/4shortcircuit. The RF matchingis doneby a simple piston tuner, which allows a quick matching to different cavity quality factors. In the window part, which usually consists of a ceramic disc and 2 pieces of waveguides with matching elements, the waveguide sections could be completely suppressed, so that the window became very compact, lightweight, and much simpler to manufacture. In this paper we present electromagnetic simulations, and tests on first prototypes, which were constructed at CERN.