At Istituto Nazionale di Fisica Nucleare Laboratori Nazionali del Sud (INFN-LNS) the commissioning of the high intensity Proton Source for the European Spallation Source (PS-ESS) is under way. Preliminary results of plasma diagnostics collected on a testbench called “Flexible Plasma Trap” (FPT) will be correlated to the peculiarities of the magnetic system design and of the microwave injection setup with a view of the possible implications on the beam extraction system. The status of the costruction is presented. INJECTOR FOR THE ESS ACCELERATOR The source named Proton Source for ESS (PS-ESS) (see Figure 1) was designed with a flexible magnetic system and a compact tetrode extraction system with the goal to minimize the emittance and the time needed for the maintenance operations. The ESS injector design has taken advantage of recent theoretical updates together with the new plasma diagnostics tools developed at INFN-LNS. The improved know-how will permit to fulfil the requirements of the ESS normal conducting front-end; the proton beam should be 74 mAwhich can be obtained with a total beam current of about 90 mA. The beam stability during the normal operations (in terms of current and emittance) shall be within ±3.5% as for pulse to pulse variation and ±2% of the beam current if averaged over a period of 50 us. The pulse duration is 2.86 ms with 14 Hz repetition rate. The requirements for the proton source and the LEBT are summarized in the Table 1. A detailed study of the beam transport in regime of space charge compensation was done and experimentally verified [1]. A reliability better than 95% is requested for the whole accelerator, thus meaning that the source reliability is expected to be greater than 99%. FUNCTIONAL TESTS OF SUBSYSTEMS Body Source and Microwave Line Status The source design already described in previous papers [2] has been upgraded according to the new requirements. Figure 1 shows the general layout of the source, including the plasma chamber, themagnetic and extraction systems and the LEBT components. The racks containing the three power supplies for the magnetic system, the magnetron and the ∗ celona@lns.infn.it Table 1: PS-ESS Requirements