ESS is completing the installation of the first phase of operation, which will start in fall 2024 on the partial beam dump and proceed with operation on the target in 2025, after receiving the intentional neutron production license from the authorities. All modules for this operation phase, with an energy reach of 870 MeV and a power capability of 2 MW, will be tested by spring 2024. The CM performance, associated statistics and the resulting linac composition is discussed here. Testing activities for the remaining CM for the full ESS 5 MW scope will continue until mid 2026.

The ESS Linac on-going installation and technical commissioning are progressing towards the first operation at 870 MeV on the beam dump in fall 2024. Four out of five DTL tanks were commissioned with beam in the normal conducting section (NCL) and a pilot installation of 1 spoke and 1 elliptical cryomodule was conducted in the superconducting (SCL) part of the ESS tunnel in spring 2023. Regarding the latter, the goal was both to demonstrate the installation sequence as well as the completion of the cryogenic distribution system (CDS) commissioning. A total of 13 spoke and 14 elliptical cryomodules (9MB + 5HB) are being installed. Overall, 30 elliptical cryomodules will be necessary to allow the 5 MW potential power after the target commissioning. The CM test plan along with the installation of the necessary RF power stations up to the 2 MW stage for the first project phase is advancing well.
This contribution will report on the deliveries from the In-kind partners, SRF activities at the ESS test stands including the resolution of non-conformities and focus on the installation and technical commissioning of the linac components.

ESS elliptical cryomodules, CEA-INFN-STFC in-kind contribution, undergo site acceptance test at ESS Lund Test Stand (TS2). Here the Field Emission operation experience, modules performances statistics and limiting mechanism, diagnostics equipment and analysis tool are described. High energy field emission and dose rate operational challenges and long-term superconducting LINAC operational strategy are described.

We study the effects of high voltage DC bias on the fundamental power couplers of the ESS elliptical SRF cavities. These tests were carried out at the TS2 facility, where cryomodule acceptance and characterization tests are carried out. We present the observed effects of positive and negative bias field on multipacting in the RF couplers, as well as the implications for operation in the ESS linac.