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At the European Spallation Source (ESS), a 5 MW beam of 2.0 GeV proton with a nominal current of 62.5 mA driven by an accelerator will strike a tungsten wheel target at a repetition of 14 Hz and a pulse length of 2.86 ms. The fast neutrons produced via spallation process are reduced to cold and thermal neutrons of a lower energy level by passing through a thermal water pre-moderator, and up to four liquid hydrogen moderators. At the beginning, the ESS will install two hydrogen moderators above the target wheel and plans to replace them by four ones above and below the target in the future. The calculated nuclear heating is 6.7 kW for the proton beam power of 5 MW, while that for the four moderators is 17.2 kW. A cryogenic moderator system (CMS) has been designed to continuously supply subcooled liquid hydrogen with a temperature of 17 K and a parahydrogen fraction of more than 99.5% to each moderator placed in parallel at the flow rate of more than 240 g/s in order to maintain an average temperature rise at the moderator within 3 K. For the 5-MW proton beams, the total heat load is 21.9 kW, which includes a static load of 4.6 kW. The heat load is removed by a large-scale 20 K helium refrigeration plant, which is called the Target Moderator Cryoplant (TMCP), with a maximum cooling capacity of 30.3 kW at 15 K. Two compressors are operated at a discharge pressure of up to 2.2 MPa to deliver a high pressure helium stream to the CMS of up to 1125 g/s, operating all the three expansion turbines are operated. The TMCP cooling capacity will be controlled by the so-called floating pressure process. All the ESS helium cryoplants are co-located in order to facilitate maintenance and consolidate utilities like a helium recovery system and external purifier. Therefore, the HP helium stream is delivered from the TMCP cold box to a valve box close to the CMS cold box in the Target building through a 385 m-long vacuum insulated cryogenic helium transfer line (CTL). The valve box has functions to not only adjust the flow rate and the supply temperature to the CMS but also the return temperature to the TMCP cold box. The TMCP installation and commissioning plans are split into three phases. Phase 1 commissioning that comprised the compressor skids and the cold box alone has been finished in 2019. In the Phase 2, the 385 m-long CTL, the warm helium line and the valve box have been installed and integrated into the existing TMCP cold box in summer 2022. Subsequently, the TMCP commissioning has been conducted without connecting the CMS until December 2022. The performance evaluation tests such as the expansion turbines efficiency, the CTL pressure drop, the heat load and the cooling capacity have been conducted. We have studied how to operate in each operation mode such as a cooldown, warmup and beam injection modes in order to establish an automatic TMCP-CMS control system. Furthermore, safety functions as an instrument air failure have also been tested. The final phase of the installation, where the CMS cold box will be integrated, is planned in 2023. This paper will describe the performance test results and the safety function test conducted in the Phase 2 TMCP commissioning.
