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Description
The CSNS I linac delivers 80 MeV H⁻ beam as injector for the Rapid Cycling Synchrotron. Its RF system consists of RFQ, bunchers and four klystron based DTL power sources. The digital LLRF control system achieves cavity field stability of 1 % in amplitude and ±1° in phase. Based on operational fault statistics covering the beam production period from Oct. 2025 to Jun. 2026, total RF related beam downtime reached 104.1 hours, among which DTL1-4 klystron power source failures contributed 26.3 hours, accounting for 25.3 % of linac RF induced outages. DTL3 exhibited the highest fault frequency, dominated by abrupt reflected power excursions that triggered downstream RCS beam loss interlocks. DTL4 frequently suffered unannounced high voltage trips originating from electromagnetic interference to its monitoring unit. Additional recurrent operational issues include LLRF hardware lock ups, parameter configuration loss following software restarts, and spurious interlocks caused by marginal sensor threshold settings. This paper presents observed fault signatures, on shift mitigation procedures and root cause analysis. Practical improvements are proposed, including enhanced alarm coverage and revised operational SOPs. Lessons learned from the room temperature DTL RF operation are summarized, providing practical references for operation oriented design and operator training of the next generation linac RF system for the CSNS II upgrade.