On 25^th April 2017, a huge step forward was taken with the β=0.4 325 MHz single spoke superconducting cavity (Spoke040) for the ADS main linac. The cavity was designed in-house at IHEP, manufactured and finally vertical tested at 2 K. The maximum peak magnetic field reached 143 mT with cavity Q₀ of 2.17×10⁹, greatly exceeding the design goal (B_peak=65 mT with Q₀>3×10⁹). The success of this spoke040 cavity is an important milestone in the ADS project, and the cavity will be a cornerstone of the CIADS project.

Spoke040 cavities will be used more than any other type of cavity in the main linac of the CIADS project. The challenges of this cavity lie in fabrication, electron beam welding and maintaining mechanical stability due to its large geometric size, which comes from its high beta (0.4). Based on previous experience of spoke cavities with lower beta, spoke040 has been carefully optimized to ensure easy access to the cavity inner surface if subsequent polishing is required. This was proved to be useful for its performance leap.

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