Fig. 1. Design and photo of TESLA 9-cell superconducting cavity (Unit: mm)

Fig. 2. Large grain niobium material produced by Ningxia OTIC

Fig. 3. Anti-Q-slope of superconducting cavities after N-doping^[31]

Fig. 4. Vertical test results of single cell cavities after N-doping at Peking University

Fig. 5. Vertical test result of superconducting cavities after mid-T treatment at IHEP

Fig. 6. Vertical test system of Peking University

Fig. 7. Layout of an accelerating cryomodule including two 9-cell superconducting cavities