## 5 Fabrication and RF Measurement Results  
After the completion of the whole design, a deflecting cavity made of oxygen-free high thermal conductivity copper is fabricated to reduce the ohmic losses. To guarantee the actual resonant frequency of the cavity is almost the same as the desired frequency,  
Figure 9: Temperature distribution of the cavity with water cooling.  
the radii of the three cells are slightly cut twice before brazing. Simulations indicate the frequency deviation  
\[\Delta f\approx(-2.6\times\Delta b_{e}-3.8\times\Delta b_{m})\text{MHz/mm} \tag{6}\]  
where \(\Delta b_{m}\) and \(\Delta b_{e}\) are the radius variations of middle cell and one end cell, respectively. RF measurements are taken before the brazing using a vector network analyzer (VNA). The initial frequency is 1301.636 MHz at 21 \({}^{\circ}\)C. After all the three cells are cut 0.1 mm in radius, the change of the resonant frequency is 0.89 MHz, which is consistent well with the simulation results. The reference value of the second cutting value is 0.094 mm, and the measured resonant frequency is 1299.933 MHz at 21 \({}^{\circ}\)C. This frequency is within expectations, it is estimated to 1300.284 MHz after the cavity is pumping to vacuum due to the different inside dielectrics. Finally, the cavity can be operated at the frequency of 1300 MHz with cooling water with temperature of 35 \({}^{\circ}\)C which is the goal frequency. The deflecting cavity is brazed after the second cutting.  
RF measurements of the deflecting cavity after brazing are carried out. The frequency of the cavity is 1299.932 MHz, \(Q_{0}\) is 1.87 \(\times\) 10\({}^{4}\), \(Q_{e}\) is 1.72 \(\times\) 10\({}^{4}\) which are measured with the room temperature of 21 \({}^{\circ}\)C and under atmospheric pressure. The frequency of the deflecting cavity is almost unchanged before and after brazing as expected.  
The field distribution of the working mode is measured by bead-pull method [26] shown in Figure 10. Meanwhile, one of the measurement results with normalized frequency change is also presented in Figure 10. The braided wire with a nominal diameter of 0.105 mm is used in the measurement which has much weaker ductility than commonly used nylon material wire, which can improve the measurement stability. The bead is a rotational symmetric cylinder with length of \(\sim\)10 mm and diameter of \(\sim\)1 mm made of aluminum tape, so that even in the process of pulling the wire, the rotation of the wire has little effect on the field distribution. As shown in Figure 10, a \(\sim\)2 mm diameter hole is made in the center of the flange protector cover, and the wire is aligned through the small hole to ensure that the wire is on the axis, the deviation of the axis is controlled to be less than 1 mm. Eventually, the wire is pulled at a low speed which is less prone to jitter to acquire a stable and repeatable measurement result. Ten groups of measurements have been taken totally by using VNA, and the repeatability is quite good, the average value of the field flatness is 99.18 \(\pm\) 0.08%. In conclusion, the measured values of the physical parameters are in good agreement with the simulation design ones.  
The vacuum of deflecting cavity is reach to 2.3 \(\times\) 10\({}^{-7}\) Pa with ion pump after baking and is installed in beamline of the DC photocathode gun. The beamline is shown in Figure 11. Next, we will test the beamline and the bunch length measurement experiment will be taken in the near future.  
Figure 10: Bead-pull measurement device with measurement result. (**a**) The measurement device; (**b**) One of the measurement results.