## 1 Introduction  
The 150 kV DC photocathode gun at Peking University will be used as the source to produce electron beams which can be manipulated in temporal and spatial distribution as requirements freely. The measurements of the electron beam bunch length are proposed. Till now, many well-known measurement methods have been developed including electro-optical sampling [1], streak camera [2], auto-correlation method [3], harmonic analysis [4], zero-phase cross [5], ponderomotive scattering [6], etc. In recent years, deflecting cavities have been widely used for bunch length measurement because there is no limitation of the bunch charge and beam energy. Its principle is that the head and tail of the bunch experience opposite transverse deflecting force through the cavity and then the bunch drifts a certain length producing a spot on the YAG screen, the size of the spot is linearly related to the bunch length [7]. Generally, a higher operation frequency can provide a higher measurement resolution, and increasing the number of cells could enhance the deflecting ability of the cavity with the same input power. To diagnose electron beams with energy of several MeV or even GeV, many laboratories developed different deflecting cavities. Two 117-cell disk-loaded X-band deflectors at LCLS [8], two 1.7 m disk-loaded C-band deflectors at Spring-8 [9], a 96-cell and a 120-cell disk-loaded X-band deflectors at SwissFEL [10], a 47-cell disk-loaded X-band deflector at SINAP [11] were used for GeV electron beam diagnosis. A 1.3 GHz single-cell deflecting cavity with protrusions inside at Cornell University [12], a 2.9985 GHz 9-cell deflecting cavity at Daresbury Laboratory [13], a 2.856 GHz 2-cell rectangular deflecting cavity at Waseda University [14], a 2.856 GHz 7-cell disk-loaded deflecting cavity at Tsinghua University [15], a 2.856 GHz single-cell rectangular deflecting cavity at KAERI [16] were developed for electron beam diagnosis with energy of several MeV. The bunch length measurements of the electron beam with energy lower than 1 MeV are also being developed, Eindhoven University of Technology developed a 2.9995 GHz reentrant cavity to measure the length of 95 keV electron beams in their UED experiment [17]. KEK fabricated a 2.6 GHz single-cell deflecting cavity similar to a rectangular cavity at compact ERL injector, to measure the electron beam from their 500 kV high voltage photoemission DC gun [18]. Different from the ones just mentioned, a 1.3 GHz medium-\(\beta\) disk-loaded standing-wave cylindrical deflecting cavity is adopted, since the fabrication of a cylindrical cavity is more convenient and much easier than that of a rectangular cavity and a reentrant cavity.  
In this paper, the deflecting cavity is fabricated and tested, which is also installed in the beamline eventually. Firstly, the design of the 1.3 GHz standing-wave normal-conducting disk-loaded deflecting cavity including the microwave design is presented. In addition, the beam dynamics simulation for the deflecting cavity is taken. Next, the mechanical design and thermodynamic analysis is carried out. Finally, after fabricating the RF measurement results is presented including the resonant frequency, the intrinsic quality factor (\(Q_{0}\)), external quality factor (\(Q_{e}\)), and field distribution.