Design optimization and cold RF test of a 2.6-cell cryogenic RF gun

To further improve the performance of accelerators, the first cryogenic normal-conducting RF gun in China was designed and manufactured. As a new and attractive trend, this optimized cryogenic RF gun can generate a low-emittance beam with a short-driven laser pulse because of its promising high gradient on the cathode. In this paper, optimization of the RF design and beam dynamics, including suppression of the peak RF field and elimination of the multipole mode, is presented. In addition, the emittance growth caused by the alignment deviation and RF jitter is discussed. After the gun was manufactured, a cold test was conducted at both room temperature and cryogenic conditions. At room temperature, the field distribution was obtained by the bead pull method. Under cryogenic conditions, the RF properties, such as the coupling coefficient and quality factor, varied with temperature. The test results agreed with the design. In the cryogenic test, vibration measurements were performed. Without vibration isolation, a maximum vibration of 50 $$\mu \text{m}$$ was observed. These cold test results are the basis of the following high-power test.