According to the design requirement of the 3MeV/40mA high frequency
high voltage electron accelerator
the structure of its scanning magnet has been improved: A thermistor was installed on the wall of core tube and an air-colling machine was added. The measured beam characteristics from the Ti-window stopping plate showed that the design requirement has been fulfilled. The scanning frequency is 50 -200 cycles and the uniformity is better than 7%.