Abstract: Aspects of the present disclosure provide a betatron for accelerating electrons. For example, the betatron can include magnet core parts spaced apart by an air gap. At least one main coil can be arranged on the magnet core parts. A betatron tube can be arranged in the air gap for electrons to circulate therein. A control circuit can be electrically coupled to the main coil. The control circuit can be configured to control a main coil current flowing through the main coil, such that as the control circuit increases the main coil current during a current ramp up period, the control circuit maintains the main coil current at a constant level during an injection period when the electrons are injected into the betatron. The current ramp up period can include a short pause and the injection period.