Design of nanosecond edge and high-frequency bipolar beam chopper pulse power supply for CSNS

Background The beam chopper system of China Spallation Neutron Source (CSNS) is used to pulsed chop the negative hydrogen ion beam from ion source; in order to meet the beam time structure of rapid cycling synchrotron (RCS), it is the key to control emittance growth of low energy beam and decrease beam loss during the beam injection process from the linac to RCS. After beam chopped, the particle beam is required to deviate completely and then lose at entrance of radiofrequency quadrupole (RFQ) cavity; considering high duty cycle of ion source and beam high chop rate, the effect of deflected particles on RFQ is difficult to predict.
Purpose A bipolar beam chopper pulse power supply is developed, which makes the beam spot at the entrance of RFQ twice that of unipolar beam chopper power supply, and reduces the damage of deflected particles to RFQ cavity and vacuum.
Methods The beam chopper power supply provides a fast high voltage pulse source; two fast reversing switches are used to quickly change the polarity of the output high voltage pulse in 40 ms.
Results and conclusion The power supply has been installed in the low beam energy transport line (LEBT), the output high voltage pulse is ± 6 kV, frequency is about 1 MHz, and the pulse edge is less than 10 ns.