Test results of a fast beam chopper with MA cores

A new type of fast beam chopper was developed and installed at the HIMAC facility. Test operations of the chopper have been carried out. The chopper is basically a periodic beam-energy transformer that performs 10% modulation of beam's kinetic energy. The modulated fraction of the beam is chopped off by the downstream RFQ due to the relatively narrow injection energy window of the RFQ. Some of the recent test results with the chopper are presented. Measured chopped beams show sharp spikes at the pulse edges. Their origin is studied by numerical calculations. Another topic is the beam injection studies at the HIMAC's main-ring with the use of the chopped beams.