Electron-cooling experiments have been carried out at the HIMAC-synchrotron in order to provide high-quality beams for medical and related research.For investigating the behavior of the free radicals,especially,the beam bunch was compressed by electron cooling with a triangle-wave RF-field.The dependences of the bunch length on the electron energy and the RF voltage were investigated under various intensities of Ar18+ beam. As a result,the bunch length was limited by around 20 ns due to the space-charge effect under an intensity of 1.33E+6 ions/bunch and an RF amplitude of 340 V
