PURPOSE: To extend the life of beam in a storage ring by adding a power of a frequency close to the betatron frequency of an electron bunch from a high frequency power source to an electrode through a matching circuit and a transmission line.

CONSTITUTION: An Al electrode 14 is arranged facing an orbit in a beam duct 10. A power of a frequency equal to the betatron frequency fβ of an electron bunch 11 is applied from a power source 14 through a matching device 16 and a conductor 15. At this time, the betatron frequency of the electron bunch 11 is resonantly excited in y-axial (vertical) direction or x-axial (horizontal) direction to increase the amplitude of betatron vibration. Thus, the distribution of a residual gas ion 12 is extended in the y-axial direction or x-axial direction, and the distribution density is reduced. Consequently, the scattering probability in the electron bunch 11 by the collision with the residual gas ion 12 is reduced, and the life of the electron beam can be extended.