Ion implanter and electrostatic quadrupole lens device

An ion implanter comprising:

• a high energy multistage linear acceleration unit for accelerating an ion beam,
• wherein the high energy multistage linear acceleration unit includes high frequency accelerators in a plurality of stages provided along a beamline through which the ion beam travels, and electrostatic quadrupole lens devices in a plurality of stages provided along the beamline,
• the electrostatic quadrupole lens device in each of the stages includes
• a plurality of lens electrodes facing each other in a radial direction perpendicular to an axial direction in which the beamline extends while the beamline is interposed between the plurality of lens electrodes facing each other, and disposed at an interval in a circumferential direction perpendicular to both the axial direction and the radial direction,
• an upstream side cover electrode covering a beamline upstream side of the plurality of lens electrodes, and including a beam incident port opening in the axial direction, and
• a downstream side cover electrode covering a beamline downstream side of the plurality of lens electrodes, and including a beam exiting port opening in the axial direction, and
• at least one of the upstream side cover electrode and the downstream side cover electrode which are included in the electrostatic quadrupole lens device in at least one of the plurality of stages includes at least one gas exhaust port opening in the radial direction.