Development of High-Rep-Rate Ion Induced Secondary Emission Electron Gun and Its Application

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A secondary emission electron gun applicable to a gas treatment was designed, fabricated and tested.The gun is set beside an ion source, which is called a wire ion plasma source (WIPS). In the gun, ions extracted from the WIPS are accelerated toward a cathode surface, which is set oblique to the ion loci. By collision of ions, secondary electrons emitted from the cathode surface are then accelerated toward the electron window and form a very wide electron beam. The electron window, which is between the electron gun and a gas treatment chamber, is set orthogonal to the ion extraction window and is on earth potential. In order to design a structure of cathode, which can inject the electron beam perpendicular to the electron window, the ion and the electron trajectories were numerically simulated for several conditions. The characteristic of the electron gun has been subsequently evaluated in terms of ion and electron beam currents at the accelerating voltage up to 100 kV.A 15 μm thick aluminum foil supported by a honeycomb board is placed at the electron window as a vacuum seal between the electron gun and the gas treatment chamber. The electron beam current distribution inside the gas treatment chamber has been evaluated in a vacuum condition. A uniform electron beam has been detected inside the gas treatment chamber. A relatively large cross section (64.5 cm^2) electron beam with a current density of about 15 mA/cm^2 is available for the gas treatment. It is expected that such current density level will offer an efficient NO_X treatment.