An operating method of a terminal for using a cloud system is provided. In addition, the electron gun of the present invention is such that a second grid thereof is comprised of a plurality of grid plates each having the beam aperture. A plurality of through-holes is formed as slender holes elongated along a length direction of each of the portions in each of the plurality of portions. The transfer boom according to the present invention provides a redundant containment system wherein the LNG duct is supported by the structurally strong and self-supporting transfer boom which confines the natural gas in case of a leak in the inner LNG duct.