Thermal and mechanical considerations for a liquid-cooled high-fluence electron-beam transmission window

Summary form only given. A transmission window at an atmospheric pressure to vacuum interface has both thermal loading due to energy loss from electrons passing through the window and mechanical loading due to atmospheric pressure. Thermal loading during continuous operation limits the beam current because heating reduces the mechanical strength of the window material. A technique using water under high pressure in capillary channels has been demonstrated and can provide cooling of /spl sim/2.8 kW/cm/sup 2/. This cooling can be incorporated, within an electron beam transmission window to increase current loading several orders of magnitude. Heat in the window is conducted to capillary channels and then convectively transferred to water. As water within capillary channels transits the window, its temperature, convective heat transfer coefficient, and vapor pressure all increase. A mechanical design based on mechanical properties at a temperature below the triple-point of water suggests that a window thickness of 1.87.4 /spl mu/m is sufficient to span a 5-cm circular aperture. Computer modeling of heat transfer in a capillary channel is discussed, as well as a window design that can support heat dissipation of 2.8 kW/cm/sup 2/. At 500 keV this window would dissipate 14.7% of the total incident beam power but could maintain a continuous beam current of 30 mA/cm/sup 2/.