Polymer foil windows for gas–vacuum separation in accelerator applications

Various applications in modern particle accelerators or experiments involving high energy particle beams require a gas atmosphere or involve the production of big amounts of residual gas. Among these are, e.g., gas cells for plasma acceleration, gas jet targets, or plasma lenses. As high beam quality and stable operation of RF-accelerator cavities demand for ultra-high vacuum (UHV) conditions, a separation between high pressure and UHV beamline sections is needed. Commonly, this is realized by differential pumping or thin windows, the main advantages of the latter being a simple and compact setup. Nevertheless, the interaction between the window and the beam particles reduces the beam quality via scattering. In this paper, low scattering, low permeability polymer foils that can withstand pressure differences up to 1 bar are investigated as electron beam windows. Measurements, analytical considerations, and simulations on the gas permeation, radiation, and UV resistivity as well as electron beam scattering are presented.