Effects of Pressure Gradients on Laser Beam Propagation Through an Optical Window for Tokamak Plasma Diagnostics

In the current study, investigations are reported on the effect of pressure gradients on the optical properties of the window used in optical diagnostics of plasma. Window surface deformations due to pressure gradients (differences between the inside and outside pressures of a vacuum vessel) at the vacuum interface are monitored with a digital dial gauge. The effects of these surface deformations on laser beam propagation through the window are discussed in the context of optical diagnostics. Ultra-high-vacuum sealing of a large rectangular glass window with a metal assembly using a Helicoflex seal is also discussed.