In order to make clear the influence of discharge tube structure on the flow field and discharge processes of a fast-axialflow
CO<sub>2</sub> laser, three-dimensional modeling have been made on two different structures of tubes under the same boundary conditions. The computational results show the differences of flow field in two different structures of tubes which lead to the different discharging conditions. There is also a good agreement between the computational results and the experimental observations. The results prove that the two tubes have advantages respectively, and it can explain the
instability of discharge which happened in experiments.
The Very high Angular Resolution ULtraviolet Telescope experiment was successfully launched on May 7, 1999 on a Black Brant sounding rocket vehicle from White Sands Missile Range. The instrument consists of a 30 cm UV diffraction limited telescope followed by a double grating spectroheliograph tuned to isolate the solar Lyman (alpha) emission line. During the flight, the instrument successfully obtained a series of images of the upper chromosphere with a limiting resolution of approximately 0.33 arc-seconds. The resulting observations are the highest resolution images of the solar atmosphere obtained from space to date. The flight demonstrated that subarc-second ultraviolet images of the solar atmosphere are achievable with a high quality, moderate aperture space telescope and associated optics. Herein, we describe the payload and its in- flight performance.