Photochronographic method for studying the expansion of plasma clouds
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DIAGNOSTICS
Photochronographic Method for Studying the Expansion of Plasma Clouds A. G. Kravchenko, D. N. Litvin, V. V. Mis’ko, V. M. Murugov, A. V. Senik, and V. A. Starodubtsev All-Russia Research Institute of Experimental Physics, Russian Federal Nuclear Center, Sarov, Nizhni Novgorod oblast, 607188 Russia Received July 5, 2005
Abstract—A novel method for studying the expansion of plasma clouds is developed. The method makes use of electron-optical cameras operating in the streak and frame-by-frame modes and provides a time resolution of 0.01–1 µs and spatial resolution of 1 mm. The experimental results obtained with this method are presented. PACS numbers: 52.70.–m DOI: 10.1134/S1063780X06020115
1. INTRODUCTION Experiments on studying the expansion of plasma clouds in a vacuum and low-pressure gases (at pressures of ~10–3 atm) are presently being carried out on the Iskra-5 high-power laser facility at the All-Russia Research Institute of Experimental Physics (VNIIEF) [1]. The main objective of these studies is to test and further develop analytic and numerical methods for describing the physical processes occurring in hightemperature nonequilibrium plasmas [2]. An important task in these studies is to investigate the time evolution of a glowing plasma cloud: its intensity, dimensions, and spatial structure, as well as the velocity and degree of symmetry of its expansion. The characteristic time of expansion is 10–20 µs. To study its initial stage, which lasts for ~1 µs, a time resolution of a few nanoseconds is required. Later on, when the expansion becomes more stable, the required time resolution is ~1 µs. Here, we present a novel method for recording the optical glow of an expanding plasma cloud. The method is based on the use of electron-optical cameras operating in the streak and frame-by-frame modes. The required spatial and time resolutions dictate the following measurement procedure: the early stage of expansion is recorded with the help of a streak camera, whereas, in the subsequent stages, a frame camera is used.
this hole with the help of an aspheric lens with a focal length of f = 2 m. The focal spot with a diameter of 300 µm was located in the hole plane. The energy of laser pulses with a wavelength of λ = 1.315 µm was ~300 J, the pulse duration being τ ≈ 0.5 ns. Reduced images of the target, which was viewed through a diagnostic window of interaction chamber 3, were produced at the entry ends of optical fiber bundles 7 with the help of objectives 6. The exit ends of the fiber bundles were attached to electron-optical cameras 9 and 10. Besides the convenient adjustment of the optical system, the fiber bundles with an aperture of 10 × 10 mm provided the matching between the chosen cross section of the object and the scanning directions of the streak and frame cameras. In the streak images, the position of the target center was indicated by 100-µm wire 12, placed on the entry end of the fiber
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2. EXPERIMENTAL TECHNIQUES Figure 1 shows a scheme of
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