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Effectiveness decrease of the phosphor screens of the P11 and P20 types for streak tubes in the picosecond region is shown. It is shown that the complete amplification of the circuit 'streak tube + image intensifier + CCD' in the picosecond region is the same as one of the circuit 'streak tube + etched CCD instead of the screen in a whole volume,' though the static amplification in the first case is by two orders higher. A special streak tube of the PV series has been manufactured. The screen of this tube consists of 4 various phosphor screens prepared on the same fiber-optical disk in the form of closely placed strips of 5 mm width: K-71 (blue), K-78 (green), 'cadmium' (green), IL-3P (red). A streak tube with the phosphor screen KL3-2 (green) has also been investigated. Principal scheme of the experiment is shown in Figure 1. In these experiments, the voltage between the tube's photocathode and screen was of 14 KeV, photocathode current density approximately 100 (mu) A/mm2, and duration of the pulse initiating the photocathode -- of 10-7 s. The shape of the phosphor screen irradiation response is presented in Figure 2 as an oscillogram. For each phosphor screen type the oscillogram is normalized to unit. In Table 1, the time intervals are presented during which the phosphor screen is lighting up being excited by current pulses of 10-7 s. With the use of the phosphor screen decaying curves it is possible to determine the duration of time during which the image amplifier (usually with MCP) should remain open being placed in the electron-optical camera between the streak tube and readout system. The time interval, during which about 70% of the lightsum for phosphor screens of three types are lighting up, is presented in Table 2. Taking into account that high noise level is inherent to the image intensifiers with MCP, it is advisable to use in streak tubes the phosphor screens with minor lighting-up time duration, and to turn on the MCP for a minimal required time. In the Russian streak camera 'Agat' this time is equal to (6 - 8) (DOT) 10-4 s, which significantly exceeds the required time.
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