Development and investigation of a pulsed x-ray generator

Abstract

Portable and transportable instrumentation complexes based on pulsed x-ray generators with more stringent requirements for the spatio-temporal structure of the radiation field are needed for effective fast analysis of the state of the components of main pipelines. Specifically, aside from having small dimensions (maximum linear size ≤0.5 m), the radiation source must provide at distance 0.5 m from the target an exposure dose rate of at least ~0.1 mSv/sec with minimal area of the emitting surface of the target (source which is nearly a point source). These parameters can be attained with x-ray generators based on accelerator tubes operating in a pulsed regime with accelerated-electron current amplitude in the tube I m~ 1 kA, nanosecond pulse duration, and maximum electron energy of several hundreds of keV [1].To improve the sharpness of the x-ray image, the effective area of the emitting surface of the target must be reduced to a minimum. This is achieved by using diode systems with spherical coaxial acceleration geometry and an internal anodetarget with a small radius or in combined systems which incorporate the properties of spherical and coaxial diodes. The most interesting system is a system with an internal conical configuration [2, 3], which makes it possible to form effectively an explosive-emission cathode plasma which propagates toward the anode and is an intense source of electrons. In this case, the intensity of the electric field near the anode can reach ~10 8 V/m. A variant of such a diode system is displayed in Fig. 1. It was used as a basis for creating an accelerating tube where ceramic insulators were used to increase the mechanical and electrical strength. An exterior view of one variant of a part with a fluted insulator is shown in Fig. 2.The accelerator tube operates from a pulsed high-voltage source, which is placed together with it into an airtight pressure-stable vessel filled with an insulating gas under pressure 15-20 Pa. It is based on sulfur hexafluoride (SF 6 ). A well-known scheme with a discharger-peaker for starting the pulsed tube [4], shown in Fig. 3, is used in the source. The storage capacitor C 1 is charged through the resistor R from a dc voltage source U 0 , which is an integral part of the interface of the x-ray radiator (Fig. 4) Periodic-pulse start up of the accelerator tube can be accomplished in a self-generation regime, which corresponds to the scheme shown in Fig. 4, as well as by forced startup with a prescribed frequency. In the latter case, a controllable vacuum or gas-filled apparatus, equipped with a special high-voltage electrode to which a high-voltage pulse that ignites a discharge in vacuum or gas between the working electrodes of the discharger is applied, can be used instead of an uncontrollable gas-filled dual-electrode discharge P 1 .The self-generation regime is obtained as follows. After the storage capacitor C 1 is charged to the breakdown voltage U bd of the discharge P 1 , commutation of the first circuit occurs. The working frequency of the discharger...

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