RU2284071C1 - X-ray pulse generator - Google Patents

Abstract

FIELD: roentgen diagnostics and therapy in medicine and various processes including flaw detection and scientific research.

SUBSTANCE: proposed X-ray pulse generator has X-ray tube effective surface area of whose point cathode and anode is not over 10^-6 m² and preset cathode-to-anode distance is minimum, 10^-3 m; it also has high-voltage pulse generator whose heavy-current high-voltage pulse shaper is made in the form of heavy-current high-voltage vacuum or gas-discharge switching unit incorporating electrode that controls switching unit triggering and is provided with additional high-voltage filter inserted in its circuit. Linear size of X-ray radiator focal spot is 0.1-0.5 mm. X-ray quanta energy can be regulated between 20 and 150 keV; X-ray pulse length is about 10^-8 to 10^-6 s.

EFFECT: reduced size of X-ray tube.

1 cl, 1 dwg

Description

The proposed device relates to sources of pulsed x-ray radiation, intended for use in various technological processes, in particular for flaw detection, as well as in medicine and scientific research.

A device for generating pulsed x-ray radiation (XR 150), consisting of a pulsed x-ray tube and a pulse voltage generator, with a duration of x-ray radiation of 60 ns and a fixed energy of x-ray quanta of 150 keV. The linear size of the focal spot of the x-ray emitter is 2.2 mm (US, XTEK, www.xtek.net).

The inability to control the duration of the X-ray pulse and the energy of the X-ray quanta along with the large linear size of the focal spot significantly limits the capabilities of this device, in particular, in the field of X-ray flaw detection and medical X-ray diagnostics due to the large linear dimensions of the focal spot, which determines the resolution of the device.

A known generator of pulsed x-ray radiation, which includes a pulsed x-ray tube and a generator of high voltage pulse voltage. This device allows you to receive x-ray pulses with a fixed energy of x-ray quanta, determined by a pulse voltage of 200 kV, accelerating the electron beam in the x-ray tube. The duration of the radiation pulses is ~ 10 ^-9 s, the linear size of the focal spot of the x-ray radiation is 2 mm. An X-ray tube is a two-electrode system - a vacuum high-voltage diode with a cathode in the form of a flat disk and an anode in the form of a cone-shaped extended rod. The high-voltage pulse generator consists of a primary energy storage device with a low-voltage switch, a high-voltage pulse transformer, a secondary storage device and a high-voltage switch in the form of a two-electrode gas spark gap (RF patent No. 2095947, H 05 G 1/06, H 01 J 35/00, publ. 10.11 .1997).

The considered device has a number of significant drawbacks: the design of the x-ray tube and the physical properties of the electron beam formed in it are such that they do not allow the generation of an x-ray pulse of a duration of more than 10 ^-8 s, significantly limiting the regulation of the time of the pulse radiation; the linear size of the focal spot of the x-ray emitter is at least 2 mm; the energy of x-ray quanta is not regulated. The pulse voltage generator does not have an operational and autonomous device for starting a high-voltage switch, which does not allow efficiently synchronizing the operation of the generator with the work of other devices.

This device is selected as a prototype.

The basis of the invention is the task of obtaining a high-intensity beam of pulsed x-ray radiation with linear dimensions of the focal spot of the x-ray emitter 0.1 - 0.5 mm, with the ability to control the energy of x-ray quanta within 20-150 keV and the duration of the x-ray pulse of ~ 10 ^-8 -10 ^-6 s, as well as reducing the dimensions of the x-ray tube.

The solution to the above problem is provided by the fact that in the generator of pulsed x-ray radiation, which consists of an x-ray emitter - an x-ray tube containing a vacuum-tight electrically insulating body, in the vacuum volume of which there is a high-voltage diode system with a cathode mounted with an electrical contact on the high-voltage input and installed opposite target anode with a window for outputting x-ray radiation from the vacuum volume and the generator of high voltage voltage pulses, consisting th from the high voltage source with the accumulation capacitance and a high-current high-voltage pulse generator, the proposed X-ray tube cathode and the anode are made by point, with a working surface area of not more than 10 ^-6 m ^2, the distance between the cathode and the anode are given at least 10 ^-3 m, and in the generator of high-voltage voltage pulses, the high-voltage high-current pulse shaper is made in the form of a high-voltage high-current vacuum or gas-discharge switch, of which The electrode that controls the start of the switch is switched on, while an additional high-voltage filter is included in the control electrode circuit.

The solution to the problem provide the specified differences.

The use of a point cathode and anode with strictly limited working surfaces provides a pulsed electron current to the anode of ~ 10-10 ² A and sets an electron beam with a current density of the anode of ~ 10 ³ -10 ⁵ A / cm ² . At the indicated accelerating voltages of 20-150 kV, a pulsed power of 10 ⁵ -10 ⁷ W is released at the target anode, which makes it possible to obtain a dose of x-ray radiation per pulse of at least 0.5 R.

The design of the proposed diode system, first of all, the cathode-anode gap length of ~ 10 ^-4 -10 ^{-2 -2} m makes it possible to work with pulsed voltages in the specified range of 20-150 kV.

The extremely limited working area of the target anode sets the minimum focal spot area of the x-ray emitter.

The applied geometry of the diode system together with the point design of the cathode and anode create the possibility of stable operation of the device in a wide range of pulsed voltages of ~ 10 ^-8 -10 ^-6 s.

The ultra-small dimensions of the working elements of the x-ray tube provide small dimensions of the x-ray emitter, which at the same time has a simple, technologically advanced and reliable design.

An x-ray tube consists of two electrodes - a cathode and a target anode, as well as a window that is transparent to x-ray radiation. At the target anode, the energy of the electron beam, whose source is the cathode, is converted into X-ray energy. The anode-cathode system is located in a vacuum flask of electrically insulating material, which provides electrical isolation of the cathode from the anode. The cathode is mounted on a high-voltage input and guarantees the effective operation of the X-ray tube at a residual gas pressure of ~ 10 ^-3 -10 ^-4 Torr in a vacuum flask. The low working vacuum also simplifies tube manufacturing technology. The proposed x-ray emitter does not need a cooling system for the target anode. Tests of the device at maximum X-ray intensities showed that, with a service life of 10 ⁴ pulse inclusions, the destruction of the target does not occur.

The design of the proposed pulsed x-ray tube is shown schematically in the drawing, according to which it contains a dielectric insulating body (flask) 1, for example, of glass or ceramic, the inner volume of which is evacuated. A cathode 2 is placed in the vacuum volume, and a target anode 3 opposite the cathode. The cathode is fixed with an electrical contact to the high-voltage electrical input 4. The target anode is fixed to the electrical input 5. Electrical inputs 4 and 5 are removed from the vacuum housing 1 without violating the vacuum conditions. In the region of the working surface of the target anode, in the wall of the vacuum casing, a window 6 is created from a vacuum-tight material, for example, from beryllium, glass or aluminum, transparent to x-ray radiation. The target anode is made of an electrically conductive material and simultaneously performs the function of converting the energy of the electron beam into x-ray energy. A pulse voltage generator is connected to an external part of the high-voltage input 3, which is external to the housing 1. Anode input 4 is grounded.

The pulse voltage generator, the block diagram of which is shown in the drawing, consists of a high-voltage power supply I, a high-current high-voltage switch II and a start-up pulse generating unit III of switch II. The high-voltage power supply I includes a source of constant high voltage of 20-150 kV, operating from a network of alternating or direct voltage of 12-220 V, and a high-voltage storage capacitance charged by the source. The high-current high-voltage switch II is a vacuum or gas-discharge device designed for controlled switching of currents with a power of at least 100 A, with a breakdown voltage in the absence of an external trigger of at least 200 kV. Switching time 10 ^-8 -10 ^-6 s. Controlled switching is provided by the trigger pulse generator 3, connected to the control electrode of switch II. To exclude the breakdown of the trigger pulse generator III by a high-voltage pulse that occurs during switching on the control electrode of switch II, an inductance-capacitive filter IY is included in the circuit connecting the generator III to the control electrode.

The work of the proposed generator of pulsed x-ray radiation is as follows.

At the point cathode 1 of the x-ray tube through the high-voltage input 4, a high-voltage pulse of negative polarity voltage is supplied from the pulse voltage generator. The target anode 2 is grounded. The voltage pulse causes intense electron emission from the cathode 1 (emission current from the cathode 10-100 A) and the subsequent formation of an electron beam in the gap of the anode-target 2 - cathode 1 in accordance with the geometry of the diode gap. An electron beam, falling on the working surface of the target anode 2, interacts with the target material, as a result of which the generation of x-ray radiation emerging through the window 6.

The area of the focal spot of the x-ray emitter is determined by the cross-sectional area of the interaction of the electron beam with the target surface.

According to the design of the proposed device, a working model was developed and manufactured. Tests of the layout showed its efficiency and the ability to obtain the above parameters, which confirms the compliance of the proposed utility model with the criterion of "industrial applicability".

Claims (1)

A pulsed X-ray generator, including an X-ray emitter — an X-ray tube containing a vacuum-tight electrical insulating body, in the vacuum volume of which there is a high-voltage diode system with a cathode mounted with an electrical contact on the high-voltage input and mounted opposite the target anode, with a window for removing X-rays from the vacuum volume, and a generator of high voltage voltage pulses, consisting of a high voltage voltage source with storage electric nical capacity and high voltage high current pulse generator, characterized in that the X-ray tube cathode and the anode are made by point, with a working surface area of not more than 10 ^-6 m ^2, the distance between the cathode and the anode are set not less than 10 ^-3 m, and a high-voltage pulse generator high-voltage high-current pulse shaper is made in the form of a high-voltage high-current vacuum or gas-discharge switch, which includes an electrode that controls the start-up of the switch, and the gate electrode is turned on an additional high-voltage filter.