GB2119610A - Improvements in or relating to pulsed X-ray units - Google Patents

Abstract

A pulsed X-ray unit comprises a pulsed X-ray tube 1 connected to a discharge capacitor 2. The discharge capacitor 2 comprises two coaxially arranged cylinders 7, 8. One cylinder 8 of the discharge capacitor 2 is connected to the X-ray tube 1 and to the high-voltage end 10 of the secondary winding 6 of the pulsed transformer 3, which is shaped as a truncated cone, and is arranged internally of this winding 6 coaxially therewith. The other cylinder 7 of the discharge capacitor 2 is also connected to the X- ray tube and to the low-voltage end 9 of the secondary winding 6 of the pulsed transformer 3, and is arranged intermediate this winding 6 and the primary winding 4, of the pulsed transformer 3, which is shaped as a hollow cylinder, and connected to the charging device 5. The cylinders 7, 8 of the discharge capacitor 2 have ports 11, 12 made therein for the passage therethrough of the magnetic flux produced by the windings 4, 6 of the pulsed transformer 3. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pulsed X-ray units The invention relates to X-ray apparatuses, and more particularly to pulsed X-ray units of enhanced output, operable in the nanosecond pulse duration range.

According to the invention, there is provided a pulsed X-ray unit comprising: a pulsed X-ray tube; a discharge capacitor including a pair of coaxially arranged inner and outer cylinders connected to the.

X-ray tube; a pulsed transformer having a primary winding in the shape of a hollow cylinder, containing the outer cylinder of the discharge capacitor, and a secondary winding in the shape of a truncated cone, arranged coaxially with the primary winding internally of the outer cylinder and coaxiallytherewith, containing the inner cylinder and having its low-voltage end connected to the outer cylinder and its high-voltage end connected to the inner cylinder; ports made in the outer and inner cylinders for the passage therethrough of magnetic flux produced by the windings of the pulsed transformer; and a charging device connected to the primary winding of the pulsed transformer.

Such a unit may be used for the study of and research in highly transient hydrodynamic phenomena, in the physics of shock and detonation waves in fluids and powders, in research in high-velocity impact and in explosion welding.

Such a unit allows the capacitance of the discharge capacitor to be increased, the inductance of the discharge circuit to be reduced, and the loss of useful power output to be reduced in comparison with previously known units.

Preferably the discharge capacitor includes an additional cylinder arranged coaxially internally of the inner cylinder of the discharge capacitor and electrically connected to the outer cylinder of the discharge capacitor, this additional cylinder having ports made therein for the passage therethrough of the magnetic flux created by the windings of the pulsed transformer.

Preferably, the cylinders of the discharge capacitor have an axial length in excess of that of the primary and secondary windings of the pulsed transformer, respectively, the ports being in the form of openings situated, respectively, in the opposite end portions of the cylinders of the primary and secondary windings of the pulsed transformer, the openings being connected in pairs by slits.

Preferably, the cylinders of the discharge capacitor, connected to the secondary winding of the pulsed transformer, are connected to the X-ray tube through frustoconical conductors.

With the discharge capacitor being in the form of two coaxially arranged cylinders receiving the secondary winding therebetween, it is preferable, in order to avoid storing a charge in the parasitic capacitances of the turns of the secondary winding and distorting the electric field between the cylinders of the discharge capacitor, to have the winding pitch of the turns of the secondary winding of the pulsed transformer selected in direct proportion with the cube if the varying radius of the secondary winding in the direction from the turn of the maximum radius toward the turn of the minimum radius.

Such a pulse X-ray unit has as significant increase of the discharge capacitance, while retaining the high coupling coefficient between the windings of the transformer, i.e. there is assured the storage of considerable energy in the discharge capacitor. Furthermore, it has become possible to reduce substantially the inductance of the discharge circuit, i.e. to reduce the duration and increase the amplitude of the pulse of the discharge current through the X-ray tube, while decreasing the loss of the useful power factor in the parasitic capacitances of the unit. Taken together, this enables a very short pulse of X-rays with- a high power and dose in the pulse to be produced.

The invention will be further described, by way of example, with -reference to the accompanying drawings, wherein: Figure 1 shows a pulsed X-ray unit constituting a preferred embodiment of the invention, in a partly broken away general view; Figure 2 shows a pulsed X-ray unit constituting another embodiment of the present invention, also in a partly broken away general view; and Figure 3 is a schematic representation of the unit of Figure 2.

A pulsed X-ray unit comprises a pulsed X-ray tube 1 (Figure 1), a discharge capacitor 2 connected to the tube 1, and a pulsed transformer 3. The primary winding 4 of the transformer 3 is shaped as a hollow cylinder and is connected to a charging device 5, while the secondary winding 6 is shaped as a truncated cone arranged coaxially with the primary winding 4 internally thereof, and is connected to the discharge capacitor 2.

The discharge capacitor 2 includes two coaxially arranged cylinders, viz. an outer one 7 and an inner one 8. The outer cylinder 7 is connected to the X-ray tube 1 and is arranged intermediate the primary winding 4 and the secondary winding 6 of the pulsed transformer 3.

The cylinder 7 is connected to the iow-voltage end 9 of the secondary winding 65 of the transformer 3. The cylinder 8 is also connected to X-ray tube 1, is arranged internally of the secondary winding 6 of the pulsed transformer 3 coaxially therewith, and is connected to the high-voltage end 10 of this winding 6. The axial length of the cylinders 7 and 8 is in excess of that of the secondary winding 6 and primary winding 4 of the transformer 3, respectively, as shown in Figure 1.

The cylinders 7 and 8 of the capacitor 2 have made therein respective ports 11 and 1 2 for the passage therethrough of the magnetic flux produced by the windings 4 and 6 of the pulsed transformer 3. The ports 11 and 12 are in the form of openings 1 3 and 14 situated, respectively in the opposite end portions of the cylinders 7 and 8, extending beyond the axial length of the primary and secondary windings 4 and 6. The openings 13 and 14 at the opposite ends of the cylinders 7 and 8 are connected in pairs, respectively, by slits 1 5 and 16.

The cylinders 7 and 8 of the discharge capacitor 2 are connected to the X-ray tube 1 through respective frustoconical conductors 17 and 18.

The winding pitch of the turns of the secondary winding 6 of the pulsed transformer 3 is selected in direct proportion with the cube of the varying value of its radius in the direction (shown with arrow A) from the turn with the maximum radius to the turn with the minimum radius.

The charging device 5 includes a capacitor 1 9 and a switching discharge device 20, connected in series with the primary winding 4 of the pulsed transformer 3.

In the modified embodiment of the invention, illustrated in Figures 2 and 3, the X-ray unit additionally has in its discharge capacitor 2 a cylinder 21 coaxially arranged inside the cylinder 8 and electrically connected with the cylinder 7. The length of this additional cylinder 21 is in excess of the length of the secondary winding 6.

The cylinder 21 (Figure 2) has ports 22 made therein for the passage therethrough of the magnetic flux created by the windings 4 and 6 of the-transformer 3. The ports 22 are in the form of openings 23 situated in the opposite end portions of the cylinder 21, extending beyond the length of the secondary winding 6. These openings 23 in the opposite end portions of the cylinder 21 are connected in pairs by slits 24.

The cylinders of the discharge capacitor may be either metallic or they may be of a dielectric material with a metal foil lining on their surface, with the ports made through this foil lining. In the embodiments of the unit, illustrated in Figures 1 to 3, the outer dielectric cylinder may also serve as a fluid-tight housing, for filling the interior of the pulsed X-ray unit with transformer oil or some other dielectric liquid or gas.

The operating principle of the pulsed X-ray unit is as follows.

When a voltage pulse is fed to the primary winding 4 (Figure 1) of the pulsed transformer 3, a current flows in this winding 4, creating an alternating magnetic flux which is intended to penetrate the internal volume of the unit. To increase the capacitance of the discharge capacitor 2, the axial length of the cylinders 7 and 8 is in excess of that of the primary and secondary windings 4 and 6 of the pulsed transformer 3.

However, the alternating magnetic flux tends to generate in the cylinders 7 and 8 eddy currents opposing the propagation of the magnetic flux into the unit and affecting the coupling coefficient of the transformer windings. To avoid this, the cylinders 7 and 8 have the ports 11 and 12 made therein, in the form of respective openings 13 and 14 extending beyond the length of the primary winding 4 and secondary winding 6. Thus, the magnetic flux of the primary winding 4, which has a radial component in these areas, passes through the openings 13 and 14 of the cylinders 7 and 8 into the internal volume of the unit.The axial component of the alternating magnetic flux within the internal volume induces eddy currents in the cylinders 7 and 8, directed in opposition to the direction of the current through the primary winding 4, these eddy currents opposing the progress of the magnetic flux in the axial direction.

The slits 1 5 and 1 6 connecting the respective pairs of the openings 13 and 14 oppose the completion of the paths of these eddy currents, thus ensuring jointly with the openings 13 and 14 that the magnetic flux penetrates the internal volume of the unit.

The total area of the ports 11 should be at least equal to the value of the cross-sectional area enclosed within the outer cylinder 7, which allows, in the volume occupied by the secondary winding 6, a magnetic flux to be produced which is essentially uniform both axially and radially and of the maximum intensity, while ensuring a high coupling coefficient between the primary winding 4 and the first turns of the secondary winding 6 (the greater-radius turns).

The ports 12 in the cylinder 8 enable the passage of the magnetic flux into the central portion of the volume of the unit and provide for effective coupling of the magnetic flux with the subsequent turns of the secondary winding 6 (the smaller-radius turns).

Eddy currents would not be induced in the cylinders 7 and 8 in the axial direction, for the magnetic flux passing through each pair of the openings 13 or 14 advances therethrough in opposing directions, i.e. the total magnetic flux through each pair of ports 11 or 12 is essentially equal to zero.

The axial length of the secondary winding 6 should not exceed that of the primary winding 4, to ensure that the magnetic flux produced by the winding 4 passes through all the turns of the secondary winding 6. On the other hand, the axial length of the secondary winding 6 should be in excess of the length broken down by the working voltage along the surface of the dielectric body supporting the secondary winding 6.

The secondary winding 6 has a single-layer, with the varying pitch decreasing in the direction toward the high-voltage end 10 of the winding.

The advisability of having the secondary winding 6 with the varying winding pitch is explained by the following reasoning.

There is established a certain distribution of the electric potential among the cylinders 7 and 8 of the discharge capacitor 2. At the same time, there takes place at each turn of the secondary winding 6 the distribution of the induced EMF created by the alternating magnetic fiux. Should the distribution of the potential among the cylinders 7 and 8 of the discharge capacitor 2 be different from the induced EMF among the turns, the electric field of the capacitor 2 would become distorted, whereby an electric charge will be stored by each turn of the winding 6. This would lead to a considerable amount of energy being stored by the parasitic capacitance of the winding 6, which would not be converted into X-radiation at break-down of the X-ray tube 1.By having the varying winding pitch of the winding 6, it is ensured that the EMF of induction at the turns corresponds to the potential, and the electric field within the discharge capacitor 2 would not become distorted. In this case the charge at each turn of the winding 6 is essentially equal to zero, the energy would not be stored in the parasitic capacitance, and electric overvoltage of the turns would not take place, which enhances the electric strength of the unit and increases its efficiency factor. With the uniform magnetic flux within the volume of the transformer 3 and with the coaxial arrangement of the cylinders 7 and 8 of the discharge capacitor 32, the pitch of the turns should be directionally proportional to the cube of the varying radius of the winding 6 in the direction (shown with arrow A) from the turn of the maximum radius toward the turn with the minimum radius.

Thus, the arrangement of the secondary radius 6 intermediate the coaxially arranged cylinders 7 and 8 of the discharge capacitor 2 and the introduction of the varying pitch of the turns of the secondary winding 6 allow the loss of energy in the parasitic capacitance of the secondary winding 6 of the capacitor 3 to be avoided.

A substantial increase of the capacitance of the discharge capacitor 2 together with the increase of the amount of stored energy would, however, result in its more prolonged discharge through the X-ray tube, which is undesirable.

To avoid this, the inductance of the discharge circuit is to be substantially reduced, so as to retain the short duration of the X-ray pulse and to increase its amplitude. This is attained by connecting the cylinder 7 to the cathode of the pulsed X-ray tube through the frustoconical conductor 17, and by connecting the cylinder 8 to the anode of the X-ray tube 1 likewise through the frustoconical conductor 1 8. Owing to the abovedescribed patterns of the ports 11 and 12, the conductors 17 and 18 are beyond the magnetic flux. Thus, they are made of a solid structure, which allows the inductance of the discharge circuit (the discharge capacitor -- X-ray tube) to be susbtantially reduced, whereby the duration of the X-ray burst is substantially reduced, and its amplitude is susbtantially increased, accordingly.

Upon the discharge capacitor 2 having been charged to the working voltage, there takes place a breakdown of the X-ray tube 1, and the entire charge stored by the cylinders 7 and 8 of the capacitor 2 flows through the inter-electrode gap of the X-ray tube 1, creating a powerful pulse of Xradiation.

The pulsed X-ray unit according to the modified embodiment illustrated in Figures 2 and 3 operates in a manner similar to the abovedescribed operation of th embodiment illustrated in Figure 1.

The difference arises from the fact that, in order to increase the capacitance of the discharge capacitor 2, there is the additional cylinder 21 arranged internally of the cylinder 8 and electrically connected to the cylinder 7. Owing to the ports 22 made in the cylinder 21 in the form of openings 23 connected in pairs by the slits 24, the alternating magnetic flux penetrates the entire internal volume of the secondary winding 6 of the transformer 3, which provides for uniform distribution of the magnetic flux over the entire section of the secondary winding 6, with the intensity of the electric field, which rises toward the axis of the coaxially arranged cylinders 7, 8 and 21, significantly increasing the capacitance of the discharge capacitor 2, and with relatively small radial dimensions of the additional cylinders 21.

The pulsed X-ray unit allows considerable energy to be stored in the discharge capacitor with a high working voltage, offers the discharge current of short duration and high amplitude flowing through the X-ray tube, and curbs the loss of useful energy. Thus, there is ensured the output of a short-duration pulse of X-ray radiation of high hardness, with a high power and dose of the pulse.

Claims (6)

1. A pulsed X-ray unit comprising: a pulsed Xray tube; a discharge capacitor including a pair of coaxially arranged inner and outer cylinders connected to the X-ray tube; a pulsed transformer having a primary winding in the shape of a hollow cylinder, containing the outer cylinder of the discharge capacitor, and a secondary winding in the shape of a truncated cone, arranged coaxially with the primary winding internally of the outer cylinder and coaxially therewith, containing the inner cylinder and having its low-voltage end connected to the outer cylinder and its highvoltage end connected to the inner cylinder; ports made in the outer and inner cylinders for the passage therethrough of magnetic flux produced by the windings of the pulsed transformer; and a charging device connected to the primary winding of the pulsed transformer.

2. A pulsed X-ray unit as claimed in claim 1, wherein the discharge capacitor includes an additional cylinder coaxially arranged internally of the inner cylinder of the discharge capacitor and electrically connected to the outer cylinder of the discharge capacitor, the additional cylinder having ports made therein for the passage therethrough of the magnetic flux produced by the windings of the pulsed transformer.

3. A pulsed X-ray unit as claimed in claim 1 or 2, wherein the cylinders of the discharge capacitor are of an axial length in excess of the axial length of the primary and secondary windings of the pulsed transformer, the ports being in the form of openings situated in the opposite end portions of the cylinders of the discharge capacitor, extending beyond the axial length of the primary and secondary windings of the pulsed transformer, and connected in pairs by slits.

4. A pulsed X-ray unit as claimed in any one of claims 1 to 3, wherein the cylinders of the discharge capacitor, connected to the secondary winding of the pulsed transformer, are connected to the X-ray tube through frustoconical conductors.

5. A pulsed X-ray unit as claimed in any one of claims 1 to 4, wherein the winding pitch of the turns of the secondary winding of the pulsed transformer is in direct proportion to the cube of the radius of the winding in the direction from the turn of the maximum of radius toward the turn of the minimum radius.

6. A pulsed X-ray unit substantially as hereintofore described with reference to and as illustrated in the accompanying drawings.