EP0692176B1 - Pulse mode x ray generator - Google Patents

Abstract

Pulse mode X ray generator comprising a high tension source (HT), an X ray emitting head (4) capable of producing X rays when it receives an electrical pulse, a plurality of power cables (C1 to C6) disposed between the source and the head, means (S1, S2) for storing the electrical energy supplied by the source and means (TH) for releasing the electrical energy that has accumulated in the storage means and triggering the pulse which is then transferred to the head through the power cables. The power cables are wound into spirals and are connected in parallel to storage means and connected in series to the head. Applications in science, medicine and industry.

Description

The present invention relates to an X-ray pulse generator.

Its applications are scientific, industrial and medical such as for example crystallography, radiography, sterilization.

An impulse X-ray generator is already known from the following document:

US-A-5,044,004 (Collins et al.), Entitled "Flash X-Ray Apparatus".

This known generator comprises a set of Blumleins mounted between a high voltage source, associated with a thyratron, and an X-ray emitting head.

However, these Blumleins are power lines which are straight and rigid and which have a long length, hence a bulky generator whose head emitting X-rays is hardly or not mobile.

The present invention solves the problem of designing an impulse X-ray generator capable of being much less bulky than this known generator.

• une source de haute tension,
• une tête émettrice de rayons X, qui est capable de produire des rayons X lorsqu'elle reçoit une impulsion électrique, et
• une pluralité de lignes électriques qui sont comprises entre la source de haute tension et la tête émettrice de rayons X, chaque ligne électrique comprenant un premier conducteur électrique et un deuxième conducteur électrique qui sont séparés par un diélectrique,

ledit générateur comprenant en outre :

• des moyens de stockage de l'énergie électrique fournie par la source de haute tension, et
• des moyens de déclenchement qui sont prévus pour libérer l'énergie électrique accumulée dans les moyens de stockage et déclencher l'impulsion électrique qui est alors transférée à la tête émettrice de rayons X par l'intermédiaire des lignes électriques,

ces lignes électriques étant enroulées et étant, d'un côté, connectées en parallèle aux moyens de stockage de l'énergie électrique et, de l'autre côté, connectées en série à la tête émettrice de rayons X.To solve this problem, the X-ray pulse generator object of the present invention, comprising:

• a high voltage source,
• an X-ray emitting head, which is capable of producing X-rays when it receives an electrical pulse, and
• a plurality of power lines which are between the high voltage source and the head X-ray emitter, each electrical line comprising a first electrical conductor and a second electrical conductor which are separated by a dielectric,

said generator further comprising:

• means for storing the electrical energy supplied by the high voltage source, and
• triggering means which are provided for releasing the electrical energy accumulated in the storage means and triggering the electrical pulse which is then transferred to the X-ray emitting head via the electrical lines,

these electric lines being wound up and being, on one side, connected in parallel to the means for storing electrical energy and, on the other side, connected in series to the head emitting X-rays.

The generator which is the subject of the invention is capable of emitting, over very short times (equivalent to the length of the pulse), much more intense X-ray radiation than that which is emitted by conventional generators generally used in laboratories and in industry.

In addition, the use of coiled power lines allows the production of a generator of small dimensions, which can be placed on a table and which can be transported by one person.

Preferably, the power lines of the generator object of the invention all have the same length, to obtain a good overvoltage factor.

The generator object of the invention may further comprise a plurality of parallel and electrically insulating supports, which are placed one beside the other and respectively associated with the lines electric coils, each support comprising a groove, in which the corresponding electric line is coiled.

In order to reduce the Corona effect, the generator which is the subject of the invention also preferably comprises means provided for pressing the supports against each other.

To further reduce this Corona effect, the lines are preferably coated, in the grooves, with an electrically insulating material.

Each line can be wound in a spiral or double spiral.

Preferably, each line is a flexible coaxial cable, the first and second electrical conductors of this line being respectively constituted by the core and the braid of this coaxial cable.

Such flexible coaxial cables are commercially available, which simplifies the manufacture of the generator object of the invention.

According to a particular embodiment of the generator object of the invention, each line is a flexible coaxial cable wound in a spiral, the first and second electrical conductors of this line being respectively constituted by the core and the braid of this coaxial cable, l spiral winding of each cable is done by approaching the center of the corresponding support and the supports are drilled in their central part, to allow the passage of cables, from the side where these cables are connected to the energy storage means electric, to the supports which correspond to them respectively.

Preferably, part of the flexible coaxial cables which are connected to the x-ray emitting head is left free to allow mobility of this emitting head relative to the rest of the generator.

This facilitates the implementation of the generator object of the invention.

• la figure 1 montre un schéma électrique d'un générateur conforme à l'invention,
• la figure 2 est une vue schématique de plaques électriquement isolantes, portant des câbles coaxiaux souples enroulés en spirale qui sont utilisables dans un générateur conforme à l'invention,
• la figure 3 montre un assemblage de ces plaques,
• la figure 4 est une vue schématique d'une plaque électriquement isolante, portant un câble coaxial souple qui est enroulé en double spirale et qui est utilisable dans un autre générateur conforme à l'invention, et
• la figure 5 est une vue schématique d'une variante de réalisation de la tête émettrice du générateur objet de l'invention.

The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which:

• FIG. 1 shows an electrical diagram of a generator according to the invention,
• FIG. 2 is a schematic view of electrically insulating plates, carrying flexible coaxial cables wound in a spiral which can be used in a generator according to the invention,
• FIG. 3 shows an assembly of these plates,
• FIG. 4 is a schematic view of an electrically insulating plate, carrying a flexible coaxial cable which is wound in a double spiral and which can be used in another generator according to the invention, and
• Figure 5 is a schematic view of an alternative embodiment of the emitting head of the generator object of the invention.

The pulse X-ray generator, which is schematically represented in FIG. 1, comprises means 2 provided for forming electrical pulses, a head 4 emitting X-rays and a cable generator 6 which connects the means 2 to the head 4.

• une source de haute tension HT,
• deux condensateurs de stockage S1 et S2 prévus pour stocker l'énergie électrique fournie par la source de haute tension HT, et
• des moyens de déclenchement TH qui sont prévus pour libérer l'énergie électrique accumulée dans les condensateurs de stockage et déclencher une impulsion électrique, ces moyens de déclenchement TH étant commandés par des moyens symbolisés par une flèche M sur la figure 1.

These means 2 provided for supplying electrical pulses include:

• a high voltage HV source,
• two storage capacitors S1 and S2 provided for storing the electrical energy supplied by the high voltage source HT, and
• TH triggering means which are provided for releasing the electrical energy accumulated in the storage capacitors and triggering an electrical pulse, these TH triggering means being controlled by means symbolized by an arrow M in FIG. 1.

As can be seen in FIG. 1, the storage capacitors S1 and S2 are mounted in series, the capacitor S2 is mounted between the terminals of the high voltage source HT and the triggering means TH are also mounted between these terminals of the high voltage source HT.

This HV source can be a constant high voltage source or a pulse high voltage source (in which case the electrical pulse, at the input of the cable generator, is triggered when the charge of the capacitors S1 and S2 reaches a desired value) .

As a purely indicative and in no way limitative, a high voltage source is used which can vary between 0 and 40 kV and which is capable of recharging the capacitors S1 and S2 at frequencies which can vary between 0.1 Hz and 1 kHz, depending on the desired configuration.

The capacitors S1 and S2 can be discrete capacitors also called "button capacitors", or can be flat lines or even coaxial cables.

The triggering means TH comprise a single rapid trigger, for high voltage, such as for example a thyratron or a sparkgap or a trigger known as "pseudo-spark", or another rotary spark gap, which reduces energy losses and increases efficiency.

Purely as an indication and in no way limitative, triggering means are used which are capable of operating between 0.1 Hz and 1 kHz.

The head 4 emitting X-rays is waterproof and made of an electrically insulating material such as, for example, glass, ceramic, Plexiglas (registered trademark), polycarbonate, polyvinyl chloride or polysulfone.

If necessary, this emitting head 4 can be wrapped in a thin X-ray absorption envelope, which can be made of lead.

Pumping means 8 communicate in leaktight manner with the interior of the emitting head 4 in order to create a vacuum there.

It is specified in this connection that the duration of an X-ray pulse, obtained as will be indicated below, is a function of the residual pressure inside the emitting head 4.

This emitting head 4 is provided with an anode 10 and a cathode 12 which are placed opposite one another in the emitting head 4 and which pass through the walls of the latter by sealed passages.

It is between the anode and the cathode that the electrical discharges take place, leading to the formation of X-rays.

The emitting head 4 is provided with an orifice 14 facing the space between the anode and the cathode, to allow the exit of the X-ray referenced 16.

This orifice 14 is closed in a leaktight manner using a thin waterproof wall 18 and made of a material transparent to the generated X-rays.

The nature of the material constituting the anode determines the spectrum of the X-ray radiation emitted by this anode as well as the braking radiation of the electrons emitted by the cathode, which will be discussed below.

For the cathode one chooses a material able to easily supply electrons like for example copper or graphite and, for the anode, one can choose a metallic constituent material like for example copper, molybdenum, tungsten or silver .

The relative position of the anode and the cathode determines the shape of the X-ray emission lobe and the spatial distribution of these X-rays.

The spacing E between the anode and the cathode can be made adjustable.

The anode 10 can be made rotating by providing it with a rotation means symbolized by the arrow F in FIG. 1.

In addition, this anode 10 can be provided with means R for cooling by circulation of an appropriate fluid.

The cable generator 6 comprises at least two electric lines preferably constituted by flexible coaxial cables (which are six in number in the example shown in FIG. 1 and bear the references C1, C2, C3, C4, C5 and C6).

Each coaxial cable comprises a first electrical conductor A called "core" and a second electrical conductor T called "braid" which surrounds the core A and is separated from it by a dielectric D.

In addition, the braid of each cable is surrounded by an electrically insulating envelope, not shown.

These flexible coaxial cables are connected in parallel to the means for producing electrical pulses 2 and connected in series to the transmitting head.

More specifically, on the side of the means for producing electrical pulses 2, the ends of the cores of the coaxial cables are electrically connected to each other as well as to the terminal a of the capacitor S2.

On the same side, the braids of the coaxial cables are electrically connected to each other as well as to the terminal b of the capacitor S1, the terminal common to the capacitors S1 and S2 bearing the reference c , as seen in FIG. 1.

On the other side of the cable generator 6, that is to say on the side of the emitting head 4, the end of the core of the coaxial cable C6 is electrically connected to the anode 10 while the end of the braid of the coaxial cable C1 is electrically connected to the cathode 12 and the end of the braid of the coaxial cable C6 is electrically connected to the end of the core of the coaxial cable C5 while the end of the braid of this coaxial cable C5 is electrically connected to the end of the core of the coaxial cable C4 ... and the end of the braid of the coaxial cable C2 is electrically connected to the end of the core of the coaxial cable C1.

The use of such a cable generator 6 makes it possible to obtain extremely rapid and very high voltage electrical discharges (from a few kV to 240 kV in the example shown), the duration of the pulses being less than 25 ns.

TH trigger releases electrical energy stored in capacitors S1 and S2 and to transfer part of this electrical energy to the cable generator 6.

This cable generator 6 allows the multiplication of the electric voltage of the pulse supplied by the means 2, the multiplying factor being a function of the number of flexible coaxial cables.

In the example shown, with six coaxial cables and a voltage of 10 kV at the input of the cable generator, a voltage of 60 kV is obtained between the anode and the cathode of the X-ray emitting head.

An 80 kV voltage would be obtained using eight coaxial cables and the same 10 kV input voltage, or alternatively using six coaxial cables but an input voltage of 13.3 kV.

Under the effect of the high voltage electrical pulse which arrives at the emitting head 4, electrons are emitted very quickly by the cathode 12 (in the form of pulses whose duration is of the order of 10 ns to 25 ns depending on the residual pressure in the emitting head 4) and are braked when they reach the anode 10.

There is then emission of X-rays characteristic of the material constituting the anode 10 and emission of X-ray braking (Bremstrahlung).

Figures 2 and 3 illustrate the arrangement of the coaxial cables C1 to C6.

These coaxial cables C1 to C6 are respectively mounted on electrically insulating plates P1 to P6 (for example made of polyvinyl chloride).

More specifically, each flexible coaxial cable is wound on the plate associated with it.

In the example shown, each coaxial cable is wound in a spiral in a groove G (FIG. 3) provided for this purpose on one face of the corresponding plate.

The plates P1 to P6 are stacked from the plate P1 to the plate P6, as seen in FIG. 3 which is a top view of the stack obtained.

The faces of the plates carrying the grooves G in a spiral are all turned on the same side of the stack.

In addition, an electrically insulating protective plate P7, for example made of polyvinyl chloride, is placed opposite the face of the plate P1 carrying the corresponding spiral groove.

The plates P1 to P7 are pressed against each other (so that there is no air between them, which limits the Corona effect), using appropriate means which, in the example shown on FIG. 3 are electrically insulating threaded rods 20, for example made of polyvinyl chloride, which pass through aligned holes 21 of the plates P1 to P6, the end of each rod situated on the side of the plate P6 being provided with a head 22 which presses against this plate P6 while the other end of each threaded rod is provided with a nut 23 which clamps the plates against each other by means of an electrically insulating washer 24 as are nut 23 and head 22.

To further reduce the Corona radiation and improve the efficiency of the generator, the coaxial cables are coated, in their respective grooves, with an electrically insulating paste P, for example silicone.

On the side of the parallel connections of the flexible coaxial cables, connections which are symbolized by the dotted lines CP in FIG. 3, the arrival of the flexible coaxial cables up to their respective plates is carried out through orifices formed in the central part of the plates P1 to P6.

As can be seen in FIG. 3, the six cables arrive from their connections in parallel, towards the face of the plate P7 which does not carry a groove.

It can be seen in FIG. 2 that the plate P1 has an orifice 01, the plate P2 has two orifices O1 and O2, ..., and the plate P6 has six orifices C1 to O6.

The orifices bearing the same reference are aligned and all the orifices are located on the same cylinder of revolution, the circular trace 26 of which is dotted on each of the plates.

The distance between two adjacent holes is the same for each of the plates.

The coaxial cables arrive at the assembly of the plates towards the central part of this assembly and the spiral development of each cable takes place away from the center of the corresponding plate as seen in FIG. 2.

Thus, the cable C1 crosses the six openings O1 to wind in a spiral on the plate P1, the cable C2 crosses the five openings 02 to wind on the plate P2, ..., and the cable C6 crosses the opening 06 to wind on the plate P6.

In order to obtain a good overvoltage factor and short duration X-ray pulses, the flexible coaxial cables are all the same length.

To do this, given the different thicknesses of the plate assembly than the cables C1 to C6 have to cross, the length of the spiral portion closest to the center of a plate is calculated according to the thickness of the assembly to be crossed for the corresponding cable.

FIG. 2 illustrates this: we see that this portion increases from cable C1 to cable C6 so that there remains a greater length for the cable C1, allowing this cable C1 to pass through the assembly, than for the cable C6 which is closest to the parallel connections of the coaxial cables.

As we have seen, the other ends of the coaxial cables are connected in series, which is symbolized by the dotted lines CS in FIG. 3.

On the side of this series connection, part of each winding can be left free, the resulting flexibility allowing exceptional mobility of the head 4 emitting X-rays.

It is specified that a sufficient thickness of insulating material must be provided between the adjacent cables and between the adjacent turns of the spiral of each cable so as not to have electrical breakdown during operation of the generator.

For the same consumed electrical power of 3 W, the generator which has been described with reference to FIGS. 1 to 3 leads to an exposure time of 20 ns whereas a conventional generator (conventional X tube) requires an exposure time 6 s, for the same dose of X-radiation received at the same distance.

In an alternative embodiment, schematically illustrated in FIG. 4, each of the flexible coaxial cables, such as the cable C1, is wound in a double spiral as shown in FIG. 4, in a groove provided for this purpose on one face of the corresponding plate.

Thus, the two ends of the cable terminate at two opposite sides of the plate and the electrical connections between the cables are made as explained with reference to FIG. 1, which is simpler with such double spiral windings. with spiral windings as shown in Figure 2.

It is also possible to produce the double spiral to cause the two ends of the flexible cable to end on the same side of the plate as indicated by the dotted lines in FIG. 4.

FIG. 5 is a schematic view of another embodiment of the X-ray emitting head.

The emitter head of FIG. 5 has a symmetry of revolution about a Z axis and includes an annular anode 10 provided with a bore along the Z axis as well as a cathode 12 of elongated shape along the Z axis and finished by a point opposite the piercing of the anode.

The cathode 12 is adjustable in translation along the Z axis in an internally threaded part 28, the cathode having a corresponding external thread.

This part 28 is housed in an electrically insulating tube 30 of axis X, one end of which is closed by an external shoulder of the part 28 while the other end of the tube 30 is closed by the anode 10.

On the side thereof, the emitting head is extended by a tubular piece 32 of electrically conductive axis X, which is in contact with the anode and closed in leaktight manner by a thin wall 18 transparent to the generated X-rays and which delimits a zone communicating with pumping means 8 making it possible to create a vacuum in the emitting head, the parts 28 and 32 comprising seals 34 for maintaining the vacuum.

FIG. 5 also shows electrical conductors 36 by which the anode and the cathode are connected to the cable generator 6.

The assembly of the generator according to the invention, which has been described with reference to FIGS. 1 to 5, can be reduced to a size and a weight which are compatible with use in a portable generator.

Claims (10)

1. X-ray pulse generator comprising:

   - a high voltage source (HT),

   - a X-ray emitting head (4) able to produce X-rays when it receives an electric pulse and

   - a plurality of electric lines (C1 to C6) between the high voltage source and the X-ray emitting head, each electric line comprising a first electrical conductor (A) and a second electrical conductor (T) separated by a dielectric (D),

   said generator also comprising:

   - means (S1, S2) for storing the electric power supplied by the high voltage source (HT) and

   - triggering means (TH) provided for releasing the electric power stored in the storage means (S1, S2) and for triggering the electric pulse, which is then transferred to the X-ray emitting head (4) by electric lines (C1 to C6),

   said electric lines being wound and on one side connected in parallel to the electric power storage means (S1, S2) and on the other side are connected in series to the X-ray emitting head (4).
2. Generator according to claim 1, characterized in that all the electric lines (C1 to C6) have the same length.
3. Generator according to either of the claims 1 and 2, characterized in that it also comprises a plurality of electrically insulating, parallel supports (P1 to P6), which are juxtaposed and respectively associated with the wound electric lines (C1 to C6), each support having a groove (G) in which the corresponding electric line is wound.
4. Generator according to claim 3, characterized in that it also comprises means (20, 22, 23, 24) for pressing the supports (P1 to P6) against one another.
5. Generator according to either of the claims 4 and 5, characterized in that, in the grooves (G), the lines are coated with an electrically insulating material (P).
6. Generator according to any one of the claims 1 to 5, characterized in that each line (C1 to C6) is spirally wound.
7. Generator according to any one of the claims 1 to 6, characterized in that each line (C1 to C6) is wound in double spiral form.
8. Generator according to any one of the claims 1 to 7, characterized in that each line is a flexible, coaxial cable (C1 to C6), the first and second electrical conductors of said line being respectively constituted by the core (A) and the braid (T) of said coaxial cable.
9. Generator according to any one of the claims 3 to 5, characterized in that each line (C1 to C6) is spirally wound, in that each line is a flexible, coaxial cable, the first and second electrical conductors of said line being respectively constituted by the core (A) and the braid (T) of said coaxial cable, in that the spiral winding of each cable takes place on moving towards the centre of the corresponding support (P1 to P6) and in that the supports are perforated in their central portion in order to permit the passage of cables from the side where the cables are connected to the electric power storage means (S1 to S3) to the supports (P1 to P6) respectively corresponding thereto.
10. Generator according to either of the claims 8 and 9, characterized in that a portion of the flexible, coaxial cables connected to the X-ray emitting head (4) is left free to permit the mobility of said emitting head with respect to the remainder of the generator.

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