Pulse generator

This pulse generator which is of the Marx generator type and is applicable to obtaining high pulse voltages cmprises n+1 capacitors connected n parallel by resistors and spark gap switches for discharging said capacitors into a load circuit, in such a way that if V is the charging voltage of the capacitors, the voltage applied to the load circuit is equal to (n+1)V. This generator is characterized in that the capacitors and spark gap switches form a stack of circular plates, which are provided with axial openings. These plates and the resistors are located in a tight enclosure containing a gas aiding the priming of the spark gap switches, which is triggered by the radiation of a source passing through the opening.

BACKGROUND OF THE INVENTION 
The present invention relates to a pulse generator and more particularly to 
a high voltage pulse generator, more particularly known in the art as a 
Marx generator. 
The invention applies to the supply of high voltage pulses having a pulse 
front with a very fast rise time. 
The prior art discloses high voltage pulse generators comprising 
cascade-connected cells, respectively having capacitors charged across 
resistors. The high voltage pulse is obtained at the generator output by 
bringing about the discharge of the capacitors across resistors, by means 
of spark gap switches connected to said capacitors. These spark gap 
switches are switched in cascade, e.g. using ultraviolet radiation. If the 
d.c. voltage applied to the generator input for charging the capacitors 
has a value Vo and if the generator has n capacitors, the voltage of the 
generator output pulse is equal to n.Vo. 
In a more detailed manner, this type of high voltage pulse generator or 
Marx generator comprises, as shown in FIG. 1, a succession of spark gap 
switches E.sub.1, E.sub.2, . . . , E.sub.n-1, E.sub.n. Each of these spark 
gap switches, such as e.g. switch E.sub.1, comprises a first electrode 1 
and a second electrode 2. The first electrode of each spark gap switch is 
connected to the first electrode of the following spark gap switch of said 
succession of spark gap gap switches by a first resistor in the case of 
spark gap switches of rank 1 to n-1. These first resistors are designated 
R.sub.1, R.sub.2, . . . , R.sub.n in FIG. 1. Thus, for example, resistor 
R.sub.1 connects the first electrode 1 of spark gap switch E.sub.1 to the 
first electrode 3 of spark gap switch E.sub.2. In the same way, the second 
electrode of each spark gap switch is connected by a second resistor to 
the second electrode of the following spark gap switch of said succession 
for spark gaps of ranks 1 to n-1. These second resistors are designated 
R'.sub.1, R'.sub.2, . . . , R'.sub.n in FIG. 1. For example, the second 
resistor R'.sub.1 connects the second electrode 2 of spark gap switch 
E.sub.1 to the second electrode 4 of spark gap switch E.sub.2. In 
addition, the second electrode of each spark gap switch is connected by a 
capacitor to the first electrode of the following spark gap switch of the 
succession of spark gaps for spark gaps of ranks 1 to n-1. These 
capacitors are designated C.sub.1, C.sub.2, . . . , C.sub.n-1, C.sub.n in 
FIG. 1. Thus, for example capacitor C.sub.1 connects the second electrode 
2 of spark gap switch E.sub.1 to the first electrode 3 of spark gap switch 
E.sub.2. 
The generator shown in FIG. 1 is applied by a d.c. voltage source 5, which 
is connected by a second resistor R' to a common point A between the 
second electrode 2 of spark gap switch E.sub.1 of rank 1 and the second 
resistor R'.sub.1 connecting said second electrode of spark gap switch 
E.sub.1 to the second electrode 4 of spark gap switch E.sub.2 of rank 2. 
The second electrode 7 of spark gap switch E.sub.n of rank n is connected 
to a first coating 9 of an output capacitor C, a first resistor R 
connecting the first electrode 6 of spark gap switch E.sub.n of rank n to 
a first coating 8 of output capacitor C. The output voltage of the 
generator shown in the drawing is a voltage of pulse type and which 
appears at the time of triggering the spark gap switches. This vol age can 
be applied to a load circuit L. It is available on the first coating 8 of 
output capacitor C. In the example shown in FIG. 1, the generator has n-1 
capacitors if the input d.c. voltage applied by source 5 is equal to Vo, 
the output pulse voltage being equal to (n-1).Vo. In FIG. 1, M designates 
the reference earth. 
The realization of a Marx generator of the type whose circuit has just been 
described generally takes place by using capacitors protected by a 
covering, equipped with a group of terminals making it possible to connect 
the different components of said circuit, e.g. paper capacitors. These 
capacitors are contained in metal or plastic boxes having insulators for 
the output terminals of the capacitors. It is also possible to use 
capacitors having ceramic dielectrics, said capacitors being sealed and 
consequently far from easy to manufacture. 
Marx generators whose circuits are constructed in the manner described 
hereinbefore and which use paper capacitors contained in metal boxes or 
sealed ceramic dielectric capacitors suffer from the important 
disadvantage of a lack of compactness, as a result of the supplementary 
overall dimensions due to the coverings and connections. Thus, the 
electrical energy which can be supplied by the known Marx generators is 
reduced and the equivalent inductance of the generator is high, which is 
prejudicial to the power supplied. 
SUMMARY OF THE INVENTION 
The object of the present invention is to obviate the disadvantages of the 
known pulse generators of the Marx type and more particularly aims at 
providing a very compact pulse generator having a greatly reduced 
inductance compared with the known generators. This compactness is more 
particularly obtained through the use of ceramic capacitors arranged in 
stack form. 
The present invention more specifically relates to a pulse generator having 
a succession of spark gap switches ranging from rank 1 to rank n, each 
having first and second electrodes, the first electrode of each spark gap 
switch being connected by a first resistor to the first electrode of the 
following spark gap switch of said succession, for spark gap switches of 
rank 1 to n-1, the second electrode of each spark gap switch being 
connected by a second resistor R'.sub.1 to the second electrode of the 
following spark gap switch of said succession, for spark gap switches of 
rank 1 to n-1, the second electrode of each spark gap switch also being 
connected to a capacitor to the first electrode of the following spark gap 
switch of said succession, for spark gap switches of rank 1 to n-1, said 
generator being supplied by a d.c. voltage source connected by a second 
resistor of a common point between the second electrode of the spark gap 
switch of rank 1 and the second resistor connecting said second electrode 
of the spark gap switch of rank 1 to the second electrode of the spark gap 
switch of rank 2, the second electrode of the spark gap switch of rank n 
being connected to a second coating of an output capacitor, a first 
resistor connecting the first electrode of the spark gap switch of rank n 
to the first coating of the output capacitor, the output voltage being 
available on said first coating, wherein the electrodes of the spark gap 
switches are parallel conductor plates forming a stack, the capacitors 
comprising at least two planar conductive coatings which, for each 
capacitor, are respectively in contact with the second electrode of the 
corresponding spark gap switch of said succession and to the first 
electrode of the following spark gap switch in said succession, two facing 
electrodes of two successive spark gap switches being separated by an 
insulating spacer and the electrodes of the same spark gap switch also 
being separated by an insulating spacer, the electrodes and capacitors 
being located in a tight enclosure containing a gas, the electrodes and 
the capacitors having aligned openings, along an axis passing through the 
stack, the triggering of the spark gap switch being brought about by 
ultraviolet radiation applied by a source to one of the openings. 
According to another feature, the capacitors have metal coatings and 
ceramic dielectrics. 
According to another feature, the plates constituting the electrodes of the 
spark gap switches, as well as the coatings of the capacitors and the 
insulating coatings of said capacitors have a circular shape, the spacers 
being annular, the axis along which said openings are located 
corresponding to the axis of said plates, said coatings and said spacers. 
According to another feature, the contact between the coating of each 
capacitor and the electrode of the corresponding spark gap switch is 
assured by a layer of a flexible conductive material. 
According to another feature, the first and second resistors have the same 
value. 
According to another feature, the capacitors of the stack, as well as the 
output capacitor have the same value. 
According to another feature, the tight enclosure is a metal enclosure 
insulated from the plates constituting the electrodes of the spark gap 
switches and insulated from the capacitor coatings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The pulse generator according to the invention show in FIG. 2 is in 
accordance with the circuit of FIG. 1. The same elements carry the same 
references in both FIGS. 2 and 1. 
Thus, it is possible to see spark gap switches E.sub.1, E.sub.2, . . . , 
E.sub.n, capacitors C.sub.1, C.sub.2, . . . , C.sub.n, C, first resistors 
R.sub.1, . . . , R.sub.n, R, second resistors R', R'.sub.1, R'.sub.n-1, 
R'.sub.n. The d.c. voltage source 5 is also shown and is connected to the 
second electrode 2 of spark gap switch E.sub.1 via resistor R'. The load L 
is also shown, as are the first and second electrodes 1, 2 of spark gap 
switch E.sub.1, electrodes 3, 4 of spark gap switch E.sub.2, electrodes 6, 
7 of spark gap switch E.sub.n and the coatings 8, 9 of output capacitor C. 
According to the invention, electrodes 1, 2, 3, 4, . . . , of spark gap 
switches E.sub.1, . . . , E.sub.n are parallel conductive metal plates 
forming a stack. Each of the capacitors C.sub.1, C.sub.2, . . . , C.sub.n, 
C comprises at least two planar metal conductive coatings, which are 
respectively in contact with the second electrode of the corresponding 
spark gap switch of the succession of spark gap switches and with the 
first electrode of the following spark gap switch in said succession. 
Thus, for example, capacitor C.sub.1 comprises a planar conductive coating 
10 in contact with the second electrode 2 of the first spark gap switch 
E.sub.1, and with a second planar coating 11 in contact with the first 
electrode 3 of the second spark gap switch E.sub.2. The facing electrodes 
of two successive spark gap switches are separated by an insulating 
spacer. The electrodes of the same spark gap switch are also separated by 
an insulating spacer. In the embodiment shown in FIG. 2, electrodes 2, 3 
of the successive spark gap switches E.sub.1, E.sub.2 are separated by an 
insulating spacer 12. Electrodes 1, 2 of spark gap switch E.sub.1 are 
separated by an insulating spacer 13. 
The electrodes and capacitors described hereinbefore are located in a tight 
enclosure 14 diagrammatically shown in FIG. 2. This tight enclosure 
contains a gas which is able to assist the triggering of the spark gap 
switches by a priming phenomenon. For this purpose, the electrodes have 
openings such as 15, 16, which are aligned along an axis X passing through 
the stack. When all the capacitors have been charged by means of the power 
supply 5, the triggering of the spark gap switches is brought about by 
ultraviolet radiation, e.g. supplied by a source 17, applying said 
radiation to one of the openings described hereinbefore. 
In a preferred manner, all the capacitors C.sub.1, C.sub.2, . . . , 
C.sub.n, C have the same value. In the same way, the first resistors 
R.sub.1, R.sub.n, R and the second resistors R', R'.sub.1, . . . , 
R'.sub.n have the same values. 
The coatings 10, 11 of the capacitors are planar metal coatings, whilst the 
dielectric 18 placed in the form of one or more layers between the 
coatings is made from a ceramic material. The capacitor coatings can be 
constituted e.g. by a metal layer 19, in contact with the corresponding 
electrode by means of a flexible conductive layer, e.g. of rubber 20, in 
which is incorporated a conductive material. This conductive rubber layer 
makes it possible to absorb the shocks and vibrations to which the 
generator can be exposed, as well as the stresses occurring during the 
triggering of the spark gap switches. 
The plates constituting the electrodes of the spark gap switches, as well 
as the capacitor coatings of the insulating layers of the capacitors all 
have a circular configuration. Axis X along which are located the openings 
corresponds to the axis of said plates and said coatings. The insulating 
spacers 12, 13 are annular, and have the same axis X. 
Tight enclosure 14 is a metal enclosure insulated from the plates 
constituting the electrodes, the spark gap switches, as well as the 
capacitor coatings, the metal enclosure has tight insulating bushings or 
ducts 21 to permit the connection, outside said enclosure, of source 5 and 
charge L. This enclosure is preferably connected to the reference earth. 
In known manner, the aforementioned generator having n+1 capacitors makes 
it possible, when the voltage of the power supply 5 has a value Vo, to 
obtain at the output of said generator a voltage of value (n+1).Vo. 
Due to the fact that the complete column of spark gap switches is at the 
same pressure in enclosure 14, as a result of the openings made in the 
spark gap switches and in the capacitors, the triggering of a spark gap 
switch is stimulated by the ultraviolet radiation emitted by its 
collaterals, so that there is a synchronization of the triggering of the 
stack of spark gap switches and consequently a reduction in the speed of 
the rise front of the pulse obtained at the generator output. 
The generator described hereinbefore has a compact shape, due to the stack 
of spark gap switches and capacitors.