Method of operating a gas discharge switch and an arrangement for carrying out the method

The invention relates to a gas discharge switch with a low-pressure gas discharge segment, which is provided with an anode and at least one main cathode, and arranged in an ionizable working gas. It is provided with a control unit for flow discharge, which contains a cathode. For the working gas, a gas storage with automatic pressure control is provided. According to the invention, the energy of glow discharge is provided as the setting value for regulating the pressure of the working gas. With this module (30), consisting of the cathode (31) for glow discharge with the gas storage (32), the pressure of the working gas, preferably hydrogen, remains at least approximately constant over a long period of time, in a closed system of this so-called pseudo-spark switch.

BACKGROUND OF THE INVENTION 
The present invention relates to a gas discharge switch and more 
particularly to such a switch with a low-pressure gas discharge segment 
which is provided with an anode and at least one main cathode and arranged 
in an ionizable working gas and to which a control device which contains a 
cathode is assigned. 
The ignition voltage for a predetermined gas discharge segment and its 
usual graphic representation as a function of the product of the gas 
pressure p and the electrode distance D in the ignition characteristic 
curve is known to be formed by taking the ignition probability, an 
important aid in characterizing electric discharge apparatus, into 
consideration. In the determination of the electric voltage resistance of 
the preset gas discharge segment, an infinitely large plate capacitor and 
its ignition characteristic curve are generally used for a comparison. 
However, the practical embodiment of such discharge segments has 
electrodes with finite dimensions. While it is sufficient, in order to 
determine the right branch of the ignition characteristic curve known as 
the Paschen curve (i.e., in order to study the so-called far breakdown 
zone, including the voltage minimum), merely to arrange two flat, 
rounded-off plates, possibly provided with a so-called Rogowski profile at 
the edges, parallel to one another, such a design arrangement is not 
usable to study ignition characteristic lines in the left part of the 
Paschen curve, i.e., in the so-called post breakdown zone, because then 
indirect charges can occur. Such indirect discharges can be avoided with 
an electrode design with flat plate electrodes which are arranged coaxial 
to one another, and are bent away from one another at their edges, with a 
small radius of curvature relative to the electrode distance, and guided 
along the inside cylindrical insulator surface. In this way, a gap is 
always formed between the bent-away, cylinder-shaped edge zone of the 
electrodes and the inside wall of the hollow cylinder insulator. Such 
embodiments of low-pressure gas discharge segments are also suitable for 
the near breakdown zone. 
Low-pressure gas discharge segments are known to be suitable as switches 
for high currents, for example of about 50 kA to 2 MA, and high voltages 
up to about 100 kV. These gas discharge switches work with a pressure of 
the working gas, preferably hydrogen, of less than 1 torr at an electrode 
gap of less than 1 cm, with a voltage about 10 kV in the left branch of 
the Paschen curve. Since these switches can only turn a current on, but 
not off again, they are particularly suited for discharging large 
capacitors, for example at a voltage of 10 to 100 Kv and currents up to 10 
MA, at which several switches are then generally switched in parallel. The 
discharge switch contains an anode and a main cathode, which are arranged 
coaxial to one another and are separated at the edge by a ring-shaped 
insulator (Proc. IEE, Volume 111, Number 1, January 1964, pages 203 to 
213). 
Such gas discharge switches can be controlled by a pulsed low-pressure gas 
discharge. The main discharge is initiated by a hollow cathode discharge 
and ignited by injection of charge carriers. For this purpose, a control 
device is provided, which contains a cage provided with holes, which 
surrounds the rear space of the cathode. The discharge segment is 
separated from the zone of a preionization discharge, which is a flow 
discharge, by the cage. Between the cage and the zone of the glow 
discharge, various auxiliary electrodes for shielding and potential 
control can also be provided as disclosed in Sci. Instr. 19 (1986), The 
Inst. of Physics, Great Britain, pages 466 to 470. 
In this closed system, the pressure of the working gas decreases with an 
increasing number of switching processes. The reason for this lies in the 
implantation of charged high-energy particles during the discharge. In 
order to counteract this, the gas discharge system can be provided with a 
gas storage for the working gas, which can consist of a metal suitable as 
a storage or reservoir, for example titanium, zirconium, tantalum, 
palladium or even lanthane. Furthermore, intermetallic cubic Laves phases, 
which consist of a compound of iron hydride with one of the rare earth 
elements are suitable as storage material. This storage material absorbs 
gas, at a raised temperature, in an atmosphere enriched with the working 
gas, and this gas is stored in the lattice. In a vacuum or in the working 
gas of a gas discharge switch, it gives the working gas off again when 
heated. 
To regulate the working gas to a constant pressure, a gas storage with an 
automatic pressure control can be provided. A known embodiment of such a 
gas storage consists of two generators, one of which serves as a storage 
and the other of which serves as a getter. The generator gives off gas 
when heated, for example by a heating coil, and the storage absorbs gas if 
too much gas is released and therefore a pressure increase occurs. The 
distance between the storage metal and the generator sheath is selected so 
it is not greater than the mean free path length of the working gas, i.e., 
at most approximately 0.4 mm for hydrogen as disclosed in Sov. Phys. Tech. 
Phys. Volume 21, Number 4, April 1976, pages 487 to 489. 
SUMMARY OF THE INVENTION 
The present invention is based on the task of simplifying and improving a 
gas discharge switch with a low-pressure gas discharge segment and an 
integrated glow discharge segment as the trigger part, and the pressure 
control for the working gas, in particular, is supposed to be simplified. 
This task is accomplished, according to the present invention which 
provides a gas discharge switch with a low-pressure gas discharge segment 
that has an anode and at least one main cathode. The segment is arranged 
in a working gas and a control device for glow discharge is assigned to 
the segment. In this embodiment of a gas discharge switch, the energy of 
the glow discharge is provided as the setting value for control of the 
pressure of the working gas, which can preferably consist of hydrogen. 
In a preferred embodiment of the gas discharge switch, the gas storage can 
be integrated into the cathode of the glow discharge. This cathode can 
preferably consist of a stack of ring disks, which are connected with each 
other with thermal conductivity, and consist of a material which serves as 
storage for the working gas. The distance of the plates relative to one 
another is then preferably selected to be less than the mean free path 
length of the working gas. 
Furthermore, storage material can also be provided in powder form, and 
placed against the cathode to form a good heat-conducting connection. A 
further advantageous possibility is the implementation of the storage in 
the form of a paste or a sintered element containing the storage material.

DETAILED DESCRIPTION 
In the embodiment of a gas discharge switch according to the present 
invention illustrated in FIG. 1, two electrodes 2 and 3, of which the 
electrode 2, for example, is switched as the main cathode and the 
electrode 3 is switched as an anode, and which each form a rotation 
element, are arranged coaxially to one another. The axis of rotation, 
indicated with a dot-dash line, is designated as 4. The electrodes 2 and 3 
are provided with coaxial bores 5 and 6, respectively, at which a gas 
discharge segment 10 is formed. The electrodes 2 and 3 consist of an 
electrically conductive material, for example special steel, and, at the 
discharge segment 10, can preferably include inserts 8 and 9, 
respectively, of a metal which melts at high temperature, for example, 
tungsten or molybdenum, or their alloys. The diameter of the bores 5 and 7 
is selected to be preferably less than the distance between the electrodes 
2 and 3. The electrical current leads to the main cathode 2 and the anode 
3 are designated as 12 and 13, respectively, in the figure. In general, 
the main cathode 2 will lie at zero potential or ground and a positive 
potential of about 20 kV, for example, will be applied to the anode. The 
current leads 12 and 13 are passed vacuum-sealed through a housing 14, 
which preferably can consist of a ceramic. 
Below the discharge segment 10 there is a control device 20 with a housing 
16, which surrounds a rear cathode space 18. The housing 16 is provided 
with openings 22 and 23, which are shielded by a hollow cylinder trigger 
electrode. This trigger electrode 24 is provided with a control connection 
26, which is passed vacuum-sealed through the housing 14. The housing 14 
furthermore contains a module 30 consisting of a cathode 31 for glow 
discharge and a gas storage element 32 for the working gas, preferably 
hydrogen or deuterium, or a gas mixture containing these gases. The 
cathode 31 for glow discharge, the connection conductor 29 of which is 
also passed vacuum-sealed through the housing 14, form a discharge space 
28 for the glow discharge, together with the cylindrical side wall of the 
housing 14 and the housing 16 for the rear cathode space. The gas storage 
element 32 can include, for example, a stack of sheets 34 of storage 
material, which are connected with the cathode 31 to provide good heat 
conductivity, via spacers 36. The distance between the sheets 34, which 
can comprise, for example, titanium or zirconium, is preferably selected 
to be at most as great as the mean free path length of the working gas, 
i.e., about 0.3 to 0.4 mm for hydrogen as the working gas. 
Due to the operating conditions, especially the current at the cathode 31, 
a glow discharge is set, which burns in the discharge space 28, 
anomalously and impeded, at the same time. In an anomalous glow discharge, 
the available surface of the cathode 31 is completely covered by the 
discharge. Since the burning voltage of the discharge is dependent on the 
quotient of the current density j and the square of the gas pressure p, a 
reduction in the gas pressure p results in an increase in the burning 
voltage. In the case of impeded discharge, the distance between the anode 
3 and the cathode 31 is not sufficient for an undisturbed formation of the 
negative flow light; in an extreme case, the anode 3 dips into the cathode 
drop space. With an increasing degree of impedance, the burning voltage of 
the discharge increases. The degree of impedance can be estimated from the 
rule known for normal glow discharge, that the product of the length of 
the cathode dark space d and the gas pressure p is constant. If the 
distance between the anode 3 and the cathode 31 is reduced until it is 
significantly less than 2.times. d then the discharge is impeded and the 
burning voltage will increase. If the pressure is increased in the case of 
a glow discharge which is already burning in impeded manner, a 
corresponding reduction of the burning voltage will occur. In a gas 
discharge switch with a low-pressure gas discharge segment, the burning 
voltage of the glow discharge is therefore influenced by the pressure. If 
the pressure drops, the burning voltage will increase, and vice versa. 
An increase in the burning voltage also means a corresponding increase in 
the output absorbed by the cathode 31, with a corresponding increase in 
the temperature. In the module 30 consisting of the cathode 31 and the gas 
storage 32, hydrogen is released from the storage 32 if the temperature of 
the cathode 31 increases, and the original decrease in pressure is 
compensated for. 
To initiate the glow discharge, a negative voltage, which can amount to 
-2.5 kV, for example, is applied to the cathode 31. In contrast, a trigger 
voltage is provided for the trigger electrode 24, which can amount to +50 
V and -50 V, switchable, for example. It is also practical if the cathode 
31 is provided with a coating, not shown in the figure, which consists of 
a metal with a low sputter yield, for example of molybdenum or nickel. 
In the embodiment according to FIG. 2, with the same arrangement of the 
main cathode 2 and the anode 3, as well as the gas discharge segment 10 
and the rear cathode space 18 with the trigger electrode 24, a module 30 
consisting of a hollow cylinder cathode and a gas storage is provided, 
which includes a stack of ring-shaped sheets 35 of storage material, which 
are arranged in a stack with spacers 37 of an electrically and thermally 
conductive material, especially storage material, with this stack 
partially surrounding the discharge space 28. The distance "a" between the 
individual storage sheets 35 and their distance b from the inside wall of 
the housing 14 is selected in such a way that it is not significantly 
greater, and preferably less, than the median free path length of the 
charge carriers of the working gas. At a gas pressure p of 20 Pa, for 
example, the median free path length of hydrogen is approximately 0.3 mm. 
Under some circumstances, it can be practical to produce each of the 
ring-shaped storage sheets 35 with the adjacent spacers 37 according to 
FIG. 2 in one piece. Furthermore, it is possible that only the 
ring-disk-shaped storage sheets 35 consist of storage material and that 
those sheets are attached at the outside mantle surface of a hollow 
cylinder cathode 31, which then preferably consists of a material with a 
low sputter yield Likewise, the storage material can consist of a paste 
which is applied for example, to the outside mantle surface of a 
ring-cylinder cathode. 
At greater pressures and correspondingly lesser free path lengths of the 
charge carriers, in particular, it can be practical to apply the storage 
material 40 according to FIG. 3 in powder form, between the hollow 
cylinder cathode 31 and a container 39 of gas-permeable material, which 
can consist, for example, of a metallic lattice or network or also of 
porous ceramic. 
In an embodiment of the module 30 consisting of the cathode 31 and the gas 
storage, in which the storage material 40 consists of a sintered element 
which is connected with the cathode 31 to conduct heat well, a special 
container 39 is not required. In this embodiment, the inside surface of 
the ring cylinder sintered element consisting of the storage material 40 
can preferably serve as the cathode 31.