Patent Number: 
Section: description

FIG. 2 depicts the inventive device with additional auxiliary electrodes (9a, 9b) to increase the conversion efficiency or the radiation yield. A radiation emitting pinched plasma (11) forms in the gas-filled space (7) between the electrodes (1, 2), to which voltage is applied. On the side of the cathode (1) facing away from the space (7) there is an auxiliary electrode (9a), by means of which the sparking field strength of the gas discharge can be increased. This in turn allows an operation at higher gas pressures at higher radiation yield. The auxiliary electrode (9a) exhibits in operation a positive potential with respect to the cathode (1). Furthermore, between the main electrodes there is an auxiliary electrode (9b) to provide a longer pinched plasma column (11). Studies have shown that the plasma column (11) does not project or projects only slightly into the openings (3, 8) of the main electrodes, and thus in the case of a cylindrically symmetrical design of the openings only a small solid angle is available for the radiation decoupling. Thus, the cylindrically symmetrical opening (3) in this embodiment exhibits a diameter of 10 mm, with which, given the specified thickness of the electrodes, an observer could still see the plasma at an angle of  xcex1=14 degrees relative to the axis of symmetry (5). Therefore, to increase the radiation yield the opening (8) is designed conically. In the case of the conical opening (8) the plasma (11) can still be recognized by the observer (12) at an angle of  xcex1=60 degrees relative to the axis of symmetry (5). Thus, when the same energy is fed into the plasma, the result is a decoupled radiation intensity, which, compared to the case of the cylindrically symmetrical opening, is larger by approximately a factor of 20. FIG. 3 depicts in principle the same electrode configuration as in FIG. 2, but without the auxiliary electrodes. In addition, there are auxiliary openings (13a, 13b) for the gas inlet and/or the gas outlet from the area (14) of the hollow cathode (1). Thus, the discharge gas, such as xenon, oxygen or SF6, which is required for the gas discharge, can be admitted through the openings (13b). Said gas is ignited in the space (7). In the rearward areas of the electrode system, which are illustrated in FIG. 3, there is a gas with slight absorption, like helium or hydrogen. This gas, which is transparent to the generated radiation, is admitted through the openings (13a) into the area (14). The openings (13a) for admitting the transparent gas are farther away from the opening (8) than the openings (13b) for admitting the discharge gas. Thus, the light gas is first in that part of the area (14) of the cathode (1) that faces the x-ray gate (10); and the heavier discharge gas is in that part of the area (14) that faces away from the protecting glass (10) or in the vicinity of the opening (8). At this stage this procedure has two possibilities. First, both gases can be siphoned off in such a manner through openings, which are not shown in FIG. 3, in the area of the gas-filled space (7) that the result is a thorough mixing of both types of gases. The advantage lies in the fact that a higher plasma particle density can be obtained in the plasma channel located in the electrode space (7). As an alternative a part of the openings (13a) can be used in such a manner by initiating a laminar flow of the light gas in the rearward areas of the electrode system that thorough mixing is largely avoided by siphoning off the light gas. Thus, the light gas remains permanently in that part of the area (14) that faces the x-ray gate (10). However, this light gas absorbs the radiation significantly less than the discharge gas so that a higher radiant power is available to the user. Another possibility for using the openings (13a, 13b) consists of admitting the discharge gas not through the openings (13b), but rather through the openings, which are not shown in FIG. 3, in the area of the gas-filled space (7) or the anode (2) and siphoning off through the openings (13b). The light gas or transparent gas is admitted in turn through the openings (13a). These designs show that the openings (13a) can be used both to admit and to discharge the discharge gas(es); and the openings (13a) can be used only to admit the light gas(es). FIG. 4 depicts an embodiment of the inventive device, wherein the electrodes (1, 2) exhibit additional circular openings (14). The openings (14) are circular inside the respective electrode and are arranged equidistant in relation to the circle. Anode (1) and cathode (2) exhibit the same number of identical openings in the same geometric arrangement with respect to the axis of symmetry (5). When viewed along the axis of symmetry (5) in the direction of every opening (4) in the anode (2), the result of this design is an opening, located behind it, in the cathode (1). When a voltage is applied to the electrodes, the result is a formation of several plasma lines (15) in the sparking phase of the gas discharge. The plasma lines (15) contract subsequently into a single central radiation-emitting pinched plasma channel (11) on the axis of symmetry (5) owing to the self magnetic field of the flowing electrical current. The radiation is decoupled axially along the axis of symmetry (5). If the electrode facing the x-ray gate is the cathode (1), then it is advantageous to provide a shield (16) between the central opening (4) and the additional openings (14). The shield (16) has the advantage that the sparking that occurs only in the channels of the thin plasma lines (15), but not in the central channel along the axis of symmetry (5), is facilitated. The shield (16) can be omitted, if the electrode facing the x-ray gate (10) is the anode (2), since sparking takes place only on the cathode side. FIG. 5 is a view of an electrode with a central opening (3), which additionally exhibits a ring-shaped opening (17). The ring-shaped opening (17) exhibits a center or an axis of symmetry, which coincides with the axis of symmetry (5) of the electrode configuration. An electrode, which faces the x-ray gate (10) and belongs to this design, requires, as in the embodiment according to FIG. 4, an additional shield (16). 1: cathode 2: anode 3, 4: (main) opening 5: axis of symmetry 6: insulator as the space holder 7: gas-filled space 8: conically designed opening 9a: auxiliary electrode behind the opening of the main electrode 9b: auxiliary electrode between the main electrodes 10: x-ray gate 11: pinched plasma 12: observer 13a, 13b: gas inlet and/or gas outlet opening 14: additional opening in the electrode 15: plasma lines 16: shield 17: ring-shaped opening 19: ultra high vacuum (UHV) area of the device