Pulsed discharge source electron beam (options)

 

Usage: in the physical electronics, quantum electronics, rechentechnik, spectroscopy, plasma diagnostic measurements. The inventive pulsed discharge source electron beam contains the cathode, on the working surface of which is a dielectric plate, a grid anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply connected to the cathode and the grid anode, and a grid anode is located directly on the surface of the dielectric plate. In the second embodiment, the pulsed gas-discharge source of electron beam in discharge chamber an additional electrode, and the distance between the mesh anode and the additional electrode are selected so that the voltage of the electrical breakdown between them provided the specified range of operating voltages of the device, the pulsed high voltage power supply connected to the cathode and auxiliary electrode. The technical result of the invention is the extension of more than an order of magnitude of the range of operating pressures in the proposed source by increasing difficulties and stabil the yle=" page-break-before:always;">

The invention relates to electronics and can be used in physical electronics, quantum electronics, rechentechnik, spectroscopy, plasma diagnostic measurements.

Known pulsed discharge source of electron beam, containing a cathode, a grid anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply, while the mesh anode is located opposite the cathode away from it on the target distance d, and the high-voltage pulse power source is connected to the cathode and the grid anode [Sorokin A. R. // technical physics Letters, So-28, No. 9, S. 14-21, 2002].

The disadvantage of this device that implements the open category, is a narrow range of operating gas pressure. In a typical discharge gap d=0.5-1 mm operating pressure does not exceed several tens of Torr. The main problem: you want to hold for pulse high value of the potential drop in the near-cathode layer and to maintain the stability of the discharge. So for pressure helium pHe=100 Torr established the length of the cathode fall of potential abnormal discharge will be only lcf=0,37(pNotlcf)n=0,05 Toda, for example, for a voltage U=5 kV will be Ec2U/lcf=2· 106V/cm, which is much higher than that required for the beginning of explosive processes on the cathode metal. The equivalent current of the abnormal discharge in this case would have reached the jAD2,5· 10-12p2(Ucf)3=600 A/cm2. Fair, if all the applied voltage U is concentrated in the cathode potential drop Ucf[Klimenko, K. A. Korolev, J. D. // journal of technical physics, I. 60, No. 9, S. 138-142, 1990]. In pulse mode, the discharge stability at such high fields at the cathode can be kept within a few NS. Additionally, the problem of formation of excitatory discharge voltage pulses with short duration of the leading edge, which for d>>lcfshould be a few NS, otherwise the breakdown of the discharge gap will occur at the forefront at low voltage. To increase the charge formation by increasing the difficulty of development of the discharge, reducing d to the size of ~lcf, i.e., 50 μm while maintaining high transparency and large areas of mesh anode, is practically impossible.

The closest to the technical nature of the present device is Yonago beam for mesh anode, placed in the discharge chamber, and a pulsed high voltage power supply, while on the working surface of the cathode is the dielectric plate, the mesh anode is located opposite the cathode at a distance from the dielectric plate on the target distance d, and the high-voltage pulse power source is connected to the cathode and the grid anode [Azarov A. C., Mitko S. C., Ochkin Century. And. // Quantum electronics, so 32, No. 8, S. 675-679, 2002].

The disadvantage of this device that implements outdoor barrier discharge, is also a narrow range operating pressure of the gas (helium up to ~20 Torr). Shortness of development and rate of flow of the discharge, and therefore, the retention time in the discharge gap d is sufficiently high voltage U before and after electrical breakdown of the discharge gap depends, as in the discharge with hollow anode [Zavialov M. A., Crandall Y. E. and other Plasma processes in technological electron guns. M.: Energoatomizdat. 1989. 256 S.], parameters of the pd and RA, where a is the size of the holes in the hollow anode or in our case, the characteristic size of the holes in the mesh anode. If A<d, what is usually done in open places different type, the shortness of the discharge will depend largely on the operating level, comes from seanodes the plasma formed in the weakened electric field, sagging in the cavities of the anode grid. For atmospheric pressure helium length of the cathode potential drop will be only lcf=6.3 μm, which is two orders of magnitude smaller than the typical length of the discharge gap d=0.5 mm, in which the parameter pd=38 Torr· cm, and the breakdown voltage according to the Paschen curve, will not exceed the Ub~500 C. In a pulsed mode, the breakdown voltage will be higher, but interesting for practice when the front of the exciting pulse voltage is ~20 NS, Ub when such a high pressure that will not exceed the value of ~2 kV. Therefore, in the best case, the energy of the electrons in the beam can be 2 Kev. For the efficient formation of the electron beam, it is additionally necessary that the electrons move in an electric field E, at least one order of magnitude higher than that required for initiation of the continuous acceleration of electrons (E/pNot)SG=150/(cm· Torr), i.e. it should be: E/pNot~1.5 kV/(cm·Torr) and more. In the considered conditions (pNot=760 Torr, d=0.5 mm, U=2 kV) at the initial stage of the breakdown electric field in the discharge gap weakly distorted volumetric charges, E/pNotU/(lcf·pNot)=4,2 kV/(cm· Torr). Actually, due to the fact that lcf·pNot<<pHed, a large part of the applied voltage will focus outside the scope of the cathode potential drop and the energy of the electrons and in this case will be very small, significantly less than 2 Kev. Moreover, although the stability of the barrier open discharge in the device is higher than in conventional open discharge with metallic cathode, the stability will be limited by the escalating spontaneously and locally incurred heterogeneity discharge in the spark. The current heterogeneity in the local charging the surface of the dielectric plate will cause the tangential component of the electric field at the dielectric surface and to the development of surface discharge, charging the entire surface of the dielectric plate through this heterogeneity, combined with a spark. Practically, the range of operating pressures in the prototype is not wider than analog.

The technical result of the invention is the extension of more than an order of magnitude range Rango discharge in it.

The technical result is achieved by the pulsed gas-discharge source of electron beam, containing the cathode, on the working surface of which is a dielectric plate, a grid anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply connected to the cathode and the grid anode, grid anode is located directly on the surface of the dielectric plate.

The technical result is also achieved by the fact that in a pulsed discharge source electron beam containing the cathode, on the working surface of which is a dielectric plate, a grid anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply, the mesh anode is located directly on the surface of the dielectric plate, in addition, in the gas discharge chamber an additional electrode, and the distance between the mesh anode and the additional electrode are selected so that the voltage of the electrical breakdown between them provided the specified range of operating voltages of the device, and pulse wesnaes the following description and the accompanying drawings.

In Fig.1 is a diagram of the proposed device with the planar arrangement of the electrodes. In Fig.2 shows a variant of the proposed device with a coaxial arrangement of the electrodes. In Fig.3 shows the electric diagram of measurements of discharge parameters in the proposed Fig.1, the device. In Fig.4 shows voltage waveforms illustrating the discharge in the analog and in the proposed Fig.1, the device. In Fig.5 shows the proposed device with the additional electrode. In Fig.6 shows waveforms illustrating the discharge in the proposed Fig.5, the device with the additional electrode.

In the drawings, showing: 1 - pulsed high voltage power supply; 2 - cathode, on the working surface of which is a dielectric plate 3; 4 - mesh anode, located on the dielectric plate 3 on the opposite side from the cathode -2; 5 - area of drift of the electron beam; 6 - collector grid; 7 - manifold; R1, R2 resistor divider to measure the pulse voltage; R3, R4, R5 resistance measurements, respectively, of the anode current, the current collector grid and the collector current; 8,9 - waveform voltage, illustrating the discharge in helium with a pressure of 400 Torr, respectively, and for the U2 - the appropriate values of time delay and breakdown voltage; 10 - additional electrode for the proposed, Fig.5, devices 11 and 12 are waveforms of voltage and current, illustrating the discharge in helium with a pressure of 600 Torr, for the proposed device of Fig.5.

The device operates as follows.

The increased stability of the discharge in the proposed device, Fig.1, 2, is achieved by the fact that the current incurred in the discharge of heterogeneity quickly resets the local field strength, charging the surface of the dielectric plate, the limited size of holes in the anode grid. This prevents the development of spark breakdown of the gap. Shortness of discharge in such a device depends largely on the size And holes in the anode grid, which can in particular be directly formed on the surface of the dielectric plate, for example, through the use of technology sputtering and photolithography. Increased shortness of discharge, in the absence of the discharge gap in the conventional sense (d=0), is provided by the shielding mesh anode penetration of a strong electric field far into the depths of space drift. The development of surface discharge is tangentially component of the electric field due to the proximity of the opposite jumpers grid (tangential fields, make edge effects from these jumpers are oppositely directed and are therefore compensated). In the process of forming the cathode fall of potential electric field even more edge to the surface of the dielectric plate and all the applied voltage is concentrated in the near-cathode region. For guidance in choosing a suitable material for the dielectric plate depending on the discharge parameters, you can use the inequality following from the analysis of electrical circuits [Ishchenko C. N., Lisitsyn B. N., Sorokin, A. R. // Quantum electronics, so 5, No. 4, S. 788-794, 1978]: U/Ebd<<U/(jtj), where U[V] - operating voltage, Ebd[V/cm] electric field breakdown of the dielectric material,[cm] is the thickness of the dielectric plate- permittivity dielectric plate j [A/cm2] - the average discharge current duration - tj[sec]. Keep in mind that in pulsed mode Ebdcan be several times higher than Ebdfor static fields. The configuration of the dielectric plates 3 and other throne beam, determined by the intended purpose of electron beams (excitation laser media, materials processing, and so on). This refers to the choice of configuration drift region is 5.

An important question about the parameters of the mesh anode will be discussed below.

For proposed, Fig.1, the device dielectric plate was manufactured from ceramics from the capacitors KWI-2: 68 pF, 16 kV DK~1000, diameter 10 mm, a Capacitor with one side zashlifovyvaetsja to size=2 mm in the center axis, and its own conclusion on the other hand connected to the minus high-voltage pulse power source. Flat anode grid of molybdenum with a thickness of 0.1 mm had holes 0.17 mm, and the geometrical transparency=0,72. To control the beam current were introduced collector grid (step 0.5 mm,=0,65) - 6 and the collector - 7, located respectively in 5 and 10 mm from the dielectric plate, Fig.3. These elements could affect the discharge. Indeed, while the anode mesh with holes And=0.17 mm screens sagging field in the interior space of the drift and concentrates it in the dielectric between cathode collector grid and the collector to leave under the free capacity disabling them for a small pressure, for example 30 Torr of helium, because of the growing difficulties of the discharge between the dielectric plate collector grid, he now is not formed) repeatedly falls glow gas, decreases the discharge current and increases the delay of the breakdown. However, it has been found that for high pressures, pNot>100 Torr, the discharge parameters cease to depend on whether the collector grid and the collector under the free capacity or not. I.e. all bit processes occur in the near-cathode region, where quickly reset all the applied voltage, and the voltage for the occurrence of discharge between the dielectric plate collector grid is not enough. The density of all currents were determined as the ratio of the detected current to the active area of the cathode, i.e. the total area of the holes in the grid, which was S=0,45 cm2. In Fig.4 shows waveforms of voltage for normal open discharge (d=0.6 mm), curve 8, and proposed, Fig.1, barrier discharge, curve - 9 to 400 Torr of helium. Shortness barrier discharge is higher than for conventional open discharge: two times increased latency ( 2· U1) breakdown. Moreover, under these conditions, the usual outdoor discharge, in contrast to the barrier, losing stability. As an example, we give the parameters of barrier discharge, obtained for the two pressures of helium. For pNa=200 Torr: latency breakdown -=25 NS, the breakdown voltage - Ub=20 kV, current collector - jc=40 A/cm2. For pNot=600 Torr:=15 NS, Ub=6 kV, the collector current of jc=8 A/cm2for this case was measured at a shorter distance of 5 mm from the surface of the dielectric plate. In the latter case, the electron beam current is small, since for U6 kV is only a small part of the electron beam reaches the collector: the length of the free path of the electron is only 1=0,2 U/pNot=2 mm For some applications, for example in gas lasers, require electron beams generated in the gas mixtures of different composition. As an example, studies have been conducted with a mixture of CO2:N2:No=1:1:8. In this mixture the limiting pressure at which registered the beam current collector, located at 5 mm from the dielectric plate, it was three times less than in helium in the mixture is less than the path length of Eloy to 7.5 kV. In all studied conditions, the discharge was maintained stability. To increase pressure, or the burning voltage of the discharge in the device, reducing holes And in mesh anode - 4. The holes may have any shape, it is only necessary size And save one dimension of the hole. For example, you can take the grid in the form of alternating strips with a spacing A. the Modern technique of photolithography allows you to create a grid in the form of strips with a size of several micrometers while maintaining the transparency of the grid at 0.5.

Was tested circuit, Fig.5, the device connected high-voltage pulse power source - 1 to the cathode 2 and the additional electrode 10, played mesh collector 6 in the previously considered scheme of Fig.3. Mesh anode - 4 remained under free potential. This power scheme was previously proposed for common open discharge [Sorokin A. R.// technical physics Letters, so 16, No. 8, S. 27-30]. Formation of a normal glow discharge between a wire mesh anode and the additional electrode and all of the voltage appears between the cathode grid anode, the discharge which generates the electron beam. With this scheme, you receive the freedom in placing dopolnitelnost electrical input mesh anode, that can be important for a number of applications of the device. The distance D between the mesh anode 4 and the additional electrode 10 is taken such that the voltage of the electrical breakdown between them provided the specified range of operating voltages of the device. Barrier outdoor discharge in the device of Fig.5, has a number of features. Thus, at sufficiently high pressure is possible by selection of the distance D substantially increase the breakdown voltage, now due to the large value of the parameter pD. Another feature relates to kontrolirovat normal glow discharge, starting, for example, in helium with a pressure of ~100 Torr. To reduce the contraction of the discharge between the mesh anode and additional grid anode electrode on the dielectric plate formed by sputtering A1 (layer thickness of 1.3 μm) in the form of separate spots 25× 25 μm with a pitch of 50 μm, so that the geometrical transparency of the anode grid was=0,75. The additional electrode 10 in the form of a grid (step 0.5 mm,=0,65) was located 6 mm from the dielectric plate. For pressure helium pNot=600 Torr the discharge parameters were as follows, Fig.6: latency breakdown -=22 NS, on the surface of the dielectric plate, significantly better than the parameters obtained with the circuit of Fig.1. An anode grid in the form of separate spots was able to significantly suppress the contraction of the discharge between the grid anode - auxiliary electrode. However, the current density of the discharge on the spot at elevated pressures were high enough spots have undergone significant erosion due to cathode sputtering. Therefore, unless absolutely necessary, in this scheme it is recommended to work at lower pressures in helium at ~ 100 Torr, which is still significantly higher than in the analogue and the prototype. The upper limit of the operating voltage is also limited to an acceptable cathode sputtering anode grid - 4.

Claims

1. Pulsed discharge source of electron beam, containing the cathode, on the working surface of which is a dielectric plate, a grid anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply connected to the cathode and the grid anode, characterized in that the mesh anode is located directly on the surface of the dielectric plate.

2. Pulse the electric plate, mesh anode region of the drift of the electron beam for mesh anode, is placed in the discharge chamber, and a pulsed high voltage power supply, wherein the mesh anode is located directly on the surface of the dielectric plate, in addition, in the gas discharge chamber an additional electrode, and the distance between the mesh anode and the additional electrode are selected so that the voltage of the electrical breakdown between them provided the specified range of operating voltages of the device, and a pulsed high voltage power supply connected to the cathode and auxiliary electrode.



 

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