SU1563488A1 - Method of modulating current in gas discharge of heavy-current switch member - Google Patents

Abstract

The invention relates to the field of high-current high-temperature gas electronics and can be used to create powerful high-temperature current transducers, to switch high currents with low losses, to develop high-current kilohertz frequency generators. The purpose of the invention is to increase the modulation reliability by creating conditions for re-igniting the discharge in a diode mode, as well as stabilizing the modulation frequency. The method is implemented as follows. In a two-electrode key element with a discharge gap, the interelectrode distance of which is less than the electron mean free path, the pressure of the storage gas is chosen so that the product of the pressure and the interelectrode distance is higher than the minimum value at which the discharge may exist. At the same time, the volt-ampere characteristic (VAC) consists of two branches — low voltage and high voltage. The anode current density is set higher than the critical value, at which the volume charge of the current can be compensated for when the plasma-forming substance is fully ionized and below the cathode maximum current emission density is determined by the mass ratio of the electrons and ions, the pressure and temperature of the gas, the average velocity of the ions. The discharge voltage across the gap is chosen above the ignition voltage of the discharge at the low-voltage portion of the I – V characteristic and below the ignition voltage at the high-voltage portion of the same characteristic with decreasing voltage. In order to stabilize the modulation frequency, the key element is included in an oscillating circuit, the parameters of which are chosen in such a way that the time of the nonconducting state of the key element exceeds the pressure recovery time in the discharge gap. 1 hp f-ly, 4 ill. Sl S ale Os from 4 00 00

Description

This invention relates to the field of current control in high-current gas discharge devices, in particular

areas of high-current high-temperature gas electronics, and can be used to create a gas discharge

315634

devices for various areas of industry, for example, when creating powerful high-temperature current transducers for solving problems of high-current switching with low losses, while creating powerful high-current high-temperature generators of kilohertz frequency.

The aim of the invention is to increase the modulation reliability by ensuring the conditions for re-igniting the discharge in the diode mode, as well as stabilizing the modulation frequency.

For a discharge gap, the interelectrodeposition, the distance of which d is less than the electron mean free path in a gas, is applied such a voltage, while

25

where the anode current density 1 is greater than the critical value I ev; / kTa Va x 2Q r-rt

Xnt-h volumetric charge which can

be compensated for the complete ionization of the plasma-forming substance atoms, but less than the maximum emission current of the thermal cathode 15 (t ;, tag are the masses of ions and electrons; e is the electron charge; a, TQ is the pressure and temperature of the filler gas atoms; k is the Boltzmann constant ; vj - 30 average velocity of ions in the plasma). The magnitude of the voltage at the bit bottom. set above the ignition voltage at the low-voltage portion of the predischarge volt-ampere characteristic (35) of the voltage (VAC) U {and lower than the ignition voltage at low voltage. the voltage on the high-voltage portion of the predischarge VAC, and the gas pressure of the filler is above the minimum 40 discharge pressure.

In order to stabilize the modulation frequency, the gas-discharge key element is connected in series with a circuit containing inductance L, capacitance C and resistance R, the parameters of which would be chosen based on the time that the non-conductive state of the key element Tpn is exceeded by the recovery time of the initial pressure in the discharge interval

Figure 1 shows the family of calculated CVC with cesium filling; in fig. Figure 2 shows the dependences of the minimum ignition voltage U and the maximum voltage at which there is a discharge; FIG. 3 shows the “A” of a gas-filled diode and the source loading characteristic; Figure 4 shows current and voltage waveforms on a key element in one embodiment of the method.

It has been established that, due to the non-monotonic dependence of the ionization cross section of the plasma-forming component on the electron energy, ignition of a non-self-sustaining arc discharge is possible in the region of not too low 1 value of reduction of the PQ filling gas pressure d to the size of the interelectrode gap d, when the dimensionless parameter

greater than b0 (CQ maxi

 sh

e and ° cta

five

Q

0 5 0

five

the maximum value of the ionization cross section of the filler gas). If, the ignition of the arc discharge turns out to be impossible. The region of existence of a discharge for a given Pfld is limited both on the side of the low and on the side of high voltages on the discharge gap. When) in the diode, a stable pre-aerial mode t is applied with a current of the order of the vacuum. When the discharge is ignited, a current is established in the diode, the magnitude of which, at a sufficiently high emissivity of the cathode, is determined by the number of ions formed in the interelectrode gap with full ionization of the filler atoms and the parameters of the external circuit. It is significant that with sufficiently high voltages (b) due to a decrease in the ionization capacity of electrons with an increase in their energy, the diode again goes into discharge mode with a current close to the vacuum one, determined from the 3/2 law. As the unit of measurement for the voltage on the key element (Fig. 1), the ionization potential of the IO filler atoms was selected (, (for cesium, 89 V), and the unit of current measurement is the current according to the 3/2 J-2.33 x law

 where it is measured in volts, d in centimeters, and J in A / cm2. At, 55 (curves 1–3), the current – voltage characteristics correspond to the predischarge mode, and the diode has a positive differential resistance at any voltage. With (curves 4-6), the pre-discharge modes correspond to two sections of the I – V characteristic at UC cU4 (b) and (b) „where II and ig points of the zero differential resistance of the diode on the left and right | branch x respectively. From figure 2 it follows that with increasing parameter b (assuming Lg.b0) U, 1 (b) over a-

em, a Uji (b) grows, i.e. there is an expansion of the range of existence of the discharge for voltage0

Analysis of the proposed solution shows that in order to re-ignite the discharge after a current interruption and the transition of the high-current key element to the non-conducting state, a voltage U, determined from the ratio

U, (b) Ј UЈU2 (b).

Since at current interruption in the interelectrode gap a sharp decrease in pressure Рd occurs, the value of parameter b becomes less than b. In this case, the ignition is possible when the pressure again takes its initial value corresponding to

parameter value. The restoration of pressure in the interelectrode gap occurs during a finite interval of time, which is determined experimentally for each specific experimental condition. If the operating point coincides with the voltage U before the time when the full pressure is restored in the interelectrode gap, then in this case the earlier ignition of the discharge may lead to the position of the operating point on the BAK corresponding to another value of b. This can lead to unstable modulation of the current in frequency and amplitude. Therefore, in order to stabilize the modulation frequency, the moment of re-ignition of the discharge is controlled by selecting the parameters of the circuit R, L. C, the outcome of the conditions Tnepr TvOSST.

Thus, in the inventive method there is no need for a control grid and a control signal generator.

The proposed method of modulating the current in the gas discharge of a high-current key element is carried out as follows.

Curves 7–8 in FIG. 3 show the current-voltage characteristics of the key element in the high-voltage and low-voltage branches x, respectively, for a given parameter value. U voltage (point 9

on Fig.) 1) with |, tvets vurt cha / p1G p.-shch raz pa with an increase in shr-kenich

to the bottom c1

and the voltage

U9 (dot and))

five

0

five

0

0 5

0

five

five

corresponds to the ignition of the discharge with decreasing voltage on the diode. The moment of ignition of the discharge is characterized by a relatively low level of the passing current, therefore the voltage applied to the diode is almost equal to the emf of the source EE. Thus, the choice of voltages and and U for the ignition of the discharge is possible; U xK and After ignition of the discharge, the voltage and current on the diode are determined by the point of intersection of the load characteristic of the source K (curve 11 for flash, 3) with the discharge section of the IV curve of the diode (point 12 in FIG. 3).

For a given EMF value of source E, find the parameter b ,, for which U () E or) E (figure 2). Then, obviously, with b b bmi 11, (b) (b). Next, pol, go /

by communication ---, mg mg. q

product P d and, thus, choose the filler pressure Pa and the interelectrode gap j. It should be noted that the selected pressure value at a given bM (1t (corresponds to the minimum pressure value Pd at which the discharge can be ignited for a given value of E.) According to the prototype, the maximum pressure PMQKC is found at which the current does not occur Thus, the pressure range of PMQirc corresponds to the operating mode at which it is possible to implement the proposed method of current modulation.

After ignition of the discharge (point 12 in Fig. 3), the stationary conductive state of the diode exists for a finite time interval Tcc, during which ions are pumped out from the interelectrode blockage. As a result of this process, Pierce-type instability develops in the discharge, leading to an interruption of the current and the transition of the diode to the locked state. Since the circuit has a finite inductance L, the current in the circuit cannot immediately jump to zero. Therefore, the operating point moves from the high current branch to the low current high voltage branch of the predischarge VAK (point 13 in FIG. 3) along the path of 14 ° C. The voltage value at point 13 is determined by the parameters of the circuit K, L, C based on the ratios

for R t. i

ten

J0

tf

s

- expC- arctg)

QC

tf,

x sin (arctg g) + Kt

 .L.

2kc-JuTlks

Where

Jn - current at the moment of break;

g, 1 P

for R g -U Ј j

IP E + lЈ L ° eXr ())

l - | LC-4R2 C2 GD p.

2RC HLC

Since the voltage at point 13 is greater than the voltage of source E, the latter cannot ensure the maintenance of such a voltage. Therefore, the operating point 13 moves along the high voltage branch of the predischarge IVC towards the value of E, thereby reducing the voltage across the diode. The time of the non-conducting state of a high-current key element during which the operating point moves from a value of U to U2 can be estimated.

from the expression

tL

L

1nepr with

where (0

4l4R2 C2-LC

2KS - $ U

The parameters of the circuit R, L, C are selected in such a way as to satisfy the condition of Tier Twosct.

The proposed method was implemented in a Knudsen diode with a cesium-barium filling with a flat electrode geometry. The ends of the cylinders with a diameter of 15 mm served as the working surfaces of the cathode and anode; the inter-, electrode gap could vary from 0.1 to 2 mm. At a distance of 2 mm from the side surfaces of the electrodes, insulated

five

0

five

0

five

0

five

0

five

A cylindrical electrode from the cathode and anode.

Current and voltage modulation was observed in a wide range of cathode temperatures and barium pressure and in the range of cesium pressure from (G4 to 5-U-3m). Figure 4 shows, as an example, the current and voltage waveforms obtained by applying anode of a rectangular voltage pulse with a duration of 1 ms from a voltage source of EMF 21 V. The cathode temperature was 14CO, the anode temperature was 1100 K, 5-10-3 mm Hg, Vfa mm pT .CT., D - 1.6 mm. A circuit consisting of parallel-connected resistances, ind In this case, the experimental results confirm that the proposed modulation / current method in the field of current and capacitance: Ohm, μg,. In this case, the magnitude of the modulated current reaches “10 L / cm2, and the voltage at the burning stage of the discharge is # 4 V”. The gas discharge of the high current key element can be realized in practice.

Using the proposed method of modulating the current in a gas discharge of a high-current key element provides, in comparison with the prototype, increasing the modulation reliability and simplifying the modulation scheme due to the possibility of controlling the moment of re-ignition of the discharge and modulating the current of a stable frequency without generating a control signal that allows significantly reduce the overall dimensions of the high-current key element.

Claims (1)

1. A method for modulating a current in a gas discharge of a high-current key element by applying a voltage to a discharge gap with an interelectrode distance shorter than the electron mean free path in a gas when the anode current density exceeds a critical value and is less than the current density emission, distinguished by the fact that, in order to increase the modulation reliability by providing the condition of repeated ignition discharge in a diode mode, the voltage across the discharge gap is set higher than the ignition voltage of the discharge while increasing the voltage on the low-voltage portion of the predischarge volt-ampere characteristic and lower than the discharge ignition voltage when: decreasing the voltage of the high-voltage portion of the same characteristic and the gas discharge is performed under the condition that the product of the filler pressure by the interelectrode value no less than the minimum value of the existence of the discharge. 20. The method according to claim 1, characterized in that, in order to increase the modulation frequency stabilization factor, the key element is included in the oscillating circuit and the parameters are adjusted for the time required for the nonconductive state of the key element to restore the initial pressure in the discharge interval. .- Uw h g / 5 10 15 1 iz 20.15 ten Wi  and he iv / # t i l i i go  IT  ..Gl : 0 ZOO 400 W 800 G.mks 4 i t I