SU693472A1 - Method of modulation of current in gas discharge - Google Patents

Claims (2)

-., t The image relates to the problem of current control in gas-powered devices and can be used to create various gas-discharge and ion devices for many industries, for example, in power engineering for creating powerful high-temperature switching elements and for inverting and converting p low-voltage high-current deposits, when solving various problems of switching high currents with low losses. A known method of modulating a current in a gas discharge, carried out in cesium devices with grid control Ll. However, it has a limitation on the value of the switched current density of the order of units of amperes per cm. The closest to the invention is a method of modulating the current in a gas discharge of supply voltage on the control electrode, which is carried out in tacitrons 2. In these irbesf the grid, which is under negative potential, is supported by | The discharge gap lives in a locked state at high (up to kilovolts and more) anode voltages. Prygig Row and Transition B to the wired state are performed by 11dDBs to the positive voltage grid. The most false rceration — discharge quenching — is produced by applying a significant negative voltage to the grid, which overlaps the Langmuir shells of adjacent turns. When implementing this method, it is not necessary: there is a large amount of voltage (of a few hundred volts) voltage across the grid. In addition, the method is characterized by a fundamental limitation of controlled currents of the order of one ampere per square centimeter of grid area. The purpose of the invention. is an increase in the modulated current density and power, as well as the control of the iglana for pulse power, the synchronization of the trailing edge of the current pulse, and the control of the pulse duration. This is achieved by the fact that the pressure of the component gaea and the temperature of the cathode are selected from the conditions. l - l.,, --p-pv-p ;, 1 and the working point is chosen, based on the service «. J. L-- the mean free path of the electrons; O, “the value of the interelectrode gap} is the-average velocity and (zhv in; plasma} ni () is the ion mass (e1H &ron); p“ is the pressure of the gas-forming com- partment; T is the temperature of the atoms of the plasma-forming component; K is the Boltzmann constant ; e is the electron charge; j is the electron emission current of the cathode;} d is the anode current; j ",; is the critical current whose volume charge can be compensated for by the complete ionization of the atoms of the plasma-forming gas component. THAT will change the density of the supercritical discharge Toica (с1 3крит) by adjusting In the course of the cathode temperature, pulses of negative polarity are applied to the control electrode with a duration of the order of the deionization time and an amplitude of the order of the direct voltage drop in the conductor with the stop. It is experimentally found that the J currents in the plasma exceeding; d turn into an unstable state; div and plasma at discharge, there is a limited time, during which an independent current break occurs, and the duration of the current pulse / a significantly determines the process of desorption of atoms from the surfaces node and grids. Thus, if these conditions are fulfilled (Zcrit creates an internal instability of the discharge in the ground state, which makes it easier to quench the discharge at discharge densities of the order of tens of amps per square centimeter and more. The instability of the discharge is due to the fact that when the free path length of electrons is Ag. significantly higher than the interelectrode potential d, the current in the discharge is transferred by a beam of electrons accelerated at the near-cathodic potential drop. In this case, the magnitude of the discharge current is the paired ratio of the plasma ion concentration H in the plasma and their average speed) ratio. .RS (Physical processes occurring in a plasma with an increase in the density of the passing discharge current and, in particular, when the current density exceeds a critical value, the following occurs. With increasing current density, the degree of ionization of Neutral atoms increases. Under these conditions, everything the growing removal of ions by the electric field of the cathode. Atoms that fly off from the surface of the cathode due to the short ionization length are ionized mainly near its surface. The formed ions are again rejected by the field to the cathode. This leads to the fact that, due to the condition of constant pressure, the concentration of neutral gas in the interelectrode gap decreases with an increase in the degree of ionization and the frequency of ionizing collisions decreases. And when the concentration of ions in the distance fy cathode becomes lower and the critical mode occurs, V. In this mode, an imbalance between the ionization rate and the rate of ion drift to the cathode occurs. Further; the lightest attempts to increase the current density lead to a current interruption in the discharge some time after Ode to the grid of a positive momentum. After current is drawn, the concentration of neutral atoms in the interelectrode gap increases, however, the grid, which is under negative potential, prevents the resumption of the discharge. Before applying the next positive voltage pulse to it. In a mode in which an unstable discharge state exists, the modulation is performed as follows. The locked state of the discharge gap is maintained by a negative potential on the grid (constituting several of the PEROCITOPE of the POSTHY POINTON CHR). Podzhi (-RPZR d, as in narsecTttbtx cito, ocytr (ocTjvistK) T iolaco short (since DKP 1.0 + 10 sec.) Positive imiulsp n weave. Kpk ukpeyvalos vshyu, with supercritical marrow; rn rp при rk, with supercritical test). discharge arith) during the finite time G. During this time, the concentration of ions near the anode significantly decreases, as a result of which a potential is minimized and the discharge goes to an unstable state. causes shorting of the adjacent layers of the grid, and the discharge current is interrupted. In this way, the discharge is quenched independently without applying an extinguishing negative voltage pulse to the grid. The current pulse duration G substantially depends on the magnitude of the discharge current and the smaller, greater than j rat. If, under the conditions considered, a substance (gas) with a high adsorption capacity with respect to the anode material and the grid is used as a plasma-forming component, the current pulse in the conducting state can be increase significantly (by more than an order of magnitude). This is due to the fact that with a high degree of ionization of atoms, being found in the interelectrode gap, the equilibrium between the rates of ionization and leaving the cathodes to the cathode is still maintained for some time by the atoms desorbing from the anode and the grid, some change in the duration of the conducting state C of the instability of the discharge parameters. In cases where a current is required to modulate with stringent requirements on the magnitude and constancy of the current pulse, it is easy to enforce the quenching of the fault by applying a small negative voltage pulse to the grid at any time to an independent discharge pattern. current. FIG. Figure 1 shows the voltampera characteristic of the triode on a mixture of cesium and barium vapors for PCS; 8.10, Tg 800 ° K, TC - 1728 K; in fig. 2 dependence of the critical current density on the cesium vapor pressure. Curve 1 is a calculation for the case when the fluxes of neutral atoms from the cathode to the agtod and back are balanced; curve 2 - jwicnor for the no-stationary mode, in which um:; e neutral atoms fall only on the cathode; curve 3 - experiment; Fig. 3 shows supercritical discharge modulation for Pc5 - b.b. T a, T 168 O K Ej., 50 in; (a, b — when positive voltage pulses are applied to the grid; c, d — when bipolar control of pulses is applied to the grid); in fig. Figure 4 shows the dependences of the supercritical-discharge pulse duration for PCS 6.6.10 — a torus, TBO, 850 ° K, a — cathode temperature, and b — discharge current density. The proposed modulation method was implemented in a three-electrode device of parallel-parallel geometry with an indirectly heated cathode. The interelectrode gap is 4 mm. A grid of nanosecond molybdenum wire with a diameter of 30 microns and a cell size ISO x ISO microns, located in the center of the electrode gap, was used as a control electrode. The transparency of the grid, taking into account the cooling radiators, is 0, S. A mixture of cesium and ginger vapor is used as a triode. The pressure of the mixture components is controlled by the temperatures of the liquid phases and is chosen such that the electron mean free path exceeds the interelectrode gap (.lO torus, (H. „4.10 tf e). At the indicated barium vapor pressure, cathodes of ordinary refractory metals provide the electron density emissions are of the order of several tens of amperes per square centimeter, which exceeds the critical current densities for 1 S. 10 torr. As a result, experimentally performed critical values of the discharge current density and the self The current-voltage characteristic of the triode for one of these modes is shown in Fig. 1. In the area a – c, the characteristics of the 1A is stable and can be registered by static methods. At point b, when the current reaches a critical value, self-extinguishing occurs therefore, the dotted portion of the V-s was recorded in a pulsed mode (the type of pulses of the neutrastic current, depending on the temperature of the cathode, is shown on the SP. four). Experimental studies have shown that the magnitude of the critical current in a triode on a mixture of cesium and barium vapors is entirely determined by the vapor pressure of the chain and does not depend on the vapor pressure of barium in the pressure range under study. , E s with: it is 6 toM, that the flame-forming component is a pair of pedi atoms, while a pair of bariums provide the necessary electron emission of the cathode. Blowdown is then unstable in the regime of unstable burning (section), which is selected either by changing the cathode or changing the values of the load of the load, or by the voltage of the strains. , ... ..-. . -,,. Modulation Examples: Shown in FIG. 3 aV 1b, FIG. 3 and the shape of the polysytile impulses, for example, of the hsen, is given, yyyyyosh kGna c6Tky LH rerayd. The amplitude of the control pulses in iecex modes was chosen by the ia range + 8 4 3 1О .. В ..--. .;,; :, .. / .. In IR 3b, a form of pulses of supercritical discharge current is presented. After a triode of a triode, a suppressive control impulse of the discharge is lit in a limited and time-limited manner. YoJoin j oToporo independent locking of the triode: and without a single impulse on the grid. The picture of the MODULE 1ZII is well defined in the range of frequencies under study 1-10 KHz. The use of cesium atoms as a goyus-forming additive that is well adsorbed on the electrodes has led to the fact that the absolute value of the time of survival in the current term (current pulse duration) tTj- significantly (up to two orders of magnitude) exceeds the time of atoms (ions). between the electrodes. From FIG. 3 b, it is clear that the order of i, 5, at that time is equivalent to that of the mercury vapor in inert gases,. as a rule, does not exceed 10 - 10 sec. Such a large tr p is due to the participation in ionization of not only cesium atoms that are initially in the microsphere, but also the atoms desorbing from the anode and the grid. -, v By changing the temperature of the cathode, the magnitude of the supercritical discharge current was leaked, which allowed for a wide pre. change the duration of the current state of the triode (see Fig. 4). The dependence of T, - on pt, jp (see Fig. 4) is due to the fact that at a higher density, the pumping of atoms from the discharge channel is more intense, and to compensate for the electron charge, a higher neutralization of ions is necessary. This circumstance allows the modulation frequency to be changed by changing the discharge current. To stabilize the duration of the current pulses and to regulate it in the range of / C C :, short (10 µs) negative pulses were applied to the grid (see Fig. 3). The measurements were carried out both at the subcritical and yjpoBHe level of the supercritical values of the discharge current density. It turned out that in regimes with supercritical density of current Dc6tHJ of current it is enough to apply a negative voltage pulse of 2-3 V to the grid, while in subcritical solid HOCTii: negative current for quenching the discharge the amplitude of the negative pore pulse is necessary ten ten volts. An example of a modulus of a supercritical discharge current using bipolar grid pulses is shown in FIG. 3 g. It can be seen that the unlocking and locking of the triode proceeds with a steep front and a strong pulse, which illustrates the high efficiency of the proposed method of modulating the discharge wave. A similar picture of the modulation of the discharge current in a triode on a mixture of cesium and barium vapors was observed experimentally in the Daniyan range of cesium vapors from 5. to 4.10 torr. In this case, the universal dependence of the critical current density goes to the independent extinction of the discharge; cesium vapor pressures shown in FIG. 2 .. In the same figure, the calculated, naukhennye of the ratio of two ratio of Crete cases are shown. In the first case, curve 1 - flows of neutral atoms from the cathode to the anode and back are uranium suspended; in the second curve 2, the non-stationary mode, in which all neutral atoms fall on the cathode. It can be seen that the experimental data are in fairly good agreement with the calculated values. The proposed modulation method over the critical discharge-current allowed the PCS P range to be controlled by a 60 V anodic voltage with a good reproducibility. power in the range from 0.6 to 4 kW / s Claim 1. The method of modulating the current in the gas discharge, by applying voltage to the control electrode, is also different in order to increase the modulated density the current and power, the pressure of the gas components and the temperature of the cathode are chosen from the conditions,, CRIT 141Mig and the operating point is chosen, the outcome is where Ag is the mean free path; d is the interelectrode gap; - average ion velocity in a plasma; ni- (Wg) is the mass of an ion (electron); p is the pressure of the plasma-forming component; T is the temperature of the atoms of the plasma-forming component; K is the Boltzmann constant; e is the electron charge; and - cathode electron emission current; anode current; . —critical current, the volume charge of which can be compensated for with the full isuization of the atoms of the plasma-forming component of the gds. 2. The method according to claim 1, distinguished by the fact that, in order to control the magnitude of the current pulse tr, the density of the supercritical discharge current {, dq j cpt "t) is changed by the TeMnepatti cathode. 3, the method according to claim 1, that is, so that, in order to synchronize the rear current pulse and control the Pulse Duration, negative pulse polarity pulses are fed in the direction of the current pulse. For the duration of the delay and the amplitude of the order of the direct fall, iapr $ 1 live in the master condition. Information exhausts taken into account 1st examination 1.Zak vek number 214585O, cl. H O1T17 / 74, 20.O6.76, according to which a decision was made on the higher copyright certificate. 2.J-OCmstead u.aTtie Taciii-on and Noise T1iiVoitro i, Proc., 42, p. 1350, 1954 (prototype). UcS IS a to five -five Uc6 100 700 wo 00 SOU / t W 300 ftoo SBo J / /. l f / w y a / Cf 0 / G too 00 300 00 500 1rig.Z