Discharge Burning Voltage Research Articles

APPLICATION OF A NON-SELF-SUSTAINED GLOW DISCHARGE INITIATED BY A FOCUSED ELECTRON BEAM IN THE FOREVACUUM PRESSURE REGION FOR NITRIDING THE INNER SURFACE OF NARROW METAL TUBES

We have explored some of the features of ion-plasma nitriding the inner surface of narrow extended metal tubes by the plasma of a non-self-sustained glow discharge initiated by a focused electron beam in the forevacuum pressure range. The influence of electron beam current on the discharge parameters was determined. We found a non-monotonic dependence of plasma density, nitrogen content in the nitrided surface layer, and layer microhardness on discharge burning voltage. The microhardness of the inner surface of the nitrided tubes reaches values of 1500 kgf/mm<sup>2</sup> for AISI 321 stainless steel and 700 kgf/mm<sup>2</sup> for alloy carbon steel AISI 5135.

Parameters and ion mass-to-charge composition of a high-power impulse magnetron discharge with electron injection

We have explored the effect of electron injection on the burning conditions and parameters of a high-power impulse magnetron sputtering discharge, including the ion mass-to-charge composition of the discharge plasma. We find that with stabilized discharge burning voltage, electron injection leads to a significant increase in the discharge current and sustains discharge operation in the low pressure regime, but also leads to a lower fraction of metal ions in the plasma. By using a reflecting electrode, conditions are created that provide transport of the injected electron flux directly into the region of intense ionization, and one can preserve the fraction of metal ions in the plasma corresponding to the self-sputtering mode, and also decrease the limiting operating pressure.

The Regimes for Sustaining a Hollow-Cathode Glow Discharge with a Hot Filament Inside the Cavity

The results of investigations of a low-pressure hollow-cathode glow discharge with a hot filament (thermionic cathode) inside the cavity are presented. The current-voltage characteristics (CVCs) of the discharge and the dependences of the current delivered to the thermionic and hollow cathodes on the discharge burning voltage are obtained at different gas pressures and filament currents. It is shown that the major fraction of the current is transferred in the thermionic cathode circuit. For interpretation of the CVCs, a model is accepted, which uses a generalized coefficient (rather than a conventionally utilized secondary-emission coefficient), which includes not only the cathode bombardment with ions but also the emission current induced by an external source. An estimation is made of the discharge parameters. The model is shown to be quite consistent with the experiment.

Special Features of Parasitic Current Formation in a Sealed-Off Cold-Cathode Thyratron with Trigger Unit Based On an Auxiliary Glow Discharge

Results of investigation of the glow discharge with hollow cathode and ring anode in the trigger unit of a coldcathode thyratron TPI1-10k/50 are presented. A specific feature of the discharge sustainment is that a highly emissive tablet containing cesium carbonate is placed in the cathode cavity. The current-voltage characteristics of the discharge in the trigger unit are obtained for different tablet compositions together with the measured parasitic current to the main cathode cavity. Stepwise transitions to the regime with decreased discharge burning voltage accompanied by an increase in the parasitic current are observed. A model of current sustainment in a hollow-cathode glow discharge is used to interpret the characteristics obtained. Instead of the conventional secondary emission yield, the model uses a generalized emission yield that takes into account not only the ion bombardment of the cathode, but also the emission current from an external source. Based on estimations of the discharge parameters in the trigger unit, a reason for a parasitic current increase is revealed.

Non-Self-Sustained Hollow-Cathode Glow Discharge at Low Burning Voltages

The results of investigations of low-voltage burning modes of a non-self-sustained glow discharge with a ~0.2 m3 hollow cathode at low (≈1 Pa) pressure, which is assisted by an external injection of electrons from the electric-arc plasma. The current-voltage characteristics recorded at low burning voltages 20–80 V demonstrate that there is a threshold glow-discharge burning voltage, at which a stepwise transition takes place from the burning conditions with high plasma inhomogeneity to the conditions of homogeneous plasma glow in the entire volume of the hollow cathode. This transition, accompanied by an enhanced hollow-cathode effect, is characterized by a 20–40% increase in the main discharge current. The glow discharge burning voltage, at which this current jump takes place lies within the range 45–60 V and depends on the value of the auxiliary discharge current and working pressure.

Plasma Generation in a Pulsed Mode of a Non-Self-Sustained Arc Discharge with a Hybrid Hot-and-hollow Cathode

The results of investigation of pulsed burning modes of a non-self-sustained arc discharge with a combined hot-and-hollow cathode are presented. The principal discharge characteristics are measured at the currents up to 350 A and discharge burning voltages up to 200 V within the working pressure range 0.2–1 Pa. It is shown that an increase in the working pressure gives rise to an increase in the discharge current as a result of gas amplification, resulting from an improvement in the processes of fast electron energy utilization during gas ionization. The maximum resulting discharge current in a nitrogen atmosphere at a pressure of 0.8 Pa is found to be 550 A at the discharge burning voltage up to 200 V and the maximum pulsed power up to 80 kV. The concentration of plasma in the center of the ≈0.2 m3 chamber is found to be about 4·1017 m–3 at the density of the ion current from plasma approximately 6.5 mA/cm2 and the discharge pulsed power 18 kW.

On Optimization of a Power-Supply System of a Magneto-Plasma Compressor

The operation of a miniature magneto-plasma compressor with low-voltage power-supply system was studied experimentally and the current and voltage drop under discharge were measured. It was found that the voltage drop remains practically constant during discharge and amounts to a few tens of volts. The performed electrotechnical analysis made it possible to determine the efficiency of the power-supply system depending on the initial voltage of the energy storage, the discharge burning voltage and the discharge circuit parameters (capacitance, inductance, and resistance).

Low-voltage beam discharge in light inert gases to solve problems of voltage stabilization

By means of the flat one-sided probe, the electron velocity distribution function is investigated along with plasma parameters distribution and electrokinetic characteristics in short (without positive column) low-voltage beam discharge in helium, neon, and argon. With the pressure increase, the discharge voltage obtains the value of the excitation potential of the metastable level of the filling gas, U m. The results of the probe measurements of the electron velocity distribution function make it possible to calculate the generation functions of the inelastic process and to make the conclusion that, at attaining the critical pressure, P cr, when the processes of atom stepwise ionization begin to dominate over the direct ionization, the discharge burning voltage drops below the ionization potential, U ion. Based on the performed studies, a technique and a device are proposed to stabilize the voltage within the range of 9–50 V by filling the interelectrode gap with inert gases of different excitation and ionization potentials.

Auxiliary glow discharge in the trigger unit of a hollow-cathode thyratron

Results from studies of a low-current glow discharge with a hollow cathode are presented. A specific feature of the discharge conditions was that a highly emissive tablet containing cesium carbonate was placed in the cathode cavity. In the absence of a tablet, the discharge ignition voltage was typically ≥3.5 kV, while the burning voltage was in the range of 500–600 V. The use of the tablet made it possible to decrease the ignition voltage to 280 V and maintain the discharge burning voltage at a level of about 130 V. A model of the current sustainment in a hollow-cathode discharge is proposed. Instead of the conventional secondary emission yield, the model uses a generalized emission yield that takes into account not only ion bombardment of the cathode, but also the emission current from an external source. The model is used to interpret the observed current−voltage characteristics. The results of calculations agree well with the experimental data. It is shown that, in some discharge modes, the external emission current from the cathode can reach 25% of the total discharge current.

Low-current hollow-cathode discharge in a trigger unit of a cold cathode thyratron

The paper deals with the investigations of the effect of cathode emissivity on the regimes of low-current hollow-cathode glow discharge. It is shown that an increase in the emissivity due to the so-called high-emissivity tablet allows the essential decrease in the discharge initiation voltage and the discharge burning voltage. The model of current sustaining for the hollow-cathode discharge, which takes into account the external emission current has been developed. On basis of the model, the current-voltage characteristics of the discharge have been interpreted.

A device and procedure for measurements of the effective secondary emission coefficient

The design of the device and procedure of measuring the effective secondary emission coefficient γeff in glow discharges with a large-area cathode are described. The values of γeff and the density of the ion current on the cathode in the self-sustained and nonself-sustained (under the additional external injection of electrons) discharge burning modes are determined. It is shown that for the self-sustained burning mode of the basic discharge with a current of 30 A, the value γeff ≈ 0.15, being in good agreement with both the theoretically calculated and known reference data. When the basic discharge occurs in the nonself-sustained mode, γeff = 0.08–0.12, depending on the discharge burning voltage, and the ion current density on the cathode surface is equal to 0.8–1.1 mA/cm2, being ≈10% lower than the value characteristic of the self-sustained discharge mode.

Theory of a normal high-pressure glow discharge

In the present work, a theoretical model considering the processes of generation and losses of charged particles in the cathode region of a glow discharge in the drift approximation for ion and electron motion is developed. Exact analytical solutions, which can be used to calculate the current-voltage characteristics of the glow discharge in an arbitrary gas with the known Townsend ionization coefficient, are derived. The calculated parameters of the normal glow discharge (the current density, discharge burning voltage, and width of the space charge region) for different gases are in good agreement with the available experimental data.