G D Liziakin

Parameters influencing plasma column potential in a reflex discharge

Distribution of electrostatic potential in direct current reflex discharge plasma has been studied experimentally. Measurements have been conducted by the single floating probe method. The influence of 0–0.2 T magnetic field, 1–200 mTorr pressure, 0–2 kV discharge voltage, and electrodes geometry on plasma column electrostatic potential was investigated. The possibility for the formation of a preset potential profile required for the realization of plasma separation of spent nuclear fuel was demonstrated.

Diffuse Vacuum Arc on the Nonthermionic Lead Cathode

Experimental study of the diffuse vacuum arc discharge on the nonthermionic lead cathode is presented. At the working cathode temperatures of 1.2-1.6-kK current-voltage characteristic of the discharge, cathode heat operation regime and its erosion rate were measured. Using probe methods, electron temperature (0.3-1.2 eV) and heavy particles (atoms and ions) mean charge (0.17-0.28 e) were determined in after-anode plasma. Evaluated current densities on the cathode are in agreement with a hypothesis on the ion mechanism of charge transfer on its surface. Parameters of the obtained discharge have been compared with the characteristics of the earlier investigated diffuse vacuum arcs on nonthermionic chromium and on thermionic gadolinium cathodes. The obtained data might be useful when creating plasma sources for verifying the plasma separation method of the spent nuclear fuel using the nonradioactive substances.

Electric potential profile created by end electrodes in a magnetized rf discharge plasma

The problem of generating a stationary electric field in a magnetized radio-frequency discharge (rf) plasma is studied experimentally. Helmholtz coils produce magnetic field in a cylindrical vacuum chamber with diameter of 85.6 cm and length of 220 cm. RF discharge is generated at a frequency of ∼ 5 MHz. The rf power absorbed by plasma lies in the range 0.5-1.5 kW. Electrodes defining a negative potential are placed at the ends of the chamber. Two pairs of circular flat electrodes with diameter of 5.5 and 45 cm are investigated. The working gas is argon. Radial profiles of electron density and temperature are obtained. Radial profile of the plasma potential is investigated, as well as the dependence of plasma potential on the voltage applied to the end-electrodes.

Study of the feasibility of distributed cathodic arc as a plasma source for development of the technology for plasma separation of SNF and radioactive wastes

One of the key problems in the development of plasma separation technology is designing a plasma source which uses condensed spent nuclear fuel (SNF) or nuclear wastes as a raw material. This paper covers the experimental study of the evaporation and ionization of model materials (gadolinium, niobium oxide, and titanium oxide). For these purposes, a vacuum arc with a heated cathode on the studied material was initiated and its parameters in different regimes were studied. During the experiment, the cathode temperature, arc current, arc voltage, and plasma radiation spectra were measured, and also probe measurements were carried out. It was found that the increase in the cathode heating power leads to the decrease in the arc voltage (to 3 V). This fact makes it possible to reduce the electron energy and achieve singly ionized plasma with a high degree of ionization to fulfill one of the requirements for plasma separation of SNF. This finding is supported by the analysis of the plasma radiation spectrum and the results of the probe diagnostics.

High-voltage discharge in supersonic jet of plumbum vapor

During study of vacuum discharge in plumbum evaporating from molybdenum crucible in identical geometry of discharge gap and the same crucible temperature existence of two different discharge forms were observed. These two forms are vacuum arc with current above 10 A and voltage about 15 V and high-voltage discharge with current about 10 mA and voltage of 340 V. Plumbum was placed in heat-isolated crucible (cathode). Electron-beam heater was situated under the crucible. At the temperature of 1.25 kK that corresponds to plumbum saturated vapor pressure about 0.1 kPa voltage from power source (380 V, 200 A) was applied to anode and high-voltage discharge initiated with characteristics mentioned above. After a few seconds this discharge could turn into arc or could exist hundreds of seconds until total plumbum evaporation. Glow of discharge could take the form of a cone, harness or plasma bunch that hanged at the appreciable distance from the electrodes. The estimations of plasma parameters are presented.

Diffuse vacuum arc on cerium dioxide hot cathode

A diffuse (spotless) vacuum arc was investigated on a hot cathode made from cerium dioxide. The discharge is obtained in the following range of current, voltage, and cathode temperature of I = 15–150 A, Va = 9–14 V, and Tc = 2.1–2.4 kK. The main characteristics of the plasma flow in space behind the anode with a hole were determined: it was found that the electron temperature at the working parameters lies in the range of 0.4–1 eV, the ions are predominantly singly charged, the average charge of the outgoing heavy particles reaches 0.9 e (elementary charge), and the most probable kinetic energy of the ions does not exceed 9 eV. Potentially found regimes of vacuum arc operation are promising for use in the work on implementation of the plasma method for spent nuclear fuel and/or radioactive waste reprocessing.

Diffuse vacuum arc with cerium oxide hot cathode

Diffuse vacuum arc with hot cathode is one of the perspective plasma sources for the development of spent nuclear fuel plasma reprocessing technology. Experimental data is known for such type of discharges on metal cathodes. In this work discharge with cerium dioxide hot cathode was studied. Cerium dioxide properties are similar to uranium dioxide. Its feature as dielectric is that it becomes conductive in oxygen-free atmosphere. Vacuum arc was studied at following parameters: cathode temperatures were between 2.0 and 2.2 kK, discharge currents was between 30 and 65 A and voltages was in range from 15 to 25 V. Power flows from plasma to cathode were estimated in achieved regimes. Analysis of generated plasma component composition was made by radiation spectrum diagnostics. These results were compared with calculations of equilibrium gaseous phase above solid sample of cerium dioxide in close to experimental conditions. Cerium dioxide vacuum evaporation rate and evaporation rate in arc were measured.

Experimental study of vacuum arc with low cathode current density as a source of metal plasma

Summary form only given. Sources of metal plasma are applied in plenty of technological tasks, for example, in coatings deposition or electromagnetic separation of isotopes. Vacuum arc may be used as one of such source. Its main advantages are high productivity and ionization degree, but plasma of usual vacuum arc contains micro particles of cathode erosion products. External cathode heating decreases its current density and problem of micro particles disappears. In this work such diffusive vacuum arc was studied. Gadolinium and plumbum were used as cathode materials. For gadolinium 90% of arc current consist of thermal electron emission from cathode, and for plumbum this part is less than 0.01%.Arc was initiated in vacuum chamber with pressure of residual gases less than 10 mPa. The investigated substance which was the arc cathode was placed in molybdenum crucible with outer diameter 25 mm. Under the crucible there was an electron-beam heater with maximum power about 1 kW. Heater allowed changing the cathode temperature at fixed arc current. A stainless steel water-cooling disk was used as the anode. It had a hole with the diameter of 32 or 15 mm. The distance between electrodes was about 30 mm. Arc plasma was studied by spectrometric and probe methods. The discharge with plumbum cathode was studied in current range from 20 to 70 A and cathode temperatures from 1.2 kK to 1.4 kK. Typical discharge voltage was about 15 V. The arc with gadolinium cathode was studied in current range from 15 to 150 A, cathode temperatures from 1.9 to 2.1 kK and voltages form 3 to 50 V. Arc regime with singly high ionized (ionization degree is about 100%) gadolinium plasma was revealed. The average ion charge of plumbum plasma was estimated at the arc current 40 A. Average evaporation speed of gadolinium and plumbum was measured in arc conditions. It was almost two times less than without discharge at the same cathode temperature.

The sag of the potential in low pressure reflex discharge

Summary form only given. In this work Penning discharge was studied in order to investigate how cathode potential penetrates into magnetized plasma along magnetic field. If negative voltage was applied on end electrodes and there was a magnetic field while cylindrical vacuum chamber was grounded then reflex discharge initiated. The distinctive feature of this discharge was geometry factor. Cathode was greatly ranged from anode (cathode radius r=20 mm, anode radius R=400 mm), but dielectric plates were on the chamber ends.The length of vacuum chamber made of stainless steel was 2000 mm. There was uniform magnetic field in the range of 0-2 kG along the axis. The Penning discharge was studied with the usage of different cathodes: solid disk (r=20 mm) and ring (r1=235 mm, r2=295 mm). The gas was helium by pressure in range from 1 to 35 mTorr, maximum voltage was 1.2 kV. Two mode of discharge operating was found in the case of 35 mTorr. Current-voltage characteristic (CVC) of discharge and radial potential profile was measured. The electron temperature and plasma density was obtained using double probe CVC.

The stationary vacuum arc on non-thermionic hot cathode

Experimental study of vacuum arc with distributed spot on plumbum cathode at temperatures 1.25-1.45 kK has been presented. At these conditions current density of thermionic emission from cathode was less than 1 μA/cm2, while the mean current density on the cathode was about 10 A/cm2. Plumbum was placed in heat-insulated crucible (cathode) with external diameter 25 mm. Electron-beam heater was situated under the crucible. Arc current was changed in the range 20-70 A, arc voltage was about 15 V. The studied arc is characterized by the absence of the random voltage fluctuations; the micro particles of cathode erosion products were observed only in transition regimes. Spectral data of plasma radiation and values of the heat flow from plasma to cathode were obtained. It has been experimentally established that the evaporation rate in arc approximately two times less than without discharge. The average charge of plumbum particles in the cathode jet was in range 0.2-0.3e. Comparison of the characteristics of studied discharge on thermionic gadolinium cathode and non-thermionic cathodes was fulfilled. One can assume that ions provide the charge transfer on the cathode in the studied discharge.