S. P. Gorbunov

Flow of multiple charged accelerated metal ions from low-inductance vacuum spark

Results of studies of the short-run beams of multiple charged fast ions that have been found earlier by the authors in a low voltage vacuum spark are presented. The ion emission was due to the formation of micropinches in the cathode plasma jet by the action of the self-magnetic field. A relation between the average velocity of the fast ions and that of the bulk of the ions of the cathode jet was obtained over a wide range of the discharge current amplitudes. The total yield of the multiple charged fast ions per pulse Nf was evaluated from the direct collector measurements with regard to a decrease in ion flow due to several reasons. This value was in satisfactory agreement with evaluation that was obtained from the ballistic pendulum measurements and gave Nf ? 5 ? 1013?1014 ions per pulse at the average ion charge state of +9 at the maximum of the discharge current Id = 12?kA. Evaluation of current density for these ions gave jf ? 3?mA?cm?2 at a distance of about 1?m from the anode.

The vacuum spark as a source of metal ions with variable velocity

Results of the time-of-flight measurements of the cathode plasma jet velocity in a low voltage vacuum spark are presented. It is found that the mean velocity of ions in the plasma jet varies over a wide range of values. When the discharge current increases from 0.6 to 11 kA the ion velocity at a distance of 35 cm from the copper cathode goes up to 7×104 m s−1, i.e. exceeds nearly six times the corresponding value of 1.3×104 m s−1 for the dc arc. The intensity of the ion beam in this case increases by more than two orders of magnitude.

Plasma Microthruster Based on Spark Discharge with a Liquid Metal Cathode

The parameters of low-inductance vacuum spark discharge with an In-Ga liquid metal eutectic cathode have been experimentally studied. The application of a constant magnetic field of a permanent magnet significantly modifies the character of plasma flow in discharge, which ensures a significant (1.5- to 2-fold) increase in the cathodic jet impulse. The proposed discharge provides high propulsion characteristics: jet impulse per unit energy stored amounts up to about 10 (μN s)/J, which is close to the best-known values for analogous ion sources with solid metal cathodes.

Spatial structure, dynamics and electron heating of cathode jet of a pulse vacuum discharge

Results of experimental studies of energy and charge state distributions of ions in a cathode plasma jet of a high-current vacuum discharge are presented. Measurements have been carried out by a time-of flight method with an electrostatic energy analyzer. Ions of cathode material with the charge states up to Z=+11 have been observed. Significant increase of the mean ion charge and the ion energy in compare both with the low-current discharges and with the steady-state arcs has been obtained. With the peak discharge current about 2.5 kA and the rate of current rise I/spl dot/=3/spl middot/10/sup 9/ A/s the mean ion charge state equals Z=6.4 and the mean ion energy for different ion species was within range 1.3-1.8 keV. These results are explained by pinching of the cathode jet by magnetic field of its current which occur at high values of I and the region of ions generation is rather less than the size of cathode jet.

Microthruster based on a low voltage vacuum spark

Experimental studies of thrust characteristics of a small-size low voltage vacuum spark with liquid (InGa) cathode are present. It is shown that the view of the signal in the time-of-flight measurements depends strongly on the interelectrode gap, namely, the three ion components are present with the gap of 9 mm. The thrust of the plasma source depends on the interelectrode gap length and increase by 1.5 times with application of a permanent circular magnet. The thrust attains of P = 0.8 μNs with the stored energy of 0.1 J so that we may estimate the thrust to power ratio as 8 μNs/J as well as efficiency of the thruster η = PV/CU02 ≈ 12% at U0 = 250 V. Taking in mind the very small size, rather low mass that is about of 50 g, as well as the simple design of the source, we may conclude that it is a promising one as a thruster for the microsatellites.

Wide-aperture plasma jet source based on low-voltage spark discharge with ferroelectric electrode

Low-voltage vacuum spark discharge initiated at a storage capacitor voltage of 75–600 V using a metal grid cathode situated on the front surface of a polarized ferroelectric (FE) electrode has been experimentally studied. The discharge was initiated when a control voltage pulse with an amplitude of 1 kV and a duration of 100 ns at only negative polarity was applied to the rear FE surface (irrespective of the direction of its polarization vector). Optical measurements showed that the emitting surface area on the cathode increases approximately in proportion to the discharge voltage. According to the collector measurements, the ion plasma flux has slow and fast components, the velocities of which remain almost constant when the discharge current amplitude varies in a wide interval.

Ion Erosion Rate in a High Current Vacuum Spark

Measurements of the ion erosion rate for copper cathode in the low-inductance vacuum spark are presented. The spark peak current was varied from 3 kA up to 13 kA therewith the current rise rate increases from 4middot109 up to 1.5middot1010 A/s. The mean velocity of the cathode plasma flame was obtained by means of the passive collector time-of-flight measurements. It was shown that the velocity increases from 2middot104 m/s up to 8middot10 4 m/s with the discharge enhancement. Mechanical momentum of the plasma flame was measured with a ballistic pendulum, located beyond annual anode in the immediate vicinity. From these data the ion erosion rate was derived at range of peaks of the discharge current mentioned above. This parameter holds to within the accuracy of measurements throughout the range of the current variations. Its value is of 7middot10-5 g/Q and is close to the well-known one that has been obtained earlier in low-current vacuum arcs

Charge and mass transfer in the cathode plasma jet of a low-inductance vacuum spark

The contributions of fast and slow ion components to the average mass transfer rate in the cathode plasma jet of a low-inductance vacuum spark have been determined using time-of-flight measurements. The total mechanical momentum of the cathode plasma jet has been found using the ballistic pendulum technique. The coefficient γ of ion erosion of a cathode material was evaluated in the range of discharge current amplitudes 3–13 kA and the discharge current buildup rates 4 × 109 − 1.5 × 1010 A/s. The γ value exhibits small variations in the indicated range of discharge parameters and is close to the values known for vacuum arcs.

Two-components ion flow in a low voltage vacuum spark

Ion velocities in cathode plasma flow of a low voltage vacuum spark have been studied experimentally for peak discharge currents of 1 - 10 kA. Experiments have been performed using the time-of-flight technique at different ranges of ion collector from the discharge gap. It is shown that there are two ion components in the cathode flow. The slow one presents the bulk of ion distribution and at low peak discharge current its velocity is closed to the convenient value for vacuum arc. The fast components¿ velocity is a few times higher than one for slow ions and amplitude of current for these ions at a range of 10 cm from the discharge gap was closed to one for the slow component. As the distance increases, peak of the fast ions decreases sharper than one for the slow component. Amplitudes of signals and mean velocities of both ion components increase sharply with the discharge current. The fast ion component corresponds, apparently, to beam of the multiply charged ions that had been found by the authors earlier. Total amount of these ions attains, approximately, 1013 ions per a pulse.

Source of metal ions with a variable velocity

Results of the time-of-flight measurements of the cathode plasma jet velocity in a low voltage vacuum spark are presented. It is found that the mean velocity of plasma jet is variable at a wide range of values. When the discharge current is enhanced from 0.6 kA up to 11 kA, the velocity of plasma jet at a distance of 35 cm from the copper cathode is risen linear from 2-10/sup 6/ cm/s up to 7-10/sup 6/ cm/s, i.e. near six times exceeds the corresponding value for DC arc. A simple hydrodynamic model is presented, which explains the experimental results with a satisfactory accuracy.