V. Stelmashuk

RF sputtering of hydrocarbon polymers and their derivatives

RF sputtering of polymeric targets was discussed from the point of view of history and present status of the field. RF sputtering of polytetrafluorethylene (PTFE) was mentioned in self-sputtering mode, argon, nitrogen and other gases. The emission of fragments from the target observed by means of quadrupole mass spectroscopy and target surface as observed by SEM were described. Columnar morphology of the sputtered films at substrate temperatures below room temperature was mentioned. Deposition rate of sputtered PTFE films was found up to one order of magnitude higher than polyimide (PI) sputtered films. Results of PI sputtering process and films characterization in terms of tribological coatings were reviewed. Polyethylene (PE) and polypropylene (PP) sputtering was found below 100 W power more than three times slower than PTFE sputtering. The films are hydrocarbon plasma polymers containing a lot of oxygen and OH groups. Above 100 W the co-evaporation from the erosion zone of the target took place and deposited films resemble much more the parent target as observed by FTIR. Finally, co-sputtering of metal and polymer that results in nanocomposite metal/plasma polymer films and sputtering of SiO2/PTFE composite target is shortly discussed.

Shock Waves Generated by an Electrical Discharge on Composite Electrode Immersed in Water With Different Conductivities

A generation of focused shock waves by underwater multichannel pulsed electrical discharge on a porous-ceramic-coated electrode in saline water is studied. This work describes the effect of solution conductivity of saline water on the pressure of shock waves. It was found that the amplitude of shock waves has a nonlinear dependence on water conductivity: The amplitude increases with the increase of water conductivity up to 18-20 mS/cm and then decreases again. In this paper, we show that two effects take place. First, the electrical energy dissipated in the discharge depends on the impedance of the electrode system being affected by water conductivity. Second, the velocity of streamer growth strongly depends on energy deposition time into the discharge. The two mentioned effects result in “hill-like” shape of the curve presenting the dependence of the maximum amplitude of the shock wave on water conductivity.

Inductive Sensor for Lightning Current Measurement, Fitted in Aircraft Windows—Part I: Analysis for a Circular Window

A novel sensor is described for the detection of the lightning current through the fuselage of an aircraft. The sensor relies on the penetration of the magnetic field through fuselage openings and can be embedded in a window inside the aircraft. The sensor combines good sensitivity with sufficient bandwidth to record the lightning transient current. Guidelines for the position are derived from a mathematical analysis for a circular window.

Sensors for in-flight lightning detection on aircraft

Commercial passenger aircraft are on average struck by lightning once a year. The in-flight lightning strike damage assessment system (ILDAS) project is to develop and validate a prototype of a system capable of in-flight measurement of the current waveform and reconstruction of the path of lightning current. This paper discusses the various magnetic sensors, their rationale and some tests. Inductive sensors require an integrator in the signal conditioning. Much attention has been paid to the passive integrator, which is the first integrator stage preliminarily responsible for EMC.

Sensors for lightning measurements on aircraft

Lightning strikes a commercial airliner on the average once a year. The European project ldquoIn-flight Lightning Strike Damage Assessment System (ILDAS)rdquo [1] aims to develop and validate a prototype of a system capable to 1) reconstruct the current intensity and wave form, 2) determine of the region of impact on the aircraft, 3) build a maintenance database. Suitable sensors rely on determination of the magnetic field during a strike. Probes considered are inductive coils and solid state sensors, combined in such a way that these cover the full dynamic range in amplitudes (1 A/m up to 40 kA/m) and the full bandwidth (approx. 1 Hz up to 20 MHz). External sensors should be avoided if possible.

Microsecond Electrical Discharge in Water in Plate-to-Plate Configuration With Nitrogen Bubble Injection

In this paper, a new method of generation of an electrical discharge in water using plate electrodes is proposed. The electrical discharge in plate-to-plate configuration cannot be easily generated because of a low uniform electrical field. A nitrogen bubble is injected into one of the electrodes to create a favorable condition for electrical breakdown. The generated electrical discharge is studied using a high-speed framing camera. Two interesting effects have been observed. First, the discharge is preferentially initiated on the cathode. Second, the positive streamer reveals nontypical morphology. The physical mechanisms of discharge initiation and positive streamer propagation are discussed.

Penetration of Gas Discharge Through the Gas–Liquid Interface Into the Bulk Volume of Conductive Aqueous Solution

Gas discharge plasma generated above the surface of conductive aqueous solutions in a glass capillary was used to study penetration of the discharge from the bubble (imitated by the space above meniscus of liquid surface in the capillary) into the bulk liquid. The experiments were conducted at both polarities with a high-voltage needle electrode placed above the liquid surface. Different aqueous solutions were examined (distilled water, conductive saline solutions). High-speed shadowgraphy was used as the main diagnostic tool for the study of the disturbances at the plasma-liquid interface. It has been found that electric field just beneath the liquid surface and the liquid/plasma conductivity ratio have a decisive effect on the development of plasma-liquid interface instabilities. Experiments with negative electrode above the liquid surface showed that this surface in the place of the largest current density recedes. This receding is caused by the reaction pressure resulting from liquid evaporation. Thus, long cavities with plasma inside can be formed. The cavity elongation speed is of the order of 1 m · s-1, and it depends on current density. The liquid surface remains smooth, when the liquid conductivity is larger than the conductivity of adjacent plasma. In the opposite case, if the liquid conductivity is smaller than the conductivity of adjacent plasma, the distribution of current density on the plasma-liquid boundary is unstable: any initial surface disturbance boosts the current density in a local surface valley simultaneously causing a detriment of the surrounding current density. Consequent stronger liquid evaporation in the valley causes its deepening, and hence, next enhancement of the inhomogeneity of current density distribution. The dips created in this way subsequently transform into negative streamers, when electric field larger than 1 MV · m-1 appears near the liquid surface. Experiments with the positive electrode above the liquid surface significantly showed more intense liquid evaporation than the experiments with the negative one - under otherwise the same conditions. Therefore, elongation speed of the gas cavities is also significantly higher. The development of spikes on liquid surface is also dependent on the liquid conductivity. However, electric field larger than 10 MV · m-1 near the liquid surface is necessary for the development of positive streamers.

Observation of a spark channel generated in water with shock wave assistance in plate-to-plate electrode configuration

When a high voltage pulse with an amplitude of 30 kV is applied to a pair of disk electrodes at a time when a shock wave is passing between them, an electrical spark is generated. The dynamic changes in the spark morphology are studied here using a high-speed framing camera. The primary result of this work is the provision of experimental evidence of plasma instability that was observed in the channel of the electric spark.

Time-resolved processes in a pulsed electrical discharge in water generated with shock wave assistance in a plate-to-plate configuration

Plate-to-plate geometry is not usually used for a discharge generation in water because of a low electric field that is insufficient for electrical breakdown between electrodes. In the present research, a new method of the generation of electrical discharge in water using plate electrodes is proposed. A high voltage pulse is applied to a pair of disc electrodes at a time when a shock wave is passing between them. This method allows for depositing a higher electrical energy than with the case of pin-to-pin electrodes (or pin-to-plate electrodes) without their destruction. This discharge initiation occurs in numerous cavitation bubbles generated by the shock wave. The discharge evolution was studied using a high-speed framing camera. Two interesting effects have been observed. Firstly, multiple streamers are incepted on a cathode, which is not typical for the symmetrical electrode configuration. Secondly, the plasma in the spark channel reveals not to be homogeneous. The dynamics of a vapour bubble generated by this spark were studied by a shadowgraph method. The bubble?s growth, collapse and rebound are discussed.

Pressure Field Around Underwater Negative Streamers

In this paper, experimental observations of propagation of negative streamers in distilled water (conductivity of 1.7 μS·cm-1) in a needle-plane electrode geometry (gap of 6 mm) are described. The spatially resolved pressure field surrounding the tip of streamer channel in the given moment was determined by Mach-Zehnder interferometer with second harmonic of Nd:YAG laser as a source. The high-voltage needle electrode was brought on the potential of 23 kV and that remained practically unchanged during streamers propagation, while a significant noise with amplitude of several amperes was visible on the waveform of discharge current. Analysis of captured interferograms shows that propagation of negative streamers is not uniform: an active (propagating) streamer produces continuous moving pressure field (similar to that of moving object) with maximum amplitude greater than 40 MPa on the streamer tips and an inactive streamer nearly stops propagating being surrounded by a nearly spherical pressure wave moving away from the streamers tip. The inactive state can last even longer than 200 ns.