Modulation Of Discharge Current Research Articles

Improving the adhesion of CrN coatings on TC4 alloy substrates by discharge current modulation in magnetron sputtering

ABSTRACT The study reports the formation of multilayer coatings of CrN with variable gradient modulus on TC4 substrate by varying the discharge current of the hot filament in magnetron sputtering. Results show that multilayer CrN/TC4 has a higher critical failure load (63.4 N > 29.7 N), lower maximum tensile stress (103.8 GPa < 134.3 GPa), and a higher ratio of plastic to elastic deformation work (Wp/We, 2.11 > 1.58) than a single layer CrN/TC4. This indicates that the energy absorption ability of the coating/substrate before failure can be improved by increasing the loose energy-absorbing sublayer, thus improving the coating/substrate adhesion. Notably, the wear rate of both multilayer and single-layer coatings is in the order of 10−16 m3/(N·m), demonstrating their excellent wear resistance. Structural engineering enables the application of multilayer CrN coatings on low-modulus and high-strength alloy substrates, such as TC4.

CONTROL OF CO2 LASER POWER BY ACOUSTIC FIELDS

The present study investigates the optimization of the operation of the CO2 laser in the acoustoplasma mode (i.e., dependence of the laser radiation power on the composition of the working mixture, pressure, value of the direct component of the discharge current, frequency, and modulation depth). A three-dimensional dependence on the frequency and modulation depth of the discharge current is experimentally obtained for the normalized efficiency of the conversion of the electric power supplied to the discharge tube into laser power. The maximum gain when transition to the acoustoplasma mode exceeds 2.5 times. The optimum depth of the discharge current modulation is 0.5–0.7. The laser radiation power modulation caused by the discharge current modulation is measured. Laser power is not modulated at modulation frequencies of current &gt;1 kHz. Meanwhile, at current modulation frequencies &lt;0.5 kHz, the modulation depth of the laser radiation power nonlinearly depends on the modulation depth of the discharge current and has a threshold character. The modulation depth of the laser radiation power is associated with the creation of an acoustoplasma and not simply with the discharge current modulation.

CONTROL OF CO2 LASER POWER BY ACOUSTIC FIELDS

The present study investigates the optimization of the operation of the CO2 laser in the acoustoplasma mode (i.e., dependence of the laser radiation power on the composition of the working mixture, pressure, value of the direct component of the discharge current, frequency, and modulation depth). A three-dimensional dependence on the frequency and modulation depth of the discharge current is experimentally obtained for the normalized efficiency of the conversion of the electric power supplied to the discharge tube into laser power. The maximum gain when transition to the acoustoplasma mode exceeds 2.5 times. The optimum depth of the discharge current modulation is 0.5–0.7. The laser radiation power modulation caused by the discharge current modulation is measured. Laser power is not modulated at modulation frequencies of current &gt;1 kHz. Meanwhile, at current modulation frequencies &lt;0.5 kHz, the modulation depth of the laser radiation power nonlinearly depends on the modulation depth of the discharge current and has a threshold character. The modulation depth of the laser radiation power is associated with the creation of an acoustoplasma and not simply with the discharge current modulation.

The vibrational properties of the dust trap created in standing striation

The forced vertical oscillations of a single dust particle trapped in a standing striation are investigated. The particle oscillations associated with the displacement of the striation are induced by square wave modulation of discharge current. Amplitude frequency characteristics depending on the shapes of modulating signal are measured at pressure p = 0.16 torr. The resonance frequency, the eigenfrequency, the damping constant, and the amplitude of the resonance peak are determined. The quantitative description of the resonance behaviour of the dust particle is based on the theory of the forced harmonic oscillator. The Q‐factor of a dusty plasma system is measured for the first time. The Q‐factor takes the value of the order of several units, which indicates the large energy dissipation in the dusty plasma systems.

Observation of the coupling of the driven dust acoustic wave

In this study, the coupling between the naturally occurring dust acoustic wave (DAW) and the discharge current modulation is examined. It is confirmed that, when the wave is driven by modulating the discharge current, the DAW is driven at the same frequency as the current modulation.

Spectral measurements of the probability of recombination of active particles of plasma on solid surfaces in chlorine and its mixtures with inert and molecular gases

Systematic investigations are performed of the spectral characteristics of plasma of chlorine and its mixtures with oxygen, nitrogen, hydrogen, and argon in a dc glow discharge under conditions of continuous modulation of discharge current with rectangular pulses which provide for 100% modulation of discharge current (P total = 100 Pa, i d = 11 mA). The possibility is demonstrated of using the relaxation (pulse) procedure for determining the absolute values of the probability of loss of chlorine atoms in plasma of variable-composition chlorine mixtures by atomic chlorine radiation. The absolute values are determined of the probabilities of loss of chlorine atoms on the reactor wall in plasma of mixtures of chlorine with the gases identified above, and it is demonstrated that the prevailing mechanism of the loss of atoms is the wall recombination by the first kinetic order.

Investigation of H- production in plasma of dc glow discharge

The laser photodetachment technique was applied to investigate the negative ion dynamics in the positive column of a pure hydrogen dc glow discharge at pressures P = 0.1 - 3 Torr. Upon the discharge current modulation, the negative ion H- concentration decayed with the characteristic loss time of hydrogen H(1s2S) atom concentration. The evolution of H atom concentration was investigated by the time-resolved actinometry. The axial electric field was measured by double probe technique. The analysis of the experimental data, i.e. the dependencies of H- and H concentrations as well as reduced electric field on the discharge parameters (discharge current and pressure), allowed us to determine the rate constant of H- production in the discharge, where vibrational excitation and reactions with atoms H greatly influence upon H- production and loss processes. The main processes, which contribute to H- production, are discussed in detail. The vibrational excitation of H2 is shown to increase the rate of dissociative attachment essentially not only via the excitation of the well-known lowthreshold (eth≈3 eV) resonance of H2-(X2∑u+), but also via the excitation of the high-threshold resonances of H2-(2∑g+ (eth≈6 eV), 2Πg, 2Πu (eth≈8-13 eV) etc). Detailed analysis of dissociative attachment via high-threshold resonances allowed us to describe experimental data in the whole range of E/N being investigated, whereas taking any other mechanisms into account (attachment to Rydberg states of H2 etc) failed to do that.

Negative ion destruction by O(3P) atoms and O2(a 1Δg) molecules in an oxygen plasma

Laser photodetachment was used to investigate the dynamics of negative ion density in the positive column of a pure oxygen dc glow discharge over a range of pressure (0.1–5 Torr) and current density (2–40 mA cm−2). Upon discharge current modulation, the negative ion O− concentration decayed with the characteristic loss times of oxygen O(3P) atom and metastable oxygen O2(a 1Δg) molecule concentrations over a wide range of discharge parameters. To determine the rate constants of negative ion loss by reaction with these species, the dynamics of O(3P) atoms and O2(a 1Δg) molecules was investigated using time-resolved actinometry and IR spectroscopy at 1.27 µm, respectively. At pressures greater than ∼0.5 Torr the attachment–detachment dominated regime of the oxygen discharge was realized and the main negative ion was O−. Under these conditions, electron attachment to O2 molecules to produce O− was compensated by detachment of O− with O(3P) and O2(a 1Δg). The rate constants of O− detachment with O(3P) atoms ) and singlet O2(a 1Δg) molecules ), were determined in the plasma itself for the first time.

Effect of perturbations in an active medium on the instability of the difference frequency of laser radiation

A frequency-stabilized helium-neon laser with Zeeman frequency splitting in the magnetic field was studied. A series of pulses with repetition frequency equal to the frequency difference caused by the splitting of the gain profile by the magnetic field was used as a reference signal for a laser interferometer. The modulation of discharge current by electric noise or natural oscillations of the discharge current were found to lengthen the edges of these pulses, which decreases the accuracy of measurements with a laser interferometer.

Nonlinear amplitude-tuning characteristic of a CO2 laser with pump-current modulation

The nonlinear amplitude-tuning characteristic of a CO2 laser with discharge-current modulation was investigated by mean of numerical simulation. It is shown that in the general case the magnitude and shape of the laser response depend on the ratio between the frequency of the pump modulation and the fundamental resonance frequency of the laser.

Enhanced production of negative ions in low-pressure hydrogen and deuterium discharges

A new approach to enhance the production of negative ions in low-pressure hydrogen and deuterium discharges is described. The procedure, which requires on-off modulation of the discharge current, is applied to a conventional magnetic multicusp or ``bucket'' volume negative-ion source. The extracted ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ current from a 15-A discharge at a filling pressure of 2.4 mTorr is increased from 0.5 to 2.0 mA/${\mathrm{cm}}^{2}$ by discharge-current modulation at 10 kHz and 23% duty cycle. The ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ beam current is not significantly modulated (5%). The extracted electron current density and average discharge current are reduced by over a factor of 4. The work is relevant to production of ${\mathrm{D}}^{\mathrm{\ensuremath{-}}}$ beams for neutral-beam injectors.

Infrared diode laser spectroscopy of the SiF radical

The vibration-rotation spectrum of the SiF radical produced in a glow discharge of silicon tetrafluoride (SiF4) was observed using an infrared diode laser spectrometer. The SiF lines were discriminated from much stronger SiF2 lines by the discharge current modulation and Zeeman modulation techniques. Twelve and 15 lines belonging to the 2Π12 and 2Π32 spin states, respectively, were identified for the fundamental band in the ground electronic state. Most of the lines in the 2Π12 state were observed with splitting due to the Λ-type doubling. Precise molecular constants for the v = 1 state, including the rotational, centrifugal distortion, and spin-orbit coupling constants, were obtained from the least-squares analysis, in which the ground state constants were constrained as determined by microwave spectroscopy. The fundamental band origin thus obtained is 847.7205 ± 0.0005 cm−1, where the uncertainty corresponds to three standard deviations. The equilibrium bond length re is derived as 1.601018 ± 0.000003 A from the equilibrium rotational constant, Be = 0.581241 ± 0.000002 cm−1.

Infrared diode laser spectroscopy of the ν3 band of the fluoromethyl radical, CH 2F

The ν 3 (CF stretching) band of the CH 2F radical was observed with Doppler-limited resolution, by using infrared diode laser spectroscopy with Zeeman and discharge current modulation. The CH 2F radical was generated directly in a multiple reflection absorption cell by the electrical discharge in CH 2FCOOCH 3. The observed spectrum was analyzed to yield the band origin of 1170.4165(6) cm −1 with one standard error in parentheses, in addition to the rotational constants, centrifugal distortion constants, and spin-rotation interaction constants in the v 3 = 1 state.

Diode laser spectroscopy of the SF radical

The vibration-rotation spectra of the SF radical were observed by an infrared diode laser spectrometer. The SF radical was generated directly in a cell by glow discharge in a mixture of carbonyl sulfide and carbon tetrafluoride. Zeeman modulation and discharge current modulation were employed to discriminate SF lines from many lines of the reactants and other products. Thirty two lines were assigned to the v = 1 ← 0 and 2 ← 1 bands of both 2 Π 1 2 and 2 Π 3 2 spin states. A least-squares analysis of all the assigned lines provided precise values for molecular parameters in v = 1 and 2 and the two band origins, where ground-state constants were constrained to microwave results. The harmonic frequency ω e was thus determined to be 837.6418(13) cm −1, and the equilibrium bond length r e was calculated from the B e rotational constant to be 1.596 244(22) Å with the error in parentheses, which included 2.5 standard deviations and the uncertainty of Planck's constant.