Unsteady surface signature of a pulsed vortex generator jet

Abstract  

Porous pressure-sensitive paint (PSP) is employed as a visualization technique for unsteady flow features on a low-pressure turbine blade. Recognizing that the measurement of high-frequency pressure fluctuations in unsteady flows—especially in turbomachinery—has proven to be difficult, recent advancements in the development of porous PSP have enabled the high-resolution measurement of pressure fields with frequency content of at least 20 kHz. In this work, PSP is applied to an L1A low-pressure turbine blade section (Re = 20,000 based on axial chord) to visualize the surface dynamics of a vortex generator jet (VGJ) pulsed at 10.6 Hz with nitrogen gas. Intensity-based, time-resolved PSP measurements reveal the development and the surface structure of the VGJ as well as the spanwise variation in the blowing profile.     

Three-chamber low-output-pressure glow-discharge-based plasma generator as a negatively charged ion source

A stationary glow discharge initiated in a two-chamber inverted gas magnetron is studied. In the third (emission) chamber, such a discharge system generates a plasma that can be subdivided into two, circumferential and near-axis, regions with considerably differing parameters and also provides a pressure difference in desired areas. It is concluded that the device suggested could be used as an efficient continuous-mode plasma generator making it possible to produce negatively charged gas ions. The results obtained may serve as a basis for negative ion source design optimization.     

Potential possibilities of a laser plasma as a negative-ion source

The potential possibilities of a plasma heated by laser radiation as a negative-ion source are analyzed theoretically. It is shown that the efficiency of negative-ion formation in a laser plasma in the heating phase reaches 10¹⁵−10¹⁶ ions/J when the parameters of the laser radiation are optimally adjusted. Zh. Tekh. Fiz. 67, 117–120 (July 1997)     

2.5-MeV neutron source controlled by high-intensity pulsed laser generating plasma

A laptop neutron source suited for the most demanding field or laboratory applications is presented. It is based on laser ablation of CD₂ primary targets, plasma acceleration of the D⁺ ions, and their irradiation of secondary CD₂ targets. The deuterium–deuterium (D-D) fusion reaction is induced in the secondary target, according to the values of fusion cross-section versus deuteron energy, which show a significant probability also at relatively low ion energies. The experiments were completed in the PALS laboratory, Prague, detecting monoenergetic neutrons at 2.45 MeV with an emission flux of about 10⁹ neutrons per laser shot. Other experiments demonstrating the possibility to induce D-D events were performed at IPPLM, Warsaw, and at INFN-LNS, Catania, where the deuterons were accelerated at about 4 MeV and 50 keV, respectively. In the last case, a low laser intensity and a post-ion acceleration system were employed. A special interaction chamber, under vacuum, is proposed to develop a new source of monochromatic neutrons or thermalized distribution of neutrons     

High-voltage pulsed discharge in an electron source with a plasma cathode

The nature of and mechanism for producing a high-voltage discharge in an electron source with a plasma cathode are investigated. The possibility of generating pulsed electron currents with an amplitude of 10³–10⁴ A and a length of 10^–6 sec is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 117–121, October, 1973.The authors thank B. M. Koval'chuk for help in developing the experimental arrangement and G. A. Mesyates for constant attention to the work and discussion of the results.     

面向等离子体合成射流应用的微秒脉冲源研制

为了产生高能等离子体合成射流,设计了一台面向等离子体合成射流应用的微秒脉冲源,输出电压为10 kV,重复频率为100 Hz,可承受高达250 A的放电电流。详细介绍了微秒脉冲源的工作原理,比较了不同放电电容对脉冲变压器原边电流及输出电压的影响。进一步将所设计的微秒脉冲源成功应用于等离子体合成射流实验中,研究了不同间距对等离子体合成射流的影响,比较了有无放电电容条件下的能量消耗率。实验结果表明:不同放电电容在相同激励器间距的条件下,击穿电压基本相同;击穿电压随激励器间距增大而增大。有放电电容能产生较大的放电电流,且电流值随电容值的增大而增大。有放电电容条件下的能量消耗率比无放电电容要高,易于产生高能的等离子体合成射流。     

面向等离子体合成射流应用的微秒脉冲源研制

为了产生高能等离子体合成射流,设计了一台面向等离子体合成射流应用的微秒脉冲源,输出电压为10 kV,重复频率为100 Hz,可承受高达250 A的放电电流。详细介绍了微秒脉冲源的工作原理,比较了不同放电电容对脉冲变压器原边电流及输出电压的影响。进一步将所设计的微秒脉冲源成功应用于等离子体合成射流实验中,研究了不同间距对等离子体合成射流的影响,比较了有无放电电容条件下的能量消耗率。实验结果表明:不同放电电容在相同激励器间距的条件下,击穿电压基本相同;击穿电压随激励器间距增大而增大。有放电电容能产生较大的放电电流,且电流值随电容值的增大而增大。有放电电容条件下的能量消耗率比无放电电容要高,易于产生高能的等离子体合成射流。     

A two-mode pulsed source of low-temperature erosion plasma

Journal of Applied Spectroscopy -     

A picosecond near-infrared laser source based on a self-seeded optical parametric generator

We report on the design and development of a new type of near-IR laser source. The source comprises of an optical parametric generator (OPG) and a second harmonic generator (SHG) pumped by an 80-MHz, 1064-nm, 7-ps Nd:YVO₄ laser. The OPG is self-seeded with a fraction of its own signal output, which significantly enhances its conversion efficiency. The SHG doubles the frequency of OPG signal to produce a coherent output. The final output beam has a tunable wavelength near 800 nm, an average power of over 1 W, and a pulse duration around 5 ps. The M²-factor of the output beam can reach 1.1 after spatial filtering. With the new laser source, we have successfully demonstrated coherent anti-Stokes Raman scattering microscopy on 1 μm polystyrene beads, which shows that it has the potential to be a substitute for a picosecond optical parametric oscillator in certain microscopy or spectroscopy applications.     

Acoustic field excited by a pulsed laser line source in a cylinder

The excitation and propagation of the acoustic waves in an elastic cylinder are studied by laser ultrasonics both theoretically and experimentally. The theoretical analysis of the two-dimensional acoustic field excited by a pulsed laser line source impacting on the generatrix of an elastic cylinder is presented. The dispersive properties for both cylindrical Rayleigh wave and the higher modes--whispering gallery (WG) modes are analyzed in detail. The numerical transient displacement waveforms for a detecting point located another terminal of the cylinder diameter opposite the source are calculated. The experimental excitation and detection of the acoustic waves in an aluminum cylinder are carried out on a laser ultrasonic system, which mainly consists of a Q-switched Nd:YAG laser and a laser interferometer. The wave components of bulk waves and surface waves (cylindrical Rayleigh waves and WG modes) are analyzed by comparing the numerical and experimental waveforms. The results are in good agreement.     

A point source analytical model of inverse pulsed laser deposition

A simple analytical model for inverse pulsed laser deposition is proposed. In the model the motion of the evaporated material is assumed to emerge as from a point source located above the surface of evaporation at some distance. The obtained thickness profiles of inverse deposited films agree well with those calculated by the test particle Monte Carlo method. The proposed approach has been applied for analysis of experimental data on inverse pulsed laser deposition of graphite in nitrogen atmosphere with nanosecond pulses of laser fluences between 1 and 7 J/cm². The model describes well the thickness profiles and pressure dependence of film growth rate for inverse deposition.     

Level population by recombination in a pulsed plasma jet in an He-Xe mixture

Measurements have been made on the spatial and time characteristics of the radiation from an He-Xe plasma jet emerging from a discharge channel through a nozzle with a speed of about 10⁵ cm/sec. A recombination mechanism is indicated for the line excitation by the delay between the current pulse and the production of the radiation, as well as by the substantial differences in time course for the intensities of the atomic and ionic lines and by the increase in intensity with pressure. Measurements have been made of the electron temperature and concentration, and estimates have been made of the recombination coefficients, which reflect the performance of the collisional-radiative recombination in a decaying He-Xe plasma jet.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 12–17, March, 1984.     

High-resolution cavity-tuned ringdown spectrometer using a narrow-bandwidth pulsed laser source

A novel method of cavity ringdown spectroscopy is proposed to achieve high spectral resolution with tunable narrow bandwidth pulsed lasers. We demonstrate a cavity-tuned ringdown configuration in which only a single cavity mode is kept excited near the carrier frequency of a narrow bandwidth pulse laser. This is done simply by making a cavity resonance actively track the frequency reference served by the cw injection seed of the pulsed laser source. We present the servo mechanism used in the cavity resonance tracking, reliable procedures for transverse mode matching, and the evidence of single longitudinal mode excitation. The spectrometer performance is tested to record weak molecular overtone features of acetylene around the wavelength of 570 nm, showing cavity tracking stability within 5-MHz uncertainty which overcomes the bandwidth limit of pulsed laser sources itself. PACS 42.62.Fi; 42.60.Da; 33.20.Kf     

Performance studies of a pulsed HF laser with a sliding discharge plasma cathode

The plasma electrode design concept is applied for the first time to an HF laser. The discharge along the surface of a dielectric (sliding discharge) is used as a plasma cathode for the main laser discharge. The laser operates at atmospheric pressure with a gas mixture of He/SF₆/C₃H₈. Details are presented on the efficiency of energy transfer, the dependence of laser performance on circuit parameters, gas mixture, relative energy loading and time delay between the plasma electrode and main discharges. The F atom production rate is estimated from the linear dependence of the output energy on the electric charge passed through the discharge. Output energies of 600 mJ were obtained at 1.6% efficiency from a small active discharge of 108 cm₃ volume and 38 cm length, while the maximum specific input and output energies were 370 J/1 and 5.7 J/1, respectively. These values compare favourably with those reported in the literature for non-chain-reaction-type gas mixtures at 1 atm pressure and demonstrate that the plasma electrode design is a powerful scheme for developing gas-discharge lasers.