Dunpin Hong

Study of a fast ablative capillary discharge dedicated to soft x-ray production

A capillary discharge has been developed to produce pulses of intense soft x-ray radiation of tens of nanoseconds duration. The soft x-ray photons were emitted in a plasma column resulting from polyethylene in capillary wall ablation. The spectrum was dominated by the C IV, C V, and C VI emission lines in the soft x-ray spectral range. The experimental value of the electrical circuit inductance has been measured and compared to the calculated one. The electron temperature was estimated to be higher than 50 eV from the plasma resistivity measurement. The time dependence of the electron density outside the capillary channel has been determined using spectroscopic measurement in the visible range. The time dependence of the electron temperature has been determined from the intensity ratio of C V and C VI emission lines, using a collisional radiative equilibrium code.

Thermal Characterization of a DBD Plasma Actuator: Dielectric Temperature Measurements Using Infrared Thermography

Active flow control by plasma actuators is currentl y under investigation in order to improve the aerodynamic performance of vehicles. One of these actuators consists in using a surface dielectric barrier discharge (DBD) by creat ing a non-thermal plasma at the dielectric surface. The plasma discharge induces a low-velocity airflow, the so-called “ionic wind”, which can be used to modify external flows. In this study, we focus on the description of the thermal effect of a DBD actuator in order to contribute to a better understanding of the mechanisms of interaction with the flow. The te mperature of the dielectric surface was first determined with the plasma on and secondly af ter switching off the discharge. The measurements were conducted for several amplitudes and frequencies of the applied voltage. The study comprised two parts: in the first, measur ements were performed in quiescent air, and in the second, the influence of an external bou ndary layer over the discharge on the dielectric temperature was investigated.

Negative Spark Leaders on a Surface DBD Plasma Actuator

Plasma actuators are currently under investigations in order to improve the aerodynamic performances of vehicles. Such devices induce airflow of few kilometers per hour called ionic wind. A previous study showed that ionic wind velocity is limited by a particular regime of the discharge where bright and long sparks appear. In this paper, we present some typical images of these spark leaders.

Experimental Study of the Flow Induced by a Sinusoidal Dielectric Barrier Discharge Actuator and Its Effects on a Flat Plate Natural Boundary Layer

Since the mid-1990s, electrohydrodynamic actuators have been developed for modifying on subsonic airflows. The principle of plasma action is the use of the direct conversion of electrical energy into kinetic energy in order to act on the flow boundary layer. This paper presents our contribution to such an investigation concerning an electrohydrodynamic actuator consisting of several sinusoidal dielectric barrier discharges. First, the ionic wind induced by this actuator was measured with a pressure sensing probe. The induced flow velocity increased with the applied voltage and frequency. The particle image velocimetry system without external airflow showed the presence of induced swirls, generated by the ion movement in plasma. Then the action of this actuator on a flat plate boundary layer in parallel flow at zero incidence was studied in a subsonic wind tunnel. Experiments were performed for 15 m/s and 22 m/s. They showed that electric discharges (±8 kV, 1 kHz) acting on a laminar flow tripped the laminar-to-turbulent transition. Moreover, higher applied voltages (up to ±12 kV, 1 kHz) were necessary for modifying turbulent boundary layers.

A new optical technique for investigations of low-Voltage circuit breakers

The technique of broad-band optical absorption spectroscopy has been successfully used for investigations of transient media in low-voltage circuit breakers, thanks to an intense radiation source developed at our laboratory. It enabled the determination of the concentration of copper atoms and C/sub 2/ molecules in hot gas behind a moving arc. The temperature of this gas was estimated using the molecular absorption spectrum of C/sub 2/ Swan bands. Thanks to the high-spectral intensity of the auxiliary source, measurements were also performed in an electrical arc. The measurements allowed the determination of the population of excited levels for several metallic atoms in the arc. Assuming local thermodynamic equilibrium, the electron temperature of the arc and the total concentration of these metallic atoms, coming from contacts and splitters, were deduced. This temperature is in good agreement with the one deduced from optical emission spectroscopy.

Experimental Study of a Surface DBD Actuator Supplied by an Atypical Nanosecond Rising High-Voltage Pulse

This paper presents experimental studies of a surface discharge of an aerodynamic actuator produced by a high-voltage pulse with a nanosecond rise time and a millisecond decrease time. Time-resolved imaging of the plasma and interferometric imaging of the shock wave generated by a unique nanosecond ramp were performed. Interferometry enabled shock fronts to be visualized with a 1 μs time resolution and to experimentally deduce for the first time the associated overpressure values. The interaction of the shock wave with the ionic wind generated during consecutive millisecond-scale voltage decay is also reported from phase-averaged laser Doppler velocimetry measurements. The observed phenomena were correlated with time-resolved images of the plasma developing at the dielectric surface during discharge phases.

Modification of the Laminar-to-Turbulent Transition on a Flat Plate Using DBD Plasma Actuator

Active flow control by plasma actuators, usually ca lled ElectroHydroDynamic actuators, is currently under investigation in order to modify and control external flows. One of these actuators consists in using a surface dielectric ba rrier discharge by creating a non-thermal plasma at the dielectric surface. The plasma induce s a low-velocity airflow, the “ionic wind”, which adds momentum close to the wall. In this study, the ability of such an actuator to delay or promote the transition of a boundary layer developed along a flat plate is studied experimentally.

Control of diffuse and filamentary modes in an RF asymmetric surface barrier discharge in atmospheric-pressure argon

The controlled generation of diffuse and filamentary modes is demonstrated in a radio-frequency (RF, 13.56?MHz) asymmetric surface barrier discharge in atmospheric-pressure argon. For both continuous and pulsed input power, it is shown that the transition from a streamer-driven filamentary discharge at breakdown to a low-current, diffuse plasma can be attained. Fast imaging is used to visualize the structure of the discharge and examine the transition between three distinct modes: moving filaments, branching filaments and a filament-free plasma. The breakdown of the pulsed discharge is studied for pulse periods ranging from ?5??s to 1?ms to investigate the mechanism behind the generation of the diffuse mode.

Spectroscopic and energetic investigation of capillary discharges devoted to EUV production for new lithography generation

In this work, ablative and gas capillary discharges have been investigated as potential sources for the EUV lithography technology. Carbon and lithium ablative discharge spectroscopy and EUV energy measurements have been performed. Gas (O2, Ne, Ar, Kr and Xe) capillary discharge were powered by fast, nanosecond, high voltage Blumlein-like pulser. Detailed investigation of capillary length and diameter, gas pressure, capacitance and inductance of the electrical driver are documented. The energy density, expressed in J cm-3, appears as a monitoring factor for an efficient production of 13.5 nm radiation band. The measurement and the evaluation of measurement uncertainties lead to the conclusion that the in band, 13.5 nm +/- 0.9 nm, energy radiated by the Xe lamp developed in this work ranges from 0.5 mJ/sr/shot to 20 mJ/sr/shot for a 7 J energy input. Repetition rate investigation of the first prototype have shown operation at 50 Hz in continuous mode and up to 350 Hz in burst mode.

Transition control using a single plasma actuator

The aim of this study is to modify, by using surface plasma actuators, the laminar-to-turbulent transition location of a Blasius boundary layer developing on a flat plate mounted in an opened wind tunnel. Measurements of flow velocities were performed by hot wire anemometry. Results show that an actuator placed upstream the natural transition zone enables the promotion or the delay of the transition onset, depending on the location, the voltage amplitude, and the frequency of the high voltage electrical parameters.