C. Cachoncinlle

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.

High repetition rate compact source of nanosecond pulses of 5–100 keV x-ray photons

A powerful, compact, and repetitive flash x-ray system based on a cable transformer technology powered by ceramic capacitors in a Blumlein-like configuration has been developed. Open circuit voltages in excess of 100 kV can be achieved while commutation occurs at low voltage (<20u2009kV). The x-ray emission from a low impedance x-ray diode with a hollow cathode configuration was observed under a wide range of experimental conditions. The critical parameters limiting the flash x-ray performances are mainly the pressure in the x-ray diode and the anode–cathode space. This true table top device is able to produce doses up to 1 R per shot, measured at the output window, of x-rays between 5 and 100 keV. The pulse widths were about 20 ns and the maximum repetition rate was about 60 Hz. Operation is possible in air or in other gases (He, Ne, Ar, Kr, Xe, H2, N2) at pressures varying from 10−3u2009mbar for xenon to about 1 mbar for helium.

Flash x-ray radiography of argon jets in ambient air

This paper describes the development and application of a soft x-ray flash radiography technique. A very compact soft x-ray flash source has been specially designed for these studies. The table-top x-ray source developed in this work emits strong doses, up to one roentgen at the output window, of x-ray photons, with most of them in the characteristic lines of the anode material (photon energy in the energy range 5-10 keV), in pulse of 20 ns FWHM with an x-ray emission zone smaller than . All these characteristics make this source attractive for the x-ray radiography of high-speed phenomena, down to ten nanoseconds duration and/or for the media presenting weak absorption for the harder x-ray photons emitted by more conventional flash x-ray systems. Argon streams in ambient air were chosen as a typical case to enlighten the potentialities of this method. Single-shot radiographs of such an argon jet through rectangular nozzles were obtained. No attempt of quantitative measurement of local density in the argon stream has yet been performed, only the qualitative structure of the jet has been investigated. Nevertheless, these preliminary results enable us to state that the diagnostics of gaseous or plasma media, even at rather low pressures, can proceed using soft x-ray flash radiography.

Simultaneous flash x-ray induced fluorescence imaging and radiography of argon jets in ambient air

This paper describes the development and application of a new x-ray based diagnostic technique. A compact flash x-ray source emitting 20 ns pulses of around 8 to 10 keV x-ray photons is used to induce the fluorescence of argon jets in ambient air. This x-ray induced fluorescence (XIF) is then collected for imaging experiments. In these preliminary studies, the feasibility of the XIF imaging technique is demonstrated by the characterization of argon flows in ambient air. The fluorescence of nitrogen molecules, resulting from the x-ray excitation of argon jets and successive energy transfers, is imaged on an intensified linear array CCD detector. The recording of the UV nitrogen fluorescence in our experimental conditions, pulsed excitation and atmospheric pressure, is shown to be an efficient and conclusive method for the characterization of argon flow in ambient air. The propagation paths of two converging argon jets are described and the divergence of each of the two jets expanding through a rectangular nozzle is measured. The reliability of the XIF imaging technique is successfully confirmed by a comparison with data obtained using the x-ray radiography technique. The simultaneous performance of XIF imaging and radiography for the diagnostics of one gaseous flow is achieved in this work. Some future improvements of both techniques are proposed for their application in other experiments.

A kHz and low debris capillary discharge EUV source

Summary form only given, as follows. We have developed xenon discharge plasma sources dedicated to EUV lithography and to EUV metrology. Few kA currents with fast rise time and short duration have been applied across xenon filled ceramics capillary (1 mm diameter and 10 mm length) to produce mostly EUV radiation in the wavelength range 10 to 16 nm. The radiative performances were studied by means of time resolved as well as time integrated spectroscopy and pinhole imaging measurements. The results demonstrated that the source produced intense flux of photons at 13.5 /spl plusmn/ 0.45 nm with an excellent conversion efficiency of electrical energy. This wavelength range is very well suited to EUV metrology and lithography applications. Consequently, optimization studies were undertaken to develop a source with the required specifications for metrology, (EUV reflectometry and EUV microscopy), or with the even more stringent specifications required by next generation EUV lithography. The source produces 0.3 Watt of EUV radiation in band, for a 2% bandwidth, at 13.5 nm. It can be operated repetitively at frequencies up to 300 Hz for hours with an EUV yield stability better than 0.6%. The shot to shot spatial position fluctuation of the source has been measured by pinhole imaging to be lower than 45 /spl mu/m. A high frequency regime of 1 kHz can be attained but only for short durations due to the switching element limitation. An important issue concerns the emission of debris. This was checked by examining the contamination of a silicon wafer placed 20 cm in front of the discharge in the vacuum tank. XPS, AES and RBS analysis showed that less than one monoatomic layer was deposited during a 1 million shot operation. Such a low contamination rate has been made possible by use of a special design for the electrode geometry.

Detailed investigation on the neon-xenon mixture as filling gas for mercury-free fluorescent lamps

Summary form only given. The conventional fluorescent lamp is a low-pressure mercury discharge device with a phosphor coating that converts ultraviolet light into visible light. Since mercury is toxic, it represents an environmental hazard and suggests a need for mercury-free light sources. Many years ago, several investigations were carried out in an endeavour to use inert gases as a substitute for mercury. Most recent studies of neon-xenon mixtures showed that a significant fraction of the input power delivered to the plasma can be converted into UV radiation. Nowadays, this mixture is most frequently used in plasma displays. While the role of neon is to decrease the operating voltage, the xenon is the active source of UV photons. Herein we report experimental investigations of a neon-xenon plasma in a cylindrical axially homogenous positive column at low pressure. The set-up of this experiment consists of three principal devices: the discharge tubes with special design, the spectroscopic detection tools with data acquisition devices and a shelling device. The tubes are made of conventional glass coated with an ordinary phosphor layer. Every tube is equipped with a pair of hollow electrodes and a pumping port. This port is connected both to the shelling device and to a vacuum ultraviolet spectrometer through an MgF/sub 2/ window and permits the evacuation and the filling of the discharge vessel as well as the performance of spectroscopic diagnostics of the glow discharge in the VUV wavelength region. End-on and side-on spectroscopic analysis of both the positive column and the near by cathode region can be performed. The main results are obtained by optimizing the xenon VUV radiation. Neon used as the primary gas, has been mixed with a suitable amount of xenon which emits mainly the VUV resonance radiation at 146.96nm and 129.56nm.

Soft X-ray diagnostics of density and dynamics of dodecane sprays

The optimization of vehicle engine injectors has been and is still today a critical issue for the reduction of fuel consumption, the limitation of air pollutant release and the development of alternative fuels. An extended panel of diagnostic techniques is applied for the spray atomisation description in connection with a large effort in modelling works. Dealing with the near nozzle region, i.e. the dense region of the spray, only the X-ray absorption technique was shown to be able to provide valuable data. Very significant improvement of this high density region characterization was recently achieved using unique features of synchrotron X-rays1.

Characterization and optimization of a flash X-ray source for dense spray radiography

Summary form only given. Liquid sprays analysis, as those generated by fuel injection systems, implies diagnosis procedures able to produce information for matter in different phases from liquid to vapor. The high speed sprays produced by the fuel injection systems, need a fast and reliable diagnosis technology. Previous works on N2 cryogenic jets in a high pressure chamber had shown that the use of flash X-ray system can provide valuable data over wide range of parameter conditions. The flash X-ray (called DIKEV), is a transportable blumlein table top source build at GREMI laboratory to perform radiography of fuel injection sprays. This device delivers high X-ray doses, a few mGy per pulse at the output window, in pulses of tens of nanoseconds duration and operates from single shot up to 50 Hz repetition rate. DIKEV efficiency optimized for charging voltage ranging from 10 to 25 kV, leads to the production of X-ray photons with energy ranging from 5 to 40 keV. The low part of this photon energy range, where most photon are produced , is matched for the radiography of dense spray of light elements. The X-ray focus size is not controlled by electrostatic grids as in case of conventional X-ray tubes, but is correlated with the pulsed electric field topography in the X-ray diode. A significant reduction of the X-ray focus size was achieved. This have been possible thanks to the high efficiency of the carbon fiber as field emitter cathode; which permitted an important reduction of cathode size (graphite rods of diameter ranging from 0.5 mm to 2 mm and 10 mum carbon fiber) without dose reduction up to 1000 shots. The density calculation from Beer Lamberts law, requires the precise knowledge of X-ray spectrum. For four different metallic anodes, a DIKEV full spectra characterization has been made with a germanium photodetector. The most important K,L characteristics lines below 30 keV for each anode were identified together with Bremsstrahlung spectra. In contrast to Mo case where continuum spectrum is dominant, a very high, characteristic line to Bremsstrahlung ratio was measured for Cu anode. Best anode material can be easily selected to be adapted to given spray characteristics.

Energetic Photons From Transient Plasma Discharges

An overview of the plasma based sources of energetic photons, ranging from UV to hard X‐rays, developed in GREMI is proposed. Each source principle is shortly described and applications of these specially designed sources are documented. The possibility of producing energetic photons over a very broad wavelength domain, together with the versatility of the mode of operations allow for a very large range of applications. The matching of the photon energy, the pulse repetition rate, the short duration, of a few nanosecond, of photon pulses offer for instance unique possibility for fast dynamic study, low Z element spray characterization, X‐ray fluorescence of dense targets, lithography issues, and UV VUV radiating plasma optimization.

Spectroscopic and energetic characterization of capillary discharge plasmas devoted to EUV production for new lithography generation

Summary form only given. We report on the investigation of three types of capillary discharges likely to produce significant amount of EUV photons for the new lithography generation The discharges are driven by low inductance capacitor banks connected in Blumlein configuration and switched by high repetition rate commutation devices. Currents of a few kA are produced for driving capillaries of selected material or filled with appropriate gas or excited between different electrode shapes and material. The main goal of our investigations was to optimize the EUV power in the 10 to 14 nm spectral range. The influence of the charging voltage, current rise time, capillary parameters (gas, material, length, diameter, pressure) on the EUV production has been analyzed by electrical measurements and time resolved EUV spectroscopic experiments. The energy radiated in the different capillaries was measured with the use of XUV silicon photodiodes and selected spectral filters. A first conclusion was that the energy injected in the capillary had to be matched to an optimal value depending on the capillary parameters and on the gas.