Xenon Discharge Research Articles

Double discharges in unipolar-pulsed dielectric barrier discharge xenon excimer lamps

Excitation of dielectric barrier discharge xenon excimer lamps by unipolar short square pulses is studied in this paper. Two discharges with different polarity are excited by each voltage pulse (double discharge phenomenon). The primary discharge occurs at the top or at the rising flank of the applied unipolar square pulse, which is directly energized by the external circuit. The secondary discharge with the reversed polarity occurs at the falling flank or shortly after the falling flank end (zero external voltage) depending on the pulse width, which is energized by the energy stored by memory charges deposited by the primary discharge. Fast-speed ICCD imaging shows the primary discharge has a conic discharge appearance with a channel broadening on the anode side. This channel broadening increases with increasing the pulse top level. Only the anode-side surface discharge is observed in the primary discharge. The surface discharge on the cathode side which is present in bipolar sine voltage excitation is not observed. On the contrary, the secondary discharge has only the cathode-side surface discharge. The surface discharge on the anode side is not observed. The secondary discharge is much more diffuse than the primary discharge. Time-resolved emission measurement of double discharges show the secondary discharge emits more VUV xenon excimer radiation but less infrared (IR) xenon atomic emission than the primary discharge. It was found that the IR xenon atomic emission from the secondary discharge can be reduced by shortening the pulse width. The energy efficiency of unipolar-pulsed xenon excimer lamps (the overall energy efficiency of double discharges) is much higher than that obtained under bipolar sine wave excitation. The output VUV spectrum under unipolar pulse excitation is found to be identical to that under sine wave excitation and independent of injected electric power.

On the decay of metastable and resonance Xe atoms in the afterglow of a constricted discharge

The radial and temporal dependences of the metastable 6 3P2 (Xem) and resonance 6 3P1 (Xer) state densities are measured in the active phase and afterglow of pulsed discharge in xenon by laser absorption technique at pressure 10 Torr and currents 200–500 mA. It is found that the densities grow by a factor of 25 during the transition from the active discharge phase to the afterglow and there is no decrease of the density after switching the field off. It is shown that the collisional-radiative recombination prevails over the dissociative recombination because of high electron density and relatively low electron temperature in a constricted discharge. The electron cooling after the field switching-off is caused mainly by electron–ion collisions whereas the electron–atom elastic collisions are less effective due to the Ramsauer effect. The quantitative modelling of the active phase and afterglow is performed on the basis of the time-dependent system of balance equations for densities of excited atoms and charged particles, as well as electron temperature. The results of the modelling reflect all peculiarities of the excited atom behaviour both in the active phase and afterglow.

Calculation of the parameters of vacuum-ultraviolet emission of excimers in the plasma of a barrier discharge in a krypton-xenon mixture

The intensities of vacuum-ultraviolet emission of excimers in a krypton-xenon mixture are calculated in terms of the homogeneous model of a barrier discharge. The mechanisms of the formation of excimer molecules are investigated at different xenon concentrations. The obtained dependences of the efficiency of vacuum-ultraviolet emission on the reduced electric field E/N (where E is the electric field strength and N is the particle concentration of the gas) and the xenon content exhibit a plateau and a subsequent steep decline. The efficiency of vacuum-ultraviolet emission reaches a maximum at the plateau when the xenon content δ is approximately equal to 40%. The concentrations of xenon excimers can be as high as 1014–1015 cm−3. This is comparable to the concentrations in a barrier discharge in pure xenon.

A capillary discharge plasma source of intense VUV radiation

The results of investigation of a capillary discharge plasma, used as a source of intense VUV radiation and soft X-rays, are presented. The plasma was generated during the discharge of low-inductance condensers in a gas-filled ceramic capillary. Intense line radiation was observed in a broad spectral range (30-400 Å) in various gases (CO2, Ne, Ar, Kr, Xe). The absolute radiation yield for the xenon discharge was ~5 mJ (2π sr)-1 pulse-1 within a spectral band of width 9 Å at 135 Å. Such a radiation source can be used for various practical applications, such as EUV projection lithography, microscopy of biological objects in a 'water window', reflectometry, etc.

片側外部電極型キセノン放電管の放電進展に関する研究

We investigated a developing mechanism of emission in a xenon discharge lamp with inner and outer electrodes using a high-speed electronic camera. At a low operating frequency, a negative glow appears on the inner surface of the glass tube during the positive half cycle while the inner electrode operates as an anode, and a diffused positive column appears in the discharge space during the negative half cycle while the inner electrode works as a cathode. At a high operating frequency, a contracted positive column appears in the center of discharge space near the inner electrode during the positive half cycle and the negative half cycle. VUV radiation intensity and phosphor emission intensity in the diffused positive column are three-times greater than those in the contracted positive column.

Computer modelling of a short-pulse excited dielectric barrier discharge xenon excimer lamp (λ∼172 nm)

A detailed rate-equation analysis has been used to simulate the plasma kinetics in a pulsed-excited dielectric barrier discharge in xenon, under operating conditions where the discharge structure is spatially homogeneous. The one-dimensional model, incorporating 14 species and 70 reaction processes, predicts results that are in good agreement with experimental measurements of the electrical characteristics, and optical (vaccum-ultraviolet (VUV) and visible) pulse shapes. The model reveals that electrical breakdown of the discharge gap occurs via a fast-moving ionization/excitation wavefront that starts close to the anode dielectric and propagates towards the cathode at ∼3×105 m s−1. The wavefront appears as a result of successive avalanches of electrons that propagate across the discharge gap after release from the cathode dielectric. During breakdown, the mean electron energy in the bulk plasma is close to optimum for preferential excitation of the Xe* 1s4,5 states that feed the VUV emitting Xe2* excimer states. Calculations suggest that the overall conversion efficiency from electrical energy to VUV output in the plasma is greater than 60%, with >99% of the light output emitted in the VUV. Parasitic processes that act to reduce the key Xe* 1s4,5 and Xe2* populations are found to be essentially negligible. For pulsed excitation, the longer-term spatio-temporal behaviour of the electron/ions during the afterglow or inter-pulse period is important, resulting in a remnant `pre-pulse' ion density of ∼1015 m−3 close to the cathode dielectric. These ions bombard the cathode during the subsequent excitation period to release the secondary (seed) electrons required to achieve electrical breakdown.

Turbulence in Plasma-Induced Hypersonic Drag Reduction

With the use of a pressure-ruptured shock tube, an experimental study of the dynamics of shock waves in weakly ionized argon, krypton, xenon, and neon glow discharge plasmas has been performed. For Mach numbers in the range 1.5 ‐3, our results show that there is an increase in the velocity of a shock wave when it makes a transition from a neutral gas to a weakly ionized plasma, and the effect increases with increasing atomic weight. The observations indicate that the shock acceleration cannot be accounted for by thermal effects. However, the useof turbulence models based on reduced kinetic theory and second-order phase transitions suggests a consistent role for turbulence in plasma-induced hypersonic drag reduction.

Computer modeling of electrical breakdown in a pulsed dielectric barrier discharge in xenon

Computer modeling of the plasma kinetics in a short-pulse excited dielectric barrier discharge in Xe has been used to simulate the spatial-temporal evolution of the homogeneous plasma during the electrical breakdown phase. The breakdown coincides with the development of a streamer-like ionization wavefront propagating toward the cathode at /spl sim/10/sup 5/ ms/sup -1/.

A flat glow discharge excimer radiation source

Increasing the current of a microhollow cathode discharge in high-pressure xenon allowed us to generate disc-shaped 100- to 150-/spl mu/m-thick plasma layers on the planar cathode of a microhollow electrode system, with diameters approaching 1 cm. The plasma layer has been found to emit intense excimer radiation at 172 nm. The maximum of the excimer emission shifts with increased current toward the perimeter of the plasma disc, and the spectral distribution in the area close to the cathode hole changes from vacuum ultraviolet to visible. Plasma filaments, radiating in the visible, are formed which extend from the center to the perimeter of the disc shaped plasma. They correspond to areas of reduced excimer emission, indicating a transition from nonthermal to thermal plasma.

キセノン放電管における拡散陽光柱の形成条件

キセノン放電管における拡散陽光柱の形成条件

Study of Xenon Discharges for 147 nm Emission

A xenon discharge for 147 nm vacuum ultraviolet (VUV) emission was studied. The discharge was enclosed in a tube of diameter 12 mm with length of 40 mm, which was excited by RF electrodeless discharge (120 MHz). At one end of the tube, an MgF2 monocrystal disc is sealed as a VUV output window. Its axial VUV radiance is experimentally measured by a pre-calibrated VUV spectral detecting system at various xenon pressures. Its VUV output characteristics are also theoretically studied using a computational model with 10 atomic levels. It is found that the maximum axial VUV radiance (about 8.9 W Sr-1 m-2, i.e. 6.6 × 1018 photons Sr-1 m-2 s-1) was reached at a xenon pressure of about 40 Pa. The theoretical and experimental results are compared. The column VUV efficiency is estimated to be 42%.

Xenon capillary discharge extreme-ultraviolet source emitting over a large angular range

We describe a capillary discharge source configuration, allowing for collection of extreme-ultraviolet (EUV) radiation at large off-axis angles, without the need for an EUV window. Operating with xenon gas, the source emits intensely within the EUV spectral region at 11.3 and 13.5 nm. When coupled with a high-collection-efficiency optical system, this source may be suitable for a number of high-average-power EUV imaging applications.

The b-wave of the dark adapted flash electroretinogram in patients with advanced asymmetrical glaucoma and normal subjects

AIMSTo evaluate whether the b-wave of the dark adapted flash electroretinogram (ERG) is affected by glaucomatous damage.METHODSERGs were recorded in 35 patients aged 33–65 years with advanced asymmetrical glaucomas (interocular...

Numerical simulation of a barrier discharge in Xe

Components of plasma of a barrier discharge in xenon are calculated for various values of the parameter E/N. Features of excimer population are analyzed. Efficiencies of the VUV emission yield are calculated, and basic channels of energy loss determining the efficiency are established.

Energy loss mechanisms in the microdischarges in plasma display panels

Low luminous efficacy is one of the major drawbacks of plasma display panels (PDPs), where the main limiting factor is the efficiency of the microdischarges in generating UV radiation. In this work we use a two-dimensional self-consistent fluid model to analyze the energy loss mechanisms in neon–xenon discharges in coplanar-electrode color PDPs and interpret experimental data on the luminous efficacy of these PDPs. The modeling results are in good agreement with the measured UV emission spectrum and measured trends in the efficacy. Most of the electrical input energy is transferred to ions and subsequently to the gas and the surface. The electrical energy transferred to electrons is mostly used for ionization and excitation, where the part used for xenon excitation largely ends up in UV radiation. The amplitude, frequency, and rise time of the driving voltage mainly affect the energy losses due to ion heating. The xenon content also affects the conversion of electron energy into UV energy.

キセノン放電管の陽光柱状態に及ぼす電流休止期間の影響

キセノン放電管の陽光柱状態に及ぼす電流休止期間の影響

One Dimensional Self-consistent Model for Xenon Dielectic Barrier Discharge (DBD)

A one-dimensional self-consistent numerical model for dielectric barrier discharge (DBD) in Xenon is presented. Continuity equations for charged particles, rate equations for excited particles and Poisson's equation are solved. Electrons, ions, excited atoms and excimer density distributions in space and time are simulated in the model. Electrical parameters in a micro-discharge such as electric field, voltage across the gas gap, current density and accumulated charges on both dielectric surfaces are obtained. UV radiation intensities and their efficiencies in a micro-discharge are calculated.

Electron excitation coefficients for 2p and 3p levels of Xe

Electron excitation rate coefficients for 2p (2p1, 2p2, 2p3, 2p4, 2p5, 2p6) and 3p(3p5, 3p6, 3p7, 3p8, 3p10) (in Paschen notation) levels of xenon atom have been measured by using electron drift tube technique. The absolute excitation coefficients were obtained from the optical signal at the anode in Townsend xenon discharges, after correction for detector quantum efficiency. The ionization coefficients were determined from the spatial emission profile. The measurement were made for the electric field to xenon atom number density ratios (E/N) from Vm2 to Vm2. The data were obtained between moderate E/N values where electrons are in equilibrium and very high E/N values where electrons may not be in equilibrium with the local field. It was found that at the highest values of E/N heavy particles do not contribute to the excitation under the present conditions. The absolute excitation coefficients for the studied levels of xenon are to our knowledge the only experimental data available in the literature.

Comparative measurement of electron density and temperature profiles in low-temperature ECR discharges by a lithium atom beam and Thomson scattering

In this paper a method to determine spatially-resolved profiles of the electron temperature Te and density ne in an electron-cyclotron-resonance (ECR) discharge is presented. This technique is based on the observation of line emission from a neutral Li atom beam, which is injected into the plasma and excited by electron collisions. A collisional-radiative model valid for the injected Li atoms is used to predict the emission intensities as function of ne and Te for several lines theoretically. In contrast to the electron temperature regime representative for the edge of tokamak discharges (Te>5 eV), the ECR discharge offers a Te range where selected line intensity ratios strongly depend on the electron temperature. Therefore, a comparison of the measured ratios with the calculated ones yields Te profiles for the first time. The ne measurement is performed as in tokamaks by observing the attenuation of the beam due to ionization in the plasma. We present radial profiles of Te and ne for discharges in argon and xenon under different operating conditions. These results are compared with results obtained by Thomson scattering. Our measurements give evidence for a satisfying agreement between the two methods.

VUV Radiation of Afterglow Generated by Pulsed Discharge of Xenon.

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes and of xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. In both cases, that is, inner electrode type and external electrode type, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the VUV radiation of xenon excimers. The emission of light from phosphor shows that xenon excimers are generated effectively by pulsed discharge of high pressure xenon, because they are generated by three-body collision at the low electron temperature Te during the non-discharge period.