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15 Mar 2006

Volume 99, Issue 6, Articles (06xxxx)

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Ion debris characterization from a z-pinch extreme ultraviolet light source

Erik L. Antonsen, Keith C. Thompson, Matthew R. Hendricks, Darren A. Alman, Brian E. Jurczyk, and D. N. Ruzic

J. Appl. Phys. 99, 063301 (2006); http://dx.doi.org/10.1063/1.2175471 (8 pages) | Cited 19 times

Online Publication Date: 21 March 2006

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An XTREME Technologies XTS 13-35 extreme ultraviolet (EUV) light source creates a xenon z pinch that generates 13.5 nm light. Due to the near x-ray nature of light at this wavelength, extremely smooth metal mirrors for photon collection must be employed. These are exposed to the source debris. Dissolution of the z-pinch gas column results in high-energy ion and neutral release throughout the chamber that can have adverse effects on mirror surfaces. The XTREME commercial EUV emission diagnostic chamber was designed to maximize diagnostic access to the light and particulate emissions from the z pinch. The principal investigation is characterization of the debris field and the erosive effects on optics present. Light emission from the z pinch is followed by ejection of multiply charged ions and fast neutral particles that make up an erosive flux to chamber surfaces. Attenuation of this erosive flux to optical surfaces is attempted by inclusion of a debris mitigation tool consisting of foil traps and neutral buffer gas flow. Characterization of the z-pinch ejecta is performed with a spherical sector energy analyzer (ESA) that diagnoses fast ion species by energy-to-charge ratio using ion time-of-flight (ITOF) analysis. This is used to evaluate the debris tool’s ability to divert direct fast ions from impact on optic surfaces. The ITOF-ESA is used to characterize both the energy and angular distribution of the direct fast ions. Xe+ up to Xe+4 ions have been characterized along with Ar+ (the buffer gas used), W+, Mo+, Si+, Fe+, and Ni+. Energy spectra for these species from 0.5 up to 13 keV are defined at 20° and 30° from the pinch centerline in the chamber. Results show a drop in ion flux with angular increase. The dominant species is Xe+ which peaks around 8 keV. Ion flux measured against buffer gas flow rate suggests that the direct fast ion population is significantly attenuated through increases in buffer gas flow rate. This does not address momentum transfer from scattered ions or fast neutral particles. These results are discussed in the context of other investigations on the effects of total particle flux to normal incidence mirror samples exposed for 1×107 pulses. The samples (Si/Mo multilayer with Ru capping layer, Au, C, Mo, Pd, Ru, and Si) were exposed to the source plasma with 75% argon flow rate in the debris mitigation tool and surface metrology was performed using x-ray photoelectron spectroscopy, atomic force microscopy, x-ray reflectivity, and scanning electron microscopy to analyze erosion effects on mirrors. These results are compared to the measured direct ion debris field.
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52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.50.Dg Plasma sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Tx Emission, absorption, and scattering of particles
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Nc Particle measurements

Spatial distribution of soft x-ray line emissions from aluminum plasma excited by a pair of femtosecond-laser pulses

Yasuaki Okano, Katsuya Oguri, Tadashi Nishikawa, and Hidetoshi Nakano

J. Appl. Phys. 99, 063302 (2006); http://dx.doi.org/10.1063/1.2180433 (4 pages) | Cited 3 times

Online Publication Date: 21 March 2006

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We measured the time-integrated, spatially resolved spectra of soft x rays emitted from laser-induced aluminum plasma to characterize its spatial features. The plasma was excited by an intense femtosecond-laser pulse with a controlled artificial prepulse at intensities of 9.9×1015 and 6.4×1014 W/cm2, respectively. The dependence of the spectra on the time intervals between the main pulse and the prepulse was obtained for delay times of 0–3 ns. The strongest emissions in soft x-ray range occurred in a narrow region less than 50 μm from the target surface. In contrast to the continuum spectrum, the prepulse technique causes the Al3+2p6−2p53s emission to extend more than 600 μm from the target surface. We showed that the line emission can be separated spatially from the other continuum component of the emission spectra and that the extension length increased with increases in the pulse-separation time.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Ph X-ray, γ-ray, and particle generation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Characterization of a channel spark discharge and the generated electron beam

Ya. E. Krasik, S. Gleizer, K. Chirko, J. Z. Gleizer, J. Felsteiner, V. Bernshtam, and F. C. Matacotta

J. Appl. Phys. 99, 063303 (2006); http://dx.doi.org/10.1063/1.2180453 (14 pages) | Cited 6 times

Online Publication Date: 22 March 2006

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We report on an experimental study of a channel spark discharge (CSD) and the generated electron beam. The CSD was operated at a discharge voltage Ud ⩽ 30 kV and a discharge current Id ⩽ 3.5 kA. The CSD system consists of a glass tube placed between a hollow cathode and a grounded anode electrode. The parameters of the CSD operation, the potential distribution along the glass tube, and the generated beam were studied by electrical, optical, and spectroscopic diagnostics in the Ar gas pressure range of P = 0.005–2 Pa. At P ≥ 0.5 Pa, electrons with energy ∼ eUd appeared prior to the start of the main CSD with a current amplitude ⩽ 10−4Id. These high-energy electrons are responsible for the initiation of the CSD inside the glass tube. The generation of the electron beam which was composed of low-energy electrons with a current amplitude up to 3 kA occurred during a fast fall in the discharge voltage. Decreasing the Ar gas pressure below 0.1 Pa allows one to increase significantly the beam duration and the part of the high-energy electrons in the beam, and to increase the efficiency of the electron beam generation up to 75%. The high-current CSD inside the glass tube is accompanied by the formation of a plasma consisting of protons, Ar II, Ar III, C II-IV, and O II-IV ions. The plasma electron density and temperature were found to be in the ranges of 1015–1016 cm−3 and 10-15 eV, respectively.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Dg Plasma sources
52.25.Tx Emission, absorption, and scattering of particles

Effect of ambient pressure on laser ablation and plume expansion dynamics: A numerical simulation

Zhaoyang Chen, Davide Bleiner, and Annemie Bogaerts

J. Appl. Phys. 99, 063304 (2006); http://dx.doi.org/10.1063/1.2182078 (9 pages) | Cited 16 times

Online Publication Date: 23 March 2006

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A comprehensive numerical model is applied to the study of the effect of ambient pressure in laser ablation, more specifically on the copper target heating, melting and vaporization, and the resulting plume expansion in the helium gas, as well as on plasma formation in the plume. Under the laser pulse condition investigated [5 ns full width at half maximum (FWHM) and 109 W/cm2 peak irradiance], the calculated results show that the characteristics of the surface temperature and the evaporation depth are very similar even when the ambient pressure varies greatly. The influence of the ambient pressure on the fraction of absorbed laser energy is also small. The maximum ablated material vapor density in the plume is influenced slightly by the different pressures. Before 40 ns, the maximum plume temperature for various ambient pressures is in the order of a few 104 K. However, the effect of ambient pressure on the plume length is quite large. A specific calculation for a Gaussian-shaped laser pulse with 6 ns FWHM and 2.76×109 W/cm2 peak irradiance is made. The calculated evaporation depth agrees well with the experimental data. Therefore, the model can be useful to predict trends in target and plume (plasma) characteristics, which are difficult to obtain experimentally for various ambient pressures.
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52.38.Mf Laser ablation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Radio frequency glow discharge source with integrated voltage and current probes used for evaluation of discharge parameters

L. Wilken, V. Hoffmann, and K. Wetzig

J. Appl. Phys. 99, 063305 (2006); http://dx.doi.org/10.1063/1.2182077 (13 pages) | Cited 5 times

Online Publication Date: 28 March 2006

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A radio frequency (rf) Grimm-type glow discharge source for the chemical analysis of solid samples, with integrated voltage and current probes, was developed. All elements of a plasma equivalent circuit are determined from the measured current-voltage characteristics. The procedure is based on the independent evaluation of the ion current and electron current region. The physical meaning of the parameters is investigated by comparisons with measurements from dc glow discharges. We found that the reduced rf current of the powered electrode is comparable to the reduced current in dc discharges. A formula is developed that corrects the reduced current due to gas heating. The sheath thickness at the powered rf electrode is evaluated and is between 75 and 1100 μm. The voltage of the bulk plasma is in the range 2–15 V, and the resistance is between 30 and 400 Ω. The bulk plasma consumes about 3% of the total power, and the reduced voltage is comparable to the reduced electrical field in the positive column of direct current discharges. The sheath voltage at the grounded electrode is in the range 25–100 V, the capacities are between 10 and 400 pF, and the resistances are in the range 100 Ω–5000 Ω. We also found invariants for the evaluated sheath parameters.
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52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
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