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1 Dec 2005

Volume 98, Issue 11, Articles (11xxxx)

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Simplified modeling of 13.5 nm unresolved transition array emission of a Sn plasma and comparison with experiment

J. White, P. Hayden, P. Dunne, A. Cummings, N. Murphy, P. Sheridan, and G. O’Sullivan

J. Appl. Phys. 98, 113301 (2005); http://dx.doi.org/10.1063/1.2128055 (12 pages) | Cited 29 times

Online Publication Date: 1 December 2005

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One key aspect in the drive to optimize the radiative output of a laser-produced plasma for extreme ultraviolet lithography is the radiation transport through the plasma. In tin-based plasmas, the radiation in the 2% bandwidth at 13.5 nm is predominantly due to 4d-4f and 4p-4d transitions from a range of tin ions (Sn7+ to Sn12+). The complexity of the configurations involved in these transitions is such that a line-by-line analysis is, computationally, extremely intensive. This work seeks to model the emission profiles of each ion by treating the transition arrays statistically, thus greatly simplifying radiation transport modeling. The results of the model are compared with experimental spectra from tin-based laser-produced plasmas.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Hollow cathode theory and experiment. I. Plasma characterization using fast miniature scanning probes

Dan M. Goebel, Kristina K. Jameson, Ron M. Watkins, Ira Katz, and Ioannis G. Mikellides

J. Appl. Phys. 98, 113302 (2005); http://dx.doi.org/10.1063/1.2135417 (9 pages) | Cited 18 times

Online Publication Date: 1 December 2005

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A detailed study of the spatial variation of plasma density, temperature, and potential in hollow cathodes using miniature fast scanning probes has been undertaken in order to better understand the cathode operation and to provide benchmark data for the modeling of the cathode performance and life described in a companion paper. Profiles are obtained throughout the discharge and in the very high-density orifice region by pneumatically driven Langmuir probes, which are inserted directly into the hollow cathode orifice from either the upstream insert region inside the hollow cathode or from the downstream anode-plasma region. A fast transverse-scanning probe is also used to provide radial profiles of the cathode plume as a function of position from the cathode exit. The probes are extremely small to avoid perturbing the plasma; the ceramic tube insulator is 0.05 cm in diameter with a probe tip area of 0.002 cm2. A series of current-voltage characteristics are obtained by applying a rapid sawtooth voltage wave form to the probe as it is scanned through the plasma at speeds of up to 2 m/s to produce the profiles with a spatial resolution of about 0.05 cm. At discharge currents of 10–25 A from the 1.5-cm-diameter hollow cathode, the plasma density inside the cathode is found to exceed 1014 cm−3, with the peak density occurring upstream of the orifice. The plasma potentials on axis inside the cathode are found to be in the 10–20 V range with electron temperatures of 2–5 eV, depending on the discharge current and gas flow rate. A potential discontinuity or double layer of less than 10 V is observed in the orifice region, and under certain conditions appears in the bright “plasma ball” in front of the cathode. This structure tends to change location and magnitude with discharge current, gas flow, and orifice size. A potential maximum proposed in the literature to exist in or near the cathode orifice is not observed. Instead, the plasma potential increases from the orifice exit both radially and axially over several centimeters to values of 5–10 V above the anode voltage. The potential and temperature profiles inside the cathode are insensitive to anode configuration changes that alter the discharge voltage at a given flow. Application of an axial magnetic-field characteristic of the cathode region found in ring-cusp ion thrusters increases the plasma density in the cathode plume, but does not significantly change the potential or temperature. Measurements of the plasma profiles and the internal cathode parameters for a hollow cathode operating at discharge currents of up to 25 A in xenon are shown and discussed.
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52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.40.Kh Plasma sheaths

Hollow cathode theory and experiment. II. A two-dimensional theoretical model of the emitter region

Ioannis G. Mikellides, Ira Katz, Dan M. Goebel, and James E. Polk

J. Appl. Phys. 98, 113303 (2005); http://dx.doi.org/10.1063/1.2135409 (14 pages) | Cited 17 times

Online Publication Date: 1 December 2005

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Despite their long history and wide range of applicability that includes electric propulsion, detailed understanding of the driving physics inside orificed hollow cathodes remains elusive. The theoretical complexity associated with the multicomponent fluid inside the cathode, and the difficulty of accessing empirically this region, have limited our ability to design cathodes that perform better and last longer. A two-dimensional axisymmetric theoretical model of the multispecies fluid inside an orificed hollow cathode is presented. The level of detail attained by the model is allowed by its extended system of governing equations not solved for in the past within the hollow cathode. Such detail is motivated in part by the need to quantify the effect(s) of the plasma on the emitter life, and by the need to build the foundation for future modeling that will assess erosion of the keeper plate. Results from numerical simulations of a 1.2-cm-diam cathode operating at a discharge current of 25 A and a gas flow rate of 5 SCCM show that approximately 10 A of electron current, and 3.45 A of ion current return back to the emitter surface. The total emitted electron current is 33.8 A and the peak emitter temperature is found to be 1440 K. Comparisons with the measurements suggest that anomalous heating of the plasma is possible near the orifice region. The model predicts heavy species temperatures as high as 2034 K and peak voltage drops near the emitting surface not exceeding 8 V.
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52.80.Hc Glow; corona
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
52.50.Gj Plasma heating by particle beams
52.65.-y Plasma simulation

Effect of metastables on a sustaining mechanism in inductively coupled plasma in Ar

Toshikazu Sato and Toshiaki Makabe

J. Appl. Phys. 98, 113304 (2005); http://dx.doi.org/10.1063/1.2137883 (3 pages) | Cited 17 times

Online Publication Date: 5 December 2005

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We numerically predicted the spatial distribution of Ar metastables in an inductively coupled plasma (ICP) source; this distribution may be an indicator of the behavior of long-lived neutral radicals in a reactive plasma. We investigated the effect of metastables on the sustaining mechanism in ICP in Ar. The predicted two-dimensional profile of Ar metastables agreed reasonably well with experimental results. The transition of the sustaining mechanism from direct ionization to stepwise ionization is found as a function of input power at 50 mTorr. In addition, a strong hysteresis of plasma density is predicted between the increasing and decreasing phases of the input power based on the stepwise ionization of Ar metastables in the ICP.
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52.25.−b
52.27.Cm Multicomponent and negative-ion plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Properties of the plasma channel in liquid discharges inferred from cathode local temperature measurements

B. Revaz, G. Witz, and R. Flükiger

J. Appl. Phys. 98, 113305 (2005); http://dx.doi.org/10.1063/1.2137460 (6 pages) | Cited 5 times

Online Publication Date: 6 December 2005

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The properties of the plasma channel at the cathode surface in a liquid discharge have been studied by means of temperature measurements and heat transfer numerical analysis. The studied discharge (current: 5 A; duration: 100 μs; gap: 10 μm) is typical of electrical discharge machining (EDM) in the semifinishing operation. The temperature information is obtained from two independent experiments: (1) microthermocouples patterned on the cathode, close to the discharge have been used to record the temperature variation caused by a single discharge with a high local resolution and large bandwidth; (2) the geometry of the resolidified layer, which gives the maximum extension of the melting point temperature isotherm, has been measured. These temperature data have then been compared to numerical simulation using inverse calculations allowing the experimental determination of two fundamental quantities of the discharge cathode interaction: (1) the power fraction transferred from the discharge to the sample, which was found to be close to 10% and (2) the exponent n of the power law expansion of the plasma channel rplasma∝tn, which is n = 0.2. The validity of the present analysis relies on the fact that the experimental temperature information is obtained for different values of the parameter rplasma/t02, where t02 is the characteristic time of the experiment.
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52.80.Wq Discharge in liquids and solids
52.70.Ds Electric and magnetic measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
02.60.Cb Numerical simulation; solution of equations

Radio-frequency power-assisted performance improvement of a magnetohydrodynamic power generator

Tomoyuki Murakami, Yoshihiro Okuno, and Hiroyuki Yamasaki

J. Appl. Phys. 98, 113306 (2005); http://dx.doi.org/10.1063/1.2138803 (7 pages) | Cited 11 times

Online Publication Date: 7 December 2005

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We describe a radio-frequency (rf) electromagnetic-field-assisted magnetohydrodynamic power generation experiment, where an inductively coupled rf field (13.56 MHz, 5.2 kW) is continuously supplied to the disk generator. The rf power assists the precise plasma ignition, by which the otherwise irregular plasma behavior was stabilized. The rf heating suppresses the ionization instability in the plasma behavior and homogenizes the nonuniformity of the plasma structures. The power-generating performance is significantly improved with the aid of the rf power under wide seeding conditions: insufficient, optimum, and excessive seed fractions. The increment of the enthalpy extraction ratio of around 2% is significantly greater than the fraction of the net rf power, that is, 0.16%, to the thermal input.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Kn Thermodynamics of plasmas

Ion energy distributions in a pulsed plasma doping system

S. Radovanov, L. Godet, R. Dorai, Z. Fang, B. W. Koo, C. Cardinaud, G. Cartry, D. Lenoble, and A. Grouillet

J. Appl. Phys. 98, 113307 (2005); http://dx.doi.org/10.1063/1.2136211 (8 pages) | Cited 8 times

Online Publication Date: 8 December 2005

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Discharge parameters in a pulsed dc plasma doping system have been studied using measurements of time-resolved ion energy distributions, relative ion density, plasma potential, and electron temperature in BF3 and Ar plasmas during active discharge and afterglow periods. Negative plasma potentials are observed when using a hollow cathode to create a plasma while implanting at ultralow energies (<500 eV). The kinetics of ion generation and decay in BF3 during the pulse on and off periods have been discussed.
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52.25.-b Plasma properties
52.70.Ds Electric and magnetic measurements
52.70.Nc Particle measurements
52.77.Dq Plasma-based ion implantation and deposition
52.80.Hc Glow; corona
52.50.Dg Plasma sources

Two-dimensional simulation of a low-current dielectric barrier discharge in atmospheric helium

Yuan Tao Zhang, De Zhen Wang, and Michael G. Kong

J. Appl. Phys. 98, 113308 (2005); http://dx.doi.org/10.1063/1.2140890 (6 pages) | Cited 9 times

Online Publication Date: 15 December 2005

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A two-dimensional computational study is presented to unravel radial structure of a dielectric barrier discharge in atmospheric helium when the gas voltage exceeds slightly the breakdown voltage and the discharge current is low to retain a repetitive dynamic pattern of one discharge event every half cycle of the applied voltage. Simulation results reveal that during each half cycle of the applied voltage gas breakdown occurs first in a central region around the electrode axis. After it is extinguished, a second breakdown is triggered in the boundary region near the radial edge of the two electrodes as confirmed by the dynamic evolution of the radial profile of the electric field, the current density and the charged particles. These predictions are consistent with relevant experimental observations in literature. It is also shown that an increase in the applied voltage or in the excitation frequency reduces the time delay between the two breakdown events and the difference between their corresponding current densities. This offers a route to improve the uniformity of atmospheric dielectric barrier discharges for their intended applications.
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52.80.-s Electric discharges
52.65.-y Plasma simulation
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.20.-j Elementary processes in plasmas
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