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Articles With Citations to Z. Abou-Assaleh

Theoretical Plasma Physics

Controlled Thermonuclear Fusion Energy

2005

Journal of Nuclear Materials
Volumes 337-339 , 1 March 2005, Pages 246-250

"Modification of atomic physics rates due to nonlocal electron parallel heat transport in divertor plasmas"

F. Allais^a, , J.P. Matte^{a, ,} , F. Alouani-Bibi^a, C.G. Kim^a, D.P. Stotler^b and T.D. Rognlien<sup>c

a</sup>INRS-Énergie, Matériaux et Télécommunications, 1650 boul. Lionel Boulet, Varennes, Québec, Canada J3X 1S2
^bPrinceton Plasma Physics Laboratory, Princeton, NJ, USA
^cLawrence Livermore National Laboratory, Livermore, CA, USA

Abstract

The effect of steep temperature gradients on the rate of ionization of atomic hydrogen is studied numerically with the electron kinetic code ‘FPI’ [Phys. Rev. Lett. 72 (1994) 1208]. A set of cross sections [‘Atomic and Plasma-Material Interaction data for fusion’. Supplement to the journal Nucl. Fusion 4 (1993)] has been used which gives the same rates of radiation, ionization and recombination as in the well known edge modeling codes ‘UEDGE’ and ‘DEGAS’ for Maxwellian electron energy distribution functions. For this purpose, 30 energy levels are included in the computation, as stepwise ionization is dominant. The enhancement of the ionization rate by non-Maxwellian effects in the colder part of the plasma is significant.

Keywords

Collisional radiative model; Divertor modelling; Kinetics effects; Parallel transport; UEDGE

doi:10.1016/j.tsf.2005.08.114 

Thin Solid Films
Volumes 506-507 , 26 May 2006, Pages 674-678
The Joint Meeting of 7th APCPST (Asia Pacific Conference on Plasma Science and Technology) and 17th SPSM (Symposium on Plasma Science for Materials) - 7th APCPST/17th SPSM

"Ion flow and sheath physics studies in multiple ion species plasmas using diode laser based laser-induced fluorescence"

G.D. Severn^{1, a,}, Xu Wang^b, Eunsuk Ko^b, N. Hershkowitz^b, M.M. Turner^c and R. McWilliams<sup>d

a</sup>Department of Physics, University of San Diego, San Diego, CA 92110, USA
^bEngineering Physics Department, University of Wisconsin-Madison, Madison, WI 53706, USA
^cNational Center for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9, Ireland
^dDepartment of Physics and Astronomy, University of California, Irvine, CA 92049, USA

Abstract

Diode lasers have proved to be a valuable light source for laser-induced fluorescence (LIF) measurements for plasma science since the early 1990s, and they have recently improved the state of the art of measuring ion flow from ion velocity distribution functions (ivdfs) at the sheath–presheath boundary in single and multiple ion species plasmas. In the case of a low temperature two ion species plasma (ArI + HeI), we were the first to show experimentally that ion species may reach the sheath edge flowing at a very different speed than that expected from the single species Bohm Criterion (ArII ions exceed the individual Bohm flow speed by almost a factor of 2 at the sheath edge). Simulation results are found to agree. Diode laser technology relevant to LIF measurements in multiple ion species plasmas is discussed with the aim of addressing outstanding problems in sheath formation in such plasmas.

W Fundamenski 2005 Plasma Phys. Control. Fusion 47 R163-R208  

doi:10.1088/0741-3335/47/11/R01

"Parallel heat flux limits in the tokamak scrape-off layer"

W Fundamenski
Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, UK

Abstract

It is well known that the classical Spitzer–Harm–Braginskii expression for the parallel plasma heat flux breaks down in the long mean free path limit, relevant to many practical applications, most crucially power exhaust via the tokamak scrape-off layer (SOL). This problem is usually addressed by limiting the heat flux to some fraction of the free streaming value, with constants of proportionality α_σ, where σ ∈ {e,i}, ranging from 0.03 to 3. The following paper presents a brief overview of the problem, compares the results of various kinetic studies, suggests the optimal values of α_σ for use in plasma–fluid codes, and examines the impact of these values on 2D SOL simulations using the EDGE2D transport code. In this context, gyro-kinetic parallel heat flux expressions for both electrons and ions are derived from the generalized transport equations—an improved version of Grad's 21-moment approach—and their implications to tokamak modelling are discussed.

Print publication: Issue 11 (November 2005)
Received 6 December 2004, in final form 28 July 2005
Published 5 October 2005

http://www.iop.org/EJ/abstract/0741-3335/47/11/R01/

http://ej.iop.org/links/rTqyxnIWm/

SnTZP6Wg2xGkAZxsav5vpA/psst5_1_022.pdf

"Scrape-off layer physics: an introduction"

Ralf Schneider,

Max-Planck-Institut f¨ur Plasmaphysik, EURATOM association, Garching, Germany

http://www.ipp-garching.mpg.de/~dpc/rfs.pdf

Phys. Plasmas 12, 063104 (2005)

Supersonic propagation of ionization waves in an underdense, laser-produced plasma

C. Constantin, C. A. Back, K. B. Fournier, G. Gregori, O. L. Landen, S. H. Glenzer, and E. L. Dewald

Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550

M. C. Miller

Los Alamos National Laboratory, Los Alamos, New Mexico 87545

(Received 11 November 2004; accepted 8 April 2005; published online 6 June 2005)

Abstract

A laser-driven supersonic ionization wave propagating through a millimeter-scale plasma of subcritical density up to 2–3  keV electron temperatures was observed. Propagation velocities initially ten times the sound speed were measured by means of time-resolved x-ray imaging diagnostics. The measured ionization wave trajectory is modeled analytically and by a two-dimensional radiation-hydrodynamics code. The comparison to the modeling suggests that nonlocal heat transport effects may contribute to the attenuation of the heat-wave propagation. ©2005 American Institute of Physics

L Oksuz et al 2005 Plasma Sources Sci. Technol. 14 201-208

Plasma, presheath, collisional sheath and collisionless sheath potential profiles in weakly ionized, weakly collisional plasma

L Oksuz and N Hershkowitz
Department of Engineering Physics, University of Wisconsin-Madison, USA

Received 30 September 2003
Published 7 February 2005
Print publication: Issue 1 (February 2005)

Abstract

Potential variations in bulk plasma, presheath and sheath describe the plasma potential profile responsible for ion acceleration out of weakly ionized, weakly collisional plasma. Experiments with emissive probes, Langmuir probes, laser induced fluorescence (LIF) and Mach probes in a multi-dipole plasma show that the presheath potential near a negatively biased plate scales as and is insensitive to the value of the plate bias. Plasma parameters were chosen so that ε = λ_D/λ 0.02 → 0.06 and 0.2 < λ/L <0.6, where λ is the ion–neutral mean free path, λ_D is the Debye length and L is the plasma length. A Child–Langmuir-like sheath with width scaling as λ_D(e/T_e)^3/4 with a T_e/λ_D initial boundary electric field has been measured. A transition region, in which the plasma starts to deviate from being quasi-neutral, is observed between the presheath and the Child–Langmuir sheath. The transition region is approximately 2λ_D or λ^1/5λ_d^4/5. Mach probe data, calibrated by LIF data, suggest that the average ion velocity reaches the Bohm velocity inside the transition region and significantly exceeds the Bohm velocity at the Child–Langmuir sheath/transition boundary.

doi:10.1088/0963-0252/14/1/022
URL: http://stacks.iop.org/0963-0252/14/201
PII: S0963-0252(05)93759-6

http://ej.iop.org/links/q38/g,

zrlJAHsg6q,iou3NUz1w/psst5_1_022.pdf

Presheath Environment in Weakly Ionized Single and Multispecies ...

Presheath environment in weakly ionized single and multispecies plasmas

Hershkowitz, N.   Ko, E.   Xu Wang   Hala, A.M.A.  
Center for Plasma-Aided Manuf., Univ. of Wisconsin, Madison, WI, USA

This paper appears in: Plasma Science, IEEE Transactions on
Publication Date: April 2005
Volume: 33,  Issue: 2, Part 2
On page(s): 631- 636
ISSN: 0093-3813
INSPEC Accession Number: 8398049
Digital Object Identifier: 10.1109/TPS.2005.844608
Posted online: 2005-04-18 09:10:46.0

Abstract

The presheath located near boundaries in weakly ionized plasmas is a rich environment in which charge exchange, and ion-ion streaming instabilities combine to establish the electric fields that accelerate ions to close to the Bohm velocity at the sheath/presheath boundary. Charge exchange sets the presheath scale length in weakly collisional plasma, in which ionization can be neglected. The transition of mobility limited ion flow near the bulk plasma to free fall motion close to the plate for single species plasmas is explored. Measurements in argon-helium multidipole plasmas of plasma potential with emissive probes and ion energy distribution functions with laser induced fluorescence are presented. These data show that the argon ions are speeded up by the presheath electric fields, argon ions are heated, and ion-ion instability is present as ions approach the boundary.

References

[14]   S. L. Gulick, B. L. Stansfield, Z. Abouassaleh, C. Boucher, J. P. Matte,.
T. W. Johnston, and R. Marchand, “Measurement of pre-sheath flow ve- ...
ieeexplore.ieee.org/iel5/27/30693/ 01420601.pdf?arnumber=1420601

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?tp

=&arnumber=1420601&isnumber=30693

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