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Articles With Citations to Z. Abou-Assaleh

Theoretical Plasma Physics

Controlled Thermonuclear Fusion Energy

2008

https://journals.aps.org/prl/abstract

/10.1103/PhysRevLett.100.175004

https://doi.org/10.1103/PhysRevLett.100.175004

Physical Review Letters

Experimental Investigation of the Plasma-Wall Transition

Tilmann Lunt, Gerd Fussmann, and Ole Waldmann

Phys. Rev. Lett. 100, 175004 – Published 2 May 2008

Tilmann Lunt¹, Gerd Fussmann^1,2, and Ole Waldmann²

1Humboldt-Universität zu Berlin, Institut für Physik, Newtonstr. 15, 12489, Berlin, Germany

2Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748 Garching, Germany

*tilmann.lunt@physik.hu-berlin.de

Abstract

We report on measurements of the ion velocity distribution as a function of distance to a target immersed in a magnetized argon plasma. Two situations are investigated: (a) practically the whole plasma streams onto a large target, and (b) the size of the target is significantly smaller than the plasma diameter. The Mach number M=u/cs decreases from M=1 at the target surface to values around 0.5 at a typical scale of λa=30  mm and λb=5  mm, respectively. In order to explain these small decay lengths, the measurements of case (a) are compared with a source-diffusion model and those of (b) to Hutchinson’s model. In (a) good agreement between modeling and experiment is obtained assuming a low neutral gas temperature. The data in (b) also agree excellently with modeled profiles, although the large fitting parameter D=20  m2/s indicates that other processes than diffusion contribute significantly to the transport.

DOI:https://doi.org/10.1103/PhysRevLett.100.175004

Präsident der Humboldt-Universität zu Berlin:

Prof. Dr. Dr. h.c. Christoph Markschies

Dekan der Mathematisch-Naturwissenschaftlichen Fakultät I:

Prof. Dr. Christian Limberg

Gutachter:

1. Prof. Dr. Gerd Fußmann

2. Prof. Dr. Uwe Schumacher

3. Dr. habil. Hans-Stephan Bosch

eingereicht am: 14.2.2008

Tag der mündlichen Prüfung: 17.7.2008

Abstract

In the present work the streaming behavior of a magnetized argon plasma impinging on a neutralizing surface was investigated. For that purpose the ion velocity distribution was measured non-invasively as a function of the distance to the surface by means of Laser Induced Fluorescence. The spatial resolution was typically
z = 0.5 mm. Two situations are investigated, (a): when practically the whole plasma streams onto a large target (? = 100 mm), and (b): when the size of the target (? = 15 mm) is significantly smaller than the diameter of the plasma column. In both cases the streaming velocity ui was at least as high as the ion acoustic sound speed, as already predicted by Bohm in 1949. Under fusion relevant conditions this is the first direct observation of the Bohm criterion. Approaching the target surface the Mach number M = u/cs increases from values of around 0.5 to 1 on typical scales of a = 30 mm and b = 5 mm, respectively. In order to explain these very short scale lengths the measured data were compared with a collisional-diffusive model in the case of (a) and with Hutchinson’s model[27] in the case of (b). A good agreement was achieved in (a) by assuming a very low neutral gas temperature of about 400 K. In (b) the model fits the data excellently when the transport coefficient is chosen as high as D = 20 m2/s. Such a high transport cannot be caused solely by diffusion. Partly it is explained by finite gyro-radii effects, but presumably time dependent phenomena, like drift waves, play an important role. In addition the dependence on the angle between surface normal and B-field was investigated. The supersonic fluxes found in the immediate vicinity of the surface are described fairly well by the model developed by Chodura[10]. By contrast the size of the region, where Mach numbers greater one appear is significantly smaller than predicted.

Keywords:

plasma wall interaction, Bohm criterion, laser induced fluorescence, ion sensitive probes.

 

Bibliography

...

[23]  Gulick, S.L. ; Stansfield, B.L. ; Abou-Assaleh, Z. ; Boucher, C. ; Matte, J.P. ; Johnston, T.W. ; Marchand, R.: Measurement of pre-sheath flow velocities by laser-induced fluorescence. In: Journal of Nuclear Materials 176 & 177 (1990), December, 1064–1069.

....

http://www.iop.org/EJ/abstract/0963-0252/17/1/015012

Ion acoustic wave studies near the presheath/sheath boundary in a weakly collisional argon/xenon plasma

Lutfi Oksuz et al 2008 Plasma Sources Sci. Technol. 17 015012 (5pp)   doi:10.1088/0963-0252/17/1/015012

Lutfi Oksuz¹, Dongsoo Lee and Noah Hershkowitz
Department of Engineering Physics, University of Wisconsin at Madison, Madison, WI 53706, USA
¹ Present address: Department of Physics, Suleyman Demirel University, Isparta 32260, Turkey.

Abstract

Ion acoustic wave (IAW) phase velocities are measured near the sheath/presheath boundary in a weakly collisional argon/xenon plasma. Wave profiles versus position are measured using a boxcar averager with a gate width of 30 ns and CW excitation at 50 or 75 kHz. Variable gate delays allow measurement of details of the wave close to the boundary. It is shown that the phase velocity at the presheath/sheath boundary is approximately twice the phase velocity in the bulk plasma for both argon and argon/xenon plasmas, in agreement with a recent calculation (Lee D et al 2007 Phys. Rev. Lett. 99 155004). This result indicates each ion's drift velocity at the boundary is equal to the IAW phase velocity in the bulk plasma.

Print publication: Issue 1 (February 2008)
Received 28 August 2007, in final form 11 October 2007
Published 19 December 2007

References

[7]  Gulick S L, Stansfield B L, Abou-Assaleh Z, Boucher C, Matte J P, Johnston T W and Marchand R 1990 J. Nucl.

IOP PUBLISHING PLASMA SOURCES SCIENCE AND TECHNOLOGY

Plasma Sources Sci. Technol. 17 (2008) 015012 (5pp)

doi:10.1088/0963-0252/17/1/015012

Online at stacks.iop.org/PSST/17/015012

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