Plasmas generated by ultra-violet light rather than electron impact

Franklin, R N; Allen, J. E.; Thomas, D. M.; Benilov, M. S.

doi:10.1063/1.4848715

Cited by 5 publications

(14 citation statements)

References 6 publications

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“…An approximate analytical solution in the limiting case of small λ D found by means of the method of matched asymptotic expansions is reported in this paper, which is thus complementary to [1]. Also reported are results of numerical calculations for different values of λ D .…”

Section: Introductionsupporting

confidence: 60%

“…In the first part of this work [1] a collisionless plasma, generated by UV illumination localized in a central part of the plasma, was analyzed. The ions were assumed to be cold and the fluid description was used.…”

Section: Introductionmentioning

confidence: 99%

“…The quasi-neutral analytical solution [1], while clearly being useful, does not describe the double layer, hence a more sophisticated treatment is needed in order to fully understand this feature and the underlying physics. It is clear that this feature originates in the smallness of λ D , therefore the relevant procedure is to find an asymptotic solution to the considered problem in the limiting case of small λ D .…”

Section: Introductionmentioning

confidence: 99%

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Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

Benilov

Thomas

2014

Physics of Plasmas

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The method of matched asymptotic expansions is applied to the problem of a collisionless plasma generated by UV illumination localized in a central part of the plasma in the limiting case of small Debye length λ D . A second-approximation asymptotic solution is found for the double layer positioned at the boundary of the illuminated region and for the un-illuminated plasma for the plane geometry. Numerical calculations for different values of λ D are reported and found to confirm the asymptotic results. The net integral space charge of the double layer is asymptotically small, although in the plane geometry it is just sufficient to shield the ambipolar electric field existing in the illuminated region and thus to prevent it from penetrating into the un-illuminated region. The double layer has the same mathematical nature as the intermediate transition layer separating an active plasma and a collisionless sheath, and the underlying physics is also the same. In essence, the two layers represent the same physical object: a transonic layer.speed. In cylindrical geometry, the ions continue to be accelerated in the un-illuminated region and enter the near-wall space-charge sheath with a speed significantly exceeding the Bohm speed. In both geometries, a double layer forms where the illuminated and un-illuminated regions meet.A very unusual, if not unique, feature that this simple system reveals in plane geometry is the coexistence of two quasi-neutral plasmas of the same size with the ambipolar electric field being confined in one of them (the illuminated plasma), while the other (the un-illuminated plasma) is to high accuracy electric field-free and uniform. The latter is particularly surprising since in all known models a near-wall space-charge sheath is bordered by a nonuniform quasi-neutral presheath where the ions going to the sheath are accelerated and the voltage drop is of the order of the electron temperature measured in volts. (We set aside cases where the ions are produced on the surface, as in Q-machines or experiments with heated cavities [2], or inside the sheath, as in near-cathode layers of discharges burning in cathode vapour [3].) Moreover, the difference between illuminated and un-illuminated regions in terms of ion momentum is in the presence or absence of ionization friction force, and the fact that the ion fluid is accelerated in the illuminated plasma, where the ionization friction force is present, and is not accelerated in the un-illuminated plasma, where the friction force is absent, is somehow counterintuitive.The above feature is extremely interesting, also from the methodological point of view; note that the classical Bohm sheath solution [4] is sufficient to describe both the sheath and the adjacent (un-illuminated) plasma in such situation. A key to this feature is the double layer, which shields the ambipolar electric field induced in the illuminated region and prevents it from penetrating the un-illuminated region.The quasi-neutral analytical solution [1], while clearly being useful, do...

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Section: Introductionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

Benilov

Thomas

2014

Physics of Plasmas

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“…In two recent papers we have presented models of a plasma split into two regions of equal width, with ionization by ultraviolet light taking place only in the inner region and not in the outer 1,2 . At the interface between the two regions a double layer was formed, the ion velocity entering the outer plasma being greater than the Bohm (or ion-acoustic) velocity.…”

Section: Introductionmentioning

confidence: 99%

Cylindrical plasmas generated by an annular beam of ultraviolet light

Thomas

Allen

2015

Physics of Plasmas

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We investigate a cylindrical plasma system with ionization, by an annular beam of ultraviolet light, taking place only in the cylinder’s outer region. In the steady state, both the outer and inner regions contain a plasma, with that in the inner region being uniform and field-free. At the interface between the two regions, there is an infinitesimal jump in ion density, the magnitude approaching zero in the quasi-neutral (kD ! 0) limit. The system offers the possibility of producing a uniform stationary plasma in the laboratory, hitherto obtained only with thermally produced alkali plasmas

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“…Electron emission plays an important role in the physics of plasma-surface interactions and it is a central element to many plasma related applications and phenomena. Some of these include emissive probes, 1 plasma diodes, 2 plasmas generated with UV light, 3 the study of electrical arcs, 4,5 and fusion reactors. 6 Also within the extreme space environment, electron emission is an important element for a host of phenomena and applications.…”

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confidence: 99%

Electron emission in a source-collector sheath system: A kinetic study

et al. 2014

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The classical source-collector sheath system describes a plasma that forms between a Maxwellian source and an absorbing wall. The plasma is assumed to be collisionless and without ionization. Two distinct areas are being formed: the collector sheath, an ion-rich region in contact with the absorbing boundary, and the source sheath, which is an electron-rich area near the Maxwellian source. In this work, we study a modified version of the classical source-collector sheath system, where the wall is no longer absorbing but emits electrons. As a result, we have two different types of collector sheath, one where a potential well is formed and one without a potential well. We examine the effect of electron emission for a range of conditions for the plasma and the emitted electrons. In the first part of this work, we study the problem analytically, and in the second, using our kinetic Vlasov code, Yggdrasil. The simulation results are in very good agreement with the predictions of our theoretical model. V C 2014 AIP Publishing LLC.

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Plasmas generated by ultra-violet light rather than electron impact

Cited by 5 publications

References 6 publications

Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

Cylindrical plasmas generated by an annular beam of ultraviolet light

Electron emission in a source-collector sheath system: A kinetic study

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