Asymmetry reversal of ion collection by mach probes in flowing unmagnetized plasmas

Ko, Eunsuk; Hershkowitz, N.

doi:10.1088/0741-3335/48/5/009

Cited by 9 publications

(5 citation statements)

References 20 publications

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“…They assumed the trajectory of ions near the negatively charged dust (grain) with a controlled Coulomb-like potential. They did not observe any asymmetry reversal as predicted by Hutchinson, [123], and as experimentally shown by Ko and Hershkowitz [124].…”

Section: Effect Of Negative Ions On Mp Analysissupporting

confidence: 67%

“…Hutchinson also extended his model with the non-zero Debye length calculation, which shows an unexpected reversal of the current ratio [123]. This has been observed in a recent experiment by Ko and Hershkowitz [124], where both a planar and a spherical probe are used for comparison. They found the reversal of the current ratio or more ion collection on the downstream side than the upstream side for low-density plasmas with a short Debye length.…”

Section: Pic Model-spherical Hutchinsonsupporting

confidence: 56%

“…As mentioned in the section for the PIC simulation (section 3.1.1), Ko and Hershkowitz [124] found the reversal T e /m i ) of a kinetic model [78], LIF measurements without drift (u = 0) [135,143].…”

Section: A the Lif Methodsmentioning

confidence: 78%

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Mach probes

Chung

2012

Plasma Sources Sci. Technol.

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A Mach probe (MP) is an electric probe system to deduce the plasma flow velocity from the ratio of ion saturation currents. Generally, a typical MP is composed of two directional electric probes located at opposite sides of an insulator, which is mostly used as a parallel MP, but there are other MPs such as perpendicular MP (PMP), Gundestrup probe (GP) or rotating probe (RP), and visco-MP (VMP), depending on the shape of the probe holder, location of different probes or the method of collecting ions. For the parallel MP (to be called simply an MP), the relation between the ratio of the upstream ion saturation current density (J up ) to the downstream (J dn ) and the normalized drift velocity (M ∞ = v d / √ T e /m i ) of the plasma has generally been fitted into an exponential form (R = J up /J dn ≈ exp[KM ∞ ]). For the GP or RP, with oblique ion collection, the relation becomesis the normalized perpendicular flow to the magnetic field, and θ is the angle between the magnetic field and the probe surface. The normalized drift velocity of flowing plasmas is deduced from the ratio (R m ) measured by an MP as M ∞ = ln[R m ]/K, where K is a calibration factor depending on the magnetic flux density, collisionality of charged particles and neutrals, viscosity of plasmas, ion temperature, etc. Existing theories of MPs in unmagnetized and magnetized flowing plasmas are introduced in terms of kinetic, fluid and particle-in-cell models or self-consistent and self-similar methods along with key physics and comments. Experimental evidence of relevant models is shown along with validity of related theories. Calibration and error analysis are also given. For probes other than the typical parallel MP, the relation between the ratio of ion saturation currents and M ∞ can be expressed as a combination of the functional forms: exponential and/or polynomial form of M ∞ for PMP; two Rs of two separate MPs for VMP. Collisions of ions/electrons/neutrals, asymmetries of ion temperatures and the existence of hyperthermal electrons, existence of ion beam, supersonic flow and negative ions can affect the deduction of flow velocities by an MP.

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Section: Effect Of Negative Ions On Mp Analysissupporting

confidence: 67%

Section: Pic Model-spherical Hutchinsonsupporting

confidence: 56%

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Mach probes

Chung

2012

Plasma Sources Sci. Technol.

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“…Drift velocity can be deduced from the ratio of upstream to downstream current (j + /j − = exp(Kv d /c s ), with K=1.34 for T i < 3T e [11]). Unmagnetized Mach probes have been shown to be reliable when the Debye length λ De is small relative to the probe size R p [12,13], which is the case in this experiment where λ De ≤ .04R p . The probe position is changed from shot-to-shot to measure the radial profile.…”

mentioning

confidence: 61%

Stirring Unmagnetized Plasma

et al. 2012

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A new concept for spinning unmagnetized plasma is demonstrated experimentally. Plasma is confined by an axisymmetric multicusp magnetic field and biased cathodes are used to drive currents and impart a torque in the magnetized edge. Measurements show that flow viscously couples momentum from the magnetized edge (where the plasma viscosity is small) into the unmagnetized core (where the viscosity is large) and that the core rotates as a solid body. To be effective, collisional viscosity must overcome the ion-neutral drag due to charge-exchange collisions.

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“…In laboratory magnetized plasmas, the directional Langmuir or Mach probe is a well-proven "in-situ" diagnostic tool to obtain the flow velocity [1,2]. However, in nonmagnetized or weakly magnetized plasmas, this method does not readily yield reliable velocity measurements, as it has been shown by numerical and experimental studies [3,4] that the collection of upstream ions to the rearward probe surface can be significant.…”

Section: Introductionmentioning

confidence: 99%

The role of sheath and acceptance angle in front of a retarding field energy analyzer for plasma flow analysis

Fredriksen

Miloch

Gulbrandsen

et al. 2011

2011 XXXth URSI General Assembly and Scientific Symposium

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Measurements of plasma flow are of key interest in a number of plasma environments and applications. In laboratory magnetized plasmas, the directional Langmuir or Mach probe is a well-proven "in-situ" diagnostic tool to obtain the flow velocity. However, in non-magnetized or weakly magnetized plasmas, this method does not readily yield reliable velocity measurements, as it has been shown by numerical and experimental studies that the collection of upstream ions to the rearward probe surface can be significant. In this study, we utilize the analysis of data from 3D PIC simulations of ion velocity distributions in the vicinity of a negatively biased object embedded in a collision-less, source-free plasma with and without flow. The simulations allow us to study how the grounded probe housing of a retarding field ion energy analyzer (RFEA) affects the distribution of ions and their collection at different angles with a flowing, electropositive plasma. Comparisons are carried out with RFEA measurements in an inductively coupled helicon plasma.

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Asymmetry reversal of ion collection by mach probes in flowing unmagnetized plasmas

Cited by 9 publications

References 20 publications

Mach probes

Mach probes

Stirring Unmagnetized Plasma

The role of sheath and acceptance angle in front of a retarding field energy analyzer for plasma flow analysis

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