Analytic model of the current-voltage characteristic of a small probe in a magnetic field

Rozhanskii, V. A.; Ushakov, A. A.

doi:10.1134/1.1262296

Cited by 8 publications

(15 citation statements)

References 4 publications

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“…For this reason, MIGRAINe simulations were run using an updated collection model which targets dense magnetized plasmas in the regime λ De , R Le R d R Li , with R d the dust/droplet radius, and is described extensively in [19]. Electron collection is based on a fluid model version of Sanmartin's kinetic model [36,37], which first demonstrated the existence of a potential hill structure along the magnetic flux tube intersecting the collecting body and explored the transition between OML-like exponential dependences at large negative droplet potentials and Bohm's electron saturation for positive potentials [38]. Ion collection is treated in the thin-sheath regime, in which finite sheath thickness is accounted for by combining theoretical work by Lam [39] and numerical simulations by Laframboise [40].…”

Section: Collection Of Plasma Speciesmentioning

confidence: 99%

Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

et al. 2018

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The motion and temperature evolution of beryllium droplets produced by first wall surface melting after ITER major disruptions and vertical displacement events mitigated during the current quench are simulated by the MIGRAINe dust dynamics code. These simulations employ an updated physical model which addresses droplet-plasma interaction in ITER-relevant regimes characterized by magnetized electron collection and thin-sheath ion collection, as well as electron emission processes induced by electron and high-Z ion impacts. The disruption scenarios have been implemented from DINA simulations of the time-evolving plasma parameters, while the droplet injection points are set to the first-wall locations expected to receive the highest thermal quench heat flux according to field line tracing studies. The droplet size, speed and ejection angle are varied within the range of currently available experimental and theoretical constraints, and the final quantities of interest are obtained by weighting single-trajectory output with different size and speed distributions. Detailed estimates of droplet solidification into dust grains and their subsequent deposition in the vessel are obtained. For representative distributions of the droplet injection parameters, the results indicate that at most a few percents of the beryllium mass initially injected is converted into solid dust, while the remaining mass either vaporizes or forms liquid splashes on the wall. Simulated in-vessel spatial distributions are also provided for the surviving dust, with the aim of providing guidance for planned dust diagnostic, retrieval and clean-up systems on ITER.

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Section: Collection Of Plasma Speciesmentioning

confidence: 99%

Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

et al. 2018

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“…This effect may be caused by the I -V characteristic not strictly following an exponential dependence, as predicted e.g. by Rozhanski [27].…”

Section: Tangent Methodsmentioning

confidence: 71%

On the applicability of three and four parameter fits for analysis of swept embedded Langmuir probes in magnetised plasma

et al. 2022

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The problem of power exhaust is one of the grand challenges of nuclear fusion research today. In order to understand the physics phenomena occurring in the scrape-off layer and the divertor regions of tokamaks, it is essential to correctly determine the divertor plasma parameters, which are often measured by swept Langmuir probes. While the construction and operation of this diagnostic can be straightforward, the data analysis using 3- or 4-parameter fits presents a challenge and can potentially lead to erroneous values of electron temperature and ion saturation current. In this work, we present modelling and experiments aimed at determination of conditions for proper analysis of swept Langmuir probes using these two fitting models. Particle-in- cell modelling was employed to evaluate the sheath-expansion effects for particular probe geometry and plasma conditions, yielding a semi-empirical rule capable of predicting its magnitude. Experiments with unusually wide range of swept voltage in the divertor of the COMPASS tokamak explored the magnitude of voltage range required for successful analysis with either three or four-parameter fitting. With the use of our new semi-empirical rule, it is possible to improve the four-parameter fit reliability in situations where the available voltage range is limited. In addition, we introduce the tangent method - an independent and fast method of electron temperature estimation, which allows to reliably determine the available voltage range and as such assist the more complex method of probe analysis.

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“…e Bohm e 0 d e i e which was found to remain valid in later generalizations to fully ionized plasmas [17][18][19]. Note that the somewhat counter-intuitive scaling of this current, with R d instead of R d 2 , is linked to the diffusive nature of electron transport far from the dust grain.…”

Section: Overview Of Existing Probe Modelsmentioning

confidence: 68%

“…The description of electron collection is based on an algebraic version of Sanmartin's kinetic model [17][18][19], whereas the description of ion collection is based on a reformulation of Lam's model [20], guided by Laframboise's numerical results [21], in the presence of a potential overshoot. Simulations for ITER-like detached divertor plasmas with the proposed model reveal a drastic increase in the lifetime of tungsten dust and a moderate increase in the lifetime of beryllium dust compared to the OML predictions.…”

Section: Introductionmentioning

confidence: 99%

Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas

Vignitchouk¹,

Ratynskaia²,

Tolias

2017

Plasma Phys. Control. Fusion

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A comprehensive analytical description is presented for the particle and heat fluxes collected by dust in dense magnetized plasmas. Compared to the widely used orbital motion limited theory, the suppression of cross-field transport leads to a strong reduction of the electron fluxes, while ion collection is inhibited by thin-sheath effects and the formation of a potential overshoot along the field lines. As a result, the incoming heat flux loses its sensitivity to the floating potential, thereby diminishing the importance of electron emission processes in dust survivability. Numerical simulations implementing the new model for ITER-like detached divertor plasmas predict a drastic enhancement of the dust lifetime.

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Analytic model of the current-voltage characteristic of a small probe in a magnetic field

Cited by 8 publications

References 4 publications

Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

Survival and in-vessel redistribution of beryllium droplets after ITER disruptions

On the applicability of three and four parameter fits for analysis of swept embedded Langmuir probes in magnetised plasma

Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas

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