Diagnostics of fast dust particles in tokamak edge plasmas

Abstract

The use of electrostatic probes as a diagnostic tool of the dust particles in the tokamak edge plasmas is investigated. Probe measurements of electrostatic fluctuations in the scrape-off layer of the Frascati Tokamak Upgrade revealed that some features of the signals can be explained only by a local non-propagating phenomenon. These signal features are shown to be both in qualitative and quantitative agreement with ionization, and consequent extra charge collected by the probes, due to the impact of micrometre-sized dust at a velocity of the order of 10 km s−1. Electron microscope analysis of the probe surface yielded direct support for such an interpretation.

Modeling of velocity distributions of dust in tokamak edge plasmas and dust–wall collisions

“…However, recent analysis of probe data from the FTU tokamak suggests the presence of much faster particles with speed exceeding a few km/s. Such particles can produce spikes in the probe signal due to dust vaporization and ionization upon hypervelocity dust-probe collisions [6]. In this paper we analyze dust particle velocity distribution functions (VDFs) in different regions of a tokamak for various dust sizes using DUSTT code simulations.…”

Molecular dynamics simulations of interactions between energetic dust and plasma-facing materials

“…z-direction is the normal direction of PFM and x-and y-directions are perpendicular to it. According to the report from FTU, the velocity of dust particles can be over 10 km/s [29,30]. The mechanism is stated in Section 3.1.3.…”

“…It is possible the dust particle reach velocities much larger than typical velocities [29,30]. One possible solution to this phenomenon is that collision with smaller sized particles stochastically heated to very high energies by the instability resulting from dust change fluctuations.…”

Finite size effects in the static structure factor of dusty plasmas

“…: (8) It is clear that formulas (8) imply that there is no mutual penetration of the dust particles into each other and there is no intrusion of the electrons and protons of the buffer plasma into the dust particles which can only alter their charge already taken into account by introducing the parameter Z d . Note that unlike the Coulomb potential potentials (6) and (7), expressions (8) remain finite at the origin.…”

“…7 As a result, the dusty plasma is generated at the surface layer, which significantly affects the mechanical, physical, and chemical properties of the wall material. 8 Another problem to be tackled is the dusty plasma contamination appearing at plasma etching in electronics as well as at the production of thin films. 9,10 Levitating in the buffer plasma macroscopic dust particles readily absorb electrons due to their high mobility thereby acquiring a high negative charge in a very rapid rate.…”