Spectroscopic models for the characterization of energetic particle beams in tokamak edge plasmas

Abstract

We examine the possibility for a diagnostic of energetic particle beams based on passive spectroscopy, with a focus on the atomic lines observed in the edge region of tokamaks. Our investigation employs a quasi‐linear model for the collective electric field generated by the plasma‐beam instability. If the beam is sufficiently energetic, the electric field can be comparable to the thermal Holtsmark microfield, and the corresponding Stark effect on atomic energy levels can be observable on spectra. We investigate this issue and perform new hydrogen line shape calculations. The applicability of the model to the diagnostics of runaway electrons is discussed.

Possible spectroscopic signature of wave collapse in edge plasmas

“…This would be relevant if the edge plasma is interacting with a beam of energetic runaway electrons. [7] Runaway electrons have a long lifetime in a large tokamak like ITER and we conjecture that an interaction of the electron beam with the edge plasma locally creates wave collapse conditions which can be observed by spectroscopy. The paper is organized as follows: We present in section 2 the main features of wave collapse useful for plasma spectroscopy.…”

“…In the following, we use a ratio of the wave energy density to the plasma thermal energy density of the order of 1, which implies that a large amount of energy has been transferred to the wave packets. This would be relevant if the edge plasma is interacting with a beam of energetic runaway electrons . Runaway electrons have a long lifetime in a large tokamak like ITER and we conjecture that an interaction of the electron beam with the edge plasma locally creates wave collapse conditions which can be observed by spectroscopy.…”

A Coulomb collision model for weighted particle simulations with energy and momentum conservation

“…The rejection model has been applied, for example, to the collision of alpha particles in a DT (deuterium-tritium) burning plasma under inertial confinement. [7] This model, however, can be difficult to use for a plasma including high-Z impurities (Za > 50) with very small w a /w b < 10 −3 . A heavier-weight electron is affected by a collision with a high-Z impurity only very rarely.…”

Addressing the effect of oscillating electric fields on Stark profiles by computer simulations

“…They may also be created inside the plasma, resulting from a nonthermal effect driven by a plasma instability. For this case a current interest is the diagnostic of energetic particle beams in tokamak edge plasmas, with the potential use of line shape changes [1] due to the generated Langmuir waves. The effect of oscillating fields on spectral line shapes has been studied since several decades by using approaches based on kinetic theory and retaining the quantum effects of the emitting particles [2,3,4].…”