H. Capes

Transport of neutral particles in turbulent scrape-off layer plasmas

The effect of turbulence on the transport of neutral species (atom, molecules) in plasmas is investigated. A stochastic model relying on a multivariate gamma distribution is introduced to describe turbulent fluctuations, and implemented in EIRENE. The effects of fluctuations on the neutral density and ionization source radial profiles are investigated. The role of temperature fluctuations is discussed in detail. Calculations with ITER scrape-off layer parameters are presented, and two distinct regimes with respect to the effects of temperature fluctuations are identified, depending on the far SOL mean temperature. Finally, the influence of fluctuations on impurity contamination is discussed.

Narrowing of Doppler spectral line shapes by correlated ion and electron temperature fluctuations

The influence of low-frequency temperature fluctuations on Doppler line shapes is investigated. It is shown that the line profile can be strongly narrowed if the fluctuations of ion and electron temperatures are correlated. This result shows that the widely used model retaining only velocity fluctuations in the analysis of Doppler lines might lead to misleading conclusions about turbulence level.

Stark broadening of high-members of the helium diffuse series in divertor plasmas

Stark profiles of high-members (n ≥ 7) of the helium triplet diffuse series 1s2p 3Po–1snd 3D are calculated for tokamak divertor conditions using dipole reduced matrix elements obtained with a hydrogenic approximation. It is shown that the so-called standard model of Stark broadening is particularly suited to the description of the isolated lines 1s2p 3Po–1snd 3D with n = 8–10. Applications to spectroscopic diagnostics in existing and future magnetic fusion-oriented devices like ITER are discussed.

Revisiting the Stark Broadening by fluctuating electric fields using the Continuous Time Random Walk Theory

Stark broadening of atomic lines in plasmas is calculated by modelling the plasma stochastic electric field using the CTRW approach [1,2]. This allows retaining non Markovian terms in the Schrodinger equation averaged over the electric field fluctuations. As an application we consider a special case of a non separable CTRW process, the so called Kangaroo process [3]. An analytic expression for the line profile is presented for arbitrary waiting time distribution functions. A preliminary application to the hydrogen Lyman α line is discussed.

Modeling of Line Shapes using Continuous Time Random Walk Theory

In order to provide a general framework where the Stark broadening of atomic lines in plasmas can be calculated, we model the plasma stochastic electric field by using the CTRW approach [1,2]. This allows retaining non Markovian terms in the Schrodinger equation averaged over the electric field fluctuations. As an application we consider a special case of a non separable CTRW process, the so called Kangaroo process [3]. An analytic expression for the line profile is finally obtained for arbitrary waiting time distribution functions. An application to the hydrogen Lyman α line is discussed.

Modeling of Hydrogen Line Shapes for the Diagnostic of ITER

The state of art of the line shape modeling techniques involved in tokamak edge plasma spectroscopy is reported, in the context of the preparation for ITER. Hydrogen spectra are calculated assuming a line‐of‐sight crossing a 2D‐plasma background obtained from numerical simulations. The Doppler, Zeeman and Stark effects are retained. Ion dynamics effects are accounted for by using the numerical simulation method. The possibility for a line shape‐based diagnostic of the ITER divertor plasma is examined through fittings of simulated spectra and comparison with the input plasma fields.

The effect of time ordering revisited

The effects of time ordering on line shapes are investigated for the dynamic ionic broadening of the Lyman alpha line in hydrogen plasmas. The difference between calculations with and without time ordering is calculated for an electric field created by a single particle, and for a thermal average over plasma configurations with moderate temperature and density.

On the Use of Spectral Lines Emitted by Carbon Ions for Plasma Diagnostics in Magnetic Fusion Devices

Profiles of the n = 5-6 ({lambda} = 4658 A) and n = 6-7(7726 A) lines emitted by Li-like carbon C{sup +3} ions have been computed for plasma conditions of tokamak and stellarator divertors (N{sub e} = 10{sup 19}-10{sup 21} m{sup -3}, Te = 1-10 eV). The broadening and profiles of these lines are proposed to be used for plasma diagnostic purposes in particular to crosscheck the validity of the plasma parameters determined from the CIV line intensities measured in JT-60U tokamak.

Zeeman‐Stark Profiles of Low‐n Hydrogen Lines in Near Impact Regime

Calculations of hydrogen Zeeman‐Stark line profiles are presented and discussed when the conditions for impact ion broadening are almost satisfied.