Modelling of VUV/XUV spectra from the JET Tokamak

Lawson, K.; Aggarwal, K. M.; Coffey, I.; Keenan, F. P.; Reid, R. H. G.; Zacks, J.; Contributors, Jet‐Efda

doi:10.1063/1.4707874

Cited by 1 publication

(6 citation statements)

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“…This also ensures that radiative cascading from higher levels, which increases somewhat the lower level populations, can be properly treated. For example, in the C IV population calculations, increases of ∼10% due to radiative cascading are typical (Lawson et al 2008).…”

Section: IIImentioning

confidence: 99%

“…Even in the low density model, radiative cascading from higher levels should be included. Lawson et al (2008), who compared theoretical and modelled carbon line intensity ratios, find that this can lead to a ∼10% increase in certain C IV excited level populations.…”

Section: Introductionmentioning

confidence: 99%

“…The importance of recombination in the main chamber scrape-off-layer (SOL) is less clear, since there is a lack of consistency between theory and measurements. This suggests that the collisional-radiative model used to describe this plasma region is incomplete or that there is some other aspect of the analysis which is not understood (Lawson et al 2012). Certainly, recombination (free electron or charge exchange) does not explain the observed disagreement and its inclusion tends to make the discrepancy worse (Lawson et al 2008).…”

Section: Introductionmentioning

confidence: 99%

“…This suggests that the collisional-radiative model used to describe this plasma region is incomplete or that there is some other aspect of the analysis which is not understood (Lawson et al 2012). Certainly, recombination (free electron or charge exchange) does not explain the observed disagreement and its inclusion tends to make the discrepancy worse (Lawson et al 2008). Indeed, ionization might be expected to be the more important process in the main chamber SOL.…”

Section: Introductionmentioning

confidence: 99%

“…This is indeed consistent with the steady-state divertor measurements of . Nevertheless, Lawson et al (2012) found evidence that this may not always be the case, particularly during transient events such as an impurity influx, which may even affect C excited level populations within the divertor. The study of transient events is of particular interest in impurity transport modelling.…”

Section: Introductionmentioning

confidence: 99%

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The effect of ionization on the populations of excited levels of C IV and C V in tokamak edge plasmas

Lawson¹,

Coffey²,

Aggarwal³

et al. 2013

J. Phys. B: At. Mol. Opt. Phys.

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The main populating and depopulating mechanisms of the excited energy levels of ions in plasmas with densities <10 23 -10 24 m -3 are electron collisional excitation from the ion's ground state and radiative decay, respectively, with the majority of the electron population being in the ground state of the ionization stage. Electron collisional ionization is predominately expected to take place from one ground state to that of the next higher ionization stage. However, the question arises as to whether, in some cases, ionization can also affect the excited level populations. This would apply particularly to those cases involving transient events such as impurity influxes in a laboratory plasma. An analysis of the importance of ionization in populating the excited levels of ions in plasmas typical of those found in the edge of tokamaks is undertaken for the C IV and C V ionization stages. The emphasis is on those energy levels giving rise to transitions of most use for diagnostic purposes (n≤5). Carbon is chosen since it is an important contaminant of JET plasmas; it was the dominant low Z impurity before the installation of the ITER-like wall and is still present in the plasma after its installation. Direct electron collisional ionization both from and to excited levels is considered. Distorted-wave Flexible Atomic Code calculations are performed to generate the required ionization cross sections, due to a lack of atomic data in the literature. Employing these data, ionization from excited level populations is not found to be significant in comparison with radiative decay. However, for some energy levels, ionization terminating in the excited level has an effect in the steady-state of the order of the measurement errors (±10%). During transient events, ionization to excited levels will be of more importance and must be taken into account in the calculation of excited level populations. More accurate atomic data, including possible resonance contributions to the cross sections, would tend to increase further the importance of these effects.

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Section: IIImentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%