Alcator-C-Mod, this number increases to 30%, and in ITER, depending on the
regime, it rises to 60–90% [40]. Unfortunately, self-consistent modeling of radiation
transport and the atomic physics effects is very computationally expensive, so that in
many cases the radiation trapping effects are ignored. Partly it is justified by the fact
that some features important for the reactor design, such as the heat load on
the divertor targets, appear to be quite insensitive to the outcome of the radiation
trapping effects (e.g. see [53]. However, these effects appear to be crucial for proper
modeling of some particular phenomena observed in experiments (e.g. modeling of
MARFE in JET tokamak where it was found that 90% of Ly α and 70% of Ly β lines
are trapped [57]) and they are also often important for interpretation of the diagnostic
(e.g. spectroscopic) data [48].
2.4 Application of CRM to Edge Plasma Relevant Species
In this sub-section, we consider the results of the application of the CRM to different
atomic and molecular species relevant to the edge plasma in magnetic fusion
devices.
2.4.1 Hydrogen
We start with hydrogen atoms and molecules. An impact of radiation trapping on the
atomic rate constants of hydrogen species, in general, depends on the particular
distribution of the plasma and neutral gas parameters. However, just to taste a flavor
of the radiation trapping effects, one can consider a model where hydrogen radiation
in some particular lines is completely trapped. This case corresponds to a CRM
where spontaneous decay from some particular quantum states is turned off, which
mimics quick reabsorption of the resonance photons [26].
In Fig. 2.5, one can find the dependence of both the atomic hydrogen ionization
K
H
ion and the EIR K
H
rec rate constants on the temperature for different plasma densities
for the case of fully transparent plasma (Fig. 2.5a) and suppressed spontaneous
decay from the levels n ! 2 to the ground state (Fig. 2.5b), which mimics the
complete opacity conditions for the Lyman lines, obtained from the SOLPS
database [42].
As one could expect, both the increase of the electron density above ~10
14 cm
À3
and the suppression of the spontaneous decay of the transition 2 ! 1 , which enhance
the population of excited states, are boosting the ionization rate constant. In Fig. 2.5a
we also plot the charge-exchange rate constants K
1
ð Þ
cx (which will be used for our
further considerations) for different hydrogen isotopes assuming that the electron
and ion/neutral temperatures are the same. However, in practice, the analysis of edge
plasma and neutral hydrogen transport requires more detailed knowledge of the
32
2 Atomic Physics Relevant to Fusion Plasmas
regime, it rises to 60–90% [40]. Unfortunately, self-consistent modeling of radiation
transport and the atomic physics effects is very computationally expensive, so that in
many cases the radiation trapping effects are ignored. Partly it is justified by the fact
that some features important for the reactor design, such as the heat load on
the divertor targets, appear to be quite insensitive to the outcome of the radiation
trapping effects (e.g. see [53]. However, these effects appear to be crucial for proper
modeling of some particular phenomena observed in experiments (e.g. modeling of
MARFE in JET tokamak where it was found that 90% of Ly α and 70% of Ly β lines
are trapped [57]) and they are also often important for interpretation of the diagnostic
(e.g. spectroscopic) data [48].
2.4 Application of CRM to Edge Plasma Relevant Species
In this sub-section, we consider the results of the application of the CRM to different
atomic and molecular species relevant to the edge plasma in magnetic fusion
devices.
2.4.1 Hydrogen
We start with hydrogen atoms and molecules. An impact of radiation trapping on the
atomic rate constants of hydrogen species, in general, depends on the particular
distribution of the plasma and neutral gas parameters. However, just to taste a flavor
of the radiation trapping effects, one can consider a model where hydrogen radiation
in some particular lines is completely trapped. This case corresponds to a CRM
where spontaneous decay from some particular quantum states is turned off, which
mimics quick reabsorption of the resonance photons [26].
In Fig. 2.5, one can find the dependence of both the atomic hydrogen ionization
K
H
ion and the EIR K
H
rec rate constants on the temperature for different plasma densities
for the case of fully transparent plasma (Fig. 2.5a) and suppressed spontaneous
decay from the levels n ! 2 to the ground state (Fig. 2.5b), which mimics the
complete opacity conditions for the Lyman lines, obtained from the SOLPS
database [42].
As one could expect, both the increase of the electron density above ~10
14 cm
À3
and the suppression of the spontaneous decay of the transition 2 ! 1 , which enhance
the population of excited states, are boosting the ionization rate constant. In Fig. 2.5a
we also plot the charge-exchange rate constants K
1
ð Þ
cx (which will be used for our
further considerations) for different hydrogen isotopes assuming that the electron
and ion/neutral temperatures are the same. However, in practice, the analysis of edge
plasma and neutral hydrogen transport requires more detailed knowledge of the
32
2 Atomic Physics Relevant to Fusion Plasmas