2023.09.27

メタ階層ダイナミクスユニットの客員教授 Dr. Detlev Reiter によるセミナーを開催いたします。

日時：10月4日(水) 13:30-14:30

場所：核融合科学研究所 研究Ⅰ期棟８階８０１セミナー室（Zoomハイブリッド）

Zoom参加登録：https://us06web.zoom.us/meeting/register/tZwrc-ChrzgpHdas3QrKoaXBmUpGlfggiXnL

Dr. Detlev Reiter（客員教授、デュッセルドルフ大学名誉教授）
“Divertor detachment: Plasma physics meets plasma chemistry”

It was recognized as early as 1968 by Bo Lehnert [1] that a zone of powerful gas – plasma interaction, formed near intensely plasma exposed surface elements, can be the key to solving the still critical plasma surface interactions (PSI) issue for sustainable nuclear fusion reactor operation. Today the “divertor detachment” regime in large magnetic fusion devices (tokamaks, stellarators) is characterized by strong volumetric exchanges of particles, momentum and energy, provided by such a gas-plasma interaction zone near target surfaces. Computational separation of plasma chemistry from the typically only empirically known plasma transport (intermittent or turbulent) allows to quantify the latter experimentally.

Firstly, by resorting to highly accurate atomic and molecular (AM) collision data [2] This builds on rate equation concepts well established e.g. in astrophysical and chemical kinetics (aka: non-equilibrium collision radiative modelling). Secondly by building on the high standards in (kinetic) transport theory and its wide range of applications, e.g. in the nuclear (neutronics) or radiation transfer sciences. This has meanwhile led to quite mature fusion boundary plasma (often partially “Monte Carlo” based) multi-physics and multi-scale simulation tools [3].

It is shown that the dominant gas-plasma friction force in typical “detached divertor conditions” is to be expected from (ro-vibrationally excited) molecule – ion collisions, rather than from the often-quoted resonant charge exchange between fuel atoms and their ions.

In conditions relevant for the boundary region in fusion devices a high sensitivity of the friction forces and energy exchange rates (kinetic and chemical energy exchanges between plasma components) between the gas and plasma phases is observed. Originating from a combination of electron collisions via various resonant H₂^– anion states and the near resonant heavy particle ion conversion channels, such as particle rearrangement or charge transfer. The former electron collisions have recently been theoretically re-investigated and completed in [4] for a wide set of intermediate resonant states, with the Local Complex Potential approach.

Direct contributions from dissociating molecules and their ions to atomic spectral lines, typically with overlapping kinetic energy releases, complicate visible light spectroscopy. Furthermore, quite unexpected kinetic isotope effects may arise in the D-T mixture of a future reactor divertor plasma: This effect might be well accessible experimentally in dedicated small laboratory plasma devices, e.g., when operated in H/D mixtures.

[1] B.Lehnert, Journal Nuclear Fusion 8, 173, (1968)
[2] IAEA Vienna, Atomic and Molecular Data Unit (2023)
[3] R.Pitts, X.Bonnin, et al., Nuclear Materials and Energy 20, 100696 (2019)
[4] V.Laporta, R.Agnello et al., Plasma Phys. Control. Fusion 63, 085006 (2021)