Speaker
Description
Tungsten remains the element of choice for plasma facing components (PFCs) in the divertor region of ITER [1] and other past and present tokamak experiments [2, 3]. The impurity influx of tungsten from PFCs into the plasma while undesirable, as highlighted by Pütterich et al. [4], needs to be accurately quantified if we are to model tungsten erosion and redeposition. Previous work of Isler [5] and Murakami et al. [6] state that the presence of as little as 0.1% of this high-Z element, within the plasma may be sufficient to quench the reaction, confirmed by Pütterich et al. [4] but at even smaller quantities.
One accepted method to provide a prediction of the expected impurity influx of Tungsten from the divertor region of a tokamak is the SXB ratio [7]. The SXB ratio for a given line has the effective ionisation rate in the numerator; with the denominator representing the population of the upper level times the Einstein A-coefficient for a given transition.
The Dirac Atomic R-matrix Codes (DARC) have been quite successful in providing sufficiently accurate atomic structure and electron-impact collision strengths that underpin the determination of the upper level population [8,9,10]. The effective ionisation rates have a higher degree of uncertainty attached to them. Perturbative methods such as the distorted wave method have been employed but have shown to overestimate ground and meta-stable ionisation cross sections for near-neutral lighter systems. New RMPS ionisation cross sections shall be shown for W$^{2+}$ and compared with available experimental data. Future work will consider the electron-impact excitation and ionisation of W and W$^+$.
References
[1] Rebut P-H 1995, ITER: the first experimental fusion reactor, Fusion Eng. Des. 27 3–16
[2] K¨asemann C-P, Grois E, Stobbe F, Rott M and Klaster K, Pulsed power supply system of the ASDEX upgrade Tokamak research facility, 2015 IEEE 15th Int. Conf. on Environment and Electrical Engineering (EEEIC) pp 237–42
[3] Widdowson A et al 2017, Overview of the JET ITER-like wall divertor, Nucl. Mater. Energy 12 499–505
[4] Pütterich T, Neu R, Dux R, Whiteford A D and O’Mullane M G (the ASDEX Upgrade Team) 2008, Modelling of measured tungsten spectra from ASDEX upgrade and predictions for ITER, Plasma Phys. Control. Fusion 50 085016
[5] Isler R C 1984, Impurities in tokamaks, Nucl. Fusion 24 1599–678
[6] Murakami I, Kato D, Oishi T, Goto M, Kawamoto Y, Suzuki C, Sakaue H and Morita S 2021, Progress of tungsten spectral modeling for ITER edge plasma diagnostics based on tungsten spectroscopy in LHD, Nucl. Mater. Energy 26 100923
[7] Behringer K 1989, Spectroscopic studies of plasma–wall interaction and impurity behaviour in tokamaks, Plasma Phys. Control. Fusion 31 2059
[8] Smyth R, Ballance C, Ramsbottom C, Johnson C, Ennis D and Loch S 2018, Dirac R-matrix calculations for the electron-impact excitation of neutral tungsten providing non-invasive diagnostics for magnetic confinement fusion, Phys. Rev. A 97 052705
[9] Dunleavy, N L, Ballance, C P, Ramsbottom, C A, Johnson, C A, and Ennis, D A (2022). A Dirac R-matrix calculation for the electron-impact excitation of W+. Journal of Physics B: Atomic Molecular and Optical Physics, 55, Article 175002.
[10] McCann M, Ballance C P, Loch S D and Ennis D A, submitted to J Phys B.
