• Energy Research

The present study addresses the uncertainties that affect the recently performed predictions of beryllium (Be) erosion and migration in ITER using the Monte-Carlo code ERO2.0. The focus of the study is a D–T baseline discharge with fusion power gain Q=10, scrape-off layer (SOL) input power PSOL=100MW, toroidal plasma current Ip=15MA, and central toroidal field Bt=5.3T. The parameter studies used to investigate uncertainties include variations of the radial extrapolation of plasma parameters in the far-SOL (scan A), the assumptions on impact angle distributions (scan B) and the anomalous transport of eroded Be (scan C). Variations by factors ∼3, ∼18and ∼2for scans A, B and C, respectively, are found.

ITER will use beryllium as a plasma-facing material in the main chamber, covering a total surface area of about 620 m2. Given the importance of beryllium erosion and co-deposition for tritium retention in ITER, significant efforts have been made to understand the behaviour of beryllium under fusion-relevant conditions with high particle and heat loads. This paper provides a comprehensive report on the state of knowledge of beryllium behaviour under fusion-relevant conditions: the erosion mechanisms and their consequences, beryllium migration in JET, fuel retention and dust generation. The paper reviews basic laboratory studies, advanced computer simulations and experience from laboratory plasma experiments in linear simulators of plasma–wall interactions and in controlled fusion devices using beryllium plasma-facing components. A critical assessment of analytical methods and simulation codes used in beryllium studies is given. The overall objective is to review the existing set of data with a broad literature survey and to identify gaps and research needs to broaden the database for ITER.

Nuclear materials and energy 41, 101803 - (2024). doi:10.1016/j.nme.2024.101803 Published by Elsevier, Amsterdam [u.a.]

EDGE2D-EIRENE simulations of nitrogen-seeded partially detached JET l-mode plasmas show that the divertor N I to N V radiation distributions are highly sensitive to the upstream electron density, and less sensitive to changes in the assumed cross-field particle diffusivity for nitrogen ions. The EDGE2D-EIRENE simulations reproduce the peak intensities of N I to N V as measured by vertically viewing divertor filterscopes to within 50 % for a narrow range of the upstream electron density within the experimental uncertainties, while the predicted profiles are narrower than the measured ones. Including nitrogen atoms only in the ERO2.0 simulations implies lower N III and N IV peak intensities by one and two thirds, respectively, compared to EDGE2D-EIRENE. If nitrogen is assumed to recycle exclusively as molecules instead of atoms, ERO2.0 predicts that the N III and N IV intensities in the divertor increase by up to a factor of two and that the time-averaged, volume-integrated number of N5+ to N7+ ions in the plasma also increases by approximately a factor of 2.

SOLPS-ITER simulations of nitrogen-seeded, low-confinement mode plasmas in the Joint European Torus (JET) predict that the electron temperature in the low-field side (LFS) divertor leg is reduced locally by up to an order of magnitude when nitrogen is assumed to recycle as molecules (N2) instead of atoms using a fixed nitrogen injection rate. The LFS divertor temperature reduction under the assumption of molecular recycling occurs due to a three-step mechanism: (1) the plasma penetration of nitrogen atoms is increased due to the strong triple bond of the N2 molecule and the kinetic energy release in the dissociation event, both mechanisms contributing equally, (2) the abundance of (particularly multiply-charged) nitrogen ions in the divertor is increased and (3) the electron temperature is reduced due to the increase in radiation (by up to a factor of 4) from nitrogen ions. Setting the volume-integrated nitrogen radiated power to a constant value (0.6 MW) instead of the nitrogen injection rate, SOLPS-ITER predicts under the molecular nitrogen recycling assumption that the peak line-integrated N II, N III and N IV intensities in the LFS divertor are approximately within 15%, 35% and 5%, respectively, of the reference atomic nitrogen recycling case. The predicted peak N II, N III and N IV intensities under either assumption are within 30%, 65% and 5%, respectively, of measurements using the vertically viewing mirror-link divertor spectrometer (Meigs et al., 2010) in nitrogen-seeded JET L-mode plasmas (Lomanowski et al., 2019). ERO2.0 simulations using a constant nitrogen seeding rate on static background plasma solutions from EDGE2D-EIRENE (previously presented in Mäenpää et al., (2022), revised here to include fast reflections) predict that N II to N IV line emission is increased by 20% to 30% when nitrogen is assumed to recycle as molecules, demonstrating the importance of considering the effect of molecular dissociation reactions on the divertor plasma in a self-consistent manner.

Nuclear materials and energy 33, 101257 - (2022). doi:10.1016/j.nme.2022.101257 Published by Elsevier, Amsterdam [u.a.]

Wendelstein 7-X (W7-X) operation with inertially cooled graphite Test Divertor Unit (TDU) was finalised in a series of identical hydrogen plasmas with injection of 13C isotopically marked methane. The break-up of 13CH4, injected through gas inlets at one toroidal position of W7-X, and the subsequent transport and deposition of 13C in the device was studied ex-situ. The TDU was therefore extracted from the vessel and some of the removed TDU elements were examined regarding their 13C distribution in deposited layers on the surface using Laser Ablation Molecular Isotopic Spectroscopy (LAMIS). This study shows the 13C/12C distinction capabilities of LAMIS used to analyse the carbon deposition pattern on Plasma-Facing Components (PFCs) on two of the removed TDU elements. The resulted pattern was compared with complementary results from Nuclear Reaction Analysis (NRA) and simulations of 13C deposition by ERO2.0, a material transport and plasma-surface interaction code. Ultra- short laser pulses of a Nd:YAG laser were used in collinear double-pulse configuration for LAMIS. The first pulse (l1 = 355 nm, t1 = 35 ps, F = 2.3 J/cm2) produced a laser- induced plasma on the surface and 50 ns later, the second laser pulse (l2 = 1064 nm, t2 = 35 ps) was directed into this plasma to enhance the signal. Each pulse pair ablates in total 200 nm of the surface material. The analysis is conducted in 1.5 mbar N2 environment for improved signal-to-noise ratio relative to vacuum conditions. A high throughput custom-made spectrometer in Littrow-arrangement (f = 750 mm, A = 6000 at l = 473 nm, lspan = 14 nm) was used to analyse the C2 Swan bands (d3⊓g - a3⊓u, v = 1 to v’ = 0) of laser-induced plasma emission.