Browsing by Author "Pitts, R. A."

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The core-edge integrated neon-seeded scenario in deuterium-tritium at JET
(2024-10) Giroud, C.; Carvalho, I. S.; Brezinsek, S.; Huber, A.; Keeling, D.; Mailloux, J.; Pitts, R. A.; Lerche, E.; Henriques, R.; Hillesheim, J.; Lawson, K.; Marin, M.; Pawelec, E.; Sos, M.; Sun, H. J.; Tomes, M.; Aleiferis, S.; Bleasdale, A.; Brix, M.; Boboc, A.; Bernardo, J.; Carvalho, P.; Coffey, I.; Henderson, S.; King, D. B.; Rimini, F.; Maslov, M.; Alessi, E.; Craciunescu, T.; Fontana, M.; Fontdecaba, J. M.; Garzotti, L.; Ghani, Z.; Horvath, L.; Jepu, I.; Karhunen, J.; Kos, D.; Litherland-Smith, E.; Meigs, A.; Menmuir, S.; Morales, R. B.; Nowak, S.; Peluso, E.; Pereira, T.; Parail, V.; Petravich, G.; Pucella, G.; Puglia, P.; Refy, D.; Scully, S.; , JET Contributors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper reports the first experiment carried out in deuterium-tritium addressing the integration of a radiative divertor for heat-load control with good confinement. Neon seeding was carried out for the first time in a D-T plasma as part of the second D-T campaign of JET with its Be/W wall environment. The technical difficulties linked to the re-ionisation heat load are reported in T and D-T. This paper compares the impact of neon seeding on D-T plasmas and their D counterpart on the divertor detachment, localisation of the radiation, scrape-off profiles, pedestal structure, edge localised modes and global confinement.
On the role of finite grid extent in SOLPS-ITER edge plasma simulations for JET H-mode discharges with metallic wall
(2018-12-01) Wiesen, S.; Brezinsek, S.; Bonnin, X.; Delabie, E.; Frassinetti, L.; Groth, M.; Guillemaut, C.; Harrison, J.; Harting, D.; Henderson, S.; Huber, A.; Kruezi, U.; Pitts, R. A.; Wischmeier, M.; , JET Contributors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The impact of the finite grid size in SOLPS-ITER edge plasma simulations is assessed for JET H-mode discharges with a metal wall. For a semi-horizontal divertor configuration it is shown that the separatrix density is at least 30% higher when a narrow scrape-off layer (SOL) grid width is chosen in SOLPS-ITER compared to the case for which the SOL grid width is maximised. The density increase is caused by kinetic neutrals being not confined inside the divertor region because of the reduced extent of the plasma grid. In this case, an enhanced level of reflections of energetic neutrals at the low-field side (LFS) metal divertor wall is observed. This leads to a shift of the ionisation source further upstream which must be accounted for as a numerical artefact. An overestimate in the cooling at the divertor entrance is observed in this case, identified by a reduced heat flux decay parameters λq div. Otherwise and further upstream the mid-plane heat decay length λq parameter is not affected by any change in divertor dissipation. This confirms the assumptions made for the ITER divertor design studies, i.e. that λq upstream is essentially set by the assumptions for the ratio radial to parallel heat conductivity. It is also shown that even for attached conditions the decay length relations λne > λTe > λq hold in the near-SOL upstream. Thus for interpretative edge plasma simulations one must take the (experimental) value of λne into account, rather than λq, as the former actually defines the required minimum upstream SOL grid extent.
Parameter dependencies of the experimental nitrogen concentration required for detachment on ASDEX Upgrade and JET
(2021-09) Henderson, S. S.; Bernert, M.; Giroud, C.; Brida, D.; Cavedon, M.; David, P.; Dux, R.; Harrison, J. R.; Huber, A.; Kallenbach, A.; Karhunen, J.; Lomanowski, B.; Matthews, G.; Meigs, A.; Pitts, R. A.; Reimold, F.; Reinke, M. L.; Silburn, S.; Vianello, N.; Wiesen, S.; Wischmeier, M.; , EUROfusion MST1 Team; , ASDEX Upgrade Team; , JET Contributors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
While current tokamak experiments are beginning to use real-time feedback control systems to manage the plasma exhaust, future tokamaks still require validation of theoretical models used to predict the threshold impurity concentration required to sufficiently reduce the power and particle fluxes to the divertor. This work exploits new spectroscopic measurements of the divertor nitrogen concentration, cN, in partially detached N2-seeded H-mode plasmas on ASDEX Upgrade (AUG) and JET with the ITER-Like Wall (JET-ILW) to test the parameter dependencies of the power flowing to the outer divertor, Pdiv,outer, and the separatrix electron density, ne,sep. A least-squares regression of the AUG measurements demonstrates that the threshold cN required for detachment scales as cN∝Pdiv,outer1.19±0.32ne,sep-2.77±0.36. This scaling of ne,sep is also consistent with the measurements from JET which, at constant Pdiv,outer, show cN∝ne,sep-2.43±0.27. The dependencies of Pdiv,outer and ne,sep is demonstrated over at least a factor of two change in both parameters and indicates a stronger dependence on ne,sep in comparison to the Lengyel model, which could be due to the assumption in this model that the heat flux channel width is independent of density. This first assessment of detachment scaling with impurity seeding highlights the need for further analysis of the systematic uncertainties of the measurement and more consistent scenarios from more tokamaks to investigate the machine size scaling.
Validation of the ERO2.0 code using W7-X and JET experiments and predictions for ITER operation
(2024-08) Romazanov, J.; Brezinsek, S.; Baumann, C.; Rode, S.; Kirschner, A.; Wang, E.; Effenberg, F.; Borodin, D.; Navarro, M. X.; Xie, H.; Groth, M.; Kumpulainen, H.; Schmid, K.; Pitts, R. A.; Terra, A.; Knieps, A.; Gao, Y.; Krychowiak, M.; Pandey, A.; Linsmeier, Ch
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The paper provides an overview of recent modelling of global material erosion and deposition in the fusion devices Wendelstein 7-X (W7-X), JET and ITER using the Monte-Carlo code ERO2.0. For validating the modelling tool in a three-dimensional environment, W7-X simulations are performed to describe carbon erosion from the graphite test divertor units, which were equipped in operational phase OP 1.2 and analysed post-mortem. Synthetic spectroscopy of carbon line emission is compared with experimental results from the divertor spectrometer measurement system, showing a good agreement in the e-folding lengths in the radial intensity profiles of carbon. In the case of metallic wall materials, earlier modelling of the Be/W environment in JET and ITER is revisited and extended with an updated set of sputtering and reflection data, as well as including the mixing model for describing the Be/W dynamics in the divertor. Motivated by recent H/D/T isotope experiments in JET, limited and diverted configuration pulses are modelled, showing the expected trend of both Be and W erosion increasing with isotope mass. For the JET diverted configuration pulses, it is shown that Be migrates predominantly to the upper part of the inner divertor where it initially leads to strong W erosion. With longer exposure time, the growth of a Be deposited layer leads to a reduction of W erosion in that region. A similar trend is observed in simulations of the ITER baseline Q = 10 scenario, however with a more symmetric Be migration pattern leading to deposition also on the outer divertor.