Browsing by Author "Järvinen, A. E."

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Experimental research on the TCV tokamak
(2024-11) Duval, B. P.; Abdolmaleki, A.; Agostini, M.; Ajay, C. J.; Alberti, S.; Alessi, E.; Anastasiou, G.; Andrèbe, Y.; Apruzzese, G. M.; Auriemma, F.; Ayllon-Guerola, J.; Bagnato, F.; Baillod, A.; Bairaktaris, F.; Balbinot, L.; Balestri, A.; Baquero-Ruiz, M.; Barcellona, C.; Bernert, M.; Bin, W.; Blanchard, P.; Boedo, J.; Bolzonella, T.; Bombarda, F.; Boncagni, L.; Bonotto, M.; Bosman, T. O.S.J.; Brida, D.; Brunetti, D.; Buchli, J.; Buerman, J.; Buratti, P.; Burckhart, A.; Busil, D.; Caloud, J.; Camenen, Y.; Cardinali, A.; Carli, S.; Carnevale, D.; Järvinen, A. E.; Kirjasuo, A.; Kumar, U.; Lee, K.; Marin, M.; Nielsen, S. K.; Pfau, D.; Ryan, P. J.; Salmi, A.; Wang, Y.; Yang, H.; , EUROfusion Consortium
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Tokamak à configuration variable (TCV), recently celebrating 30 years of near-continual operation, continues in its missions to advance outstanding key physics and operational scenario issues for ITER and the design of future power plants such as DEMO. The main machine heating systems and operational changes are first described. Then follow five sections: plasma scenarios. ITER Base-Line (IBL) discharges, triangularity studies together with X3 heating and N2 seeding. Edge localised mode suppression, with a high radiation region near the X-point is reported with N2 injection with and without divertor baffles in a snowflake configuration. Negative triangularity (NT) discharges attained record, albeit transient, βN ∼ 3 with lower turbulence, higher low-Z impurity transport, vertical stability and density limits and core transport better than the IBL. Positive triangularity L-Mode linear and saturated ohmic confinement confinement saturation, often-correlated with intrinsic toroidal rotation reversals, was probed for D, H and He working gases. H-mode confinement and pedestal studies were extended to low collisionality with electron cyclotron heating obtaining steady state electron iternal transport barrier with neutral beam heating (NBH), and NBH driven H-mode configurations with off-axis co-electron cyclotron current drive. Fast particle physics. The physics of disruptions, runaway electrons and fast ions (FIs) was developed using near-full current conversion at disruption with recombination thresholds characterised for impurity species (Ne, Ar, Kr). Different flushing gases (D2, H2) and pathways to trigger a benign disruption were explored. The 55 kV NBH II generated a rich Alfvénic spectrum modulating the FI fas ion loss detector signal. NT configurations showed less toroidal Alfvén excitation activity preferentially affecting higher FI pitch angles. Scrape-off layer and edge physics. gas puff imaging systems characterised turbulent plasma ejection for several advanced divertor configurations, including NT. Combined diagnostic array divertor state analysis in detachment conditions was compared to modelling revealing an importance for molecular processes. Divertor physics. Internal gas baffles diversified to include shorter/longer structures on the high and/or low field side to probe compressive efficiency. Divertor studies concentrated upon mitigating target power, facilitating detachment and increasing the radiated power fraction employing alternative divertor geometries, optimised X-point radiator regimes and long-legged configurations. Smaller-than-expected improvements with total flux expansion were better modelled when including parallel flows. Peak outer target heat flux reduction was achieved (>50%) for high flux-expansion geometries, maintaining core performance (H98 > 1). A reduction in target heat loads and facilitated detachment access at lower core densities is reported. Real-time control. TCV’s real-time control upgrades employed MIMO gas injector control of stable, robust, partial detachment and plasma β feedback control avoiding neoclassical tearing modes with plasma confinement changes. Machine-learning enhancements include trajectory tracking disruption proximity and avoidance as well as a first-of-its-kind reinforcement learning-based controller for the plasma equilibrium trained entirely on a free-boundary simulator. Finally, a short description of TCV’s immediate future plans will be given.
Isotope mass scaling and transport comparison between JET Deuterium and Tritium L-mode plasmas
(2023-11) Tala, T.; Järvinen, A. E.; Maggi, C. F.; Mantica, P.; Mariani, A.; Salmi, A.; Carvalho, I. S.; Chomiczewska, A.; Delabie, E.; Devasagayam, F.; Ferreira, J.; Gromelski, W.; Hawkes, N.; Horvath, L.; Karhunen, J.; King, D.; Kirjasuo, A.; Kowalska-Strzeciwilk, E.; Leerink, S.; Lennholm, M.; Lomanowski, B.; Maslov, M.; Menmuir, S.; Morales, R. B.; Sharma, R.; Sun, H.; Tanaka, K.; , JET Contributors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The dimensionless isotope mass scaling experiment between pure Deuterium and pure Tritium plasmas with matched ρ ∗ , ν ∗ , β n , q and T e / T i has been achieved in JET L-mode with dominant electron heating (NBI+ohmic) conditions. 28% higher scaled energy confinement time B t τ E , t h / A is found in favour of the Tritium plasma. This can be cast in the form of the dimensionless energy confinement scaling law as Ω i τ E , t h ∼ A 0.48 ± 0.16 . This significant isotope mass scaling is consequently seen in the scaled one-fluid heat diffusion coefficient A χ e f f / B t which is around 50% lower in the Tritium plasma throughout the whole plasma radius. The isotope mass dependence in the particle transport channel is negligible, supported also by the perturbative particle transport analysis with gas puff modulation. The comparison of the edge particle fuelling or ionisation profiles from the EDGE2D-EIRENE simulations show that the absolute density differences that are necessary for the dimensionless match in the confined plasma dominate over any isotope mass dependencies of particle fuelling and ionization profiles at the plasma edge. Local GENE simulation results indicate a mild anti-gyroBohm effect at ρ t o r = 0.6 and thereby a small isotope mass dependence in favour of Tritium on heat transport and a negligible effect on particle transport. A significant fraction of the isotope scaling and reduced heat transport observed in the Tritium plasma is not captured in the GENE and ASTRA-TGLF-SAT2 simulations by simply changing the isotope mass for the same input profiles.