Browsing by Department "Fusion and Plasma Physics"

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    Effect of toroidal particle sources on SOL physics in the FT-2 tokamak
    (WILEY-VCH VERLAG, 2022-06-01) Albert Devasagayam, Francis Clinton Prasanth; Chôné, Laurent; Kiviniemi, Timo Petteri; Kaledina, Oksana; Shatalin, Sergei; Gurchenko, Alexey Dmitrievich; Altukhov, Alexey; Gusakov, Evgeniy; Kantor, Mikhail; Kouprienko, Denis; Lashkul, Sergei; Department of Applied Physics; University of Helsinki; Fusion and Plasma Physics; Ioffe Institute
    Two gas-puffs are used near limiters in the FT-2 tokamak for the purpose of hydrogen refuelling during plasma discharges. This creates toroidal and poloidal asymmetry in particle sources near limiters which has to be considered in modelling. Here, the effect of toroidal asymmetry is simulated using the gyrokinetic code ELMFIRE. Two slightly different toroidal particle sources are used in simulations, and their results are compared with each other, and with experimental measurements to understand the impact of toroidal particle sources on Scrape-off Layer (SOL) physics.
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    Interpretation of the hydrogen isotope effect on the density limit in JET-ILW L-mode plasmas using EDGE2D-EIRENE
    (IOP Publishing Ltd., 2021-12) Solokha, V.; Groth, M.; Corrigan, G.; Wiesen, S.; , JET Contributors; Department of Applied Physics; Fusion and Plasma Physics; JET-EFDA; Jülich Research Centre
    Experiments in JET with the Be/W ITER-like wall show that in pure hydrogen low-confinement mode (L-mode) plasmas the density limit is approximately 20% higher than their corresponding deuterium plasmas. The maximum achievable density in L-mode plasmas is limited by the magnetohydrodynamic stability of the m/n = 2/1 tearing mode. Studies with the edge fluid-neutral Monte-Carlo code package EDGE2D-EIRENE show that the density of hydrogen atoms inside the separatrix is two times lower than for deuterium in plasma conditions preceding the density limit. The difference between the isotopes is caused by the non-linear process at density limit onset which leads to more efficient dissociation and ionization of hydrogen molecules and atoms in hydrogen than in deuterium plasmas at the high-field X-point region at electron temperatures lower than 2 eV. The m/n = 2/1 island size is estimated to be 30% smaller islands for hydrogen than for deuterium cases for equal fuelling conditions and radial transport assumptions.
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    Modelling of tungsten erosion and deposition in the divertor of JET-ILW in comparison to experimental findings
    (Elsevier BV, 2019-01-01) Kirschner, A.; Brezinsek, S.; Huber, A.; Meigs, A.; Sergienko, G.; Tskhakaya, D.; Borodin, D.; Groth, M.; Jachmich, S.; Romazanov, J.; Wiesen, S.; Linsmeier, Ch; , JET Contributors; Forschungszentrum Jülich; Culham Science Centre; Vienna University of Technology; Fusion and Plasma Physics; Department of Applied Physics
    The erosion, transport and deposition of tungsten in the outer divertor of JET-ILW has been studied for an H-Mode discharge with low frequency ELMs. For this specific case with an inter-ELM electron temperature at the strike point of about 20 eV, tungsten sputtering between ELMs is almost exclusively due to beryllium impurity and self-sputtering. However, during ELMs tungsten sputtering due to deuterium becomes important and even dominates. The amount of simulated local deposition of tungsten relative to the amount of sputtered tungsten in between ELMs is very high and reaches values of 99% for an electron density of 5E13 cm−3 at the strike point and electron temperatures between 10 and 30 eV. Smaller deposition values are simulated with reduced electron density. The direction of the B-field significantly influences the local deposition and leads to a reduction if the E × B drift directs towards the scrape-off-layer. Also, the thermal force can reduce the tungsten deposition, however, an ion temperature gradient of about 0.1 eV/mm or larger is needed for a significant effect. The tungsten deposition simulated during ELMs reaches values of about 98% assuming ELM parameters according to free-streaming model. The measured WI emission profiles in between and within ELMs have been reproduced by the simulation. The contribution to the overall net tungsten erosion during ELMs is about 5 times larger than the one in between ELMs for the studied case. However, this is due to the rather low electron temperature in between ELMs, which leads to deuterium impact energies below the sputtering threshold for tungsten.
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    Progress in DIII-D towards validating divertor power exhaust predictions
    (IOP Publishing Ltd., 2020-05) Jaervinen, A. E.; Allen, S. L.; Eldon, D.; Fenstermacher, M. E.; Groth, M.; Hill, D. N.; Lasnier, C. J.; Leonard, A. W.; McLean, A. G.; Moser, A. L.; Porter, G. D.; Rognlien, T. D.; Samuell, C. M.; Wang, Huiqian; Watkins, J. G.; Fusion and Plasma Physics; Department of Applied Physics
    UEDGE simulations highlight the role of cross-field drifts on the onset of detached conditions, and new calibrated divertor vacuum ultra violet (VUV) spectroscopy is used to challenge the predictions of radiative constituents in these simulations. UEDGE simulations for DIII-D H-mode plasmas with the open divertor with the ion ∇B-drift towards the X-point show a bifurcated onset of the low field side (LFS) divertor detachment, consistent with experimentally observed step-like detachment onset (Jaervinen A.E. et al 2018 Phys. Rev. Lett. 121 075001). The divertor plasma in the simulations exhibits hysteresis in upstream separatrix density between attached and detached solution branches. Reducing the drift magnitude by a factor of 3 eliminates the step-like detachment onset in the simulations, confirming the strong role of drifts in the bifurcated detachment onset. When measured local plasma densities and temperatures are within proximity of predicted values in the simulations, there is no shortfall of the local emission of the dominant resonant radiating lines. However, the simulations systematically predict a factor of two lower total integrated radiated power than measured by the bolometer with the difference lost through radial heat flow out of the computational domain. Even though there is no shortfall in the emission of the dominant lines, a shortfall of total radiated power can be caused by underpredicted spatial extent of the radiation front, indicating a potential upstream or divertor transport physics origin for the radiation shortfall, or shortfall of radiated power in the spectrum between the dominant lines. In addition to the underpredicted spatial extent, in detached conditions, the simulations overpredict the peak radiation and dominant carbon lines near the X-point, which can be alleviated by manually increasing divertor diffusivity in the simulations, highlighting the ad hoc cross-field transport as one of the key limitations of the predictive capability of these divertor fluid codes.