Browsing by Author "Kumpulainen, Henri"

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  • Comparison of OEDGE and EDGE2D-EIRENE predictions of the scrape-off layer conditions for attached plasmas
    (2024-08-01) Rikala, Vesa Pekka; Groth, Mathias; Kumpulainen, Henri; Rees, David
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Predictions of the scrape-off layer (SOL) plasma conditions from the 2D multi-fluid code EDGE2D-EIRENE are compared to the OEDGE 1D fluid code for JET low-confinement mode (L-mode) plasmas. In the low-recycling divertor conditions (divertor target plasma collisionality (Formula presented.)), OEDGE and EDGE2D-EIRENE agree on the electron temperature, the ion temperature, and the electron density within 10% in the low-field side (LFS) divertor X-point region (divertor SOL) and within 25% in the LFS midplane region. In high-recycling conditions ((Formula presented.)), the predictions of both codes agree on the electron temperature within 20%, while differences in the ion temperature and electron density increase to as high as 50% in the divertor SOL.
  • Comparison of the scrape-off layer two-point model for deuterium and helium plasmas in JET ITER-like wall low-confinement plasma conditions
    (2024-08-01) Rees, David; Sissonen, Joona; Groth, Mathias; Rikala, Vesa Pekka; Kumpulainen, Henri; Thomas, Beth; Brix, Mathias
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The hydrogenic two-point model (H-2PM), an analytical model for the scrape-off layer that predicts a common electron and ion temperature and density along a flux tube from a target temperature and density, is adapted to a single-species helium (He) model, preserving the 2PM assumptions and analytical nature. Across a range of densities and heating powers, the predicted (Formula presented.) is within (Formula presented.) of upstream measurements by high-resolution Thomson scattering (HRTS) for low-confinement He plasmas performed in JET ITER-like wall (JET-ILW). For high-recycling conditions, He-2PM predictions of (Formula presented.) were within 10% of the Li-beam diagnostic measurements, excluding the near-SOL, when assuming (Formula presented.), suggesting the divertor SOL was not fully ionised in the JET-ILW He plasmas.
  • ERO2.0 modelling of medium-Z impurity sources in JET
    (2022-10-14) Virtanen, Pyry
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Interpretive ERO Modelling of Beryllium Migration in the JET Divertor
    (2020-10-30) Brax, Henri
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Nitrogen molecular break-up and transport simulations in the JET divertor
    (2021-06-21) Mäenpää, Roni; Kumpulainen, Henri; Groth, Mathias; Romazanov, Juri; Lomanowski, Bartosz; , JET Contributors
     A4 Artikkeli konferenssijulkaisussa
    The density of N+ ions is predicted to decrease by 25 % and the density of N2+ ions to increase by 50 % if nitrogen is assumed to recycle from the divertor walls as molecules in partially detached JET L-mode plasma simulations performed with the 3D Monte Carlo trace impurity code ERO2.0 [1]. These findings are attributed to the kinetic energy gained by the molecular dissociation fragments in the Franck-Condon process and the resulting increase in plasma penetration of the atoms.
  • Nitrogen transport in the JET divertor
    (2021-05-18) Mäenpää, Roni
     Perustieteiden korkeakoulu | Master's thesis
    Nitrogen gas injection is considered a promising option for mitigating the heat loads to plasma-facing components in magnetic confinement fusion devices. However, in the center of the plasma where the temperature is high enough for fusion reactions to occur, nitrogen ions dilute the fusion fuel and cool down the plasma by radiation. It is thus advantageous if the injected nitrogen gas is retained near the plasma-facing components under the highest heat loads, and away from the center of the plasma. To better understand nitrogen transport in the plasma edge region of the Joint European Torus (JET) fusion test device, predictions from two computational tools, EDGE2D-EIRENE and ERO2.0, are compared to each other and to experimental data. In addition, the effects of molecular break-up are investigated using ERO2.0, which is capable of simulating a set of nitrogen molecular dissociation and ionization reactions. EDGE2D-EIRENE and ERO2.0 predictions agree within a factor of two on the density of atomic and singly-charged nitrogen in the low-field side divertor region. ERO2.0 predicts a higher nitrogen ion density in the private flux region due to a spatially constant cross-field particle diffusivity (varied in EDGE2D-EIRENE) and magnetic drifts (disabled in EDGE2D-EIRENE due to numerical stability issues). In a scenario with a highly localized radiation distribution, EDGE2D-EIRENE predicts higher integrated radiation due to the coarse magnetically aligned grid. Numerical artefacts in ERO2.0 lead to unphysical behavior of multiply-charged nitrogen ions. Including the nitrogen molecular dissociation process is predicted to increase plasma penetration of nitrogen atoms and lead to higher densities of nitrogen in the main plasma, but only under the assumption that all nitrogen ion impacts with the device walls produce molecular nitrogen as opposed to atomic nitrogen. EDGE2D-EIRENE predictions were found to be more consistent with the measured emission from singly ionized nitrogen than ERO2.0 predictions for actual diagnostics lines of sight. At the radially most inward measurement point, the ERO2.0 predictions are more consistent with the experimental data than the EDGE2D-EIRENE predictions.
  • Sähköisen potentiaalin ja elektronin transmissiokertoimen mallinnus pyyhkäisytunnelointimikroskoopissa
    (2015-06-07) Kumpulainen, Henri
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Tungsten transport in the scrape-off layer of JET low-confinement mode plasmas
    (2019-03-12) Kumpulainen, Henri
     Perustieteiden korkeakoulu | Master's thesis
    Tungsten transport is studied in the scrape-off layer of L-mode plasmas in the JET tokamak using the simulation codes EDGE2D-EIRENE and DIVIMP. Predictions by the two codes are compared and differences are analyzed. Synthetic diagnostics of W I and W II line radiation are compared against spectroscopic measurements in the outer divertor. The background plasma conditions and tungsten ionization profile are simulated in EDGE2D-EIRENE and used as inputs to DIVIMP. Each code produces a solution for tungsten ion densities. The divertor conditions are varied through a density scan, yielding sheath-limited to partially detached plasma conditions. The tungsten source is physical sputtering from the divertor tiles, predominantly due to intrinsic beryllium ions and deuterium charge-exchange atoms. The predicted absolute W concentration in the core region varies from 10−5 in sheath-limited cases to 10−8 in partially detached cases. The bundling of W charge states in EDGE2D results in an approximately 30% lower average charge for tungsten ions in the scrape-off layer compared to DIVIMP. The sonic boundary condition used in EDGE2D for parallel impurity velocity at the targets agrees within a few percent with DIVIMP at low plasma densities, but in high-density cases W target velocity is up to 10 times higher in DIVIMP than in EDGE2D. Consequently, the W density at the target boundaries ranges from being the same to 10 times lower in DIVIMP compared to EDGE2D. Differences in the tungsten charge lead to stronger W forces and W accumulation in the upstream and core region in DIVIMP, leading to approximately 50% higher W content at low and intermediate plasma density. EDGE2D-EIRENE predicts that the main W I radiation source on the low-field side is near the outer vertical divertor, while spectroscopy in similar target and upstream plasma conditions shows a significantly stronger W I peak at the strike point. Earlier research suggests that the code-experiment discrepancy is largely explained by W sputtering due to beryllium ions at the strike point, which appears to be underestimated in the EDGE2D-EIRENE cases. The W II line intensity predicted by EDGE2D-EIRENE and DIVIMP is lower than experimentally observed by a factor of 2 in the far scrape-off layer and by a factor of 10 near the strike point.
  • Validation of tungsten erosion and transport simulations in tokamaks
    (2023) Kumpulainen, Henri
     School of Science | Doctoral dissertation (article-based)
    This dissertation evaluates the validity and options for improvement of simulation codes in predicting tungsten erosion and transport in tokamaks, by code-code comparisons and validation against measurements from JET and ASDEX Upgrade experiments. Tungsten is a leading candidate as the plasma-facing material in magnetic confinement fusion power plants. However, W contamination of the fusion plasma is highly detrimental to reactor performance and impedes the attainment of viable power production. The ability to predict the erosion rate of W components and the resulting W density in the plasma is crucial for designing fusion reactors. The simulations studied in this thesis predict the sputtering of W atoms from plasma-facing components, their ionisation in the scrape-off layer, and the transport of W ions parallel and perpendicular to the magnetic field in the scrape-off layer, pedestal, and core plasma regions. In this thesis, the predicted W erosion rate at the JET divertor targets is found to have a negligible impact on the W density in the main plasma due to efficient divertor screening. According to EDGE2D-EIRENE, DIVIMP, and ERO2.0 predictions, the W influx to the main plasma is predominately due to W sputtering near the low-field side divertor entrance due to energetic D atoms created by charge-exchange. EDGE2D-EIRENE consistently predicts 30--40% lower W density in the main plasma compared to DIVIMP in both L-mode and H-mode plasmas. In this work, the difference is demonstrated to be mostly due to the bundling of the 74 W ionised charge states into 6 fluid species in EDGE2D-EIRENE. Integrated core-edge JINTRAC predictions agree with measurements of the main plasma W density in L-mode, indicating that both the DIVIMP and EDGE2D-EIRENE predictions are consistent with the experimentally inferred W density within a factor of 2. Simulations of high-power type-I ELMy H-mode plasmas, using ERO2.0 for W erosion and transport in the edge plasma and JINTRAC with NEO for core W transport, predict the 2D poloidal W density profile in agreement with the inferred W density within the modelling uncertainties. Accurate predictions of the main plasma W density in type-I ELMy H-mode require thorough validation of the simulated ELM and edge transport barrier properties, as well as precise reproduction of the toroidal rotation frequency, and the ion temperature and density gradients in the main plasma.