arXiv subjects

F. Subba

Publications and source records attributed to F. Subba.

7 recordsLinked to original sources

arXiv2026

Implementation and first application of EMC3-EIRENE on DTT for assessing the heat load on the ICRH antenna

This paper reports on the implementation process of the three-dimensional (3D) edge plasma transport code EMC3-EIRENE on the Divertor Tokamak Test (DTT) facility and the results of its first application, with a focus on assessing the heat load on the Ion Cyclotron Resonance Heating (ICRH) antenna surfaces. Using axisymmetric geometries and the SOLPS-ITER simulation results as a reference, we first evaluate the performance of the EMC3-EIRENE in describing axisymmetric plasmas to ensure correct code modelling setup for later complex 3D applications. We then incorporate the ICRH antenna structure in our 3D simulations, assuming different toroidal symmetry for the antenna to determine whether the heat load assessment can be carried out with reduced computational effort, and to what extent a 3D assessment deviates from a 2D approximation. The predictions of the 3D antenna heat load distribution are obtained and the peak values on the top plate and the two side plates reach 0.9, 2.1 and 3.8 MW/m2, respectively. Finally, 3D gas puffing is included to evaluate its impact on the antenna heat load. The corresponding 3D edge plasma behavior is presented under the coupled effects of gas puffing and the antenna geometrical structure.

physics.plasm-ph↗

arXiv2025

Runaway electron avalanche and macroscopic beam formation: simulations of the DTT full power scenario

The transition of the Divertor Tokamak Test (DTT) facility from its initial commissioning phase (Day-0, plasma current $I_{p}=2$ MA) to the full power scenario ($I_{p}=5.5$ MA) introduces a critical shift in the dynamics of runaway electrons (REs) generation. While previous predictive studies of the low-current scenario indicated a robust safety margin against RE beam formation, this work reveals that the exponential scaling of the RE avalanche gain with plasma current severely narrows the safe operational window in the full power scenario. Using the non-linear magnetohydrodynamic code JOREK, we perform comprehensive 2D simulations of the current quench (CQ) phase of several disruption scenarios, systematically scanning initial RE seed currents and injected impurity levels. The results demonstrate that in the full power scenario, the avalanche multiplication factor is sufficiently high ($G_\text{av} \approx 1.3 \cdot 10^5$) to convert a mere 5.5 A seed current into macroscopic RE beams of $\approx 0.7$ MA when large amounts of impurities are present. For even higher RE seeds, the RE current can peak at $ \approx 3.2$ MA, constituting up to $\approx$ 80% of the total plasma current during the CQ. These findings suggest that, unlike the Day-0 phase, the disruption mitigation strategy for the full power scenario involves a careful balance between thermal load mitigation and RE avoidance, necessitating a well-chosen quantity of injected impurities. This work provides the baseline needed for future estimations of RE loads on the plasma-facing components of DTT, which will be essential for designing and positioning mitigation components like sacrificial limiters.

physics.plasm-ph↗

arXiv2025

SOLPS-ITER Numerical Simulations of ITER-scale Snowflake Divertors: Low-Field-Side SF-/SF+ and High-Field-Side SF-/SF+ Configurations

With edge plasma code SOLS-ITER, we study four Snowflake (SF) configurations for an ITER-size tokamak, with toroidal magnetic field BT=5T, major radius R=5m and plasma current Ip=10MA. Our aim is to provide insights on SF divertor design for future devices. In this work, the impacts of magnetic geometry and divertor target geometry in the four types of SF configurations on plasma behavior and power exhaust performance are investigated in detail. Low-recycling regime, high-recycling and detachment in the four types of SF divertors are obtained through an upstream density scan. The secondary X-point positions of SF divertors are systematically varied to examine their impact. For Low-Field-Side (LFS) SF- and High-Field-Side (HFS) SF- divertors the observed power splitting, induced by the secondary X-point, is consistent with experimental observations. The effect of target geometry is studied by comparing the flat target plates with the ITER-like divertor shape. The overall simulation results reveal a notable consequence of the LFS SF- divertor: closed structure of the inner target with high inclined plate can compress recycling neutrals originating from the HFS divertor region into the LFS SOL and PFR regions. This results in considerable volumetric dissipation through strong ionization and recombination, causing the connected outer target region to detach. This feature can be considered in the design of the LFS SF- divertor for future devices. For the LFS and HFS SF+ divertors, the region between the two X-points exhibits strong ionization and recombination sources close to the primary X-point. This feature might be beneficial for the formation of an X-point radiator, but would require further impurity seeding simulation study.

physics.plasm-ph↗

arXiv2025

Assessment of the Runaway Electrons induced damage to the Tokamak First Wall

The study assessed the damage caused by Runaway Electrons (RE) on First Wall tiles, comparing the effects on Beryllium and Tungsten. This was done by using realistic RE energy distribution functions to replicate RE impacts through the FLUKA code. These energy distribution functions are based on the ASDEX Upgrade experiment # 39012. The parametric analysis carried out with FLUKA in the presence of magnetic fields indicated a clear relationship between the beam impact angle and the material deposited energy, demonstrating that higher impact angles lead to deeper electron penetration and greater deposited energies. A finite element model based on apparent heat capacity formulation in FreeFem++ was developed to analyze the material thermal response to such thermal loads using volumetric energy density profiles from FLUKA simulations as input. Different RE current values were simulated to show its influence on the evolution of the material temperature and melting thickness

physics.plasm-ph↗

arXiv2023

Post disruption reconnection event driven by a runaway current

The role of a runaway current in a post disruption plasma is investigated through numerical simulations in an asymmetric magnetic reconnection event. While the runaways do not alter the linear growth of the island, they lead to a rotation of the island in the poloidal direction as found in [C. Liu et al. Physics of Plasmas 27, 092507 (2020)]. The role of a microlayer smaller than the resistive one is thoroughly investigated. While the resistive layer controls the transition of the island from the linear to the nonlinear stage, the microlayer width causes the runaways to become nonlinear as soon as the size of the island exceeds it. Moreover, this transition of the runways electrons to the nonlinear phase is accompanied by a drastic redistribution of runaways within the island with respect to the symmetric case. The influence of the electron skin depth on the linear evolution is also taken into account. Finally, nonlinear simulations show that the rotation frequency tends toward zero when the island saturates.

physics.plasm-ph↗

arXiv2023

SOLPS-ITER numerical evaluation about the effect of drifts in a divertor configuration of ASDEX-Upgrade and a limiter configuration of J-TEXT

The High Field High Density Region (HFSFD) has been experimentally observed in both divertor and limiter tokamak devices. In order to numerically reproduced the HFSHD region in the limiter tokamak device J-TEXT, we first performed SOLPS-ITER simulations on the J-TEXT limiter tokamak with the activation of drifts, which is associated with the HFSHD region. The validated physical models, which is from ASDEX Upgrade (AUG) divertor modelling including full drifts and currents, were applied. Through a gas puffing rate scan, both attached and detached regimes were numerically obtained in the AUG divertor and J-TEXT limiter. The key plasma parameters in the J-TEXT limiter are evaluated with and without drifts that have a qualitative performance like AUG except the roll-overment of the total ion flux at the targets. The drift effects on the target profiles are investigated in which the maximum electron temperature at the outer targets is 15eV and 5eV respectively. When the outer targets are attached in the J-TEXT limiter and AUG divertor, the drifts result in the partial detachment of the inner targets. In the detached regimes, the drifts decrease the electron temperature on AUG divertor targets. However, for the J-TEXT limiter, the electron temperature only decreases at the far SOL region. The effect of drifts on the neutral density is also presented.

physics.plasm-ph↗

arXiv2022

Parametric scaling of power exhaust in EU-DEMO alternative divertor simulations

Investigations of parametric scaling of power exhaust in the alternative divertor configuration (ADC) SOLPS-ITER simulation database of the EU-DEMO are conducted and compared to predictions based on the Lengyel model. The Lengyel model overpredicts the necessary argon concentrations for LFS divertor detachment by about a factor of 5-10 relative to the SOLPS-ITER simulations. Therefore, while the Lengyel model predicts that plasmas with accetable divertor heat loads in EU-DEMO would exceed the tolerable upstream impurity concentrations by a large margin, there are several SOLPS-ITER solutions within an acceptable operational space. The SOLPS-ITER simulations indicate that, unlike assumed by the standard Lengyel model, there are significant heat dissipation mechanisms other than argon radiation, such as cross-field transport, that reduce the role of argon radiation by a factor of 2 to 3. Furthermore, the Lengyel model assumes that the radiation front is powered by parallel heat conduction only, which tends to lead to a narrow radiation front as the radiative efficiency increases strongly with reducing thermal conductivity. As a result, the radiative volume and total impurity radiation are suppressed for a given impurity concentration. However, the SOLPS-ITER simulations indicate that other mechanisms, such as cross-field transport, can compete with parallel heat conduction within the radiative front and increase the radiative volume. Due to these findings, usage of the standard Lengyel model for analyzing scaling between divertor conditions and configurations for devices such as EU-DEMO is strongly discouraged.

physics.plasm-ph↗