Search

Numerical scan at constant β shows that core and scrape‐off layer (SOL) radiations do not depend on the plasma current (Ip). Whereas the SOL radiation increases with seeding, the core radiation, however, does not continue to increase with seeding but rolls over at higher seeding rates in the simulations. The core plasma contamination by W ions is low, cW ≪ 10−4. When the seeding starts, an increase in radiation power leading to a reduction in Ploss = (Paux − Prad) is observed, influencing the plasma confinement. The power scan at constant Ip indicates that the core radiation, Pplate, PSOL (and even SOL radiation), saturates with seeding. In addition, strong dilution with increasing seeding (Zeff ≫ 3) and large W concentrations with increasing power are found. Comparing neon with nitrogen seeding, it is seen that neon leads to slightly larger total radiation than nitrogen. However, that is achieved with much higher plasma contamination (Zeff ∼ 4–5) and dilution in the case of Ne, and simultaneously the power crossing the separatrix is lower for Ne than for N, indicating better H‐mode performance in N2‐seeded discharges. [ABSTRACT FROM AUTHOR]

Edge plasma properties have been modified in the Saskatchewan Torus-Modified tokamak by means of resonant magnetic perturbations (RMP). It has been found that the radial profiles of ion saturation current and floating potential in the edge region can be modified by an externally applied static (m = 2, n = 1) RMP field. An increase in the pedestal plasma density (n) and more negative electric field (Er) have been observed in the plasma edge region. It is believed that the RMP field altered the plasma transport in the edge and scrape-off layer regions, leading to a higher density pedestal and a potential drop in some cases. During the enhanced confinement phase, it is possible to identify a region where intermittent transport events, the so-called blobs, are created and the holes of lower density left behind. [ABSTRACT FROM AUTHOR]

In this work, we use a method based on the concept of particle confinement time uniqueness to calculate the electron density and temperature in ohmically heated, edge plasma of the Hefei tokamak-7. Here, with the help of the data taken from Johnson and Hinnov's table, we have done an extensive work to find electron densities and temperatures that satisfy the uniqueness to evaluate the temporal evolution of electron density and temperature . The results are in good agreement as measured from the Langmuir probe array in previous works. [ABSTRACT FROM AUTHOR]

A two dimension-in-space and three dimension-in-velocity (2d3v) Particle-In-Cell (PIC) code is applied to investigate the plasma behaviors at the divertor gaps region in this work. Electron and D + ion fluxes to the tile surface in the poloidal and toroidal gaps for different shaped edges are compared to demonstrate the optimized tile geometry. For poloidal gap, shaped edge in the shadowing side makes more ions penetrate into the gap, while shaped edge in the wetted side can mitigate the peak flux value. For toroidal gap, most ions entering the gap impinge on the side tile mainly due to the E × B drift, and shaped wetted edges also can mitigate the peak heat fluxes. In addition, effects of magnetic field inclination angle from toroidal direction on the plasma behaviors are simulated for poloidal and toroidal gaps, respectively. It is found that the magnetic field angles don’t influence the plasma behaviors in poloidal gap; while significant changes have been observed in the toroidal gap. [ABSTRACT FROM AUTHOR]

ITER expects to produce fusion power of about 0.5GW when operating with tungsten (W) divertor and beryllium (Be) wall. The influx of W from divertor can have significant influence on the discharge performance. This work describes predictive integrated numerical modeling of ITER discharges using the COREDIV code, which self-consistently solves the 1D radial energy and particle transport in the core region and 2D multi-fluid transport in the SOL. Calculations are performed for inductive ITER scenarios with intrinsic (W, Be and He) impurities and with seeded impurities (Ne and Ar) for different particle and heat transport in the core and different radial transport in the SOL. Simulations show, that only for sufficiently high radial diffusion (both in the core and in the SOL regions), it is possible to achieve H-mode mode plasma operation (power to SOL > L-H threshold power) with acceptable low level of power reaching the divertor plates. For argon seeding, the operational window is much smaller than for neon case due to enhanced core radiation (in comparison to Ne). Particle transport in the core characterized by the ratio of particle diffusion to thermal conductivity) has strong influence on the predicted ITER performance. [ABSTRACT FROM AUTHOR]

Numerical simulation with COREDIV code of DEMO H-mode discharges (tungsten divertor and wall) are performed considering the influence of seeding impurities with different atomic numbers: Ne, Ar and Kr on the DEMO scenarios. The approach is based on integrated numerical modeling using the COREDIV code, which self-consistently solves radial transport equations in the core region and 2D multi-fluid transport in the SOL. In this paper we focus on investigations how the operational domain of DEMO can be influenced by seeding gasses. Simulations with the updated prompt re-deposition model implemented in the code show that only for Ar and Kr, for high enough radial diffusion in the SOL, it is possible to achieve H-mode plasma operation (power to the SOL> L-H transition threshold power) with acceptable level of the power to the target plates. For neon seeding such regime of operation seems not to be possible. [ABSTRACT FROM AUTHOR]

Due to the extreme conditions required to produce energy by nuclear fusion in tokamaks, simulating the plasma behavior is an important but challenging task. We focus on the edge part of the plasma, where fluid approaches are probably the best suited, and our approach relies on the Braginskii ion–electron model. Assuming that the electric field is electrostatic, this yields a set of 10 strongly coupled and non-linear conservation equations that exhibit multiscale and anisotropy features. The computational domain is a torus of complex geometrical section, that corresponds to the divertor configuration, i.e. with an “X-point” in the magnetic surfaces. To capture the complex physics that is involved, high order methods are used: The time-discretization is based on a Strang splitting, that combines implicit and explicit high order Runge–Kutta schemes, and the space discretization makes use of the spectral element method in the poloidal plane together with Fourier expansions in the toroidal direction. The paper thoroughly describes the algorithms that have been developed, provides some numerical validations of the key algorithms and exhibits the results of preliminary numerical experiments. In particular, we point out that the highest frequency of the system is intermediate between the ion and electron cyclotron frequencies. [ABSTRACT FROM AUTHOR]

The new code TOKAM3X simulates plasma turbulence in full torus geometry including the open field lines of the Scrape-off Layer (SOL) and the edge closed field lines region in the vicinity of the separatrix. Based on drift-reduced Braginskii equations, TOKAM3X is able to simulate both limited and diverted plasmas. Turbulence is flux driven by incoming particles from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed so that interactions between large scale flows and turbulence are consistently treated. Based on a domain decomposition, specific numerical schemes are proposed using conservative finite-differences associated to a semi-implicit time advancement. The process computation is multi-threaded and based on MPI and OpenMP libraries. In this paper, fluid model equations are presented together with the proposed numerical methods. The code is verified using the manufactured solution technique and validated through documented simple experiments. Finally, first simulations of edge plasma turbulence in X-point geometry are also introduced in a JET geometry. [ABSTRACT FROM AUTHOR]

The modeling of the ITER edge is performed with the use of the code B2SOLPS5.2 in the presence of the electron conductivity caused by RMPs as well as for the reference case with the same input parameters but without RMPs. The radial electric field close to the neoclassical one is obtained without RMPs. Even the modest level of RMPs changes the direction of the electric field and causes the toroidal spin-up of the edge plasma. At the same time the pump-out effect is small. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Power exhaust is one of the major challenges that future devices such as ITER and DEMO will face. Because of the lack of identified scaling parameters, predictions for divertor plasma conditions in these devices have to rely on detailed modelling. Most plasma edge simulations carried out so far rely on transport codes, which most of the times consist of a fluid code for the plasma coupled to a kinetic Monte Carlo (MC) code for neutral particles. One of the main difficulties in interpreting code results is the statistical noise from the MC procedure, which makes it difficult to define a convergence criterion for the simulations. In this work, we elaborate on similarities between noisy transport code simulations and turbulence simulations, and argue that the time averaged solution is a well defined stationary solution for the system. We illustrate these ideas with a simple slab test case with fluid neutrals, to which we add synthetic noise. In this case, the effects of noise are found to be significant only at high noise levels and for large enough correlations times. [ABSTRACT FROM AUTHOR]

Possibilities of obtaining the analytical solutions of the one-dimensional equation of radiative transfer in resonance atomic/ionic lines in the Biberman-Holstein model for testing the edge plasma codes are investigated. It is shown that for some types of similarity of spatial profiles of three characteristics, namely, background plasma density, line shape width and non-radiation source of atomic excitation, the profile of excited atoms density may be described analytically in terms of the similarity of the above-mentioned profiles. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Implementation of self-consistent model of plasma recombination into the BIT1 PIC code and the simulation of detached SOL plasma are described. Our simulations indicate that in a strongly recombining plasma edge the sheath properties do not change qualitatively. The most affected parameter is the sheath heat transmission coefficient, which can increase by order of magnitude. [ABSTRACT FROM AUTHOR]

Five ELMy H-mode Ne seeded JET pulses have been simulated with the self-consistent core-SOL model COREDIV. In this five pulse series only the Ne seeding rate was changed shot by shot, allowing a thorough study of the effect of Ne seeding on the total radiated power and of its distribution between core and SOL tobe made. The increase in the simulations of the Ne seeding rate level above that achieved in experiments shows saturation of the total radiated power at a relatively low radiated-heating power ratio ( f rad = 0.60) and a further increase of the ratio of SOL to core radiation, in agreement with the reduction of W release at high Ne seeding level. In spite of the uncertainties caused by the simplified SOL model of COREDIV (neutral model, absence of ELMs and slab model for the SOL), the increase of the perpendicular transport in the SOL with increasing Ne seeding rate, which allows to reproduce numerically the experimental distribution core-SOL of the radiated power, appears to be of general applicability. [ABSTRACT FROM AUTHOR]

There is experimental evidence that the pedestal dynamics in type-I ELMy H-mode discharges is significantly affected by a change in the recycling conditions at the tungsten plasma-facing components (W-PFCs) after an ELM event. The integrated code JINTRAC has been employed to assess the impact of recycling conditions during type-I ELMs in JET ITER-like wall H-mode discharges. By employing a heuristic approach, a model to mimic the physical processes leading to formation and release (i.e. outgassing) of finite near-surface fuel reservoirs in W-PFCs has been implemented into the EDGE2D-EIRENE plasma-wall interaction code being part of JINTRAC. As main result it is shown, that a delay in the density pedestal build-up after an ELM event can be provoked by reduced recycling induced by depleted W-PFC particle near-surface reservoirs. However the pedestal temperature evolution is barely affected by the change in recycling parameters suggesting that the presented model is incomplete. [ABSTRACT FROM AUTHOR]

In this paper we present the comparison of simulations with the numerical codes COREDIV and SOLPS5.0 for JET L-mode discharges with ITER like wall (ILW). The simulations have been performed for L-mode shots with and without nitrogen seeding (#82291 - 9) which are characterised by relatively low auxiliary heating power ( P NBI = 1.1 MW) and low electron density ( ne = 2.35 × 1019 m-3). Comparisons are made to the experimental measurements (e.g. radiation levels, plasma profiles) and the differences between the results from the two codes (e.g. temperature and density profiles at the outer divertor plate) are shown and discussed. [ABSTRACT FROM AUTHOR]

In this paper numerical simulations with the self-consistent COREDIV code of the planned JET DT experiments have been performed. First, record shot from the 1997 experiments was simulated and good agreement with experimental data has been found. Direct extrapolation of the carbon wall results to the new ILW configuration (discharge parameters as for the shot #42746) shows very good core plasma performance with even higher fusion power but with too large power to the divertor. However, with the neon seeding the heat load and plate temperatures can be efficiently reduced keeping good the plasma performance. Investigations have been done also for the planned DT operation scenario based on a conventional ELMy H-mode at high plasma current and magnetic field. Simulations for the reference ELMy H-mode shot #87412 show good agreement with the experimental data but the direct extrapolation of the DD results to deuterium-tritium operation shows relatively poor performance in terms of the achieved fusion power. The situation improves, if the highest heating power is assumed (41 MW) and fusion powers in the excess of 12 MW can be achieved. All the high performance shots require the heat load control by neon seeding which shows rather beneficial effect on the plasma performance allowing for relatively wide operational window in terms of the amount of the allowed neon influx. [ABSTRACT FROM AUTHOR]

The self-consistent COREDIV code is used to simulate discharges in a tokamak plasma, especially the influence of impurities during nitrogen and argon seeding on the key plasma parameters. The calculations are performed with and without taking into account the W prompt redeposition in the divertor area and are compared to the experimental results acquired on ASDEX Upgrade tokamak (shots #29254 and #29257). For both impurities the modeling shows a better agreement with the experiment in the case without prompt redeposition. It is attributed to higher average tungsten concentration, which on the other hand seriously exceeds the experimental value. By turning the prompt redeposition process on, the W concentration is lowered, what, in turn, results in underestimation of the radiative power losses. By analyzing the influence of the transport coefficients on the radiative power loss and average W concentration it is concluded that the way to compromise the opposing tendencies is to include the edge-localized mode flushing mechanism into the code, which dominates the experimental particle and energy balance. Also performing the calculations with both anomalous and neoclassical diffusion transport mechanisms included is suggested. [ABSTRACT FROM AUTHOR]

To facilitate the design of the China Fusion Engineering Testing Reactor (CFETR), predictive modeling for the assessment and optimization of the divertor performances is an indispensable approach. This paper presents the modeling of the edge plasma behaviors as well as the W erosion and transport properties in CFETR with ITER-like divertor by using the B2-Eirene/SOLPS 5.0 code package together with the Monte Carlo impurity transport code DIVIMP. As expected, SOLPS modeling of divertor-SOL plasmas finds that the peak heat flux onto the divertor targets greatly exceeds 10 MW/m, an engineering limit posed to the steady-state and/or long-pulse operation of the next-step fusion devices, for a wide range of plasma conditions, and thus modeling of Ar puffing by scanning the puffing rate for radiative divertor is performed. As the increase of the Ar puffing rate, the peak target heat fluxes and plasma temperature decreases exponentially,reflecting that Ar puffing is highly effective at power exhausting. Based on the ion fluxes from SOLPS, the W erosion is calculated by taking into consideration the bombardment of both D and Ar ions, and then the W plasma concentrations are calculated based on the W erosion fluxes using DIVIMP. The calculations show that if the Ar puffing only being used to reduce the divertor heat load, the W plasma contamination in the core plasma exceeds the tolerable value (<10), which demonstrates that some further upgrading of the divertor geometry is still needed. [ABSTRACT FROM AUTHOR]

The penalization method Ref. [1] is used to model the interaction of 3D probe with an isothermal plasma. Density maps show that the region perturbed by the obstacle, is not restricted to its near neighbourhood, but can extend to the whole SOL. In the particular case of a probe, which is used to measure local plasma parameters, this impact can lead to violation of assumptions of locality of the perturbation usually used in determining Mach number from the imbalance in density on both sides of the probe. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The EMC3-Eirene code is improved in many aspects. Ad hoc boundary conditions for intrinsic impurities at the SOL-core interface are removed by implicitly coupling to a 1D core model. Non-uniform cross-field transport coefficients are allowed in the new code version. A particle splitting technique is implemented for improving the Monte Carlo statistic in low-temperature ranges of most interest. Domain splitting, which was possible for the toroidal direction only, is now feasible for all three directions, facilitating mesh optimization for any specific divertor configuration. Stellarator-specific constraints on mesh construction have been relaxed. Axisymmetric neutral-facing components have been moved to cylindrical coordinates. All these features have improved the code performance and capability significantly. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

After the code parameters have been fixed by the numerical modeling of a well diagnosed JET pulse, the electron density and the input power have been changed, resulting in 4 density scans ( 〈ne〉 in the range 3.8 - 8.2 x 1019m-3) at P in = 17, 22, 27, 32 MW. At any given power level, W flux decreases with increasing 〈ne〉 as a consequence of the decrease in Te at the target plates. Also the W concentration in the core ( cW) decreases, but this not necessarily leads to reduced core radiation. Indeed, while at high P in the core radiation decreases with density, at low P in it increases. At high 〈ne〉 the increase in the input power leads to enhanced P radPrad, leaving, however, nearly unchanged the power radiated fraction f rad Indeed, the increase in f rad with P in is observed only at low 〈ne〉, up to a level of about f rad = 0.4. These numerical results, linked to the non-linear self-consistent physics of W production and transport, suggest the best conditions are achieved when the level of the electron density is adapted to the level of the available P in. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The importance of core-edge coupling in the WEST tokamak via tungsten production and core radiation is investigated with the COREDIV code. We first focus on the idealized situation where the plasma is free of light impurities, and show that for achievable high density discharges tungsten production can be essentially extinguished. For lower densities, core edge coupling is strong, that is tungsten plays a major role in regulating the power flowing through the Scrape-off layer. The latter is found to saturate with increasing heating power due to increasing radiation losses in the core. Then we investigate the extent to which light impurities change this picture by performing a scan in boron concentration, since Ion Cyclotron Resonance Heating antenna protections may be boron coated. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The article discusses the role of electric field, drifts, and currents in the edge plasma of fusion devices and its effect on pedestal, divertor assymetry, and resonant magnetic perturbations (RMP) consequences. Topics include the radial electric field in the edge plasma, the direction of drifts and currents in the scrape off layer (SOL) and divertors, and the parallel flows in the SOL.

The several Demo design concepts have been analyzed using the code Corediv solving self consistently the core and scrape off layer regions. The numerical analyses show that there exists the limit on the concentration of impurities above which the solution with burning plasma does not exists. This limits reduce the possibility of reduction of power loads to target plate. In the paper the admissible range of seeded impurity concentration introduced to reduce the power load to divertor plate is analyzed. The possible mechanisms leading to the limitation are shown. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

It is argued that the structure observed in radial profiles in the tokamak edge plasma is determined by the requirements of ion particle, momentum and energy conservation and the underlying transport mechanisms in the presence of sources and losses of particles, energy and momentum. The intent of this paper is to define a systematic formalism that can be employed for evaluating these transport coefficients from experimental inference and comparison with theory. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Fusion performance of ITER H-mode plasmas in presence of intrinsic (He, Be and W) and seeded (Ne) im purities is investigated in self-consistent core-pedestal-SOL simulations for two values of pedestal density n ped e = 6.12 × 1019m-3 (reference case) and 9 × 1019m-3 using the JETTO and COREDIV codes iteratively. The theory-based GLF23 transport model which predicts a relatively high density peaking ( n e0/〈 n e〉 = 1.37 ÷ 1.39) has been used for this study. For medium density case the H-mode operation with a power across the separatrix well above the L-H power threshold has been obtained, but the divertor heat loads exceed 10 MW/m2. Neon gas puff strongly reduces the power to divertor plate in this scenario, increasing at the same time the tungsten sputtering by Ne that leads to even larger core radiation and dilution, than in the case without Ne. As a result, the medium density H-mode operation with Ne seeding and low divertor heat loads is barely above the L-H power threshold. This operational point is weakly sensitive to tungsten inward pinch due to a strong coupling between W transport, radiation and sputtering. At high density with much larger core radiation (90 MW), the possibility of H-mode operation strongly depends on the choice transport model, with the power through the separatrix well below (above) the L-H power threshold in simulations with the GLF23 ( H98 y scaling-based) transport model. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this paper numerical simulations with COREDIV code of JET discharges with ITER-like wall are presented. We concentrate on the JET H-mode and hybrid scenarios with nitrogen seeding and all simulations have been performed with the same transport model and only the discharge input parameters like auxiliary heating P aux, line average plasma density n lin e, confinement factor H98, nitrogen input flux Γ puff N were changed in the calcu lations. The separatrix density n sep e is an input parameter in our model and has been kept equal to 0.4÷0.5 n lin ein the simulations, with the recycling coefficient adjusted accordingly. It has been shown that COREDIV is able to reproduce basic parameters of nitrogen seeded discharges for both H-mode and hybrid scenarios. We have achieved reasonable agreement with global plasma parameters like radiations levels, Z eff and tungsten concentrations and the plasma profiles, including density, temperature and radiation are in very good agreement with experimental data. The agreement of the code results with the experimental data might be even better, if the simulations are further tuned taking into account uncertainties to the sputtering model, separatrix density or SOL transport. Simulations show that the observed Z eff level is defined mostly by the low Z impurity content, Be and N2 in the considered shots. It has been found that the tungsten radiation plays always very important role and can not be mitigated even by strong influx of nitrogen. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: In this work, we compare different interpolation operators in the context of particle tracking with an emphasis on situations involving velocity field with steep gradients. Since, in this case, most classical methods give rise to the Gibbs phenomenon (generation of oscillations near discontinuities), we present new methods for particle tracking based on subdivision schemes and especially on the Piecewise Parabolic Harmonic (PPH) scheme which has shown its advantage in image processing in presence of strong contrasts. First an analytic univariate case with a discontinuous velocity field is considered in order to highlight the effect of the Gibbs phenomenon on trajectory calculation. Theoretical results are provided. Then, we show, regardless of the interpolation method, the need to use a conservative approach when integrating a conservative problem with a velocity field deriving from a potential. Finally, the PPH scheme is applied in a more realistic case of a time-dependent potential encountered in the edge turbulence of magnetically confined plasmas, to compare the propagation of density structures (turbulence bursts) with the dynamics of test particles. This study highlights the difference between particle transport and density transport in turbulent fields. [Copyright &y& Elsevier]