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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 νe≈30$$ {\nu}_e\approx 30 $$), 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 (νe≈55,000$$ {\nu}_e\approx 55,000 $$), 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An ion temperature anisotropy model including cross‐field drifts has been implemented in the 2D transport code UEDGE. Two ion temperature equations are solved in the model to give separate ion temperatures perpendicular and parallel to the magnetic field, which results in an additional mirror force for ion parallel transport and also leads to an additional curvature drift in the perpendicular direction. In our previous work, an ion temperature anisotropy model was implemented and applied to the full 2D version of UEDGE including recycled neutrals. The simulation results showed that the mirror force due to anisotropy reduces ion parallel flow velocity, however, the simulations were presented without cross‐field electric and magnetic drifts. Nevertheless, in present medium‐size tokamaks or future compact fusion devices, cross‐fields are important. In this work, the anisotropy model is extended to be compatible with the inclusion of cross‐field drifts. Preliminary results on comparison between the model solutions with and without cross‐field drifts are presented. [ABSTRACT FROM AUTHOR]

SOLPS‐ITER L‐mode‐like simulations with the full set of currents and drift velocities activated, and fluid neutrals have been carried out to interpret experimental results obtained in AUG. Drifts are critical to quantitatively reproduce the experimental results; however, simulations without drifts can also reproduce some trends qualitatively. The magnitude and dependence of the peak heat flux onto both targets on the upstream collisionality are, in general, in quantitative agreement within uncertainties with infrared thermography measurements in favourable field direction. The onset of power detachment is observed. In unfavourable toroidal field direction, a more symmetrical inner/outer target solution with regards to the power distribution is predicted, in agreement with experimental observations. However, also in unfavourable toroidal field direction, insufficient power is dissipated in the simulations and therefore qpeak, inn is overpredicted by up to a factor of 4 and qpeak, out by up to a factor of 1.5. The largest contribution to the sources due to radial transport in the energy balance equation is the radial divergence of the energy flux due to VE × B. [ABSTRACT FROM AUTHOR]

Advanced divertor configurations modify the magnetic geometry of the divertor to achieve a combination of strong magnetic flux expansion, increased connection length and higher divertor volume—to improve detachment stability, neutral/impurity confinement and heat‐channel broadening. In this paper, we discuss the modification of the flux‐coordinate independent (FCI) turbulence code GRILLIX to treat generalized magnetic geometry, to allow for the investigation of the effect of magnetic geometry on turbulent structures in the edge and scrape‐off layer (SOL). The development of grids and parallel operators from numerically defined magnetic equilibria is discussed, as is the application of boundary conditions via penalization, with the finite‐width method generalized to treat complex non‐conformal boundaries. Initial testing of hyperbolic (advection) and parabolic (diffusion) test cases are presented for the Snowflake scenario. [ABSTRACT FROM AUTHOR]

Applying gyrokinetic simulations in theoretical turbulence and transport studies for the plasma edge and scrape‐off layer (SOL) presents significant challenges. To particularly account for steep density and temperature gradients in the SOL, the "full‐f" code PICLS was developed. PICLS is a gyrokinetic particle‐in‐cell (PIC) code, is based on an electrostatic model with a linearized field equation, and uses kinetic electrons. In previously published results, we applied PICLS to the well‐studied 1D parallel transport problem during an edge‐localized mode (ELM) in the SOL without collisions. As an extension to this collision‐less case and in preparation for 3D simulations, in this work, a collisional model will be introduced. The implemented Lenard–Bernstein collision operator and its Langevin discretization will be shown. Conservation properties of the collision operator, as well as a comparison of the collisional and non‐collisional case, will be discussed. [ABSTRACT FROM AUTHOR]

We report new results of full‐torus gyrokinetic simulations of electrostatic turbulence with Elmfire spanning from the magnetic axis to the scrape‐off layer (SOL). The new implementation presented here uses the logical boundary condition, which allows for improved stability and flexibility in terms of geometry. We simulate the full plasma of the FT‐2 tokamak (Ioffe Institute, Saint‐Petersburg, Russian Federation), with two poloidal limiters defining the SOL. We recover expected results in the SOL and find an improvement in our capacity to model the experimental particle and energy sinks in the SOL. [ABSTRACT FROM AUTHOR]

An investigation is proposed on the dynamics of blobs in scrape‐off layer (SOL) plasmas. Starting from a common reduced model predicting the dynamics of isolated blobs, we emphasize the necessity of verifying the meaningfulness of the notion of generic or average blob. A definition and methodology is proposed and tested on turbulent data built from two‐dimensional (2D) flux‐driven simulations. Average blobs are shown to possess physical properties in relatively good agreement with predictions made using the isolated blob model. An application to experimental data from Tore Supra is then demonstrated. A striking agreement is found between average blob velocities measured in experiments and isolated blob model predictions. It suggests that the turbulent transport in the SOL of limited plasmas is correctly described by 2D interchange models. A discussion is finally proposed that blob models have to focus on intermittency in order to find a field of application. [ABSTRACT FROM AUTHOR]

Hotspot generation by lower‐hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D‐1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function. An island structure is formed in the suprathermal part at the phase velocity of the external electrostatic drive. The non‐linear features enhance the plasma response, driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function, with extent reaching one thermal velocity, is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of the small‐scale features generated by the LH launchers, which are responsible for the interaction with the cold electrons. This mechanism can trigger hotspot generation further in the scrape‐off layer than otherwise expected. [ABSTRACT FROM AUTHOR]

Two mechanisms able to generate a transport barrier by the stabilization of turbulence are analysed: the radial shear of the E × B velocity and the radial gradient of this shear. These two mechanisms are artificially forced in dedicated 2D non-linear fluid simulations to study their impact on turbulence in the Scrape-Off Layer. Generated barriers are characterized by their turbulence stopping capability and a key parameter, the barrier efficiency, is pointed out. The first two moments of this criterion can be studied to quantify the global efficiency, shape and width of the barrier as well as its intermittency. It is found that both mechanisms can drive intermittent or stable barriers but the radial shear mechanism generates stronger relaxation events. Small scale structures are damped by the E × B velocity shear while the radial shear gradient acts mainly on large scales. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Benchmarks of the new 1D2V kinetic code KIPP (KInetic code for Plasma Periphery) for parallel plasma transport in the scrape-off layer (SOL) and divertor of magnetic confinement fusion devices are presented. The code is based on the continuum discretisation scheme for the Vlasov-Fokker-Planck equation. It assumes plasma quasi-neutrality, maintained by the electron parallel momentum balance, and uses a logical sheath boundary condition for the Debye potential drop at material surfaces. The code is parallelized under the MPI environment, with the most time consuming part, Coulomb collisions, being calculated simultaneously for all spatial locations by separate processors using a sparse matrix solver for the full non-linear collision operator in two velocity variables: parallel and gyro-averaged perpendicular velocities. KIPP is being developed with the aim of integrating it into SOLPS (B2-Eirene), to replace fluid treatment of parallel plasma transport with the kinetic one. Benchmark results for parallel electron heat conduction and electron-ion thermoforce for highly collisional plasmas are presented, as well as some results for less collisional plasmas. This paper focuses on the 1d2v features of the code, with the 0d2v features presented earlier in [1, 2]. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A reciprocating probe head with six pins was used for localized measurements of electric fields and densities in the scrape-off layer (SOL) of ASDEX Upgrade (AUG) up to the edge shear layer (SL) near the Last Closed Flux Surface (LCFS). The edge SL is characterized by a strong sudden change in the poloidal velocity vθ close to the separatrix. The probes were used to determine this velocity by different methods which are critically compared to each other concerning their reliability. By the first method the poloidal velocity was deduced from the radial electric field Er measured by two radially staggered probe pins, with vθ being due to the E r × Bϕ-drift ( Bϕ is the toroidal field). The two other methods utilized the cross correlation of two poloidally staggered ion-biased probes and two poloidally staggered floating probes, respectively. In this case the time lags with maximum cross correlation were used to determine the poloidal velocity and its jump, yielding comparable results to the first method. Also the method of conditional averaging was applied to the latter signals. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

New measurements of ion transport in the scrape-off layer (SOL) during inter-ELM periods are obtained from a retarding field analyzer (RFA) in the ASDEX Upgrade tokamak. The ion current density measured in the far SOL features large-amplitude bursts associated with turbulent plasma filaments passing the RFA. These filaments convect plasma to the wall with larger density than the background plasma density. The ions in the filament also have higher impact energies than the background ion impact energies. These observations indicate that a filament-wall interaction can lead to erosion of the first wall in the burning plasma tokamaks such as ITER (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

An accurate calculation of heat load on the divertor plates in a tokamak must take into account kinetic effects, present when the electron velocity distribution function (EVDF) in the plasma column departs from a thermal distribution. In this work PARASOL-1D, a particle-in-cell code with a Monte-Carlo binary collision model, is used to find and explain the electron heat flux-limiting factor αe and the heat transmission coefficient (HTC) γe in the complex SOL. We develop and test two simple models for these kinetic factors that take as input the temperature of the SOL and the temperature of the electrons striking the divertor plates. Both models assume a piecewise EVDF, with a symmetric bulk electron population and a high-energy tail of electrons moving only in the direction of the nearest diverter plate. The model EVDF are fit to the simulation-derived EVDF by allowing the variables for the densities and temperatures in the bulk and tail to vary independently. The block model, which assumes a bulk population of infinite parallel temperature in the bulk, is found to reproduce the kinetic factors for a wide range of conditions in the complex SOL much better than both the classical and Gaussian models (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The time and space averaged profiles of temperature, particle density, and momentum are in the scrape off layer determined by the intermittent transport generated at the edge shear layer. The distinction between profiles and fluctuations becomes arbitrary for situations where the transport is highly intermittent and shows long range correlations. Without this distinction the full range in parameter variability has to be taken into account for simulations, posing extreme demands on the used models. Numerical investigations and experimental results show how the interplay between radially propagating structures and parallel transport sets up the observed profiles and how intermittency influences edge conditions. The filamentary blob structures also transport and generate currents in the SOL, which can be investigated by means of local magnetic diagnostics. Finally, the ratio of ion to electron temperature in the SOL is an important measure for the influence of finite larmor radius effects on the propagation properties of blobs. Numerical investigations indicate that these effects can lead to an increased self confinement and radial reach of these structures (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]