Simulations of Argon plasmas in the linear plasma device GyM with the SOLPS-ITER code

Abstract

Edge plasma codes, such as SOLPS, are widely used to study plasma transport in tokamaks scrape-off layers (SOL). The possibility to apply these codes to non hydrogenic plasmas and to linear plasma devices (LPDs) is gaining the interests of the fusion community. These facilities play a pivotal role in plasma-material interaction (PMI) studies for future fusion devices and may allow to test the code capabilities both in terms of geometry and simulated plasma species. In this contribution, we apply the SOLPS-ITER code for the simulations of Argon plasmas in the medium-flux linear machine GyM. A sensitivity scan over the pumping efficiency, transport coefficients and absorbed electron power was done, performing B2.5-EIRENE coupled simulations. A quantitative analysis of the different flux contributions is provided through the use of a twopoint modelling. Comparison with experiments shows a promising qualitative and quantitative agreement, with the sole exception of the simulated neutrals pressure. Dedicated EIRENE standalone simulations were performed to investigate this issue, also highlighting the role of neutral-neutral elastic collisions at high values of the puffing intensity.

A point plasma model for linear plasma devices based on SOLPS-ITER equations: application to helium plasma

“…Anomalous particle and heat transport is treated in the diffusion approximation, with anomalous diffusion coefficients D ⊥ = 0.5 m 2 /s and χ ⊥ = 1.5 m 2 /s, respectively. These values of anomalous transport coefficients are consistent with the ones chosen in previous simulations of GyM with SOLPS-ITER [26]. Neutral particles are fed in through a puffing surface, located at the west target and removed through a pumping surface, with albedo p a = 0.018.…”

“…Another relevant aspect about the importance of excitation processes in LPDs needs to be pointed out. According to our previous work [26], SOLPS-ITER simulations of pure Ar plasma predict that a relevant fraction of input power is dissipated through electron excitation processes. Also in this case SOLPS does not include electron-neutral excitation, so that we must assume that the ion excitation is important in this case.…”

“…Although the code was developed for the modelling of plasma boundary in tokamaks, its application to the cylindrical geometry of a LPD is found in few works, e.g. [49,50], and a systematic analysis of SOLPS-ITER equations in linear geometry is reported in [26]. In this section, we present original simulations of a pure helium plasma in the linear device GyM: 25 simulations were performed varying the total external power absorbed by the electron population (P ext = 180 W, 360 W, 540 W, 720 W, 900 W) and the neutral puffing intensity (Gas in = 5 sccm, 10 sccm, 15 sccm, 20 sccm, 25 sccm).…”

“…Perfect axial symmetry was assumed. Simulations were performed employing the physical model described in [26]: no drift velocities were considered and currents only developed in the direction parallel to B. The boundary conditions imposed are the standard SOLPS-ITER ones [12]: sheath boundary conditions at the east and west targets and exponentially decaying density, temperature and potential profiles at the lateral wall boundary, with decay lengths λ n = 5 cm, λ T = 5 cm and λ φ = 10 cm, respectively.…”

ERO2.0 modelling of nanoscale surface morphology evolution

“…We simulated the surface evolution due to plasma irradiation for an overall fluence of 1.74× 10 24 ions m −2 . The impinging ion energy is set to 150 eV, well above the sputtering threshold of Ar on W. Having the intention of making comparisons with experimental results, we choose these parameters since they are typical of Ar plasmas produced in the GyM linear device, on condition that a proper bias voltage is applied to the sample to achieve the above energy value [23]. In figure 7, we show the topography obtained at the end of the ERO2.0 simulations for different values of the ion fluence, while the corresponding average surface roughnesses are reported in table 4.…”