Assessment of the effects of scrape-off layer fluctuations on first wall sputtering with the TOKAM-2D turbulence code

Abstract

Plasma material interactions on the first wall of future tokamaks such as ITER and DEMO are likely to play an important role, because of turbulent radial transport. The latter results to a large extent from the radial propagation of plasma filaments through a tenuous background. In such a situation, mean field descriptions (on which transport codes rely) become questionable. First wall sputtering is of particular interest, especially in a full W machine, since it has been shown experimentally that first wall sources control core contamination. In ITER, beryllium sources will be one of the important actors in determining the fuel retention level through codeposition. In this work, we study the effect of turbulent fluctuations on mean sputtering yields and fluxes, relying on a new version of the TOKAM-2D code which includes ion temperature fluctuations. We show that fluctuations enhance sputtering at sub-threshold impact energies, by more than an order of magnitude when fluctuation levels are of order unity.

A new mean‐field plasma edge transport model based on turbulent kinetic energy and enstrophy

“…The remainder of this paper is structured as follows. Section 2 introduces the TOKAM2D turbulence code [10,11,12] that is used as a reference in this work, as well as the one-equation k ⊥ model. Next, section 3 defines the enstrophy, and shows that the turbulent enstrophy (ζ ⊥ ) can be combined with the turbulent kinetic energy to obtain an improved model for the turbulent particle diffusion coefficient.…”

Universality of Poisson-driven plasma fluctuations in the Alcator C-Mod scrape-off layer

“…Extensive scientific investigations have revealed that cross-field transport of particles and heat in the scrape-off layer (SOL) of magnetically confined plasmas is caused by radial motion of blob-like filament structures [1][2][3][4][5]. This poses several challenges for future magnetic fusion energy reactors, including enhanced erosion rates of the main chamber walls [6][7][8][9][10]. There is also strong evidence that the turbulence-driven cross-field transport is related to the empirical discharge density limit [11][12][13][14][15].…”

The Dynamics of Electrons in Linear Plasma Devices and Its Impact on Plasma Surface Interaction

“…Assuming absence of ELMS, transient effects stemming from micro-turbulence seem unavoidable in fusion reactors. Although transient plasma loads have been simulated by laser irradiation or electron beams [25,22] the effect of turbulence on the sputtering yield and erosion overall is so far investigated theoretically only [26,27,28].…”

“…The top pictures of Figure 8. 26 show linear (left) and logarithmic (right) sputtering rate curves for mean temperature, a Gaussian distribution, a mix of mean or Gaussian and Γ distribution, and finally a pure Γ distributed temperature realization with a skewness of S = 2. The difference between mean temperature and Gaussian distribution are small and negligible when the Γ distribution is added.…”

“…8. 26. While determining the range of the skewness is straightforward, the estimate for the shares of Gaussian background and intermittent fluctuation parts could be based on Fig.…”