Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Turbulent transport of impurities in 3D devices   A large diffusive turbulent contribution to the radial impurity transport in
Wendelstein 7-X (W7-X) plasmas has been experimentally inferred during the
first campaigns and numerically confirmed by means of gyrokinetic simulations
with the code stella. In general, the absence of strong impurity accumulation
during the initial W7-X campaigns is attributed to this diffusive term. In the
present work the diffusive contribution is also calculated in other stellarator
plasmas. In particular, the diffusion (D) and convection (V) coefficients of
carbon and iron impurities produced by ion-temperature-gradient (ITG)
turbulence are obtained for W7-X, LHD, TJ-II and NCSX. The results show that,
although the size of D and V can differ across the four devices, inward
convection is found for all of them. For W7-X, TJ-II and NCSX the two
coefficients are comparable and the turbulent peaking factor is surprisingly
similar. In LHD, appreciably weaker diffusive and convective impurity transport
and significantly larger turbulent peaking factor are predicted. All this
suggests that ITG turbulence, although not strongly, would lead to negative
impurity density gradients in stellarators. Then, considering mixed ITG/Trapped
Electron Mode (TEM) turbulence for the specific case of W7-X, it has been
quantitatively assessed to what degree pellet fueled reduced turbulence
scenarios feature reduced turbulent transport of impurities as well. The
results for trace iron impurities show that, although their turbulent transport
is not entirely suppressed, a significant reduction of V and a stronger
decrease of D are found. Although the diffusion is still above neoclassical
levels, the neoclassical convection would gain under such conditions a greater
specific weight on the dynamics of impurities in comparison with standard ECRH
scenarios.

11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph