Speaker
Ivona Vasileska
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1110.pdf
Kinetic flux limiters for the ITER Scrape-Off Layer
I. Vasileska1 , D. Tskhakaya2 , L. Kos1 , R. A. Pitts3 , EUROfusion-IM Team∗
1Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia,
2 Institute of Applied Physics, TU Wien, Fusion@ÖAW, A-1040 Vienna,
3 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France
In next generation tokamaks such as ITER, Edge Localized Mode (ELM)-induced transient
heat loads on the divertor targets represent the greatest threat to target lifetime. Predicting the ex-
pected consequences through modelling is especially challenging and is often attempted through
the use of fluid plasma boundary modelling codes, such as SOLPS, in which the ELM is crudely
approximated as a fixed increase in anomalous cross-field transport coefficients for particles
and heat for a short duration consistent with a specified total ELM energy loss from the plasma,
∆WELM . However, one problem with this approach is that the boundary conditions at the target
sheath interface are expected to vary strongly in time through the ELM transient, whilst fixed
kinetic heat flux limiters are typically applied in the fluid codes. This contribution describes the
first results of efforts to address this issue for ITER simulations under high performance condi-
tions using the 1D3V electrostatic parallel Particle-in-Cell (PIC) code BIT1 [1] to provide time
dependent kinetic target sheath heat transmission factors (SHTF) for given ∆WELM . In a later
stage of the work, these will be used as boundary conditions for calculations of ELM target heat
loads using the SOLPS-ITER code [2].
The first, and most challenging step, is to establish BIT1 simulations of the stationary parallel
transport in the inter-ELM scrape-off layer (SOL). This has been performed for burning plasma
conditions corresponding to the ITER Q = 10, 15 MA baseline at q95 = 3, for which the poloidal
length of the 1D SOL is ∼ 20 m from inner to outer target. Typical upstream separatrix param-
eters of ne ∼ 3 − 5 · 1019 m−3 , Te ∼ 100 − 150 eV and Ti ∼ 200 − 300 eV are assumed, guided
by SOLPS-ITER code runs. Inclined magnetic fields at the targets of (∼ 5◦ ) are included, as
are particle collisions, with a total of 3.4 · 105 poloidal grid cells giving shortening factors of
20. Secondary electron emission at the tungsten targets is neglected. In the first instance, a SOL
flux tube just outside the separatrix is considered. A typical simulation requires up to 60 days
running massively parallel 1152-2304 cores of the EU Marconi super-computer. On this back-
ground the ELM transient is then launched, by injecting an ambipolar, Maxwellian source of
particles distributed around the midpoint between the two targets and at the Ti,ped , Te,ped , ne,ped
characteristic of the H-mode pedestal. The focus of the first ELM simulations will be mitigated
Type I ELMs with ∆WELM in the range 0.1 − 1.0 MJ. The ELMs are "switched on" stepwise by
increasing the strength of the particle source and incoming particle temperatures (corresponding
to ne,ped , Te,ped ). The duration of the ELM pulse is taken to be between 100-200 µs.
References
[1] D. Tskhakaya et al., Plasma Phys. Control. Fusion,59, 114001 (19pp), (2017);
[2] X. Bonnin et al., Plasma and Fusion Research, 11, 1403102, (2016).
∗
See http://www.euro-fusionscipub.org/eu-im
