Speaker
Olivier Février
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1020.pdf
Dynamics of detachment in TCV with N2 seeding and flux expansion
O. Février1, C. Theiler1, C. K. Tsui3,1, K. Verhaegh2,1, J.A. Boedo3, B. Duval1, B. Labit1, B.
Lipschultz2, R. Maurizio1, H. Reimerdes1, the TCV Teama and the EUROfusion MST1
Teamb
1
EPFL-SPC, CH-1015 Lausanne, Switzerland,
2
York Plasma Institute, University of York, Heslington, York, YO10 5DQ, UK,
3
University of California-San Diego, La Jolla, California 92093, USA
As the operation of future devices will require target heat fluxes of less than 10-20 MW/m2,
finding ways of dissipating the power is a critical issue. This can be achieved by operating in
a detached regime where a drop of the target ion flux is attributed to the onset of parallel
momentum losses. To further understand this process in the TCV open divertor, we
investigate detachment in a lower single-null X-Divertor geometry in range of flux
expansions of 2 to 20, approaching detachment through nitrogen seeding at fixed integrated
core density (25% or 45% of the Greenwald limit) or integrated core density ramps (from
30% to about 70% of the Greenwald limit) in L–Mode plasmas. We particularly focus on the
relation between the roll-over of the target ion flux, the development of a parallel pressure
gradient along the divertor leg and the evolution of the upstream profiles. The plasma profiles
at the outboard midplane reveal a saturation, and eventually a roll-over of the upstream
pressure. In the density ramp experiments, the development of a pressure drop of about 70%
between the outer midplane and the target, as measured by a fast reciprocating probe and a
set of wall-embedded Langmuir probes, is well-correlated with the roll-over of the target ion
flux, indicating a possible role of parallel momentum losses. Preliminary analysis of the
evolution of the pressure drop for N2 seeded discharges indicates a much weaker pressure
drop than in the density ramp experiments. The above results will be interpreted using an
extended two-point model with momentum and radiation losses and a one-dimensional fluid
model. We will also present the first results of detachment experiments in TCV double-null
configurations that aim to investigate a possible role of coupling between inner and outer legs
in the detachment process.
a
See the author list of S. Coda et al, 2017 Nucl. Fusion 57 102011
b
See the author list of H. Meyer et al 2017 Nucl. Fusion 57 102014
