Speaker
Vincenzo Paolo Loschiavo
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1054.pdf
Vertical stability margin studies on TCV: experiments and modelling
F. Villone1, R. Ambrosino1, V.P. Loschiavo1, S. Coda2, TCV and EUROFusion MST1* teams
1
Consorzio CREATE, DIETI, Università degli Studi di Napoli Federico II, Italy
2
Swiss Plasma Center, EPFL, Lausanne, Switzerland
*See the author list H. Meyer et al 2017 Nucl. Fusion 57 102014
The stabilization of the vertical position in future fusion devices (e.g. DEMO [1]) is particularly
challenging, due to a number of reasons. First of all, the high fusion performances required of
the plasma call for a relatively high elongation [2], which in turn increases the vertical
instability growth rate. Secondly, toroidally conducting structures providing most of the passive
stabilization (typically the vessel) are very far from the plasma, since massive blankets are
required to shield and collect neutrons produced by fusion reactions.
The electric power needed for stabilization is one of the key drivers in the design of a new
device. This quantity depends critically on the so-called stability margin [3], which is a
fundamental indication on the passive stability properties of a given configuration.
During the recent experimental campaign carried out on TCV in the frame of the EUROFusion
Medium Size Tokamak Task Force, dedicated experiments have been carried out, aimed at
extensively studying the minimum achievable stability margin beyond which stability is lost.
The results achieved, reported in the present paper, allow us in particular to experimentally
validate the modelling approach used for the design of future devices. The experimental strategy
is based on arranging a plasma configuration exhibiting a slowly decreasing stability margin,
e.g. thanks to a slow ramp in elongation during a shot. The plasma is subject to repetitive
perturbations (ELMs) during the configuration ramp. The instant at which the feedback
controller is not able to stabilize the plasma any longer corresponds to the limit value of the
stability margin, which depends on the feedback controller and the perturbation under analysis.
Since the stability margin cannot be directly measured, a specific modelling activity is carried
out with the CREATE_L model [4], which can provide indications on passive and active
stabilization even beyond the calculation of the stability margin.
[1] R. Wenninger et al 2015 Nucl. Fusion 55 063003
[2] C.M. Greenfield et al 1997 Nucl. Fusion 37 1215
[3] A. Portone 2005 Nucl. Fusion 45 926
[4] R. Albanese and F. Villone 1998 Nucl. Fusion 38 723
