Speaker
Monica Spolaore
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1061.pdf
Motivations and perspectives of RFX-mod2, the challenge of the
upgraded RFX-mod device
M. Spolaore, R. Cavazzana, L. Marrelli, S. Peruzzo, M.E. Puiatti, P.Zanca
and the RFX-mod team
Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA) Corso
Stati Uniti 4 - 35127 Padova, Italy
In recent years the RFX-mod device has been operated as a Reversed Field Pinch (RFP) and
as a low-q Tokamak. In both configurations the capability and flexibility of its active control
system of MHD instabilities have been exploited to control RWMs and tearing mode wall
locking (RFP) and to stabilize the m/n=2/1 mode to operate at q(a)≤2 (Tokamak). The
dynamics of the tearing modes has been fully characterized experimentally and simulated by
the RFXLocking code [Zanca P. 2009 Plasma Phys. Control. Fusion 51 015006].
At high current, RFP plasmas have been observed to self-organize into quasi single helicity
(QSH) states, where a single m=1 modes dominates the spectrum of all the other secondary
modes and magnetic chaos is reduced. In particular, in QSH the best plasma performance is
observed at the lowest amplitude of the secondary modes, which on the other hand also affect
wall recycling and impurity content. The beneficial effect expected from reducing the
amplitude of tearing modes and increasing their dynamics, motivated the plasma moving
closer to the conductive shell and as a consequence a modification of the device load
assembly. The present inner Inconel vacuum vessel, which is surrounded by a copper shell,
both enclosed in a stainless steel support structure, will be removed. The support structure
will be modified in order to ensure vacuum tightness. In this way, the conductive shell will
approach the plasma, whose minor radius will increase from 0.459m to 0.49m. According to
RFXLocking simulations, discussed in this contribution, the deformation related to m=1
modes will decrease by a factor ≈3. The expected improvement in confinement will be at
least by a factor ≈35%. In addition, the plasma current threshold for tearing mode locking
will increase from ≈120 kA to ≈400-600 kA.
This contribution also describes the challenges in the design of the upgraded RFX-mod
(RFX-mod2) and the innovative solutions found to solve the main issues, in particular to
fulfill vacuum and electrical requirements of the in-vessel components.
