1. magnetic confinement - ENEA - Fusione

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1. MAGNETIC CONFINEMENT
1.4 FT3 Conceptual Study
1.4.1 Introduction
Table 1.III - FT3 parameters
The FT3 concept is a proposed
upgrade of FTU, which would
enable studies of sub-ignited
plasma conditions in deuterium
plasmas (Q equiv ≈1-5) with
particular reference to the
collective effects driven by the
fast ions produced by ICRH.
Therefore, FT3 would prepare
the operational scenarios of a
burning plasma experiment by investigating the approach to ignition in the presence
of the relevant dynamics of fast ions.
FT3 is similar to JET from the point of view of dimensionless parameters, but the
expected fusion performances are much higher because of the
higher magnetic field B (the triple product nTτ is proportional to
B at fixed dimensionless parameters). Indeed, the expected fastparticle
parameters in FT3 at maximum performance are closer to
those of a burning plasma experiment than the parameters
achievable on JET at maximum performance. Note also that FT3
has greater shaping flexibility at maximum plasma current than
JET.
The large range of magnetic field values achievable in FT3
includes the ITER magnetic field value, so the proposed device
would be a natural test bed for the development of ITER
diagnostics and of auxiliary heating systems such as ECRH.
Table 1.III reports the main engineering parameters.
B(T)/I(MA) 8/6
P aux (MW) (ICRH/ECRH/LH) 25 (20/3.2/6)
R(m) 1.3
a(m)/b(m) 0.48/0.9
κ/δ≅I=6MA 1.8/0.6
t flat-top (s) ≅8T 4
Three main operational scenarios are envisaged: single X-point
(fig. 1.48) at 8 T/6 MA for investigating H-mode and ITB
formation at high magnetic-field and density; limiter scenario at 8
T/7 MA to study enhanced L-mode regimes; single X–point at 5T/2.4 MA for longpulse
scenarios and advanced tokamak physics. H-mode plasmas are expected to
achieve an equivalent Q between Q = 1 and Q = 2, whereas the formation of an ITB
could allow an equivalent Q in the range Q=5.
Fig. 1.48 - FT3 single-null
equilibrium at B=8 T and
I= 6MA.
1.4.2 Main objectives of the FT3 scientific programme
• Investigation of fast-ion collective effects in the parameter range relevant for
burning plasmas. The fast-particle concentration achievable with 20-MW ICRH is
sufficient for studying the destabilisation of resonant collective modes, such as
fishbones and energetic particle modes (EPMs), which are in principle the most
dangerous fast-particle collective effects. Investigation of these effects in negative
magnetic shear discharges at B = 5 T will allow a better understanding of the role of
these instabilities in advanced scenarios. Note that these regimes are obtained on FT3
at a slowing down time/energy confinement time ratio comparable to that of a
burning plasma experiment.
• Test of H-mode threshold at high magnetic field. FT3 could prove the validity of
the most recent scaling law for the L-H threshold (fig. 1.49), which predicts a lower
threshold power on ITER than the IPB98 scaling. This would facilitate making a final
decision on the auxiliary heating systems of ITER. Note that JET data are consistent
with both expressions of the L-H threshold and cannot provide a definitive answer.