1. magnetic confinement - ENEA - Fusione

1. MAGNETIC CONFINEMENT
23
[1.19] A. A. Tuccillo et al.,
Proc. 14 th Topical Conf. on
Radio Frequency Power in
Plasmas (Oxnard 2001),
Vol. 595, p. 209
[1.20] V. Pericoli-Ridolfini
et al., Proc. 14 th Topical
Conf. on Radio Frequency
Power in Plasmas (Oxnard
2001), Vol. 595, p. 245
[1.21] V. Pericoli-Ridolfini
et al., Study and
optimisation of lower
hybrid waves coupling
in advanced scenario
plasmas in JET, to be
submitted to Plasma Phys
Control. Fusion
the q profile during the high phase of advanced-scenario plasmas.
• Task Force S2 experiment aiming at steady-state ITBs.
• Task Force M experiments on neoclassical tearing mode (NTM) stabilisation by
LHCD and some experiments on the error field.
The H and S2 activities were carried out in close collaboration with CEA and
UKAEA.
Task Force H
1.1 Tokamak Physics
The activity here consisted mainly in continuing LH coupling optimisation in
relevant scenarios. After the success of the previous campaigns in 2000
[1.19,1.20,1.21], efforts were concentrated on the utilisation of LH to actively control
the q profile. As expected, LH proved to be very effective, both in the pre-heat phase,
to optimise the target, and in the high power phase, to maintain the q profile, of
advanced-tokamak plasmas. An example of the capability of LH to model the q
profile is given in figure 1.16. During plasma current ramp-up in the pre-heat phase
of advanced scenario plasmas, the target q profile can be changed from weakly
reversed to deeply reversed by adjusting the power level. This tool has made it
possible to lower the power threshold of electron ITBs, and with the improvement in
LH wave coupling, more than 3 MW can be routinely coupled in H-mode in ITB
plasmas.
Task Force S2
[1.22] F. Crisanti, et al.,
The new LHCD capability strongly accelerated the progress of Task Force S2. Quasi
JET quasistationary
steady-state ITBs time limited only by technical constraints were achieved, and full
internal-transportbarrier
operation with
CD was obtained during the whole high-performance phase of 1.8-MA ITB
discharges [1.22]. Later on during C4, the ENEA collaboration was extended to
active control of the
experiments on feedback control of pressure and temperature profiles by using,
pressure profile, accepted
for publication on
respectively, neutral beam and ion cyclotron waves [1.22]. Figure 1.17 reports the
time evolution of a few quantities characterising one of the longest ITB discharges
Phys. Rev. Lett.
(q 95 ≈6.0, β p ≈1.1, β N ≈1.7, β T ≈1.%, B T =3.4 T and I p =2 MA). In this discharge, an
electron ITB is triggered at the beginning of LH coupling. The ion ITB forms
immediately after neutron beam injection (NBI) and ICRH. Both barriers disappear
when the additional power is switched off and are time limited only by JET
hardware constraints. The loop voltage close to zero and the internal magnetic
inductance practically
constant all over the highpower
phase indicate a
EFIT + MSE at 44.4S
B T = 2.6 T
5
51164
possible “freezing” of the
51465
CD profile due to LHCD.
51466
The electron barrier lasts
P LH = 2.2 MW
about 37 energy confinement
times and the ion
Fig. 1.16 - Control of q
4
51467
profile with LHCD
barrier about 27. The
preheating in the
duration of the ITB is,
optimised shear scenario.
however, comparable with
Weakly to deeply 3
the current resistive
reversed q profile as a
diffusion time.
function of LHCD power.
profile
2
2.0
P LH = 1.1 MW
2.5
3.0
R maj (m)
3.5 4.0
In-depth analyses aimed at
understanding turbulencereduction
mechanisms were
performed and reported at
several conferences, e.g. the
2001 EPS and APS. The