2000 PROGRESS REPORT - ENEA - Fusione

1. Magnetic Confinement
be obtained with an ECRH power as
low as P ECRH ≈0.15 P OH , provided
that the mode is rotating. Figure 1.32
shows that stabilization with co-and
counter-ECCD is identical to the one
achieved with perpendicular launch,
provided that the absorption radius is
the same in all cases. Heating is
therefore the dominant stabilizing
term, CD effects being negligible in
this case. TM dynamics can be
modelled (fig. 1.33) by using a
Rutherford-type equation [1.16], in
which the change rate of the island
width is dependent on the balance
between de-stabilizing terms, related
to the current density and pressure
profiles, and stabilizing terms due to
ECRH and ECCD.
The beneficial effects of mode
suppression on energy confinement
are shown in fig. 1.34, where two
discharges are compared, which are
almost identical in the ohmic phase,
the only difference being that ECRH
absorption occurs in slightly
different positions. In shot #18004,
absorption is ≈3 cm internal to
the island O-point, while in shot
#18015 EC absorption is
correctly positioned inside the
island. In this case of a precise
alignment, stabilization occurs
on the expected resistive time
scale, and a much better thermal
and particle confinement is
observed.
Sawteeth are stabilized with
P ECRH >P OH (≈2.2 times) if
r dep >r inv , with a delay which is
dependent on r dep -r inv and
consistent with resistive diffusion
times (fig. 1.30 and 1.35). A
broadening of J(r), with a slow
decrease in central ohmic heating
Fig. 1.32 - T e at plasma centre
and at r≈a/2 (left), and Mirnov
oscillations (right) with co-ECCD
injection (top), counter injection
(bottom), and perpendicular
launch (centre)
keV keV keV
T/s
100
-100
50
-50
50
-50
20
-20
δR = -3 cm
δR = 0 cm
δR = 1 cm
δR = 2 cm
0.45 0.50 0.55 0.60 0.65 0.70
Time (s)
Fig. 1.31 - 4 Mirnov oscillations with different values of δR=R abs -
Fig. 1.31
R O–point . ECRH starts at 0.5 s. From top to bottom: δR=-3 cm, 0, +1
cm and +2 cm
4
3
2
4.0
3.5
3.0
2.5
4
3
2
0.8 0.9 1.0
Time (s)
10 2 T/s
10 2 T/s
10 2 T/s
1
0
-1
1
0
-1
1
0
-1
0.8 0.9 1.0
Time (s)
Fig. 1.32
31