1. magnetic confinement - ENEA - Fusione

1. MAGNETIC CONFINEMENT
25
[1.26] M.J. Mantsinen et
al., ICRF heating
scenarios in JET with
emphasis on 4 He plasmas
for the non-activated
phase of ITER, presented
at the 14 th Topical Conf.
on Radio Frequency Power
in Plasmas (Oxnard 2001),
Vol. 595
[1.27] V. G. Kiptily et al.,
Gamma-rays: measurements
and analysis at
JET, presented at the
6 th Inter. Conf. on
Advanced Diagnostics for
Magnetic and Inertial
Fusion (Varenna 2001)
[1.28] V. G. Kiptily et al.,
Gamma-rays diagnostics
of energetic ions in
JET, presented at the
7 th IAEA Technical
Committee Meeting on
Energetic Particles in
Magnetic Confinement
(Goteborg 2001) to be
published on Nuclear
Fusion
[1.29] J. Mailloux,et al.,
Progress in internal
transport barrier plasmas
with lower hybrid current
drive and heating in JET
accepted for publication
0
-1
I p (MA)
-2
n e (1020
1
m-2)
0.5
0
T
2 i (10 keV)
1.5
1
T e (eV)
8
6
4
Power (10 kW)
1.5
LH
1 #53429
0.5
40
45
Time (s)
Gamma diagnostics on JET
1.1 Tokamak Physics
Studies of fast-ion production during heating and the subsequent fast-ion behaviour
in magnetically confined plasma, and evaluations of the resulting bulk ion heating
efficiency are essentially important to fusion reactor development.
Gamma-ray emission from nuclear reactions between fast ions and the main plasma
impurities was observed during ICRH and NBI heating in the JET tokamak. Gammaray
energy spectra provided information on the energy distribution function of the
fast ions. The gamma-ray emission profiles obtained with the JET neutron profile
monitor supplied information on the spatial distribution of reaction sites.
In recent JET studies of the ITER-like ICRH scenarios ( 3 He)D and ( 3 He) 4 He,
gamma-ray measurements gave invaluable information on the fast-ion population:
a) first evidence for ICRF-induced pinch of 3 He-minority ions based on profile data;
b) variation in the fast 3 He tail temperature that depends on 3 He concentration and
c) experimental simulation of 3.5-MeV fusion-born alpha particles by diagnosing fast
4 He ions accelerated to the MeV range [1.26,1.27,1.28].
Effect of low magnetic shear induced by LHCD on high-performance ITBs in
JET
In JET a low/negative magnetic shear profile is maintained in a plasma target with
2.4-MA plasma current by using 2.2 MW of lower hybrid power combined with NBI
and ICRH. In this scenario, an ITB up to about 4 s is produced. The fraction of LH
driven current is about 25% of the total plasma current. During LH power
application, the layer with reversed shear q-profile can be maintained in a suitable
radial position to inhibit the onset of turbulence, which might otherwise force the ITB
to collapse. Lower hybrid power could be used to drive moderate amounts of noninductive
off-axis current and sustain high-performance ITBs at high plasma current.
The main plasma parameters and additional heating power time traces of two
discharges of JET [1.29] are compared in figure 1.18. In shot #53432, an increase in the
central ion and electron temperatures is observed in the time range from 45.4 s to
46.8 s. In shot #53429 the central temperatures show a prompt increase at the switchon
of LH power, during the main heating phase. The increase is maintained for
longer (3.2 s, from 45.8 s to 49.6 s). In both shots, the temperature rise is accompanied
by a peaking of the temperature profiles, which suggests
the formation of an ITB. The ITB collapse is accompanied
a) by increased plasma-edge interaction, which produces
an increase in Dα emission and the loss of LH antenna
power coupling. On the other hand, in shot #53432 the
b) ITB duration appears to be only 1.2 s (from t=45.3 s to
NBI
#53429
ICRH e)
#53429
c)
d)
Fig. 1.18 - Time traces of the main plasma parameters
of JET discharge #53429 compared with a similar
shot (#53432) without LHCD coupling in the main
heating phase. Plasma current: a) # 53429 red curve,
#53432 pink. Line integrated plasma density: b)
#53429 red curve, #53432 black. Central ion
temperature: frame c) #53429 dashed/red, #53432
continuous line/pink. Central electron temperature:
d) #53429 squares/red, #53432 rhombus/pink e)
NBI power, #53429 red, #53432 blue; ICRH power,
#53429 pink, #53432 yellow; LHCD power, #53429
green, #53432 black.