Overview of FTU results
New FTU ohmic discharges with a liquid lithium limiter at I<SUB>P</SUB>
= 0.7-0.75 MA, B<SUB>T</SUB> = 7 T and n<SUB>e0</SUB> >= 5
× 10<SUP>20</SUP> m<SUP>-3</SUP> confirm the spontaneous
transition to an enhanced confinement regime, 1.3-1.4 times
ITER-97-L, when the density peaking factor is above a threshold value of
1.7-1.8. The improved confinement derives from a reduction of
electron thermal conductivity (χ<SUB>e</SUB>) as density increases,
while ion thermal conductivity (χ<SUB>i</SUB>) remains close to
neoclassical values. Linear microstability reveals the importance of
lithium in triggering a turbulent inward flux for electrons and
deuterium by changing the growth rates and phase of the ion-driven
turbulence, while lithium flux is always directed outwards. A particle
diffusion coefficient, D ~ 0.07 m<SUP>2</SUP> s<SUP>-1</SUP>, and
an inward pinch velocity, V ~ 0.27 m s<SUP>-1</SUP>, in
qualitative agreement with Bohm-gyro-Bohm predictions are inferred
in pellet fuelled lithized discharges. Radio frequency heated plasmas
benefit from cleaner plasmas with edge optimized conditions. Lower
hybrid waves penetration and current drive effects are clearly
demonstrated at and above ITER densities thanks to a good control of
edge parameters obtained by plasma operations with the external poloidal
limiter, lithized walls and pellet fuelling. The electron cyclotron (EC)
heating system is extensively exploited in FTU for contributing to
ITER-relevant issues such as MHD control: sawtooth crash is actively
controlled and density limit disruptions are avoided by central and
off-axis deposition of 0.3 MW of EC power at 140 GHz. Fourier analysis
shows that the density drop and the temperature rise, stimulated by
modulated EC power in low collisionality plasmas are synchronous,
implying that the heating method is the common cause of both the
electron heating and the density drop. Perpendicularly injected electron
cyclotron resonance heating is demonstrated to be more efficient than
the obliquely injected one, reducing the minimum electric field required
at breakdown by a factor of 3. Theoretical activity further develops the
model to interpret high-frequency fishbones on FTU and other experiments
as well as to characterize beta-induced Alfvén eigenmodes induced
by magnetic islands in ohmic discharges. The theoretical framework of
the general fishbone-like dispersion relation is used for implementing
an extended version of the HMGC hybrid MHD gyrokinetic code. The
upgraded version of HMGC will be able to handle fully compressible
non-linear gyrokinetic equations and 3D MHD.