Overview of the FTU results

Abstract

Spontaneous increases in plasma density, up to ∼1.6 times the Greenwald value, are observed in FTU with lithized walls. These plasmas are characterized by profile peaking up to the highest obtained densities. The transport analysis of these discharges shows a 20% enhancement of the energy confinement time, with respect to the ITER97 L-mode scaling, correlated with a threshold in the peaking factor. It has been found that 0.4 MW of ECRH power, coupled at q = 2 surface, are sufficient to avoid disruptions in 0.5 MA discharges. Direct heating of magnetic islands produced by MHD modes determines current quench delay or avoidance. Supra-thermal electrons generated by 0.5 MW of lower hybrid power are sufficient to trigger precursors of the electron-fishbone instability. Evidence of spatial redistribution of fast electrons, on the ∼100 µs typical mode timescale, is shown by the fast electrons bremsstrahlung diagnostic. From the presence of new magnetic island induced accumulation points in the continuous spectrum of the shear Alfvén wave spectrum, the existence of new magnetic island induced Alfvén eigenmodes (MiAE) is suggested. Due to the frequency dependence on the magnetic island size, the feasibility of utilizing MiAE continuum effects as a novel magnetic island diagnostic is also discussed. Langmuir probes have been used on FTU to identify hypervelocity (10 km s−1), micrometre size, dust grains. The Thomson scattering diagnostic was also used to characterize the dust grains, present in the FTU vacuum chamber, following a disruption. Analysis of the broad emitted light spectrum was carried out and a model taking into account the particle vaporization is compared with the data. A new oblique ECE diagnostic has been installed and the first results, both in the presence of lower hybrid or electron cyclotron waves, are being compared with code predictions. A time-of-flight refractometer at 60 GHz, which could be a good candidate for the ITER density feedback control system, has also been tested.

Differentiating the role of lithium and oxygen in retaining deuterium on lithiated graphite plasma-facing components

“…[8][9][10] The added lithium yielded unanticipated improvements in energy confinement time, fusion power, stored energy, and the Lawson triple product nT E . 11,12 Since then, lithium has been used in CDX-U 13 , FTU 14 , DIII-D 15 , TJ-II 16 , T-11M 17 , EAST 18 , and NSTX. 19 NSTX has pioneered and advanced lithium wall conditioning over a phased effort.…”

The role of oxygen in the uptake of deuterium in lithiated graphite

“…Lithium wall coatings have improved plasma performance on a number of fusion devices including TFTR, 7 CDX-U, 8 FTU, 9 TJ-II, 10 T-11M, 11 EAST, 12 and NSTX. 5 These improvements have come via a reduction in deuterium recycling in addition to a reduction in oxygen and carbon impurities in the plasma.…”

Lithium-based surfaces controlling fusion plasma behavior at the plasma-material interface

“…FTU (Frascati Tokamak Upgrade) operated with a liquid lithium limiter since 2005 and found 20% enhancement in energy confinement time. 4 Doerner and Baldwin conducted the first studies on hydrogen retention and lithium sputtering using a linear plasma device; [15][16][17][18] shortly after, Bastasz and Whaley conducted surface analysis of lithium-based surfaces with low-energy ion scattering spectroscopy (LEISS). 19 Ruzic studied the fundamental physical sputtering mechanisms of lithium-based surfaces in a well-controlled particlebeam experiment.…”