The FTU ( R = 0.93 m, a = 0.3 m, BT 8 T, Ip 1.6MA) program aims to develop advanced scenarios relevant to ITER, not only for the magnetic field and density ( ne 1020 m-3) but also for the pure electron heating, LH (8 GHz) and EC (140 GHz) RF waves and for the absence of a momentum source. Steady internal transport barriers (ITB) in almost full current drive (LHCD), are obtained at peak density > 1.3×1020 m-3 with the energy confinement time about 1.6 times the ITER 97-L scaling. Ion collisional heating does not affect the barrier dynamics: turbulence is strongly suppressed and the ion transport tends to be neoclassical, lower than ohmic value. The barrier radius can be successfully controlled by LHCD: steady ITB radii up to r/a = 0.67 are obtained by peripheral LH absorption, favored primarily by low safety factors q. Central counter ECCD is also effective. Feedback control/suppression of MHD tearing modes (TM, m = 2) with EC heating has been demonstrated. A fast digital analysis of the EC emission detects in real-time the TM presence, determines its radial position, selects and automatically switches on which one of the 4 available EC beams, is absorbed closest to it. A liquid lithium limiter (LLL) has been tested successfully. The novelty of the design complements that of the LLL concept. A mesh of capillary tubes is filled with the liquid and the associated surface tension withstands the tearing-off J × B forces. The LLL surface showed no damage up to the maximum thermal load of 10 MW/m2. With walls ``lithized", the plasma is cleaner (all other impurities almost disappear) and the neutral gas recycling strongly drops. Progress on the issue of mitigating disruptions has shown the efficiency of the EC power in avoiding or softening them. Experimental tests on the collective Thomson scattering in ITER-relevant configuration have shown how it is very crucial that backscattered radiation does not excite spurious gyrotron modes. Theory has fully explained the evolution of fishbone-like instabilities driven by LH generated supra-thermal electrons in FTU. The relevance for burning plasmas is for the interaction of low-frequency MHD modes with trapped alpha particles that are characterized by small dimensionless orbits, as electrons; besides the trapped particle bounce averaged dynamics depends on energy and not mass.
Overview of the FTU results
W Bin;A Bruschi;L Carraro;S Cirant;F Gandini;G Granucci;G Grossetti;G Grosso;E Lazzaro;V Mellera;A Moro;V Muzzini;S Nowak;M E Puiatti;A Simonetto;C Sozzi;U Tartari;M Valisa;
2007
Abstract
The FTU ( R = 0.93 m, a = 0.3 m, BT 8 T, Ip 1.6MA) program aims to develop advanced scenarios relevant to ITER, not only for the magnetic field and density ( ne 1020 m-3) but also for the pure electron heating, LH (8 GHz) and EC (140 GHz) RF waves and for the absence of a momentum source. Steady internal transport barriers (ITB) in almost full current drive (LHCD), are obtained at peak density > 1.3×1020 m-3 with the energy confinement time about 1.6 times the ITER 97-L scaling. Ion collisional heating does not affect the barrier dynamics: turbulence is strongly suppressed and the ion transport tends to be neoclassical, lower than ohmic value. The barrier radius can be successfully controlled by LHCD: steady ITB radii up to r/a = 0.67 are obtained by peripheral LH absorption, favored primarily by low safety factors q. Central counter ECCD is also effective. Feedback control/suppression of MHD tearing modes (TM, m = 2) with EC heating has been demonstrated. A fast digital analysis of the EC emission detects in real-time the TM presence, determines its radial position, selects and automatically switches on which one of the 4 available EC beams, is absorbed closest to it. A liquid lithium limiter (LLL) has been tested successfully. The novelty of the design complements that of the LLL concept. A mesh of capillary tubes is filled with the liquid and the associated surface tension withstands the tearing-off J × B forces. The LLL surface showed no damage up to the maximum thermal load of 10 MW/m2. With walls ``lithized", the plasma is cleaner (all other impurities almost disappear) and the neutral gas recycling strongly drops. Progress on the issue of mitigating disruptions has shown the efficiency of the EC power in avoiding or softening them. Experimental tests on the collective Thomson scattering in ITER-relevant configuration have shown how it is very crucial that backscattered radiation does not excite spurious gyrotron modes. Theory has fully explained the evolution of fishbone-like instabilities driven by LH generated supra-thermal electrons in FTU. The relevance for burning plasmas is for the interaction of low-frequency MHD modes with trapped alpha particles that are characterized by small dimensionless orbits, as electrons; besides the trapped particle bounce averaged dynamics depends on energy and not mass.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
