Fusion Programme - ENEA - Fusione

14. Miscellaneous2007 Progress ReportThe 12 sectors of the plasma chamber will bewelded in sequence. The last welds, joining twoassembled 180° sectors, will have to be guidedand controlled by the remote handling systemfrom inside the plasma chamber. Deformationsand displacements due to the welding processhave to be limited, to comply with the designgeometry of the closed torus and with its functionas supporting structure of the first wall.Experimental tests and correspondingsimulations were carried out [14.2] for twowelding processes (laser welding to join adjacentsectors and tungsten inert gas-narrow gap[TIG–NG] welding with filler material) on suitablesamples which reproduce fundamental aspectsof the material and geometrical characteristics ofthe chamber sectors (fig. 14.2). The resultsindicate that a sufficiently accurate numericalmethodology has been identified for simulation ofboth types of welding.Fig. 14.2 - Experimental test for both laser and TIG–NGwelding techniquesThe design of the IGNITOR magnetic system offers a high degree of flexibility thanks to the large numberof poloidal field coils. Following the optimisation of the CS and PFC design, an updated plasma engineeringanalysis was conducted to define the current distribution scheme in all 14 sets of coils for the mainoperational scenarios, including extended limiter and double null scenarios [14.3]. Particular attention waspaid to the plasma start-up phase, and an optimal choice of the PFC currents made it possible to obtaina relatively large area where the magnetic field is nearly null and flat, without reducing the maximum fluxswing (up to 36 Wb) available from the PFC system. The design of the vertical position and shape controlleris based on the CREATE_L linearised plasma response model. Coupling between the vertical positioncontrol and plasma shape control was analysed to allow the plasma vertical position to be stabilised evenin the case where a shape disturbance is provoked by a change in the main plasma parameters [14.4].A new operating scenario with B T ≅13 T, I p ≅ 9 MA, and a double null configuration withPhysics studies, X-points just outside the first wall was investigated by means of simulations with thediagnostics JETTO transport code. The possibility of accessing H-mode regimes was verified. TheH-mode threshold power was estimated on the basis of the most recentdevelopment multi–machine scaling and was found to be consistent with the available ion cyclotronand pelletresonance heating (ICRH) auxiliary power combined with Ohmic and alpha-particleheating. Ignition conditions and plasma performances quite similar to those expectedinjectorfor the standard 11-MA scenarios with an extended first-wall configuration can bereached. Other simulations show that, even without accessing the H-regime and withpessimistic assumptions about the energy confinement time, plasma parameters of relevance to thephysics of burning plasmas can be attained [14.5].As a complement to the transport analyses, the physics of the ICRH was analysed for maximumperformance scenarios, reduced parameter scenarios and the double null configurations at 13 T and 9 MA,(2007), paper BP8.61[14.4] F. Villone et al., Bull. Am. Phys. Soc. 52(16), 45(2007), paper BP8.62[14.5] G. Cenacchi, A. Airoldi, B. Coppi, Bull. Am. Phys.Soc. 52(16), 46 (2007), paper BP8.66185