After a decision by the ITER parties to investigate the possibility of designing a reduced cost
version of ITER several possible machine layouts with different aspect ratios were studied.
Relatively early in this process it became clear that there is no significant cost difference
between different aspect ratios and that there is a maximum realistically possible aspect ratio
for a machine with 6 m major radius and rather high plasma shaping. Following this study a
machine with an intermediate aspect ratio (3.1) called the ITER Fusion Energy Advanced Tokamak
(ITER FEAT) was chosen as the basis for the outline design of a reduced cost ITER.
Several potential steady state scenarios can be investigated in ITER FEAT, i.e. monotonic or
reversed shear at full or reduced minor radius. In addition, so-called hybrid discharges, are
feasible where a mixture of inductive and non-inductive current drive as well as bootstrap
current allows long pulse discharges of the order of 2500 s. The βN values and H factors
required for these discharges are in the same range as those observed on present machines, which provides
confidence that such discharges can be studied in ITER FEAT. However, due to uncertainties in
physics knowledge, for example the current drive efficiency off-axis, it is impossible at present to
generate a completely self-consistent scenario taking all boundary conditions, for example engineering
or heating system constraints, into account. In addition, all of these regimes have a potential problem
with divertor operation compatibility (low edge density) and with helium exhaust which has to be
addressed in existing experiments. For the engineering design of the in-vessel components and for
the balance of the plant there is practically no difference between inductive (500 s) and steady
state operation. However, the choice of heating systems and the distribution of power between them will be strongly
influenced by the envisaged steady state scenarios.
The ITER vacuum vessel (VV) is designed to be large double-walled structure with a D-shaped crosssection. The achievable fabrication tolerance of this structure was unknown due to the size and complexity of shape. The Full-scale Sector Model of ITER Vacuum Vessel, which was 15m in height, was fabricated and tested to obtain the fabrication and assembly tolerances. The model was fabricated within the target tolerance of ±5mm and welding deformation during assembly operation was obtained. The port structure was also connected using remotized welding tools to demonstrate the basic maintenance activity. In parallel, the tests of advanced welding, cutting and inspection system were performed to improve the efficiency of fabrication and maintenance of the Vacuum Vessel. These activities show the feasibility of ITER Vacuum Vessel as feasible in a realistic way. This paper describes the major progress, achievement and latest status of the R&D activities on the ITER vacuum vessel.
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