Prime pagine RA2010FUS:Copia di Layout 1 - ENEA - Fusione

062
progress report
2010
ENEA Frascati laboratories have also had in charge an Early Stage Researcher (EFDA Goal Oriented Training
Programme “Tritium Technologies for the Fusion Fuel Cycle” – TRI–TOFFY) to be prepared in the
deuterium–tritium fuel cycle area for ITER. Main research activities have consisted in characterizing thin wall
Pd–based permeator tubes in terms of hydrogen permeability and selectivity and the hazard and operability
study (HAZOP) for the HTW process system of ITER. For the treatment of HTW three processes have been
studied in details [3.7]: water decomposition by using the water gas shift reaction, high temperature electrolysis
and water splitting through reduction on metals. Particularly, the use of Pd–based membrane reactor for
carrying out the water gas shift reaction of tritiated water permits high reaction yields to be reached and pure
hydrogen isotopes to be recovered, which can be directly sent to the isotopic separation system.
3.3 Magnet and Power Supply
Optimization of the toroidal field ripple reduction system
The ITER toroidal field coil (TFC) system is made of 18 D–shaped coils spaced by 20° in toroidal angle. The
discontinuity produces a deviation (ripple) from the toroidal direction of the magnetic flux surfaces that can
cause significant losses in the confinement of high energy particles (α–particles or high–energy ions from
neutral beam injectors) due to their trapping inside the “ripple valleys” and unwanted peaking in the heat loads
on the FW. Due to these reasons, an accurate evaluation of the toroidal field ripple (TFR) was performed in
various operation conditions. This evaluation was carried out by means of finite element models built only by
using structured meshes in order to obtain a very high field precision on a regular spaced grid extended to the
entire region enclosed in the FW. The model was built by taking into account the real 3–D shape of the TFC
and modelling three nested D shaped coils capable of carefully reproducing the real geometry of the TFC.
The analysis showed a high value of TFR (exceeding 1% in the outboard plasma region near the equatorial
plane) and this confirmed the need for introducing some correcting elements. The implementation of
ferromagnetic SS430 steel inserts in the outboard region between the inner and outer vessel shells, properly
optimized in shape, size and location, then allowed the maximum ripple at the plasma separatrix to be reduced
to 0.19% (fig. 3.11); this value could increase up to 0.38% when the number of inserts was limited by the filling
factor required for ITER design.
The analysis also confirmed that the introduction of ferromagnetic inserts into the equatorial region between
equatorial ports is essential to reduce the TFR to acceptable levels in the plasma region. The optimization of
the ferromagnetic inserts was performed by taking care of limiting the ripple over–compensation under 0.6%
during plasma operation at half toroidal field.
0.268×10 -3 0.736×10 -3 0.001205 0.001674 0.002142
0.502×10 -3 0.001908
SMN=0.357×10 -5
0.971×10 -3 0.001439
Optimized insert plate
SMX=0.010749
distributions each plate is 4.4 cm
thick with a filling factor of 4.4
0.357×10 -5
0.001198
Ripple in the plasma
region with optimized
insert distribution around
ports without NBI
Enlarged
scale
0.002392 0.004779 0.007167 0.009555
0.003585 0.005973 0.008361
Maximum ripple
at the separatrix
0.188%
Figure 3.11 – ITER ripple map at full toroidal field with the optimized distribution of
the inserts
Equatorial port position
Three–dimensional
magneto–static analyses
for ITER
ENEA completed the
activities related to several
magneto–static analyses
in ITER according to the
EFDA Study Contract
07–1702/1602
(TW6–TPO–3DMAGS):
the optimization of the
shape, size and location of
the ferromagnetic plates
used for the reduction of
the TFR; the evaluation
of the Maxwell’s forces on
these plates and the
analysis of the effects on
the ripple due to the
ferromagnetic materials
in the magnetic shields of