PROGRESS REPORT - ENEA - Fusione

A2 Preliminary Design of FT3
Fig. A2.6 – Active, reactive and total power for the reference FT3 pulse
A Fusion Programme
P(MW) Q(MWAr) S(MVA)
500
400
300
200
100
P: active power
Q: reactive power
S: total power
0
-21 -15 -9 -3 0 6 12 18 24 30 36 42
-100
Time (s)
(corresponding to about 80 MW requested at the
grid) and a stationary load of 25 MW. Due to the
amount of requested power, connecting to a
powerful node of the 400–kV Grid would be
desirable. Nevertheless, an accurate check by the
National Grid Regulator (GRTN), including both
active and reactive power effects on the specific
grid, might show that a 220–kV line could be
adequate. Lacking such an evaluation, the
400–kV line is taken as the reference solution.
Within the assumed 400–kV reference solution,
FT3 needs a dedicated switchyard to supply the
PFC, TFC, additional heating systems and
auxiliaries. All the loads are fed by one main step–down transformer (400/36 kV) with three
secondary windings: two (225 MVA each) star connected and grounded through a resistor, to supply
FT3, and one (80 MVA) delta connected to allow free circulation of third harmonic currents. On the
request of the GRTN, active power shedding resistors could be connected to the tertiary winding.
Sharing the total power between two secondary windings has the aim of making it possible to use
the 36–kV level on the secondary sides (instead of the more expensive 75–kV level), limiting the rated
current within the present breaker capability at this voltage. Each circuit for the supply of the TFC and
the various PFCs is generally made up of a converter transformer, a thyristor converter unit, a protective
crow-bar and high-speed, solid–state switches for the additional resistance units. No specific study for
the breakdown phase has been made so far.
Table A2.III – ICRH system parameters
Operating frequency range ( MHz) 60±90
Peak power (MW) 20
Bandwidth (MHz)
±2MHz (-1db)
Pulse width (s) ≥ 100
Time interval between two
100–s pulses (s) 1800
Type of antenna
3 rows of 2 straps
Power per strap (MW)
1 (at generator)
Power coupled per antenna (MW) 5
Max radiated power density (MW/ m 2 ) 10
N. of antennae 4
Power per generator (MW) 2
N. of rf generators 12
Heating systems. The FT3 auxiliary heating
systems are consistent with the present state
of the art and do not require additional R&D
activity. FT3 is equipped with three systems:
ICRH, ECRH and LHCD. A description of the
ICRH system is given in table A2.III. At a
magnetic field of 6.7 T, the use of 3 He minority
requires a frequency of 68 MHz. In its initial
configuration the system will couple 20 MW to
the plasma. A possible design of the ICRH
antennae could be based on an array of six
(two toroidal by three poloidal) current straps
protected by a Faraday shield made of a set of
16 non–tilted elements, with a smoothed
rectangular cross section. The Faraday shield
has to suppress the components of the emitted radiation parallel to the local B-field, and shield the
electrically active components from direct contact with the plasma. All the antenna components
(straps and Faraday shield rods) are water-cooled. Each antenna is fed by three high–power
tetrodes “TH 526”, with a maximum rf power output of 2 MW in the frequency range 35-80 MHz.
Three of the generators are supplied by a 33–kV/380 A solid–state unit. The antenna, together with
the respective vacuum transmission lines and vacuum windows, is integrated in a plug inserted in
an equatorial port and removable as a single unit.
The performance of the antenna was studied with the TOPICA code on the reference FT3 H–mode
plasma scenario at 68 MHz with 2% 3 He minority. Electric current and magnetic current/electric field
distribution were obtained in vacuum and with the plasma. The analysis in vacuum of the optimised
antenna showed very good (low) inter-strap coupling. The analysis with plasma demonstrated the
good performance of the antenna array in terms of power coupled to the plasma: for the standard
configuration and for a maximum voltage of 30 kV, a power of 5 MW can be coupled to the plasma
by each array. The launched power spectrum has a maximum for n || =±6. Figure A2.7 shows the
current distribution on the straps, demonstrating the good efficiency obtained with this geometry:
Progress Report 2006
38