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

magnetic confinement (cont’d.)
progress report
2010
015
klystron at 5 GHz with a target rf power of 500 kW continuous wave (CW) has definitely set this power as the
upper limit to the present high vacuum electron tubes technology at this frequency. From the physics point of
view, the ITER operational scenarios have been well defined, while the latest experiments have pointed out the
effectiveness of the LHCD waves at high plasma density.
Following the recommendations of the 4th meeting (19–22 May 2008) of the ITER STAC, the assigned
objectives of the task were "to perform the conceptual design and to initiate the urgent R&D activities in order
to bring the ITER LHCD system up to the point at which such activities could be transferred to the Fusion
For Energy (F4E)".
The "LH4IT" task has been performed in close collaboration between ENEA – Frascati and Commissariat à
l’Energie Atomique (CEA) – Cadarache as well as with ITER Organization (IO) and several other ITER
partners.
A 5 GHz prototype klystron (fig. 1.5) developed by Toshiba for the LHCD system of the Korean tokamak
KSTAR has demonstrated a CW output power of 350 kW, a 10s pulsed power of 455 kW, and a peak power
of 510 kW for 0.5 s.
These promising results confirm the possibility of realizing a 500 kW CW klystron with an operational
frequency of 5 GHz in a relatively short time. On the other hand these results also demonstrate the 500 kW
as the upper power limit for klystrons in this range of frequency. The required 20 MW of rf power coupled
to the plasma can be therefore obtained by 48 500 kW klystrons. Each klystron feeds a PAM module (fig. 1.6)
made of six toroidal rows and four toroidal columns of elemental alternated
active/passive waveguides. To launch an optimum rf spectrum with N 0
=1.9 with
a phase shift of 270° between active waveguides, the active waveguide width is set
to 10 mm, with a passive waveguide width of 8mm and separation wall thickness
of 3 mm at the launcher mouth.
The rf power of each klystron is carried by moderately oversized circular
waveguides (the C 16 standard with inner radius R=67.05 mm) which transmit the
TE 01
circular mode. The corresponding evaluated transmission losses are about
0.22 dB/100 m.
Suitable mode filters (fig. 1.7) have been taken into consideration and studied in
order to suppress potentially detrimental spurious modes generated by the four 45
deg and one 100 deg bends included in the main transmission lines (MTLs). These
filters are based on the attenuation introduced by the periodic corrugation of the
waveguide wall, enhanced by the presence of absorbing material silicon carbide
Active
waveguide
1st BJ
Figure 1.6 – Schematic drawing of a PAM module
Figure 1.5 – The
500 kW prototype
klystron
2nd BJs
d
a
400 mm
Base circular waveguide
P
Corrugations
SiC
100 mm
Passive
waveguide
Figure 1.7 – Longitudinal cut of a corrugated mode
filter in circular waveguide