SI-8
ダイバーター開発の進展
Progress on the development of the ITER divertor
鈴木 哲、江里 幸一郎、関 洋治、横山 堅二、毛利 憲介
Satoshi Suzuki, Koichiro Ezato, Yohji Seki, Kenji Yokoyama, Kensuke Mohri
原子力機構那珂JAEA-Naka
divertor targets since 2011, in terms of cost saving
and relevancy of DEMO divertor design. This
proposal is still in review at the IO's advisorycommittees (STAC and MAC). And the final
decision on the armor material selection of thedivertor targets will be made by the ITER Council
within 2013. As a result, JADA has started R&D'son the fully tungsten-armored divertor target. In thispaper, latest progress on the R&D's on the fully
tungsten-armored divertor target in JADA ispresented.
2. Small-scale tungsten divertor mock-ups
JADA and IO have placed the contract todevelop tungsten-armored divertor targets since theend of 2012. Based on this contract, JADA has
provided more than 10 small-scale divertor
mock-ups with pure tungsten armor tiles for highheat flux testing in order to investigate the thermal
performance and the durability. Figure 2 shows aschematic drawing and the photo of the small-scale
tungsten divertor mock-ups.
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1. Introduction
JAEA, assigned as Japanese Domestic Agency(JADA), is currently manufacturing various
components for the ITER construction. The ITER
divertor components are being manufactured by 3parties (EUDA, RFDA and JADA). JADA is
responsible for the manufacturing of the divertor
outer vertical target.
The divertor has a role to exhaust impurities
which come from plasma. The divertor is subjectedto the high heat flux from the impact of theimpurities. To withstand the high heat flux, thesurface of the divertor is covered with refractorymaterials. The inner and the outer vertical target
where the severe heat flux is subjected are covered
with carbon fiber composite and pure tungsten, andthe dome components are fully covered with puretungsten in the current baseline design. These armor
materials are metallurgically bonded to the copper
alloy (CuCrZr) cooling tubes to achieve high heatremoval capability. Figure 1 shows the schematic
drawing and the procurement sharing of the ITER
divertor components. Unique technologies, whichhave been independently developed by the 3 parties,
are utilized for the bonding of the armor materials
and the cooling tubes. JADA currently uses
"brazing" technology for the bonding.

SECTION A-A

Figure 1 Schematic and procurement sharing of
ITER divertor components (1 cassette, current)
On the other hand, ITER organization (IO) has
proposed to start with a fully tungsten-armoredFigure 2 Schematic drawing and photo ofsmall-scale tungsten divertor mock-ups (unit: mm)

The cross section of the mock-ups is similar tothat of the divertor outer vertical target in thecurrent design. The tungsten monoblock armor isbonded onto the pure copper interlayer prior to thebrazing process. And then, the pure copper
interlayer and the cooling tube made of CuCrZr arebrazed with Ni-Cu-Mn based braze filler material.
Table 1 shows the bonding method of themock-ups.
Table 1 Bonding method of small-scale tungsten
divertor mock-ups
Tungsten
Cu interlayer/Cu interlayer/CuCrZr tube
Type A Direct casting of Cu
Type B Diffusion bonding
Ni-Cu-Mn brazing
Type C HIP bonding
As shown in the table, three kinds of bonding
methods between the tungsten armor and the purecopper interlayer have been tested to qualify assuitable bonding techniques for the manufacturingof the ITER divertor targets.
3. Results of high heat flux testingHigh heat flux testing of the small-scale tungsten
divertor mock-ups has been carried out in the test
facility at JAEA and in the ITER Divertor Test
Facility (IDTF) at Efremov Institute in Russia. The
maximum heat flux of 20 MW/m2 was cyclicallyapplied to the plasma-facing surface of themock-ups to simulate the slow-transient heat flux ofITER. In this thermal cycling experiment, themaximum surface temperature of the tungsten

Type-B

Figure 3Type-A

Type-C

armor reached over 2000oC, which exceeds therecrystallization temperature of pure tungsten(=~1300oC). The trace of recrystallization of thetungsten armor was found in all mock-ups.
Although 1 out of 8 mock-ups tested showedsurface cracking, the other 7 mock-ups
demonstrated sufficient thermal performance anddurability without any failure up to 300 cycles. In
particular, 6 mock-ups tested in IDTF withstood
without any failure not only for 1000 cycles at20MW/m2 but also for additional 5000 cycles at
10MW/m2 to simulate normal operation of theITER divertor targets, which strongly encourages
IO's design change proposal described in theprevious section. Figure 3 shows the surface of thetungsten armor of the mock-ups after 1000 cycles at
20MW/m2.
Summary
JADA has successfully developed small-scale
tungsten-armored divertor mock-ups which canfulfill the acceptance criteria for the ITER divertor
target part in preparation for the final decision on
the armor material selection of the divertor targets
by ITER Council. In addition, high heat flux test
results obtained so far suggest that the current
material specification on tungsten is sufficient forthe steady-state heat flux toward the ITER divertor
targets. Those results also indicate that the current
tungsten monoblock technology including thebonding techniques is acceptable for therequirements of the full-tungsten divertor verticaltargets for ITER.

Type-A

Type-A

Type-B

Small-scale tungsten divertor mock-ups after 1000 thermal cycles at 20MW/m2 in IDTF