22P154-P
Progress of procurement on the ITER NB ultra-high voltage power supplies
ITER中性粒子入射装置用超高圧電源調達の進展
Haruhiko Yamanaka, Kazuhiro Watanabe, Kazuki Tsuchida,Hiroyuki Tobari, Jumpei Takemoto and Takashi Inoue
山中 晴彦、渡邊 和弘、土田 一輝、戸張 博之、武本 純平、井上 多加志Japan Atomic Energy Agency
801-1, Mukoyama, Naka-shi, Ibaraki 319-0193, Japan（独）日本原子力研究開発機構〒319-0193 茨城県那珂市向山801-1
High-energy neutral beam injector is under development for heating and current drive of ITER plasma incollaboration with EUDA. JAEA(JADA) will provide ultra-high voltage DC power supplies which cangenerate -1 MV DC power for the negative ion beam source. Present status of the design on the power
supply is reported as a contribution by JADA for the ITER Neutral Beam Injector. R&D status regarding
the ceramic insulation tubes for water choke and the DC -1 MV insulating transformer is also reported.

1. Introduction
Two high-energy neutral beam injectors (NBI)
with the beam energy of 1 MeV and the neutralbeam injection power of 16.5 MW/injector will be
installed in ITER for plasma heating and current
drive [1]. Before the NBI operation in ITER, theNeutral Beam Test Facility (NBTF), which isalmost the same system as the ITER NBI, will beconstructed at the RFX site in Padua of Italy toconfirm their specifications and to establish its
operation techniques. For their NBI system, JAEA
as Japan Domestic Agency (JADA) will provide
ultra-high voltage DC power supplies for NBTF
and ITER in collaboration with EUDA. Capacity ofthe power supply is supply DC -1 MV and 60 MW
for the beam source with pulse duration up to 3600
s[2]. To construct such UHV NBI power supply,
design study and R&Ds have been conducted and it
is preparation for the procurement arrangement is inprogress.
2. Requirements for ITER NB power supply
Issues for the power supply system are shown in
Table 1. Electric breakdowns often occur in theaccelerator and they make short circuit. Stored
energy also flows into the accelerator from thestray capacitances existing between the highvoltage parts and ground potential. Such energy
input produces electrical damage for theaccelerator. To accelerate the beam stably, prompt
cut-off the high voltage power is required. Furthersuppression of energy input to the accelerator isessential to avoid the accelerator voltage holding
degradation. To meet these requirements, a highfrequency inverter system and high performancecore snubber have been developed based on thetechnology for the high voltage power supply of

the JT-60 N-NBI system in JAEA [3]. The same
type of power supply has been proposed for theITER NBI system.
In the R&D work, a ceramic insulation tube havebeen developed for the water choke to provide
cooling water (<65 °C) for the ion source andaccelerator electrodes with insulation of -1MV.
Recently, DC -1MV insulating transformer
development has started as ITER R&D task. DC -1
MV insulation is a key issue for the transformer.
Table 1 Status of the AGPS design for NB power supply
Items
Design Status
1) High speed
Adoption of 150 Hz inverter system, whichswitching of -1 MV is based on the high voltage power supply
outputof JT-60 N-NBI system [3].
2) Suppression ofsurge current

Installation of resistances and highperformance core snubbers using Fe-based
soft magnetic alloys (FINEMET), which
was developed for high energy NBI powersupply [4].

-1 MV insulation by SF6 gas at 0.6
MPa. Basic performance of insulation
has been tested.
Ceramic insulation tubes with SUS4) -1 MV waterflanges for high pressure and highchokewater temperature cooling line havebeen developed [5]5) -1 MV insulating R&D started to demonstrate the DC -1
transformer with 1 MV insulation for transformer and itsMV bushingbushing .
3) -1 MVtransmission line

3. Status of design and development
3.1 -1 MV DC power supply
The ultra-high voltage DC power supply called
AGPS (Acceleration Grid Power Supply) is inverter
controlled power supply. A high frequency invertersystem (6.5kV, 150Hz) controls the high speed
switching of the DC -1MV without DC switches.

The inverter controls the voltage regulation too.
Five 200 kV DC generators (Fig. 1) are connected
in series at the DC output.
3.2 Water choke
The ion source is installed at – 1 MV, so thecooling water for the ion source needs to be
insulated by the water choke system. A temperatureof the cooling water is as high as 65 °C in ITER.
Leak current will increase as temperature. It is notwell known the insulting performance at high leakcurrent. Therefore, R&D on the water choke to test
insulation with a high leak current.

ceramic tube (100 mm dia.) could sustain
high-pressure of 5 MPa which was 2.5 times
higher than the nominal pressure.
The insulation performance of the developed tube
was confirmed in the R&D.

Fig. 2 Bird’s eye view of HV deck2 and ceramic
insulation tube for water choke line.

Fig. 1 Electric circuit diagram of the ITER NB system

For the insulation of such a high voltage, acompact insulation tube, which consists of aceramic insulation tube (100 mm dia.) and twometal flanges, was developed to satisfy therequirements of high water pressure (2 MPa), highflow rate (>100 l/m) and high water temperature(<65 °C) for the ITER NB water choke [5]. The
insulation performance of the developed tube wasconfirmed through high-voltage holding tests(110kV/tube 120 % of the rated voltage). The
obtained results are summarized below.
1) Under the water flow condition, the voltage
holding performance of a single ceramic tube
was confirmed up to the test voltages of -129
kV. The voltage holding performance of two
ceramic tubes connected in series was also
confirmed so that the voltage can be increased
linearly with number of the tube.
2) High voltage up to 110 kV was stably sustained
for the following conditions.
(1) Water temperature: 16 - 40 °C(2) Water flow rate:
50 – 140 L/min(3) Gas bubble mixing: 0 – 10 vol.% for N2 gas
3) In a long pulse test with the water flow andhigh-voltage load, no erosion and no corrosionof the ceramic tube were observed even after
50 hours of operation under high-leak current
load (>154 mA).
4) In a high pressure test, it was confirmed the4. 1 MV insulating transformer
The insulating transformer supplies AC 6.6 kV
power to the high voltage deck 1 (HVD1) where thenegative ion source power supplies are mounted at
the potential of DC - 1MV. DC - 1MV insulation inthe transformer windings, output leads lines andbushing is a key issue to realize such system.
R&D items are described as follows;
1) DC 1 MV insulation inside transformer
between the main and edge windings, andamong three phase winding leads.
2) DC 1 MV insulation between oil and air in theoutput bushing of the insulating transformer.
3) DC 1 MV insulation for the output leads
between the winding and the bushing.
A mock-up transformer model will be fabricatedand UHV insulation tests will be performed toverify the reliability of the design. These results
will be reflected the fabrication of the power supply
for the NBTF.
Considering the design activities and R&Ds,
construction schedule of the NBTF in Padua has
been discussed among ITER, EUDA and JADA andoperation of the NBTF will be started in 2017.
References[1] R.S. Hemsworth, H. Decamps, J. Graceffa, B.
Schunke and M. Tanaka, et al.: Nuclear Fusion 49,(2009) 045006.
[2] ITER web site: http://www.iter.org/.
[3] K. Watanabe, M. Kashiwagi, S. Kawashima, Y. Ono
and Y. Yamashita et al.: Nuclear Fusion 46, (2006)
S332-S339.
[4] K. Watanabe, M. Mizuno, S. Nakajima, T. Iimura
and M. Miyai : Rev. Sci. Inst 69, No.12(1998)4136.
K. Tsuchida, K. Watanabe, H. Tobari, J. Takemoto, H.
Yamanaka and T. Inoue: Denkigakkai-Kenkyukai(Sep., 2011) NE-11-004, in Japanese.