03aD08P
テント型磁場配位によるJT-60負イオン源の負イオンビームの非一様性の改善
Improvement of Uniformity of the Negative Ion Beams by Tent-shaped
Magnetic Field in the JT-60 Negative Ion Source
吉田雅史、花田磨砂也、小島有志、柏木美恵子、NB加熱開発グループ,
Masafumi Yoshida, Masaya Hanada, Atsushi Kojima, Mieko Kashiwagi, and NB heating
technology Group
日本原子力研究開発機構、Japan Atomic Energy Agency
clearly uniform in the region of Y = ±490 mm. The
calculation result on the trajectories of theprimary electrons indicates that the localizationof the primary electrons is well suppressed in thetent-shaped filter.The parent particles of negativeions, i.e., positive ions and atoms measured in thetent-shaped showed a well uniform.
The uniformity defined as the deviation fromthe averaged beam intensity was reduced from
14 % of the PG filter to ~10 % without a reductionof the negative ion production by modifying themagnetic filter to the tent-shaped filter. Thisvalue fulfills the requirement of JT-60SA.

Fig. 1. Horizontally schematic view of two magnetic fields in JT-60
negative ion source; (a) a conventional PG filter (b) a new designed
tent-shaped filter
80Seg1

Seg2

Seg3

Seg4

Seg5

Tent shaped filter

Beam current density extracted
from each aperture [A/m2]

In JT-60 Super Advanced for the fusion
experiment, 22 A, 100 s D- ions are designed to be
extracted from the world largest ion extraction
area. One of the key issues for producing such as
high current beams is to improve the non-uniform
production of the negative ions over the large ion
extraction area. In order to improve theuniformity of the negative ions, a tent-shaped
magnetic filter is newly being developed for
JT-60SA negative ion source. In this paper, we
report the design of the tent-shaped filter and theexperimental results before and after themodification of the magnetic filter.
The JT-60 negative ion source has asemi-cylindrical arc chamber of 640 mm indiameter and 1220 mm in length, and ion
extraction area of 450 mm × 1100 mm. In the ion
source, the arc chamber is fully surrounded byasymmetric 26 rows of the permanent magnets on
the wall. Figure 1 shows a cross sectional view of(a) conventional magnetic filter (PG filter) and of(b) tent-shaped magnetic filter. The tent–shaped
filter is formed by symmetrical arrangement of
the permanent magnets surrounding the wallwithout the PG current to avoid one-way
magnetic drift of primary electrons in theconventional transverse magnetic filter such as
the PG filter. In the tent-shaped filter, two way
magnetic drifts are longitudinally formed.
The tent-shaped filter was applied to the JT-60
negative ion source and tested. The arc chamber
was seeded with a small amount of cesium. The
negative ions were extracted and dumped on thecopper target located at 4.5 cm downstream fromthe extraction grids. The extracted beam profiles
were measured by IR camera behind the copper
target. Figure 2 shows the longitudinal profiles ofthe extracted H- ion beam with the Cs seeded
conditions and the arc power of 120 kW before
and after the modification of the magnetic filter.
In the tent-shaped filter, the H- ion beam profile is706050PG filter

403020100-600

Extract region designed in JT-60SA (Y =±490 mm)

Uniformity: Deviation from the averaged
intensity in the region of Y = ±490 mm
14 % (PG filter)) ~10 % (Tent-shaped filter.)-400-200

0200

400600Longitudinal direction [mm]Fig. 2. Comparison of the longitudinal profiles of the beam current
density extracted from each aperture measured by the IR camera in thePG filter and in the tent-shaped filter with the Cs seeded conditions.