24P024-P
Control of radiative/detached divertor operation with m/n=1/1 RMP applied tothe stochastic layer of LHD
LHDにおける共鳴摂動磁場によるデタッチメント制御実験
Masahiro Kobayashi, Suguru Masuzaki, Noriyasu Ohno*, Tsuyoshi Akiyama, Yoshiro Narusima,
Byron J. Peterson and the LHD experimental group
小林政弘, 増崎貴，大野哲靖*, 秋山毅志, 成嶋吉朗, ピーターソン バイロン, LHD実験グループ
National Institute for Fusion Science, Toki 509-5292, Japan* Gracuate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6*名古屋大学大学院工学研究科 〒464-8603 名古屋市千種区不老町
Effects of resonant magnetic perturbation (RMP) field on the radiative/detached divertor plasma areinvestigated by applying m/n=1/1 RMP to the edge stochastic layer of the Large Helical Device (LHD).
The remnant island in the stochastic layer created by the RMP changes the density dependence of radiation
intensity compared to the non RMP case. There appears density window where radiation becomes
insensitive to density. In this window, the radiative divertor plasma is stably sustained with concomitantdivertor power/particle flux reduction observed at several probe arrays, while the toroidal uniformity of thedetachment is not guaranteed yet. It has been demonstrated that the detachment onset can be controlledwith ramp up of RMP current and that the RMP induced detachment is compatible with further enhanced
radiation with extrinsic impurity gas puff.

2. Effects of RMP on the radiation intensity
In LHD, effects of the resonant magnetic
perturbation (RMP) field on the edge radiation areinvestigated by applying n/m=1/1 RMP to thestochastic layer. The RMP creates remnant island in
the stochastic layer. The radiation intensity
measured by resistive bolometer is plotted in Fig.1
as a function of line averaged density. The RMP
coil current is changed from 0 to 3.4kA, where
3.4kA corresponds to b~ / BT ~ 0.11%. Applicationof RMP leads to rapid increase of radiation above
19-3n e ~ 4x10 m , and enters the certain range where
the intensity becomes insensitive to ne . In thisrange the increased radiation is easily sustained forseveral seconds until the end of discharge [3]. Thetwo Langmuir probe arrays at top and inboard
divertor plates show reduction of heat and particle
load during this phase, although the divertor leg
interferometer installed at the different location thanthe probes shows no reduction of the density. The
1.9 kA
1.5 kA (collapse)
0A (collapse)

3.4 kA
3.0 kA
2.5 kA

3Radiation intensity (a.u.)

1. Introduction
In magnetically confined fusion reactors, theenergy flux to the divertor plate caused by the directcontact of plasma with the plate surface is expected
to be several tens MW/m2, which is far beyond theengineering limit of the divertor structure [1]. The
power dispersal via volumetric energy loss such asline radiation by impurity species is, at the moment,
only possible scheme to bring the divertor power
load below the engineering limit. The reduction of
the power load has been demonstrated in many
devices by increasing the radiated power fraction up
to 80 ~ 90 %. At the same time, however, it isfound that once the plasma detaches from thedivertor plates, the plasma tends to be thermallyunstable and the control of the radiationlevel/location becomes very difficult. The loss ofcontrol of the detachment plasma leads to theX-point MARFE with deterioration of core plasma
performance [2].

Collapse2

Sustaineddetach

10Experiments
02468ne (1019 m-3)

10Fig.1 Radiation intensity as a function of line
averaged density for different RMP coil current.

ratio of Hγ/Hβ measured by visible spectrometerincreased throughout the torus. The measurements
indicate divertor detachment, but with a certain
toroidal modulation probably related to the mode
structure of the RMP. The distribution of thedetached divertor plasma in toroidal/poloidal
direction is under investigation.
In the case without RMP, the radiation
increases rather slowly against density, and around8.5x1019m-3 it increases quickly beyond the density
limit resulting in radiative collapse. The change of
RMP coil current from 3.4 to 0kA gradually shifts
the curves towards non RMP case. There is a
threshold value for the sustained detachment around
1.9kA.
10ne (1019(a)-3m )

501(b)
10.5U

Iis (A)2000

LID(b)Iis (A)0

10.5U0.4306T2Prad (MW)

(A)

(c)

40.6

10H puff 3.5L (V)Ne puff 50ms

10(c)68time(s)2010NBI (MW)430

100Fig. 3. Time evolution of (a) line averaged density
and gas puff wave form, (b) divertor particle flux,(c) radiation intensity, NBI input power and Nepuff timing of 50 ms pulse (arrow).

1000
000.8

30
205200(a)ne (1019 m -3)

0.2

0.5
0
3000 IDetach1030

10H puff 3.5L (V)to confirm the effect of RMP. It is found that thedetachment onset is accordingly shifted back andforth in time. The results demonstrate theavailability of the new control knob on the divertor
detachment.

68time (s)10Fig. 2. Time traces of (a) line averaged density
and gas puff wave form, (b) the divertor particle
flux, (c) RMP coil current.

2. Control of detachment onset with RMP
current
In the 14th experimental campaign (fiscalyear 2010) of LHD, the possibility of detachment
onset control with RMP has been demonstrated.
Fig.2 shows the time trace of line averaged density,divertor particle flux and the perturbation coilcurrent for n/m=1/1 RMP. After the initiation of thedischarge at t=3 sec, the plasma density is gradually
increased by gas puff and it reaches the flat top~8x1019 m-3, while the perturbation field is also
increased during the discharge as shown in the coilcurrent. By keeping the density constant after t=5sec, only the perturbation field increases and theplasma goes to detachment at t=6.3 sec as shown inthe divertor particle flux reduction. The detachment
is sustained up to the end of discharge at t=9 sec. It
is seen that the detachment transition occurs at thecoil current of slightly above 2kA. The timing ofcoil current ramp up is shifted back and forth intime while keeping the almost same density flat top

3. Compatibility of the RMP induced
detachment with extrinsic gas puff
The compatibility of the island induced
detachment with the extrinsic gas injection, which
is often effective to increase the radiation fraction,
has been tested. Fig.3 shows the time evolution of
the line averaged density, divertor particle flux andthe radiation intensity. In this case, the full RMP
current is applied from the beginning of thedischarge, and the island detachment occurs at t=4.5sec. The density is still increased even after thedetachment onset up to 7x1019 m-3 and keeps
constant afterwards. The neon is puffed at t=7 sec
with 50 ms pulse as indicated with the arrows in thefigure. The radiation intensity increases by a factorof 1.4, while keeping the stable detachment.
References[1] “Progress in the ITER physics Basis: Chapter 4 :Power and particle control”, Nucl. Fusion 47 (2007)
S203.
[2] N. Asakura, H. Hosogane, S. Tsuji-IIO, K. Itami, K.
Shimizu, M. Shimada, Nucl. Fusion 36, 795 (1996).
[3] Kobayashi, M. et al. : Physics of Plasmas 17 (2010)
056111.