25F03
Finding the Latent Structure in Large Scale Transport Event
大規模輸送現象により見いだされた電子熱輸送の潜在的構造	 
Naoki Tamura, Katsumi Ida, Shigeru Inagaki, Hayato Tsuchiya, Tokihiko Tokuzawa, Kenji Tanaka,Takashi Shimozuma, Shin Kubo, Kimitaka Itoh, Yoshio Nagayama, Kazuo Kawahata, Shigeru
Sudo, Hiroshi Yamada and LHD Experiment Group
田村直樹1, 居田克巳1，稲垣	  滋2，土屋隼人1、徳澤季彦1、田中謙治1、下妻隆1、久保	  伸1、伊藤公孝1、長山好夫1、川端一男1、須藤	  滋1、山田弘司1、LHD実験グループ1
1

National Institute for Fusion Science322-6, Oroshi-cho, Toki-shi, Gifu 509-5292, Japan核融合科学研究所 〒509-5292	  岐阜県土岐市下石町322-6
2
Research Institute for Applied Mechanics, Kyushu University
6-1, Kasugakouen, Kasuga-shi, Fukuoka 816-8580, Japan
九州大学応用力学研究所 〒816-8580	  福岡県春日市春日公園6-1
An edge perturbation induced by a trace impurity pellet (TESPEL) injection in LHD evokes a non-local
transport phenomenon (large scale transport event, LSTE, such as a core electron temperature rise in
response to edge cooling). In order to evaluate how the local heat transport properties change in the LHD
plasma with the LSTE, a new transit time distribution analysis is applied. The results show that twolarge-scale coherent structures in the electron heat transport exist, and are qualitatively different from eachother. Therefore the non-local transport phenomenon observed in LHD is evoked by the interaction of
those structures.

1. Introduction
Nowadays it is well known that high-temperature
turbulent plasmas exhibit a fast and global response(beyond the standard local diffusive paradigm) to achange in plasma parameters at a location. The
most famous example of such a response is anabrupt rise of the core electron temperature Te inresponse to the edge cooling (so-called “non-localtransport phenomenon”) [1]. Unfortunately,
although more than 10 years have passed since thiskind of large scale transport event (LSTE) wasdiscovered, there is still no rational explanation of
the phenomenon. In the recent studies of the LSTE,
a spatial interaction of the heat transport has beenhighlighted [2]. Whatever the reason may be,
however, the local heat transport is definitely andstrangely changed in the LSTE. So we revisit theinvestigation of the local heat transport properties(∇Te) in the LSTE, especially the non-local
transport phenomenon for gaining a deeper
understanding the heat transport in the strongly
turbulent plasmas.
2. Experimental Setup
The edge perturbation experiment with a tracer
encapsulated solid pellet (TESPEL) injection iscarried out on LHD with the magnetic axis positionof Rax = 3.5 m, the average minor radius of a ~ 0.6
m and the magnetic field at the axis of Bax = 2.829
T. The plasma around the time of the edge
perturbation is heated continuously by a neutralbeam injection (NBI) and an electron cyclotron
heating (ECH). The focus of all ECH beams isadjusted near the Rax. A multi-channel heterodyne
radiometer is used to track the temporal behavior ofthe Te with a high time resolution. More detailed

information on the experimental setup can be foundin Ref. [3].
3. Typical Example of Large Scale Transport
Event in LHD
Figure 1 shows a typical temporal behavior of theTe measured with the multi-channel heterodyne
radiometer at different normalized minor radii inthe edge perturbation experiment. As can be easily
recognized from Fig. 1, a significant rise of the coreFig. 1 Typical temporal behavior of the electron
temperature measured with the radiometer atdifferent normalized minor radii. The time of theTESPEL injection, which evokes the edge
perturbation is indicated as the vertical dashed line.

values of the –dδTe/dr still can exist despite a lackof another apparent transport branch. On the otherhand, in the edge region, the transition to anothertransport branch disappears. Therefore no core Te
rise in the high-density plasma could be attributed
to the disappearance of transition to anothertransport branch in the edge region.

Fig. 2 Contour map of the transit time distribution of
the gradient of the perturbed electron temperature
for the discharge with the non-local transportphenomenon. In this case, the line-averaged electron
density is at 0.7 x 1019 m-3.

Te takes place in response to the edge coolingaccompanying the TESPEL injection. This kind of
LSTE is not peculiar to helical plasmas nor toplasmas with an impurity pellet injection, but is avery common characteristic of the magneticallyconfined toroidal plasmas.
4. Transit Time Distribution Analysis
In order to evaluate how the local heat transportproperties change in the LHD plasma with theLSTE, a new transit time distribution (TTD)
analysis is applied to the temporal behavior of theTe gradient. Figure 2 shows a contour map of theTTD of the gradient of the perturbed Te for thelow-density (line-averaged electron density ne_bar =0.7 x 1019 m-3) plasma with the typical LSTE. As
see in Fig. 2, a peak at non-zero displacement of the–dδTe/dr is found to exist over a wide region (ρ >0.55, at least 6 cm wide) in the periphery of theplasma. This peak clearly shows the existence ofanother transport branch. This branch does not havea stronger attracting force compared with theoriginal branch (at zero point f the –dδTe/dr), which
can cause the backward transition of the edge
electron heat transport. On the other hand, around ρ= 0.35 (about 10 cm wide), the TTD is found to has
a wide flat region. This demonstrates that various
values of the –dδTe/dr can exist despite a lack ofanother apparent transport branch. It should be
noted here that almost no change in the profiles ofelectron density and heat deposition in the coreplasma after the onset of the LSTE. When the valueof ne_bar increases to 1.2 x 1019 m-3, no clear rise of
the core Te in response to the edge cooling has been
observed. In this case, in the core region, even not
the exact same as the case shown in Fig. 2, various

5. Discussions and Summary
The formation mechanism of such large-scalecoherent structures of the electron heat transportremains unclear. One of the candidates for that is along-range Te fluctuation, which is very recently
discovered in LHD [4]. This long-range Te
fluctuation is defined by the long radial correlation
length comparable to the plasma minor radius, thelow frequency, 1 ~ 3 kHz, and the ballistic radial
propagation speed, ~1 km/s. Interestingly, thetime-averaged amplitude of the low-frequency
component of the long-range Te fluctuation has asimilar spatial structure to the TTD map in the coreregion. More detailed discussion on this matter will
be done in the conference.
In conclusion, the TTD analysis shows that twolarge-scale coherent structures in the electron heattransport exist in the LHD plasma exhibiting thenon-local transport phenomenon. The non-local
transport phenomenon observed in LHD could be
attributed to the interaction of those structures.
Acknowledgments
We would like to thank to all of the technical staff
of NIFS for their excellent support. This work is
supported in part by a Grant-in-Aid for Young
Scientists from a Toray scientific foundation,
Grant-in-Aids for Young Scientists (A) (23686134)
and for Scientific Research (S) (21224014) fromJSPS and NIFS grant administrative costs,
NIFS11ULHH012.
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