23P105-P
Ion Heating Characteristics of Magnetic Reconnection in Torus Plasma Merging Experiment
トーラスプラズマ合体実験を用いた磁気リコネクションのイオン加熱機構の検証
Hiroshi Tanabe, Hirotaka Oka, Akihiro Kuwahata, Shingo Ito, Masaaki Annoura, Michiaki Inomoto and Yasushi Ono
田辺博士, 岡 祐貴，桑波田晃弘，伊藤慎悟，案浦正将，井 通暁，小野 靖
Graduate school of frontier sciences, the university of Tokyo
2-11-16, Bunkyo-ku, Yayoi, Tokyo 113-8656, Japan
東大新領域 〒113-8656 東京都文京区弥生2-11-16
For the past ten years, we have developed a novel 2-D ion temperature measurement by use of computer
tomography and studied the ion heating characteristic of magnetic reconnection. The 2-D ion temperature
measurement revealed that the dissipated magnetic energy of two merging compact toroids heats ions in
the downstream area of magnetic reconnection, indicating ion outflow energy is converted to ion thermalenergy through viscosity damping and fast shock. The dependency of ion heating efficiency on the angle θof reconnecting field line is investigated by changing the guide magnetic field and have a maximum incounter helicity case (θ =180˚).

1. Introduction
Magnetic reconnection is a topological rearrangement of magnetic ﬁeld lines that converts magnetic
energy to plasma thermal and kinetic energy. For
the past decades, violent plasma acceleration andheating due to the process has been reported in theobservation of solar corona, the magnetizedplasmas and various laboratory fusion plasma
experiments. However, because of the lineintegrated effect for passive Doppler spectroscopy,
the detailed local spatial profile of ion heating has
not been investigated yet. To study the detailed
heating characteristics, we have developed a novel
local 2-D ion Doppler diagnostics by use ofcomputer tomography. It revealed where and how
ion is heated during reconnection. The section 2describes the 2-D local ion Doppler diagnostics andthe experimental results in the torus plasma
merging device TS-3 are shown in the next.
2. Tomographic 2-D ion Doppler Measurement
As shown in Fig. 1, our 2-D ion Doppler
measurement system was designed for torus plasma
whose major radius R and aspect ratio A are
200mm and 1.5. The 7×5 chords of collecting lenssystems (f=50mm, D=10mm) are installed on thecylindrical vacuum vessel to measure a R-Z profile
of line spectrum emissions integrated over 35 linesof viewing chords. This 2-D projection composedof the 35 channels of line spectrum emissions istransported through 35 optical fibers and isrealigned to 35×1 array for 50cm polychromatorconnected with ICCD image sensors (1024×256pixel, 26µm 2 /pixel, 0.00400nm/pixel) throughmagnifying optics (meridional:×4.3, sagittal:×0.7).

Fig.1. Schematic view of tomographic 2-D ion Doppler measurement system. A 2-D projection of discreteline spectrum emissions is collected by 7 × 5 chords of
optical fibers and is connected with the spectrometerwith an ICCD camera by realigning 35 fibers into 1-Darray.

The measured 35 line-integrated spectrums of Hβline which are collected by 7×5 (2-D) optical fibers.
The 35 line spectrums with 17×256 pixel for eachchord are extracted from the ICCD image, and then
are realigned to the 7×5 array equivalent to theoriginal view position on the computer. The
crosstalk is smaller than 0.3%.
In order to measure local 2-D (r-z) ion
temperature from the 35 chord-integrated spectra,
we utilize the slice-by-slice Abel inversion
technique [1]. The inversion is applied as follows: Ti: line-integrated spectra

local spectra
local Ti profile[2]The reconstruction fidelity by the method is shownin the numerical simulation results (Fig. 2). In
280mm < r < Redge in the 7 chords system, reconstruction error ∆ exceeds 30% but it is suppressedsmaller than 20% in the 8 chords system. In theregion of 70mm < r < 280mm, both of 7 and 8chord systems keep ∆ smaller than 15%. Therefore,in 7 chords system, the measurement area is limited
at 70mm < r < 280mm.

Fig.3. Time evolution of the 2-D ion temperature
measurement. Two clear hot spots are observed at thedownstream area of magnetic reconnection (referenceflux profiles are measured by magnetic probe array).

Figure 4 shows radial ion temperature profile on
the mid-plane (z = 0) of the vessel when we control
the angle θ of reconnecting field angle. The heating
efficiency strongly depends on an angle θ ofreconnecting field lines and have the maximum incounter-helicity case (θ =180˚).

Fig.2. Numerical simulation results of the proposedreconstruction of 2-D line spectrums with six different
ion temperature and emission profile. The ion
temperature profile of before and after inversion andmodels are compared with 7 and 8 viewing chords
measurement.

3. Experiment of Ion Acceleration and Heating
We installed the 2-D Doppler system in the TS-3
torus plasma merging device. The 2-D projection ofHβ line spectrum was measured at rtangential = 70, 105,
140, 175, 210, 245, 280mm and z = − 48, − 29, −10, 9, 28mm using hydrogen torus plasma
experiments in TS-3. The Hβ spectral line is used
for the measurement because the charge exchange
time between H and H+: 0.1 µsec[3] is much shorter
than the MHD timescale of plasma motions.
Figure 3 shows the measured temperature profile
during magnetic reconnection in counter-helicity
spheromak merging. Two clear hot spots of ion
temperature increase are observed at thedownstream area of magnetic reconnection. These
measured results indicate the existence of outflow
damping by viscosity and first shock.

Fig.4. The ion heating of reconnection increases
with the angle θ of reconnecting field lines

4. Summary
Local ion heating of reconnection has beenstudied clearly using the tomographic 2-D ion
Doppler measurement. The measured 2-D ion
temperature profile has two clear hot spots in thedownstream area of magnetic reconnection,
indicating that ion outflow energy is converted toion thermal energy through viscosity damping
and/or fast shock. The ion temperature increases
after the reconnection depends on the angle θ ofreconnecting field lines and decreases inverselywith the toroidal magnetic field. More detailed
investigation in tokamak merging experiment is
discussed in our presentation.
References[1] H. Tanabe et al., IEEJ Trans.PE, 130, 8, 720-721(2010) (in Japanese)[2] H. Tanabe et al., Rev. Sci. Instrum., submitted (2011)[3] Y. Ono et al, Earth Planets Space,53, 521 (2001)