24P135-P
Generation of Magnetic Fluctuations with Ion Cyclotron Frequency Range
during Magnetic Reconnection
磁気リコネクションによるイオンサイクロトロン周波数帯の磁場揺動の発生	 
Akihiro Kuwahata, Gao Boxin, Taichi Ito, Hiroshi Tanabe, Shingo Ito, Michiaki Inomoto, Yasushi
Ono
桑波田晃弘,	  高博シン，伊藤大智，田辺博士，伊藤慎悟，井通暁，小野靖Graduated school of Engineering, The University of Tokyo
260, The 10th Engineering building, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan東京大学大学院 〒113-8656	  東京都文京区弥生2−11−16	  東京大学工学部10号館	  260号室
Large amplitude magnetic fluctuation with the ion cyclotron frequency range was observed inside the current sheet region during magnetic reconnection in the plasma merging experiment with a guide field. The
fluctuation exhibited the amplitude of 10-20% of the reconnecting field and the propagating to the downstream region. The fluctuation strongly damped at current sheet edge and the reconnection electric field increased. These results indicate that the enhancement of reconnection rate and prospect of ion heating due tothe fluctuation.

1. Introduction
Magnetic reconnection has the deep relationship to a variety of magnetized plasmas, such as
solar flares[1,2], the earth’s magnetosphere[3]and laboratory plasmas[4,5]. One of the major
questions on magnetic reconnection is “How does
fast magnetic reconnection happened?”. In theresistive magnetohydrodynamics (MHD) regime,
the reconnection rate remains very small as compared that of real reconnection events observed in
the universe.
The TS-3 device has been investigated the physical properties of magnetic reconnection by using atorus plasma merging method. Previous experimentresults reported that fast magnetic reconnection isachieved when the current sheet half width is compressed shorter than ion gyroradius in conjunction
with the anomalous resistivity and significant ion
heating[4]. However, the direct mechanism thatenhances the reconnection speed still remains unclear.
2. Experimental setup
In the TS-3 device, two torus plasmas, with both
poloidal and toroidal magnetic fields, are produced
and their poloidal magnetic fields reconnect during
the plasma merging process under a guide field.
Two torus plasmas approach to the center of TS-3and collide. During the plasma merging, magnetic
field lines reconnect, and the magnetic energy isconverted to plasma kinetic and thermal energy.

Fig. 1 Schematic of TS-3 plasma merging device
with a magnetic fluctuation probe. The reconnecting field component is in the R direction and current sheet flows in theθdirection. Inflow and outflow are in the Z (axial) and R (radial) directions,respectively.
The toroidal (out-of-plane) magnetic field B θ,
which serves as a guide field in the reconnection
framework, is applied in this experiment by a center
conductor current. The guide field at the X-point Bxof 40 mT is comparable to the reconnecting magnetic field B// = Br, that is approximately 50 mT.
Typical ion and electron temperatures Ti and Te areapproximately 10 eV, and electron density ne is 11020 m-3.
The magnetic fluctuation measurement was carried out by using a magnetic probe array. The probehas 16 pickup coils and is located the mid-plane(z=0 mm) to measure reconnected magnetic fluctuations Bz at the various radial positions. (Fig. 1)
3. Experimental results
Figure 2 shows time evolution of reconnectedmagnetic fluctuation signals at 16 radial positions.
Magnetic reconnection period is 187-197 μ s.
Large magnetic fluctuations are observed during themagnetic reconnection inside the current sheet region (r=130-240 mm). The frequency spectrum of
the fluctuation signal has clear peak at 2 MHz,
which is slightly larger than ion cyclotron frequency (1 MHz). The amplitude of the fluctuation isabout 10-20 % of the reconnecting field. The fluctuation propagates to the downstream region with
about 50 km/s.
Figure 3 shows time evolution of reconnection
electric field Eθ at the X-point, which is calculated
by using equations (1,2) and assuming axial symmetry. In the large fluctuation case, the reconnection electric field increases and is a several times
large as compared with small fluctuation case.

1 "#2! r "t(1)! = " 2! r ' BZ (r ' , z) dr '(2)E! = !
rrmin

Fig. 3 Time evolution of reconnection electricfield Eθ at the X-point: the large and small fluctuation cases.
4. Conclusion
We have detected magnetic fluctuations during
magnetic reconnection under a guide field. The amplitude of fluctuations is about 10-20 % of the reconnecting magnetic field. The fluctuation propagates to the downstream region and strongly dumps
at the current sheet edge. The reconnection electricfield at the X-point increases when fluctuations appear. These results indicate that the prospect of ion
heating and enhancement reconnection rate due tothe fluctuations.
Acknowledgments
This work was supported by JSPS KAKENHI(22246119 and 22686085) and the Global COE Program“Secure-Life Electronics”, MEXT, JapanFig. 2 Time evolution of reconnected magnetic
fluctuation signals at various radial positions. Reconnection period and sheet length are 187-197 μs
and 100 mm, respectively.

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