24F16
Top-B project; Experimental research to generate 10Mgauss Ultra-Highmagnetic field
Top-Bプロジェクト
10Mgauss級超強磁場発生実験
NAMIKI Tomonori, NISHIDA Akinori, SAKAWA Youichi, KURAMITSU Yasuhiro,
MORITA Taichi, TANJI Hiroki, NISHIO Kento, IDE Takao, KODAMA Ryousuke, YONEDA Hitoki
並木智紀，西田明憲，坂和洋一，蔵満康浩，森田太智，丹治浩樹，西尾健斗，井出尭夫，
兒玉了祐,米田仁紀
Institute for Laser Science, the University of Electro-Communications
1-5-1-W7, Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan
電気通信大学レーザー新世代研究センター 〒182-8585 東京都調布市調布ケ丘1-5-1 西7号館
Generation of several 1000T magnetic field can be applicable to the new physicalstudy. That magnetic field can generate dense magnetized plasma, it can also be
applicable to the study of magnetic reconnection. The previous method to generatestrong magnetic field was used cylinder with seed field compressed byelectromagnetic force, it could generate about 600T. This experiment aspire forstronger magnetic field with laser-ablation pressure. We achieved measurement
Faraday-rotation of generated magnetic field compressed by laser-ablation.

In some methods of generation of ultra-highmagnetic field, using laser-ablation pressure isfocused for applicability for other physical study. In
this experiment, we used G-XII laser in Osaka
University as ablation power.
The compression target is made of 3 parts;
stainless steel bulk, acceleration foil, and empty
space[Fig.1]. First, seed magnetic field generated
by coil with pulse power device. Then ablation laser
exposed, seed magnetic field is compressed tostrong as inverse proportion to empty space.

polarization of lights rotates by Faraday Effect. We
can estimate amplitude of magnetic field bymeasure polarization angleof prove lights. V is
Verde constant, depends on materials. Verdeconstant of fiberglass is 0.0195[min/Oe ･ cm] in
546nm prove light wavelength. H is the amplitudeof magnetic fields, and L is the length of medium.

In the past, it has been found that empty space iscompressed by laser-ablation, but radiation from theacceleration foil block the prove light[Fig.2]. Inorder to solve the problem, we put a foil around thefiberglass, protect from the radiation. We tried
some different material (Au, Ti, Cr, Al)
combination of acceleration foil and protection foil.

4. cross-section of target

Fig. 1 Generation process of ultra-high magnetic field.
(1)add the seed magnetic field by coil.
(2)compress the target with laser.
(3)accelerate foil and generate strong magnetic field.
(4)cross section of target.

In empty space, grass fiber is put on formeasurement of magnetic field. In magnetic field,

Fig.2 Prove light intensity without fiber protection

Then, compression aspect by laser-ablation isshown in Fig.3. Empty area of the target iscompressed between initial position of accelerate
foil and t~1ns. Comparing compressed area to
non-compressed one, area width became to about
one-third. It means seed field increase threefold
strength.
Measurement of Faraday rotation result is shownin Fig.4. In this experiment, target expose spot sizeis 0.5mm. If polarization rotates 360 degree,magnetic field amplitude will be 2102T. Then rightside of Fig.4 shows intensity ratio of twopolarization of transmitted prove light. The largest
rotate point, intensity ratio was 0.4 at 4ns. In thiscase, rotation angle is estimated by considering
Framing Camera

t<0ns
t<0ns

Compression cavity
fiberglass

t~1nst~0.5ns

100m/div.

Fig.3 Cavity compression

rotate over 90 degree at 1.6ns, as 140 degrees,
correspond to 817T. If seed magnetic field strengthwas 20T, empty space in the target is supposed tobe compressed >40 times. For that compression

Fig.4 amplitude of transmitted prove

ratio, radius of the target is 1/6.4. Initial radius oftarget was 0.77mm, compressed target radius would
be 0.12mm, it shows accelerate foil was pressedgoing to fiberglass.
In summary, it was shown that using
laser-ablation pressure, seed magnetic field can becompressed and generate strong magnetic field.
That strong magnetic field can be estimated bymeasuring Faraday rotation of prove light. Thatmagnetic field strength can be up to several
hundred teslas, can make magnetized plasma.
It is challenge to the future increasing
compression rate and exact measurement of
ultra-high magnetic fields. To solve the problem,
we have to estimate the length of medium in
Faraday rotation equation.
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