Plasma and Fusion Research: Rapid Communications

Volume 1, 008 (2006)

First Plasma in the RT-1 Device
Zensho YOSHIDA, Yuichi OGAWA1) , Junji MORIKAWA, Sho WATANABE,Yoshihisa YANO, Shoichi MIZUMAKI2) , Taizo TOSAKA2) , Yasumi OHTANI2) ,Atsuro HAYAKAWA2) and Masanao SHIBUI2)
Department of Advanced Energy, Univeristy of Tokyo, Kashiwa 277-8561, Japan
High-Temperature Plasma Center, Univeristy of Tokyo, Kashiwa 277-8568, Japan2)
Toshiba Corporation, Yokohama 230-0045, Japan1)(Received 19 January 2006 / Accepted 23 January 2006)
The first plasma experiment using the Ring Trap-1 (RT-1) was performed on January 12, 2006. The RT-1
is a novel plasma device constructed to explore ways to the advanced-fuel fusion. The mechanism of plasma
confinement is based on the theory of high-beta equilibrium that is self-organized in a flowing plasma. A superconducting ring, levitated in the vacuum chamber, produces a magnetic field that traps high-temperature plasma,creating a magnetosphere-like configuration. Plasma is produced by electron cyclotron heating using an 8.2 GHzmicrowave.
c 2006 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords: flowing plasma, high-beta plasma, double beltrami field, high T c superconductor
DOI: 10.1585/pfr.1.008
The Univeristy of Tokyo constructed a new plasma device, Ring Trap 1 (RT-1), at the Kashiwa campus. Thisresearch project, started in 2004, is a joint work of the Department of Advanced Energy and the High-Temperature
Plasma Center of the University of Tokyo. We performed
the first plasma experiment using this device on January
12th, 2006.
The RT-1’s mechanism of plasma confinement isbased on the theory of self-organized states in flowing plasmas [1, 2], which predicts that the hydrodynamic pressure in a fast plasma flow can balance the thermal pressure (Bernoulli’s law) creating a relaxed state with very
high-beta value. The basic concept of a device realizing
such a configuration was developed in the Proto-RT device[3, 4], which employed an internal ring conductor producing a dipole magnetic field. The equilibrium state producedby this device simulates Jupiter’s magnetosphere [5]. To
avoid interactions of the plasma with supporting structuresand current feeds, we constructed the Mini-RT device anddeveloped the technology to levitate a high-T c superconductor [6]. “Dipole fusion” is also exploring a high-beta
confinement with a similar magnetic-field configuration[7], while it does not emphasize the flow eﬀect. The LDX
experiment developed by MIT takes this approach [8]. The
common goal of these projects is to realize a very high-beta
confinement of high-temperature (100 keV level) plasmas
that enables the fusion of advanced fuels.
The RT-1 device (Fig. 1, Table 1) employs a high-Tc
superconductor (Bi-2223) ring that is levitated in the vacuum chamber and produces dipole magnetic field. The
field strength in the confinement region varies from 0.3 T to0.03 T. The conductor is first cooled to 20 K in the maintenance chamber (located at the bottom of the plasma chamber), and, then, charged to 0.25 MA (the coil consists of
12 pancakes and has a total of 2160 turns). After detaching the current leads and coolant (He gas) transfer tubes,
the ring is moved up to the mid-plane of the plasma chamber and is then levitated by a feedback-controlled magnetic
field produced by a coil installed on the top of the device.
Three-cord laser sensors measure the position of the levitated ring. We can continue the super-conducting operationfor 7 hours before the coil temperature increases to 30 K.
Current decay is less than 1% after 7 hours.

Fig. 1 RT-1 Device. A super-conducting ring, levitated in thevacuum chamber, produces a magnetic field that traps
high-temperature plasma and creates a magnetospherelike configuration.

author’s e-mail: yoshida@k.u-tokyo.ac.jp008-1

c 2006 The Japan Society of Plasma
Science and Nuclear Fusion Research

Plasma and Fusion Research: Rapid Communications

Volume 1, 008 (2006)

size
ring magnet (HTS)

lifting magnet
plasma chamber
RF heating (1)RF heating (2)refrigerator

current
weightoperating temperature
current
dynamic range
size
frequency
power
frequency
power
power
maximum flow

R = 250 mm, cross section (casing):w = 195 mm, h = 150 mm
250 kA (2160 turns)
110 kg20 K – 32 K
88 kA (68 turns)
f < 10 Hz (feedback controlled)
R = 1000 mm, h = 560 mm
8.2 GHz100 kW (1 sec pulse)
2.45 GHz20 kW (2 sec pulse)
50 W at 20 K
2 g/sec

Table 1 Machine parameters of the RT-1 device.

[3] Z. Yoshida et al., 17th IAEA Fusion Energy Conference,
Yokohama, 1998, IAEA-CN-69/ICP/10.
[4] H. Saitoh et al., Phys. Rev. Lett. 92, 255005 (2004); H.
Saitoh et al., Phys. Plasmas 11, 3331 (2004).
[5] J. Shiraishi et al., Phys. Plasmas 12, 092901 (2005).
[6] Y. Ogawa et al., J. Plasma Fusion Res. 79, 643 (2003).
[7] A. Hasegawa et al., Nucl. Fusion 30, 2405 (1990).
[8] J. Kesner et al., 17th IAEA Fusion Energy Conference, Yokohama, 1998, IAEA-CN-69/ICP/09.

Video: The first plasma experiment performed on theRT-1 device. The plasma is produced by ECH using an8.2 GHz microwave. The pulse duration was 1 sec, as determined by the microwave operation. In the second video,
the ring magnet was levitated about 30 mm over the lifter,
while in the first video it was placed on the lifter.

Fig. 2 First plasma produced by the RT-1 device. The plasma isproduced by ECH using an 8.2 GHz microwave.

We produce plasma by injecting an X-mode microwave (8.2 GHz). The maximum power of the klystronis 100 kW (1 sec. pulse operation). The first plasma wasobtained with 1.5 kW ECH (Fig. 2). The superconductor
ring was levitated about 30 mm over the lifter. After testing the ring’s catcher, which can catch the ring in case ofan accidental drop, we will operate the device while moving the lifter away from the plasma region. Optimizationof the plasma and measurements of the parameters will beperformed after completing detailed evaluations of the machine‘s performance.
The authors are grateful to Professor T. Mito and Dr.
N. Yanagi of the National Institute for Fusion Science for
their advice regarding the design of the magnet coolingsystem. The authors also thank all the collaborators whohelped to design and construct the RT-1.
[1] S.M. Mahajan and Z. Yoshida, Phys. Rev. Lett. 81, 4863
(1998).
[2] Z. Yoshida and S.M. Mahajan, Phys. Rev. Lett. 88, 095001(2002).

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