22C01
Development of lithium ion plasmas for two-fluid plasma experiments
二流体プラズマ状態検証のためのリチウムイオンプラズマ源の開発と閉じ込め実験
Haruhiko Himura, Yuki Hana, Yuta Onishi, Takafumi Nakase,
Haruka Shimomura, Akio Sanpei, and Sadao Masamune
比村治彦，葉名祐紀，大西祐太，中瀬貴文，太田貴博，下村遥，三瓶明希夫，政宗貞男
Department of Electronics, Kyoto Institute of Technology
Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
京都工芸繊維大学・電子システム工学専攻 〒606-8585 京都市左京区松ヶ崎御所海道町
We prepare a new experimental test on whether or not the extend MHD states can exist in laboratory
plasmas. The most remarkable feature of the experiment is to use two linear non-neutral plasmas: purelithium ion (Li+) and electron plasmas. Up to now, we have finished constructing multi-ring trap that
produce both positive and negative electrostatic potential wells in order to confine those non-neutral
plasmas independently. Many electronic circuits for accurately operating the experiment are installed to themachine. A Li+ source successfully emits Li+ ions with low energy (~ 1 eV) which would probably enoughto exclude all effects due to the thermal motion from the Li+ fluid motion. Four small electron cathodes
working around 1,300 K are now assembled, and will be ready to produce four electron wires in themachine.

1. Introduction
Recently, `extended MHD models’ that include
an MHD plasma with flow, a Hall MHD plasma,
and a two-fluid plasma are proposed in boththeoretical and computational fields of plasma
physics. Those models have been applied to
explain recent experimental observations infusion plasmas. In fact, those phenomena can benever understood by the conventional MHD
model. However, no experimental tests for theextended MHD models have ever been conducted
yet.
There exist two reasons why extended MHD
models are unexplored. Firstly, those models holdin a short scale length, while the conventional
MHD is available in any scale lengths. Actually,
the ion skin depth i is considered to be thetypical scale length where the effect due to theextended MHD state could significantly emerge,
which is too short to be accessed in fusion
plasmas. Secondly, it should be a right method
for testing the extended MHD in experiments that
we investigate if the extended MHD state will
maintain after an extended MHD plasma isformed.
For this purpose, we need to produce a notable
plasma in which both ion and electron fluids
move independently; this is actually called a
two-fluid plasma. However, it is hard to produce
such plasmas by discharging neutral gas. This isbecause through the ionization process of neutralgas, both ion and electron fluids usually move
together.

2. Advantage of using non-neutral plasmas
The above difficulties may be avoided using
non-neutral plasmas (NNP). NNP can be formed
with relatively low densities, thus providing much
longer i. Also, those plasmas are extremely stable.
The confinement time of NNP lasts even more thanseveral days, alleviating experimental difficulties indiagnosing properties of the extended MHD
plasmas.
Figure 1 shows the dependence of the size
parameter S*, which is equivalently the parameter ofL/i, on the ion density ni. Here, L is a typical scale
length of a plasma and i is the ion skin depth [1].

Fig.1. Dependence of the size parameter S* on the ion
density ni. The ion species used in this experiments islithium ions.

Fig. 2. Scheme of the proposed experiments.

Values of i less than 30 are theoretically required
to produce a two-fluid plasma, one of extended
MHD plasmas. As recognized, plasmas with ni < ~1012 cm-3 is required for laboratory experiments
having L = 10 cm to which NNP produced in linear
machines can easily access.

3. The proposed experiment
Figure 2 shows a schematic diagram of theproposed experiment. In the linear machine, a pairof positive and negative electrostatic potential wells
is externally produced. In the positive potential well,an Li+ plasma is confined, while a pure electron
plasma in the negative potential one.

Then, those non-neutral plasmas are merged
together. By precisely controlling densities of both
Li+ and electron plasmas independently, we canexplore an unrevealed research field of extended
MHD plasmas.
Up to now, we have finished constructing
multi-ring trap that produce both positive andnegative electrostatic potential wells in order toconfine those non-neutral plasmas independently.
Many electronic circuits for accurately operating
the experiment are installed to the machine. A Li+
source successfully emits Li+ ions with low energy(~ 2 eV) [2] which would probably enough toexclude almost all crucial effects due to the thermal
motion from the Li+ fluid motion. Four small
electron cathodes working around 1,300 K are now
assembled, and will be ready to produce fourelectron wires in the machine.
Acknowledgments
This work is supported by the Grant-in-Aid for
Scientific Research (C), No. 22540504.
References[1] H. Himura: IEEJ Trans. FM, 130 (2010) 977.
[2] Y. Hana et al., 22C02 in this conference.