22C02
Development of electron plasmas for two-fluid plasma experiments
二流体プラズマ状態検証のための電子プラズマ源の開発と閉じ込め実験
Yuki Hana, Haruhiko Himura, Yuta Onishi, Takafumi Nakase, Takahiro Ota
Haruka Shimomura, Akio Sanpei, and Sadao Masamune
葉名祐紀，比村治彦，大西祐太，中瀬貴文，太田貴博，下村遼，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
In order to produce two-fluid plasmas by Li+ and electron plasmas, we have been developing a newexperimental device in which two non-neutral plasmas are confined separately. Up to now, we havesuccessfully finished making a Penning-type trap device, and now we are installing both ion and electron
sources in the vacuum chamber. Details on the machine and preliminary results will be presented.

1. Introduction
To examine possibilities of the extended MHD
plasma [1] state and impurities-free quantum dots
experimentally, we have developed, for the firsttime, a Penning-type trap which confines pure ion
and electron plasmas simultaneously.
2. Positive and negative potential wells
Figure 1 (a) shows the new trap. Ion and electron
plasmas are produced, and then confined in bottoms
of positive and negative potential wells,
respectively: the axial confinement. On the other
hand, the radial constraint is attained by ahomogeneous magnetic field of B0 = 0.1T.
The potential distribution called har monic
potential [2] is shown in Fig.2. Such a harmonic
profile is created by 23 multi-ring electrodes shownin Fig.1 (b). The set of electrodes is 781.5 mm intotal length and 50 mm in radius. By applying(a)(b)

Fig. 1. (a) A schematic drawing of the experimental
machine plasma trap, and (b) a photo of the multi-ringelectrodes installed in the vacuum chamber.

independent potentials to each electrode, thepotential can be formed. The blue lines in Fig. 2 arepotential values applied to each electrode externally.
On the other hand, the red curve shows the resultant
potential profile on the machine axis.
As seen in the Fig. 2, there are two potential
wells in the machine. In the positive potential well,
the ion plasma is confined, while the electron
plasma is confined in the negative potential well.
3. Diagnostics
Several measurements will be performed inexperiments. Firstly, to measure image charges
induced on the electrodes, we are developing a setof current amplifiers shown in Fig. 3. Here, one cansee that there are eight electrodes in Fig. 3. Amongring electrodes, four of them (indicated as shadow
parts in Fig.1) are azimuthally divided into eightsectors with a uniform separation of 45 degree. The
two of four segmented electrodes are used tomeasure image charges for both ion and electron
plasmas. On the other hand, the rest two of four
segmented electrodes are employed to apply arotating electric field to plasmas. In experiments,
the ion density will be close to its Brillion density
limit so that the plasma will suffer from the
diocotron instability. To avoid it, we will use thetechnique of the rotating electric field to control theplasma shape even in higher plasma density regime.

Fig. 2. Axial potential distributions of externally applied
voltage (blue lines) and the resultant profile formed on
the machine axis (red curve).

Fig. 3. Schematic drawings of the segmented electrodes
on which current amplifiers are connected to measure
image charges induced on the electrodes.

Other diagnostics are shown in Fig. 1. The
fluorescent screen will be used to measure the twodimensional distributions of both ion and electron
plasma densities. It is installed at the end of thevacuum chamber. Then, in the reverse side, both Li+
and electron sources are installed. Figure 4 shows aholder on which both ion and electron sources aremounted. On the holder, the Li+ source is set on thecenter of the holder, while four electron sources arelocated on the off center axis. Using these fourelectron sources, we will produce electron plasmas
on the center axis through a self-organization
process [3, 4].
4. I-V characteristic of Li+ source
The pure ion and electron plasmas are made byan ion and a thermal electron sources, respectively.
Regarding the ion plasma, it is required to minimize
the effect of gravity or maximize the Brillion
density limit [5] for this experiment. Thus, the ion
species must be light. For this reason, we havechosen Li in this experiment.
Li+ species are ejected from the indirect heatedion sources made of tungsten impregnated with β-eucryptite. On the other hand, the electrons are
emitted from also the indirect heated cathodeconstructed by tungsten impregnated with barium.
Figure 5 (a) shows the current – voltage (Id-Vacc)

characteristics of the Li+ source. Red circles are thedata obtained from the setup shown in Fig. 5 (b).
On the other hand, blue triangles are the dataobtained from the setup shown in Fig. 5 (c) that has
two electrodes in the gun. As compared the valuesof blue triangles with those of the red circles, Li+
can be emitted with relatively lower energy.
In Fig. 5 (c), Li+ is firstly accelerated between theion source (anode) and the electrode (indicated by
the black solid line) on the left-hand side, and thendecelerated between the two electrodes. Therefore,
the total energy of the emitted Li+ corresponds toVacc. The lowest value of Vacc is 2 V, which is much
lower than the lowest value of the red circles (~ 20eV). In addition, the value of the emission current Id
is still ~ 2 uA with even such a lower value of Vacc(~ 2 V).
(a)(b)(c)Fig. 5. (a) Id - Vacc characteristics obtained from two
different setups: (b) with one electrode (red circles
shown in (a)), (c) with two electrodes. (blue triangles
shown in (a)).

References

Fig. 4. A schematic drawing of the holder on which theon and four electron emitters are set.

[1] H. Himura et al., 22C01 in this conference.
[2] A.Mohri，H.Higaki，H.Tanaka et al. Jpn. J. Appl.
Phys. 37,664(1998).
[3] K.S.Fine et.al: Phys. Rev. Lett. 75 No.18 (1995)
3277.
[4] Y. Kawai et.al: J. Phys. Soc. Jpn 75 No.10 (2006)
104502.
[5] Y. Kiwamoto: J. Plasma Fusion Res. 79 No.12(2003) 1249-1258.