24p164-B
Development of Experimental Devices for the Research of Self Trapping
and Nonlinear Behavior of Plasma Waves
電子ビームの自己捕捉とプラズマ波動の非線形性の研究装置の立ち上げ
Genki ASOZU(A), Ritoku ANDO(A), Hatsuka INOMATA(A), Kenta MIBU(A),Takao TANIKAWA(B), Keiichiro YAMAGIWA(C)遊津 元希(A)，安藤 利得(A)，猪股 初夏(A)，壬生 健太(A), 谷川 隆夫(B), 山際 啓一郎(C)(A)

Faculty of Mathematics and Physics, Institute of Science and Engineering, Kanazawa University:
Kakuma-machi, Kanazawa 920-1192, Japan 金沢大学 理工研究域，〒920-1192 金沢市角間町.
(B)
Research Institute of Science and Technology, Tokai University: 東海大学 総合科学技術研究所.
(C)
Faculty of Science, Shizuoka University: 静岡大学 理学部.
We are preparing experiments by using the CALM2 machine. For the first step, we measured theplasma by Langmuir probe. The specification of CALM2 is described, and parameters of the firstplasma are reported here.

1. Introduction
The electron plasma waves are excited in thebeam-plasma system and make wave packets. The
wave packet undergoes glowing, saturation, anddamping in the time scale of electron response. It is
known that the growing phase is governed by a linearequation [1]. But understanding of the saturation anddamping phases need more researches and discussions.
Measurement of the non-linear phenomena is ourmajor concern. In general, part of the electrons of thebeam is trapped in wave potential, and non-linear
phenomena occur. To observe the process,experimental research was carried out, and thetrapping of beam electron and saturation wereobserved dynamically in CALM2 (Coaxial Linear
Machine-II) in Shizuoka university [2,3].
The CALM2 is replaced to Kanazawa university,recently. We are preparing experiments by using themachine. For the first step, we measured the plasma ofCALM2 by using Langmuir probe. We introduce theCALM2 and the plasma parameters are reported here.

2．Experimental Device
The configuration of CALM2 is shown in Fig. 1and Fig. 2. It is the multi-pole magnetic device, and it
can produce quiet plasma [4]. The vacuum chamber is
0.26m in diameter、1.2m in the axial length. Magnetic
coils are placed outside of the chamber, and can produce
axial magnetic field. The background pressure is 10 -7 ~10-8 [Torr]. Tungsten filaments are set inside the chamber,and those are heated and biased by the DC voltage, andemit thermionic electrons. The first electrons ionize theneutral gas, and produce plasma.

Fig. 1

Coaxial Linear Machine-II, CALM2

On the outside wall of the chamber, permanent magnet
bars, Sm-Co, are attached, 12 for side wall, and 10 foreach end walls. The magnetic field is about 0.1 [T] at thesurface of the magnet bar. The magnetic polarity isreversed one by one to form the full-line-cusp magnetic
field, see figure 2. The magnetic fields are canceled outat the center area. It is less than 0.1 [mT] inside the circle
with 100 mm diameter, and it is as small as thegeomagnetic field.

Fig. 2

Cross section of vacuum chamber

The cusp field confines the first electron emitted from thefilaments, and increases efficiency of ionization [4]. It canmake possible to produce plasma even at low pressure,-5
1.0×10 [Torr], and quiet plasma is produced around thecenter of the chamber.

3．Measurement of plasma
Single probe is used for measuring of plasma.

Fig. 3

Photograph of the probe

The probe consist of molybdenum wire with 0.4 mm
diameter and the length of 4 mm, it is shown in Fig. 3.
Molybdenum is used to prevent second electron emission
from the probe surface [5,6]. The probe is inserted toplasma from a sidewall port. Plasma density, Ne, andelectron temperature, Te, are estimated from thecurrent-voltage characteristics. Argon gas was introduced,
and the thermionic filaments are biased at –60 [V]. The
probe is positioned at center of the chamber. The results,
which are obtained for each neutral pressure, are shownin Table I. Here, the P is Ar gas pressure, and Vs isplasma potential.
Table I.
P (Torr)

4.

Characteristic of plasma of CALM2

3.4×10-5

Te (eV)

2.0×10-４
2.2-3

Ne (m )

-13

4.3×10

1.9×10-13

Vs (V)

9.3

9.6

2.9

Summary

An experimental device, CALM2, was set up.
The multi-pole magnetic device is operated, andplasma is produced. The first plasma is measured
using a single probe, and the electron temperature,density, and plasma potential are obtained. An electron
gun that produces electron beam will be prepared, nearfuture. Research of electron plasma waves will be
carried out by injecting the electron beam to theplasma. Trapping and non-linear behavior will be
investigated in the observation of wave packets.

5. References[1] R. J. Briggs, in: A. Simon, W.B. Thomson (Eds.),
Advances in Plasma Physics, vol. 4, Interscience, NewYork, 1971, p.43.
[2] T. Takeda, K. Yamagiwa: Phys. Lett. A339 (2005)
118.
[3] T. Takeda, K. Yamagiwa: J. Plasma Fusion Res., 81(2005) 120.
[4] K.N. Leung, Noah. Hershkowitz, R. MacKenzie:
Phys. Fluids, 19, No.7, (1976) 1045.
[5] Shinriki Teii: Basic Engineering of Plasma (enlargededition) , プラズマ基礎工学増補版(Uchida-roukakuho, Tokyo, 1997) Chap.3, p.125.
[6] H. Amemiya, M. Wada, H. Toyoda, K. Nakamura, A.
Ando, K. Uehara, K. Oyama, O. Sakai and K.
Tachibana: J. Plasma Fusion Res., 81, No.7 (2005)
482.