03aD07P
低エネルギーイオンビーム源の電子密度および温度計測
Measurement of the electron density and temperature in a low energy ion beamsource中宮明久1、藤原 大1、平野洋一2、木山 學2、小口治久2、榊田 創1,2
NAKAMIYA Akihisa1, FUJIWARA Yutaka1, HIRANO Yoichi2, KIYAMA Satoru2, KOGUCHI Haruhisa2,
SAKAKITA Hajime1,2
1:筑波大院システム情報, 2:産総研エネルギー技術
1:Univ. of Tsukuba, 2:AIST

1. Introduction
Low energy ion beams have been used in many fields,
for example, material processing, etc. However, a lowenergy (here, less than ~200 V) ion beam with high current
density diverges soon after the extraction from a groundedelectrode, due to the self electric field of extracted ions.
Therefore, it is necessary to prevent the divergence of theion beam by neutralizing the ion charge with electrons. To
neutralize the ion charge, an electron beam is irradiated to
the grounded electrode, and secondary electrons are emitted
from this electrode to supply slow electrons. Using thismethod, it was realized to control the beam divergence, andto obtain the focused high current density ion beam [1].
While, a spontaneous self-focusing phenomena of the low
energy ion beam around 150 eV was observed even without
active electron supply [2].
To understand above described self focusing
phenomenon, the electron density and temperature profiles
in an ion beam propagation chamber using an electrostatic
probe have been measured [3]. In this study, the spatial
distribution of the electron density and temperature in theion source chamber has been measured using anelectrostatic probe. Especially, those profiles before andafter the transition to a self focusing state are measured.

2. Experimental setupFig. 1 shows the low energy ion beam system and aprobe configuration. It consists of an ion source, ion beam
propagation chamber and measurement apparatuses. The ion
source is a bucket type with cusped magnetic fields.
Extraction electrodes consist of an acceleration electrode, adeceleration electrode and a grounded electrode. Theseelectrodes have many aperture (1.5 mmφ) and 1mm
thickness. Transparency of each electrode is 50 %. In
addition, these electrodes have a concave shape [4].
A double probe is prepared to measure an electron
density and temperature in the ion source chamber. It
composes an alumina tube (4 mmφ), four tungsten wires (0.6mmφ each) and a corner part. The alumina tube has fourholes, and tungsten wires are installed through each hole,and the length between alumina and tungsten tip isapproximately 2 mm. Due to the limitation of port
configuration, the probe is inserted from off axis position.
Then, it is required to modify the probe shape toward thecenter of the ion source chamber. As shown in Fig. 1, tomeasure the center part of the chamber and profile, the probe
shape is designed to L type. To measure three dimensional
distributions of the electron density and temperature using
this probe, a guiding instrument which can drive a liner

Fig. 1. A schematic drawing of an ion source chamber,electrodes, the ion beam propagation chamber, L-shaped probe
and the circuit of power supplies.

Fig. 2. A schematic drawing of the back view of the ion sourcechamber. The measurement area is indicated by a white line on thefigure.

motion and a rotational motion is connected to this probe.
However, there are four filaments and the accelerationelectrode in the ion source chamber. These prevent themovement of the probe. Therefore, it can be measured thatthe electron density and temperature at the cross section area
indicated in Fig. 2. Along the axis direction, the probe isswept 150 mm.

3. Summary
The “L-shaped” double probe was designed. Electrondensity and temperature profiles in the ion source chamber
are measured. At the conference, initial results will bepresented.
References[1] Y. Hirano, S. Kiyama, H. Sakakita, H. Koguchi, T. Shimada,and Y. Sato, Jpn. J. Appl. Phys 52, 066001 (2013).
[2] Y. Hirano et al., Proc. Int. Con. Ion Source 2013, submitted toRev. Sci. Instrum..
[3] Y. Fujiwara et al., Proc. Int. Con. Ion Source 2013, Rev. Sci.
Instrum., accepted.
[4] H. Sakakita, S. Kiyama, Y, Hirano, H. Koguchi, T. Shimada etal, Rev. Sci. Instrum. 83, 02B708 (2012).