24P168-B
Development of small diameter plasma channel for laser-plasma-accelerationand density measurement by laser Thompson scattering
レーザープラズマ加速のための小直径プラズマチャンネルの開発と、レーザートムソン散乱によるプラズマ密度測定
Takagi Saori A, Shoji Tatsuo A, Kono Akihiro A, Nakajima Kazuhisa B , Yamazaki Kozo A
高木沙織 A，庄司多津男 A，河野明廣 A，中島一久 B，山崎耕造 AA

Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603
B

KEK 1-1 Oho, Tsukuba, Ibaraki 305-0801 JapanA 名古屋大学〒464-8603

名古屋市千種区不老町

高エネルギー加速器研究機構〒305-0801 茨城県つくば市大穂 1-1

B KEK

The plasma based laser wakefield acceleration attracts attention due to the large gradient of acceleration.
The 1TeV scale beam acceleration needs stable long (~meter scale) plasma channel of which the diameteris less than 1mm and the electron density is 1016cm-3. We are trying to realize it by inductive RF plasma.
Now, we produced RF plasma use a small diameter capacitive quadrupole and report the result of primarymeasurement of the plasma density and the diameter distribution by Laser Thompson scattering as
primary stage.

1 Introduction

2 Experimental equipment

The plasma based laser wakefield acceleration

The experimental equipment is shown in Fig.

(LWFA) attracts attention to a next generation

1(a) A quadrupole electrode is consist of 1.2φ

accelerator for particle physics and various
applications due to the large gradient of particles
acceleration.

Recentexperiments

by

using

ultrashort pulse intense laser (few tens ,40Tw)
have demonstrated to be the acceleration ofelectron acceleration up to 1 GeV. The acceleration
was achieved by using high density (~1018cm-3)

Fig. 1.(a) quadrupole of antenna system

plasma channel of several cm length [1]. The
1TeV scale beam acceleration needed by high2mm

energy science needs stable long (~meter scale)plasma channel with the diameter which is lessthan1mm

andtheelectrondensity

is1015~1017cm-3. we are developing to produce suchplasma by the application RF of discharge.
Electron density profile measurement of suchnarrow plasma channel is important in LWFA [2].

Chamber
4mm

Matching Circuit

Fig. 1.(b) schematic of rf and antenna system

We are preparing the measurement by theThompson scattering method.

stainless-steel rods of 1.2mmφ un duaneter and130mm in length. To avoid the RF break down

and forms an extensive electric field close to thel-c-----ed on the antennas, one pair of antenna rods

electrode.

are inserted by glass tube (2mmφ). RF system for

We impressed RF (5kW, 13.56MHz, pulse width

the capacitive quadrupole discharge circuit figure

1msec, duty 0.1) in a capacitive antenna andis shown in Fig. 1(b), where frequency andmaximum power of RF are 13.56MHz and 5kHz,
respectively. Figure 2 shows the schematics ofThompson scattering diagnostic system. Nd:YAGlaser(2ω) light is focused and by, irradiated into
the plasma channel. Scattered light perpendicular
is to detected the incident laser light goes throughthe triple-grating spectrometer and is detected by
ICCD camera.
3

Preliminal results of RF plasma channel

quadrupoleFig. 3.

An photo example of narrow RFdischarge(Prf =1kW, f=P13.56MHz, PAr = 30 torr)

Triple-graring
spectrometer
ICCDcamera

produced narrow plasma. Figure 3 shows a photo of
Nd :YAG laser beam

Personalcompurer

Cameracontroller

the plasma. Used Gas is Ar, we can see narrowplasma produced in the electrode in the vicinity ofFig. 2.

Anarrangement of Thompson laser
scattering equipment

30 torr. Plasma density measured by Thompson
scattering is in progress assiduously.
Abstract

production
It is said that the next-generation LWFA expectedbeam acceleration of 1TeV scale need narrow

References

plasma density profile (1015~1017cm-3)of which[1] W. P. Leemans, B. Nagler, Cs. Toth, K. Nakamura, C.

the diameter is less than 1mm [2].And it is said

G. R. Geddes, E. Esarey, C. B. Shroeder, and S. M.

that LWFA need guiding laser driving a particle

Hooker, Nat. Phys. 2, 696 (2006).

and without being scattered by plasma straight, for[2]that[3]

purposeitneedshollow

electrondistribution[3]. A quadrupole is expected to bepossible

to obtain hollow electron density

distribution because its center electric field is 0,