CO11-1

Study of Intense Terahertz Light Source Based onSuperimposing Backward Coherent Diffraction Radiation

N. Sei and T. Takahashi1

Al u mi n u m fo i lmi rro r
Ab so r b e r

T i wi n d o w

Research Institute for Measurement and Analytical Instrumentation, National Institute of Advanced Industrial
Science and Technology
1
Research Reactor Institute, Kyoto University

Aluminum plate

El e c t r o nb e am

D i f f r ac t i o n e l e m e n t s

INTRODUCTION: A relativistic electron beam with ashort pulse width is suitable for generating intense terahertz (THz) light. We have proposed to develop amonochromatic THz light source based on a superimposing coherent diffraction radiation (CDR). We observed a sign of the superimposing CDR to the electron-beam trajectory with an L-band electron linac at theKyoto University Research Reactor Institute (KURRI-LINAC) [1]. However, the forward CDR interferedwith coherent transition radiation (CTR) generated at a Tiwindow. It is difficult to evaluate the spectrum of thesuperimposing CDR quantitatively. The CDR is also
emitted behind the electron-beam trajectory. The powerof the backward CDR in the THz region is as strong asthat of the forward CDR. Then, we have conducted experiments about superimposing backward CDR.

Accelerator room
Shield wallu r t i n - Pu p l e t t t y p e
Experimental room Mi n t erfero met er

B ac kwar dCDR

Schematic layout of the CDR experiment.

Fig. 1

CDR intensity [ a.u. ]1.0

EXPERIMENTS: When a relativistic electron-beamemits radiation by a periodic structure, the resonancewavelength in laboratory system is influenced by Lorentz
transformation. The resonance wavelength  is given byl 1(1)    cos  ,n  Al u mi n u mc o l l i m at o r

1sheet2sheets
8sheets
16sheets

0.8

0.6

0.4

0.2

0.0
1




2

34

56

7

Wavelength [mm]Fig. 2where l, , and n are the period of the diffraction elements, the velocity of the electron divided by the speed oflight, and the order of higher harmonics, respectively.
The symbol  is the angle between the electron-beam
trajectory and the direction of the CDR. It becomes  inthe case of the backward CDR. Thus, the wavelength offundamental harmonic of the backward CDR is the sameas the double of the period of diffraction elements.
Figure 1 shows the schematic layout of the experimental setup of the backward CDR at KURRI-LINAC.
Because an aluminum foil mirror was set to transport thebackward CDR to the experimental room, it did not interfere with a CTR beam emitted from the Ti window. A
thin aluminum plate, which was located behind the diffraction elements, prevented backward CTR generated bythe vacuum chamber interfering with the backward CDR.
An aluminum collimator with a diameter of 17.5 mm waslocated in front of the aluminum foil mirror. The distance
between the aluminum foil mirror and the entrance of thediffraction elements was 120 mm, and the inner diameterof the diffraction elements was 30 mm.
Figure 2 shows spectra of the CDR when the periodof the diffraction elements was 19 mm. It is noted that theSpectra of the CDR generated by the diffrac-tion elements.
CDR intensity at wavelength around 3.8 mm, which was
double of the period, increased as the number of the diffraction elements increased. However, the intensity did
not increase for the number of the diffraction elements
exponentially, so that the ratio that the CDR was superimposing was low. Because the bunch length of the electron beam was approximately 10 ps, the interaction
length of the superimposing CDR was not longer than theresonance wavelength, and the ratio would become small
as the number was larger.
RESULTS:We observed backward CDR generated
by diffraction elements with a period of 19mm. Althoughan enhancement of the CDR intensity was observed at thefundamental resonance wavelength, the ratio that theCDR was superimposing was low. We will plan to use
diffraction elements which had a shorter period.
Reference:[1] N. Sei and T. Takahashi, KURRI Progress Report2013 (2014) 222.

通常採択
採択課題番号 26004 重畳的コヒーレント回折放射による高強度テラヘルツ光源 共同通常（産総研）清 紀弘（京大・原子炉）高橋 俊晴
141CO11-2

The XEP-e (eXtremely High Energy Plasma/ Particle Sensor for Electron)of the ERG Satellite

N. Higashio, H. Matsumoto, T. Takahashi1, N. Abe1
Japan Aerospace Exploration Agency
1
Research Reactor Institute, Kyoto University
INTRODUCTION: It is well known that satellites andastronauts are always endangered in space due to plasma,radiation particles, neutral particles, ultraviolet rays/Xrays and meteoroids/debris. Since we have to support
JAXA’s projects to keep them safe from the space environment, our group has been researching the radiation
environment of space for more than 20 years. Now weare developing a sensor for the ERG (Energization andRadiation in Geospace) satellite. The purpose of the ERG
satellite is to investigate the mechanism of radiation belts.
It is well known that the energetic electron flux varies
during geomagnetic disturbance and especially the relativistic electrons in the outer radiation belt change. However, the data of the electron (10eV - 20MeV) in radiation
belt is not enough. The ERG satellite consists of four
instrument parts, Plasma/Particle (PPE), geomagneticfield (MGF), Plasma wave (PWE) and electric field(PWE). Before using KURRI-LINAC (Kyoto University),
we couldn’t calibrate our sensor over 2 MeV electrons.

Fig. 2. XEP-e

Fig. 3.

Principle of the XEP-e

We need very low count rate beam (100~1000cps), sowe tried to make this beam by using the XEP-e (EM) lastyear. And this year we calibrate the XEP-e(Flight Model).
As shown in Fig. 4, the data that is got in KURRI-LINAC and simulation data (GEANT4) were very similar between 5MeV and 14MeV. It shows KURRI-LINAC
can make very low count rate beam.

Fig. 1. ERG satellite
EXPERIMENTS: Our sensor that name is XEP-e(Extremely High-Energy Plasma/Particle Sensor forElectron) is one of the PPE. The XEP-e observes
400keV~20MeV electrons and has five solid-state silicondetectors (SSDs) and a high-Z scintillator (GSO). The
XEP-e is Fig.2. The first SSD discriminate between electron and other particles. And The 2~5 SSDs and a high-Z
scintillator detect its energy. Fig. 3.
We use KURRI-LINAC (Kyoto University) to calibrate
its energy (2MeV~20MeV electron). We also use ouraccelerator in Tsukuba space center under 2MeV electron.

Fig. 4.

Incident energy vs Loss energy of the XEP-e(energy range: 5MeV~14MeV)RESULTS:
There haven’t been facilities that can make very lowcount rate beam over 2MeV in Japan. But now KURRILINAC (Kyoto University) can only make low count rate
and monochrome beam between 5MeV and 14MeV.

採択課題番号26071
ERG 衛星搭載超高エネルギー電子観測装置(XEP-e)校正試験
通常採択(宇宙航空研究開発機構)東尾奈々、松本晴久、高島健（京大・原子炉）高橋俊晴、阿部尚也（明星電気㈱）江口信次郎、尾本敬信、(㈱ファムサイエンス)藤井雅之
142