23P155-P
Diagnostics of imploded core and the heating laser injection timeusing a X-ray streak camera in fast ignition experiment
高速点火統合実験におけるX線ストリークカメラを用いた爆縮コア及び加熱時刻計測
Takehiro Sogo, Yoshinori Ishii, Mayuko Koga, Shinsuke Fujioka, Hiroyuki Shiraga
and Hiroshi Azechi
十河 雄大, 石井 圭憲，古賀 麻由子，藤岡 慎介, 白神 宏之, 疇地 宏
Institute of Laser Engineering, Osaka University
2-6, Yamadaoka, suita,Osaka 565-0871, Japan
大阪大学レーザーエネルギー学研究センター 〒565-0871 大阪府吹田市山田丘2－6
We have coupled a multi-imaging x-ray streak camera technique with an x-ray shielding made by tungsten
to measure time-resolved 2D images, and applied it to fast ignition experiments. We have successfullymeasured the imploded core dynamics with temporal and spatial resolution of 10.5 ps and 22 µm,respectively, and the heating laser injection time with the accuracy of ±8 ps.

1. Introduction
In fast ignition experiment, it’s very importantto understand the heating process of imploded
core plasma. In measuring imploded core plasma
dynamics, because it’s necessary to observe very
short time duration transition (~100 ps) of verysmall core plasma (~50µm), measuring
instruments are required high temporal andspatial resolutions of 10 ps and 15 µm,respectively. The multi-imaging x-ray streakcamera(MIXS)
techniquemeets
therequirements [1]. This is the one of the methodsof the ultra-fast 2D x-ray imaging is based on
the concept of 1D image sampling.
Furthermore, there are the multi-channel
MIXS(McMIXS) can measure the 2D electron
temperature distribution or the 1D+McMIXS
combines the ordinary 1D streak camera with
the McMIXS [2][3].In fast ignition experiment,
there is a serious problem of the high energy
x-ray caused by the heating laser injection.

Fig.1. The typical image without the shieldIn this study, we measured the imploded coreplasma dynamics and the heating laser
injection timing by combing the 1D+McMIXS
with x-ray shields.

2. Shield from the high energy x-ray
In 2009's experiment, we confirm that the highenergy x-ray generated electrons from thephotoelectric surface of a photocathode and caused
discharge or background noise (Fig. 1). In thisstudy we shield cathode disk with the tungsten be 3
mm thick except for that slit to protect thephotoelectric surface from the high energy x-ray(Fig. 2). We estimated that energy of the highenergy x-ray is about 200 keV and the backgroundnoise can be reduced to approximately 20% withthis shield. Fig. 3 shows the typical image measured
by MIXS. The discharge has disappeared and thebackground noise has been reduced to 20%. Thisagrees with an estimate.

Fig.2. Tungsten shieldheating laser injection time is indicated by an

Fig.3. The typical image with the shieldFig.4. The time waveform of the x-ray emission fromimploded core plasma (black), gaussian curve fitting (red)and the heating laser (blue).

Fig.5. Reconstructed time-resolved 2D image. The inter-frame time is 10.5ps. The arrow shows the heating laser
injection time. The highlighted framework shows the x-ray emission from the core plasma is maximum.

3. The heating laser injection time
In this experiment, we observed the belt-shaped
non-imaging signal (Fig. 3) when the target isirradiated by the heating laser. This is caused by thehigh energy x-ray. Because this becomes noises andprevents an accurate estimate, when we reconstructtime-resolved 2D images, we must make subtract
this signal. On the other hand we can utilize this todecide the heating laser injection timing. Thetiming of the heating laser injection isT = t LFEX - t max,
(1)
where t LFEX is the time when the non-imaging
signal is observed and t max is the time when thex-ray emission from the imploded core plasma ismaximum. The accuracy of T was ±8ps. Fig. 4
shows the typical time waveform in fast ignition
experiment. This timing T was used for feedback
control of the laser condition and considerations of
the neutron yield, the x-ray emission and theelectron temperature. Fig. 5 shows time-dependentchange of reconstructed 2D x-ray image. The

arrow. By combing the 1D+McMIXS with x-ray
shields we obtained time-resolved x-ray images of
imploded core plasma and the heating laser
injection timing and we were able to discuss therelationship between the heating laser injection
timing and imploded core plasma dynamics.
References[1] H. Shiraga, et. al., J Electron Spectros Relat
Phenomena, 80 (1996) 287.
[2] H. Shiraga, et. al., Rev. Sci. Instrum. 68 (1997) 828.
[3] M. Heya, et. al., Rev. Sci. Instrum 68 (1997) 820.