22C11
Opacity of photoionization plasmas generated by laser-produced blackbodyradiator
レーザープラズマ黒体輻射光源で生成した光電離プラズマの吸収分光特性	 
Yuta Fujii1, Shinsuke Fujioka1, Norimasa Yamamoto1, Q. Dong2, S. Wang2 et al
藤井雄太1, 藤岡慎介1，山本則正1，Q. Dong2, S. Wang2, L. Zhang2, Y. J. Rhee3, D. H. Song3,
西村博明1, 高部英明11

Institute of Laser Engineering, Osaka Univ.
2-6, Yamada-oka, Suita-shi, 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２−６2Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing
1000190, People’s Republic of China
3Laboratory for Quantum Optics, Korea Atomic Energy Research Institute, 1045 Daedeok Street, Yuseong-gu, Daejon
305-353, Korea
We measured opacity of non-LTE photoionized silicon plasmas generated by a laser-produced blackbody
radiator having two roles as for a radiation source and a backlight source. We used the transmission grating
spectrometer with an observation range from 1.5 to 8 nm. We analyzed the experimental result withtheoretically predicted opacity for non-LTE photoioinized silicon plasmas with atomic kinetic codes,
FLYCHK and PrismSPECT. A large discrepancy was found between the observation and the predictionthat is attributed to contamination on the surface of silicon specimen.

1. Introduction
Photoionized plasmas are observed aroundcompact objects such as black holes [1]. The
structure and evolution of compact objects areindirectly studied in a remote distance by observing
x-ray continuum from heated accretion discs andx-ray fluorescence from the photoionized plasma of
the stellar wind in the binary systems. X-ray
spectroscopy is an important tool for diagnosing
conditions in photoionized plasmas [2]. To derive
physical properties from the observations, we must
simulate
physicalproperties
byradiation-hydrodynamics codes including complex
physical processes to simulate x-ray spectra byatomic kinetic codes. However very few
photoionized plasma experiments have been
performed to benchmark the astrophysical modelfor the photoionized regime[3]. Laboratory
experiments are essential in this field in order toimprove physics modeling in the code.
2. Experimental methods
GEKKO-XII at ILE Osaka was used to create anintense x-ray flash Plankian spectrum, whichmimick x-ray continuum from the accretion disks[4]. At the same time, cold and low-density silicon
plasma was generated by a Nd:YAG laser pulse
near the implosion core. In the way, x-ray from the
implosion core excited and photoionized the silicon
plasma.

We measured absorption spectra of photoionizedsilicon plasma. The implosion core was alsoutilized as for a backlight source. We show theexperiment scheme in Fig.1.

Fig.1. The experiment scheme
Experimental conditions for implosion cores,
silicon plasmas and transmission grating
spectrometer are shown as Table.1.
In order to control the intensity of x-ray on the Si
plasma, the distance L from implosion core tosilicon plasma was changed from 1.2 to 6 mm.
3. Experiment results
Observed transmission of photoionized silicon
plasma is shown in Fig.2.
Ionization parameter ξ is defined as! = I x / ne L2 ,(1)here Ix is x-ray luminous [erg/s], ne is electrondensity [cm-3], and L is the distance from theblackbody radiator to the silicon plasma [cm] [5].
Table1. Parameters of implosion core, silicon
plasma and transmission grating spectrometer

Implosion core
Color temperature

420

10 eV

X-ray pulse duration160

40 ps (FWHM)

Silicon plasma
Average electron temperature(before photoionization)

27.5

1.5 eV

Average electron density(before photoionization) (0.750.25)

Size of plasma

500 μmDistance from implosion core L

1.2, 3, 6 mm

10 20 cm-3Transmission Grating Spectrometer
Range of observed wavelength

1.5 ~ 8 nm

Spectle resolution λ/δλ13.3 (FWHM)

Fig.2. Absorption spectra for the silicon plasma
A large difference in the transmission curves isseen between the case of ξ= 5.9 and these of ξ=0.9 and 2.3.
In the presentation, we will discuss on the reasonof the difference together with calculations by

non-LTE collisional radiative model treated in
FLYCHK [6] and PrismSPECT [7].
Acknowledgments
We would like to acknowledge the dedicatedtechnical support by the staff at the GEKKO-XII
facility for the laser operation, target fabrication,and plasma diagnostics.
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