28E21P
高速点火の最適化のための各種ターゲットにおける電子スペクトルの比較
Comparison of Electron Spectra in targets for FIREX
尾﨑 哲1、白神宏之2、藤岡慎介2、坂上仁志1、有川安信2、波元拓也2、Z.Zhang2、砂原淳2、坂和洋一2、長井圭治2、小島完興2、長友英夫2、城崎知至3、FIREX実験グループ2
TETSUO OZAKI1, HIROYUKI SHIRAGA2, SHINSUKE FUJIOKA2, HITOSHI SAKAGAMI1,YASUNOBU ARIKAWA2, et al.
1
核融合研、2阪大レーザー、3広大工学院
1
NIFS, 2ILE Osaka Univ., 3Hiroshima Univ.
The traditional fast ignition has been performed
as follows; (1) an imploded core is produced by acompression of a shell with a guiding cone using
the imploding laser, (2) the hot electron which isproduced by the auxiliary heating laser, irradiates
the core, and (3) the core reaches the ignition
temperature and the burning occurs. The hot
electron is generated by the interaction of the
pre-plasma, formed by the pre-pulse before themain pulse of the heating laser at the tip of theguiding cone. To achieve higher coupling efficiency
between the core and the hot electron, the effective
hot electron temperature (Teff) should keep less than
2MeV. Generally, Teff becomes high when thepre-plasma scale length is long. In this case, the low
energy component, which is suitable for coreheating, decreases. Therefore the low Teff with thehigh electron conversion efficiency is required forfast ignition. Here the electron spectrum and Teff aremeasured by the electron spectrometer (ESM). It isdifficult to measure the low energy component of
the hot electron using ESM because there is astrong potential around the target. ESM can observe
the higher energy spectrum of the hot electron.
In previous experiment series FG02, Teff
increased when LFEX laser was injected at themaximum compression time. It was doubted thatthe pre-plasma with the long scale length wascreated by irradiation of the residual ω light fromthe imploding laser (Gekko XII) to the inner wall ofthe cone. In the last experimental series FI01, Teff
can decrease by elimination of ω light. In FG02,
Au-cone was used as the guiding cone. However
many hot electrons have been dissipated in theAu-cone instead of the core. Huge X-rays andn-neutron as background noise, had disturbed thediagnostics. Suitable cone material is selected by
the target competition. In this competition, Ta of 1mm-thick is set behind of the cone-shell target. Thelow energy electron flux measured by K emission
from Ta was compared in several different cones(Au-, double-, hole- and DLC- (diamond likecarbon) cones). From those, we choose DLC

instead of the Au-cone. In the integrated
experiments, we confirm that the electron flux inDLC-cone is similar to Au-cone. The Au-coated
DLC-cone is used because Teff in DLC-cone isslightly higher than Teff in Au-coated DLC-cone.
An external magnetic field induced by the laser(Bext), is applied in order to guide the diverged hotelectron to the core. The hot electron converging
can be observed by application of Bext. At this time,
the neutron can also increase. The hole-cone as theadvance target has been tried. We worried about thepre-plasma with long scale length, which comesfrom ablation because it may make higher Teff.
However Teff is not so high because the pre-plasma
is produced in the shell. The neutron can also
increase in the integration experiment using thehole-cone.
All Teff in FI01 are plotted as function of theLFEX laser intensity in Fig. 1. Lines mean thescaling by Pukov at different scale lengths. Open,
half open and closed symbols show Teff of plates,
cones and integrate, respectively. Teff of cones are
similar to Teff of integrate although Teff of cones arehigher than Teff of plates. This means that Teff isdetermined by the geometrical shape of thepre-plasma.
Pukhov(Te,15μm)
Pukhov(Te,30μm)
Pukhov(Te,60μm)
Pukhov(Te,150μm)
Te(FI01,P53,BrassPH,Al)
Te(FI01,P53,BrassPH+Pb(Al),Cu)
Te(FI01,P53,BrassPH+Pb(Al),Au)
Te(FI01,P53,BrassPH,DLC-cone wo Au-coat,woGXII)Te(FI01,P53,BrassPH,DLC-cone w Au-coat)
Te(FI01,P53,BrassPH+Pb(Al),Au-cone, woGXII)Te(FI01,DLCwoAu-Integrate)
Te(FI01,DLCwAuBrim-Integrate)
Te(FI01,DLCwAu-Integrate)
Te(FI01,AuCone-Integrate)

Te101171018101910(2ps,100-36m,82%x50%)FI01

Fig. 1 Teff of plates, cones and integrate.

2010