"Investigation of Fast Electron Spatial Energy Distribution into Imploded High Density Plasmas using Cu-doped CD Shell-Cone Targets*

 

 

 

ABSTRACT:  

 

Center for Energy Research, University of California San Diego In the cone guided fast ignition scheme, understanding of generation of fast electrons in a cone and their subsequent transport into hot dense plasma is extremely important. We have carried out experiments to investigate the spatial energy distribution of fast electrons in imploded CD shells attached to Au cone targets. In order to obtain information about the spatial energy distribution, a Cu dopant (at ~ 1% atomic number density of CD) was added to the CD shell (the inner 3/4 thickness of the shell), which allowed the characterization of fast electron transport via 8 keV Cu K-shell  fluorescence  radiation. The experiment consisted of two  parts:  i) characterization of background 8 keV x-ray emission generated from the compression (by 18 kJ of  OMEGA beams) of CD shell with and without Cu-dopant and  ii)  characterization of fast electron produced Cu fluorescence emission from the  compressed Cu-doped CD with  an additional ~ 1 kJ, 10 ps high intensity OMEGA EP beam timed and injected into the compressed core through the Au cone tip. The primary diagnostics were a narrow band Spherical Crystal Imager (SCI), a  Zinc Von Hamos (ZVH) x-ray spectrometer and a time of flight neutron detector. The copper Kα images show that the fast electrons penetrated though the cone (wall and tip) into the compressed shell producing strong Cu Kα emission from the region of the imploded high-density plasmas. The peak emission from the dense shell outside the side cone wall was ~ 100 µm further away from the cone tip which can be caused by the preplasma filling of the cone as a result of the intrinsic 3-ns long prepulse with an energy of ~ 20 mJ prior the main pulse.

 

It was also observed that the Cu Kα emission was reduced in the hot region of the core in front of the cone tip. In these experiments, fast electron energy coupling to the compressed core was found to increase with the OMEGA EP beam energy injected into the cone before the cone tip broke out by the implosion driven shocks.  Detailed experimental and modeling results will be presented in this talk.

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