Hard X-ray and hot electron environment in vacuum hohlraums at NIF

Time resolved hard x-ray images (hv > 9 keV) and time integrated hard x-ray spectra (hv = 18-150 keV from vacuum hohlraums irradiated with four 351 nm wavelength NIF laser beams are presented as a function of hohlraum size and laser power and duration. The hard x-ray images and spectra provide insight into the time evolution of the hohlraum plasma filling and the production of hot electrons. The fraction of laser energy detected as hot electrons (f hot ) shows correlation with both laser intensity and with an analytic plasma filling model.