Publications Details
Cylindrical target Li-beam-driven hohlraum experiments
The authors performed a series of experiments on the Particle Beam Fusion Accelerator II (PBFA II) in May, 1994, and obtained a brightness temperature of 61 {+-} 2 eV for an ion-beam heated hohlraum. The hohlraum was a 4-mm-diameter, right-circular cylinder with a 1.5-mm-thick gold wall, a low-density CH foam fill, and a 1.5- or 3-mm-diameter diagnostic aperture in the top. The nominal parameters of the radially-incident PBFA II Li ion beam were 9 MeV peak energy ({approximately}10 MeV at the gas cell) at the target at a peak power of 2.5 {+-} 0.3 TW/cm{sup 2} and a 15 ns pulse width. Azimuthal variations in intensity of a factor of 3, with respect to the mean, were observed. Nonuniformities in thermal x-ray emission across the area of the diagnostic hole were also observed. Time-dependent hole-closure velocities were measured: the time-averaged velocity of {approximately}2 cm/{micro}s is in good agreement with sound speed estimates. Unfolded x-ray spectra and brightness temperatures as a function of time are reported and compared to simulations. Hole closure corrections are discussed with comparisons between XRD and bolometer measurements. Temperature scaling with power on target is also presented.