Time-resolved and multiple-angle Thomson scattering on gas-puff Z-Pinch plasmas at pinch time.

ABSTRACT

A 526.5 nm Thomson scattering diagnostic laser enables probing of the plasma conditions of neon gas-puff z-pinch implosions with temporal resolution. Splitting the laser into two 2.5 J pulses, both 2.3 ns in duration and separated by 4 ns, allows observation of sub-nanosecond time-resolved spectra for a total time of 7 ns. Collection optics were set at 90° and 30° to the laser, observing the same on-axis scattering volume with a radial extent of 0.4 mm. The spectra from both angles were collected by using the same streak camera, using a coupling system that allowed us to obtain temporal, spectral, and angular resolution in the same image. By comparing the ion-acoustic spectra from the two angles, we determined electron temperature and a range of possible electron densities. Measurements made in the 1-3 ns period before pinch time show best fit (determined by a least-squares method) electron densities of around 2 × 1019 cm-3, increasing to 1.5 × 1020 cm-3 in the 3 ns following the start of the x-ray burst (t = 0 ns) from the pinch. The electron temperature increases from 300 eV to 500 eV at t = 0 ns before decreasing to below 300 eV after pinch time. With the present parameters (probe beam, collection angles, and electron temperature and density), this diagnostic method is too insensitive to electron density to provide more than a constraint on that parameter. Plasma regimes in which this technique could determine electron density with some precision are calculated.