Optical measurements of plasma dynamics in carbon fiber Z-pinches

Blackett Lab., Imperial Coll. of Sci., Technol. & Med., London
IEEE Transactions on Plasma Science (Impact Factor: 0.87). 09/1998; DOI: 10.1109/27.725138
Source: IEEE Xplore

ABSTRACT A series of experiments has been carried out on the Mega Ampere
Generator for Plasma Implosion Experiments (MAGPIE) generator in order
to study the dynamics of carbon fiber Z-pinches. The generator was
operated at 1.4 MV, with a peak current of 1 MA, and a rise time of 150
ns. In some shots, a current prepulse of about 30 kA was provided to
study its influence on the dynamics of the fiber pinch. Carbon fibers of
7, 33, and 300 μm diameter were used during these experiments. The
diagnostics employed were a self-referencing interferometer, a two-frame
Schlieren system, an optical streak camera, and a four-frame X-ray
framing camera. A novel feature of these measurements is the employment
of an optical streak camera with a set of four slits arranged along the
fiber axis and displaced in the radial direction. This permitted the
study of the temporal evolution (axial and radial) of the plasma regions
emitting in the visible part of the spectra. Correlation between these
regions of the plasma and the location of X-ray hot spots is discussed.
In carbon fibers of 33 pm diameter, the radial expansion velocity
measured from Schlieren images was 3.6×106 cm/s and
5.5×106 cm/s for shots with and without prepulse,
respectively. The dominant axial wavelengths of instabilities in the
coronal plasma were between 0.05 and 0.2 cm, which correspond to ka
values between 10 and 20, where k is the wavenumber of the instability
and a is its amplitude. The dynamics of carbon fibers of different
diameters are compared