Imploding$Z$-Pinch Plasmas Formed From a Carbon Fiber

Z-pinch experiments, which are formed from a 15-mum diameter carbon fiber in a vacuum, were conducted using a simple capacitor bank. After the breakdown, a low-density coronal plasma was formed while the fiber diameter remained almost unchanged. This low-density corona (ion density of about 10
¹⁶
cm
^-3
) was carrying almost all the current of the order of 10 kA. When the current had built up, i.e., after about 150 ns, the implosion of the corona onto the central fiber occurred. The implosion velocity approached the value of 2middot10
⁵
m/s. When the imploded corona had reached the fiber, the dip in dI/dt, a voltage peak up to 10 kV and an extreme-ultraviolet (XUV) pulse of a 10-30-ns width were observed. XUV radiation was emitted from several bright spots, which corresponded to the interaction of m=0 instability necks with the dense core. The electron temperature and density were approximately 80 eV and 10
¹⁹
cm
^-3
, respectively. Although the presence of a fiber did not significantly suppress MHD instabilities, they were not disruptive. After the fiber ablation, i.e., after 500 ns, the material evaporated from the electrodes started to play a dominant role. When MHD instabilities had developed in the imploding plasma column, XUV, soft X-ray, and hard X-ray pulses were emitted from several bright spots, particularly near the anode. At that time, the voltage peak of up to 30 kV was detected. The measurement of voltage and current enabled the determination of a plasma resistance and the energetics of the Z-pinch