Driver coupling to quasistatic Z-pinches

Quasistatic Z-pinches formed "on axis" and magnetically confined by a current layer larger than a critical current (> 1.5 MA for deuterium) are supposed to undergo radiative collapse providing high energy density thermal plasmas. Z-pinches created from solid fibers do not well couple to the necessarily high power drivers due to lacking initial conductivity and compressibility resulting in fast global plasma expansion and current leaks. Therefore experiments starting from plasmajets (n(e) less than or equal to 10(23) m(-3), T-e approximate to 1 eV) have been performed using two different drivers, namely the terawatt pulseline KALIF (2 MV, 900 kA) and the fast condenser bank SPEED 1 (200 kV, 900 kA) in order to investigate driver - load coupling with different initial power conditions. The main results of this study are: (i) plasmajets show much better initial coupling than fiber experiments, (ii) there is a critical limit of the reduced electrical field (E/n approximate to 10(-16) Vm(2)) above which fast plasma erosion and decoupling takes place preventing pinch formation and (iii) plasma loads need high initial densities (ne greater than or equal to 10(24) m(-3)) in order to well couple to terawatt drivers providing pinch electric fields above 10(7) V/m. A conductive, dense and marrow plasma column is a necessary condition for an efficient energy transfer from the driver to the load. Whether or not this is sufficient to induce radiative collapse still remains to be experimentally demonstrated.