Study of instabilities in wire-array Z pinches at stagnation

Stagnation of the wire array Z pinches was studied at a 1 MA generator with imaging UV and x-ray diagnostics. Cylindrical, linear, and star wire-array Z pinches present different sets of instabilities seeded to the pinch during implosion. Compact cylindrical wire arrays implode to Z-pinches with $m=$0 necks associated with bright spots on x-ray images. The electron temperature of bright spots measured with K-shell spectroscopy is higher by 20-40{\%} compared to cold areas. Maximum x-ray power is generated by Z pinches with strong instabilities. Fast plasma motion with a velocity $>$100 km/s was observed in the Z pinch at stagnation with two-frame shadowgraphy. Plasma instabilities may present a mechanism for conversion of magnetic energy to kinetic energy. Comparison of the implosions in small-diameter cylindrical and star wire array shows that the secondary implosion of non-imploded peripheral plasma prolongs the stagnation stage and provides the enhanced x-ray production. Development of instabilities in wire arrays is in agreement with 3D MHD Gorgon simulations.