UV laser diagnostics for the dense Z-pinch

Summary form only given. Ultraviolet (UV) laser diagnostics are powerful tools for investigation of high-energy-density plasma. UV diagnostics at 266 nm were developed for investigation of dense Z-pinch plasma at the 1 MA Zebra generator. A three-channel diagnostic can be configured as two-frame shadowgraphy and interferometry or a Faraday rotation diagnostic. Spatial resolution of diagnostics is 5-15 μm depending on the beampath configuration. Absorption and refraction of UV radiation in dense plasma is significantly smaller compare to regular diagnostics at the wavelength of 532 nm. Therefore, UV diagnostics allow direct investigation of the fine structure of the dense Z-pinch, development of instabilities, and a distribution of magnetic fields and currents in Z-pinch plasma with an unprecedented level of detail [1]. Mictopinches with diameters of 60-100 μm and instabilities with characteristic scales of 15 - 200 μm were observed in 1 MA wire-array Z pinches. Development of instabilities in wire-array Z pinches is in agreement with 3D MHD Gorgon simulations. Interferometry at the wavelength of 266 nm allow measurement of plasma density in the range of (13)x1020 cm -3 in the ablating wires, imploding plasma, stagnating pinch, and trailing material. Fast plasma motion with a speed > 100 km/s was observed at the stagnation stage with two-frame shadowgraphy. Plasma motion at stagnation and prolonged implosion of trailing mass provide additional kinetic energy in the stagnated pinch and can be a source of enhanced x-ray radiation. A Faraday rotation diagnostic reveals a distribution of magnetic fields in the pinch and trailing material. The magnetic field strength and current were reconstructed from the rotation angles and phase shifts in plasma using the Abel transform. Magnetic fields >0.5 MG were measured in the pinch. Current in the pinch can switch from the highinductance neck and redistribute to the trailing material when resistance of peripheral plasma drop due to heating by x-ray radiation. The formation of hot spots in the Z-pinch was analyzed with UV diagnostics and x-ray streak camera. Further development of UV diagnostics to 211nm VUV range can help to apply well established optical methods to Z-pinch plasma in multi-MA pulsed power facilities.