An experimental study of the effect of Rayleigh-Taylor instabilities on the energy deposition into the plasma of a Z pinch

The mechanism for the heating of the plasma of a Z pinch due to the generation of toroidal magnetic structures (magnetic bubbles) which are formed in the plasma as a result of the penetration of the azimuthal magnetic field into the gas puff plasma was investigated experimentally. The experiments were performed with single-shell and double-shell gas puffs (60/30 mm in diameter) on the IMRI-4 generator (I_max=350 kA, T/4=1.1 μs). The gases used for the gas puff material were neon, argon, and krypton. Electrical investigations have shown that the final resistance of the plasma depends on the linear mass of the gas puff and equals to ∼0.06÷0.1 Ω, which coincides in the order of magnitude with the prediction of the theory of an enhanced energy deposition into the plasma of a Z pinch. Probing of the plasma was carried out with a YAG:Nd³⁺ laser with a wavelength of 532 nm, a pulse energy of the order of 30 mJ, and a pulse full-width at half-maximum of ∼5 ns. Polarimetry has shown that at the stage of stagnation of a Z pinch, there are regions inside the plasma column where the radial distribution of the electron density has a local minimum. The rotation of the polarization plane of the electromagnetic wave probing the plasma suggests that some portion of the azimuthal magnetic field of the Z pinch is captured by the current loop (a magnetic bubble is formed). The magnetic field inside the magnetic bubble is, on the average, 600÷800 kG and coincides in the order of magnitude with the magnetic field near the pinch boundary.