10 / 2025-02-20 21:56:36

Simulations of Z-Pinches

Z-pinches, dense plasma focus, sausage" instability

In recent decades, a significant progress has been made in computational and theoretical modeling of Z-pinches and dense plasma focus, as well as in understanding the phenomena in plasma dynamics during pinching, and the processes leading to neutrons generation in Z-pinches. It was facilitated by the significantly upgraded capabilities of computer technology, which currently allow simulating turbulent development of instabilities (including the most important for describing Z-pinch necks a "sausage" instability) and even direct simulating electron-ion kinetics during pinching. Studies of the development of Z-pinch waist (neck) in the axisymmetric magnetohydrodynamic (MHD) approximation and the account for the development of two-dimensional turbulence have shown that turbulence development prevents the formation of the neck with an infinitely decreasing radius and plasma outflow from the compression zone. Under the neck compression in this approximation there is also no generation of high voltages near the axis that could contribute to the formation of ion beams and neutrons generation due to the beam-target mechanism. In the computations, a MHD marginally stable Kadomtsev equilibrium is established rather quickly. Thus, to describe neutron generation in the beam-target mechanism, it is necessary to take into account the kinetic processes of high voltage generation in plasma. 2D MHD computations with the account for kinetic processes in the phenomenological form of anomalous resistivity make it possible to achieve agreement with experimental data on current, voltage and neutron measurements for a number of plasma focus configurations, and for fast Z-pinch, in which the beam-target mechanism provides only a part of the neutron yield, to achieve agreement with the neutron yield. 2D kinetic computations of the plasma focus carried out so far for the final phase of pinch formation agree with experimental data on the neutron yield and distribution of ions in the resulting beams and confirm that the anomalous plasma resistivity may be due to lower hybrid drift instability, which was assumed in phenomenological MHD computations that describe neutron generation in Z-pinch and plasma focus.