Ultrafast Wire Loading with Multi-Megaampere Current

摘要

With a mega-ampere current rise time of several tens of nanoseconds, the high inductive impedance of a single wire (and the destruction of the wire by sausage instability already at the front of the rising current) creates certain problems for the efficient transfer of generator energy to the wire plasma. The paper presents the results of experiments on the ultrafast wire loading with multi-mega-ampere current. Metal wires with a diameter of 100 microns are driven with 2 MA current of the MIG generator. Plasma with density 10¹⁶-10¹⁷ cm⁻³ is preliminarily injected in the area of the wire load using a set of radial plasma guns. The $J imes B$ force sweeps up the injected plasma along the surface of the electrodes and the current switches to the wire in a few nanoseconds. Since the rise time of the current through the wire does not exceed the time of development of sausage instability (the radius of the wire divided by the Alfvén velocity in the material of the wire), the wire retains its cylindrical structure by the time the current reaches its maximum value. The fast wire surface explosion, the development of sausage instability and the formation of constrictions occur at the maximum current of the generator, which, in particular, significantly increases the efficiency of the conversion of the generator energy into the energy of soft X-rays.