Prolonged plasma production and dynamics of implosion of multiwire arrays

Brief review of our recent results concerning prolonged plasma production (P
³
) in multiwires arrays and its influence on their dynamics in pulse power facilities is presented. P
³
means that owing to overheating effects hot plasma with high conductivity is being produced from the relatively cold material almost during the whole period of current rising. P
³
results in formation of a plasma shell with a low aspect ratio and without any skin effect. It means that magnetic flux and electric current are distributed more or less uniformly along the shell and there is no magnetic piston. The latter fact is responsible for the more stable implosion of the plasma. P
³
is unavoidable effect for initially cold liners of all types in pulse power facilities, and it is useful for production of high power X-ray pulses with multiwires arrays because the process of P
³
leading to more stable implosion is well controlled in this case due to well defined periodic structure of the array. Theoretical evaluation of rate of plasma production is obtained, and it is compared with experiments. Simple simulation of plasma dynamics during implosion of multiwire arrays with P
³
is presented. Combining of such simulation with probe magnetic measurements inside cylindrical liners we obtain a certain information about dependence of the plasma production rate on time and about characteristics of depletion of plasma source. It appears that process of the depletion may be rather gradual, so that some amount of plasma is being placed at initial array position even till the moment of X-ray pulse maximum. It may lead to partial shunting of electric current and to some depression of X-ray pulse intensity. These results discover new opportunities to control plasma implosion and X-ray pulse parameters.