Electromagnetic-implosion generation of pulsed high-energy-density plasma

Abstract

The generation of pulsed high‐energy‐density plasmas by electromagnetic implosion of cylindrical foils (i.e., imploding liners or hollow Z pinches) has been investigated experimentally and theoretically at the Air Force Weapons Laboratory. The experimental studies involve discharging a 1.3‐μsec 1.1‐MJ capacitor bank through 7‐cm‐radius 2‐cm‐tall 3–30‐mg cylindrical foil liners. Typical discharge parameters are 7–12‐MA peak current and 1–1.5‐μsec current rise time. Current and voltage waveforms indicate strong coupling of the load to the capacitor bank, and analysis of the waveforms indicates good implosion of the current sheath. Optical‐ and magnetic‐probe measurements are consistent with 1–2‐cm thickness of the imploding plasma shell and with final implosion velocities ∼15–20 cm/sec. Radiation‐diagnostic measurements indicate ultrasoft x‐ray yields ∼50–100 kJ with the FWHM of the photon pulse ∼80–100 nsec. The radiation data is consistent with a quasiblackbody spectrum (T∼30–50 eV) comprising most of the energy, with additional higher temperature and optically thin spectral components. Al¹¹⁺ and Al¹²⁺ line and recombination radiation is frequently observed. Comparison of electrical, magnetic, and radiation data with one‐dimensional MHD and two‐dimensional MHD calculations is presented. The prospects for improving the performance with the present energy source and scaling to larger energy sources are briefly discussed.