Probe characterization of high-current driven metal plasma in a vacuum-arc rail gun

摘要

The characteristics of metal plasma launched by high-current electric arc in a vacuum-arc rail gun are determined by employing electrical and magnetic probes. These measurements are validated by results from theoretical simulations. The arc coupled nonlinear circuit equations are solved simultaneously with the Newtonian arc motion and revealed the undercritically damped behavior of the arc current identical to the arc-current signal recorded by the Rogowski magnetic probe. Similarly the arc velocity and displacement derived from the signatures of B-dot probes are shown to concur closely with the results of JxB propulsion from simulation. The heating of plasma is formulated in a three-electron population regime with direct arc energy coupling through magnetohydrodynamic, ion-acoustic, Coulomb, and neutral interactions. This results in high temperature (T-e) of hundreds of eV in the arc as revealed by the simulation. Hence T-e of the rapidly cooling and equilibrating plasma that emerged from the muzzle is high around 80-90 eV, which is confirmed by Langmuir electric probe measurements. Density n(e) of this metal plasma is shown to be in the range 4x10(21)-6x10(21) m(-3) and includes multiple ion charge states. The exit velocity of the plasma measured by a pair of Langmuir probes is close to 2.2x10(6) cm/s and matched well with the arc velocity determined by the B-dot probes and the results from simulation. (C) 2004 American Institute of Physics.