Interchange instability in railgun arcs

Plasma arcs used to accelerate projectiles in railguns are examined to determine their susceptibility to the Rayleigh-Taylor interchange instability. The model used is similar to that developed by Tsai, Liskow, and Wilcox, although a number of modifications are made and discussed. Numerical solutions of the appropriate eigenvalue problem suggest that the plasma is unstable for any nonzero acceleration of the projectile. Furthermore, for the dispersion curves calculated the growth rates of the short-wavelength modes are accurately approximated by the well-known expression ω= √${\mathrm{ka}}_0$ , where k is the wave number of the perturbation and $a_0$ is the acceleration. Growth rates calculated for typical experimental parameters indicate that the instability should be seen in experiments of interest. Some effort to reconcile the results with existing experimental data is made but the need for more work, both theoretical and experimental, is indicated.