Sheared Flow as a Stabilizing Mechanism in Astrophysical Jets

Summary form only given. It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from young stellar objects (YSO) suggests that an intrinsic collimating mechanism is present in these jets. The j x B force observed in z-pinch plasmas {j_zldrB_thetas) is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory on the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets. Experimental, analytical, and numerical analysis of sheared flow in magnetohydrodynamic plasmas with and without helical magnetic fields is presented. The results support the hypothesis that sheared flow may impart a stabilizing influence in astrophysical jets. Future laboratory experiments are proposed that will provide enhanced support for this conclusion.