On the basis of incompressible viscid magnetohydrodynamic equations, a
formula is developed to study the mitigation of viscosity on the
Rayleigh–Taylor instability in Z pinches. The results indicate that in
the whole wavenumber region, the viscosity effect can mitigate the
instability. In addition, we compare the viscosity effect with the
finite Larmor radius effect [Chin. Phys. Lett. 19 (2002) 217], and the
calculation results show that in the temperature region of interest, the
former is stronger than the latter. Moreover, for heavy wire-array
implosion the viscosity effect is stronger than the finite Larmor
radius one, because the former is proportional to mi1/2 and the
latter is independent of mi.