An eigenmode equation for electrostatic drift waves in a low-aspect-ratio spherical spheromak geometry is derived using the ballooning mode representation. In the calculation of the density responses, the ions are treated as a cold fluid, and the electrons are assumed to be adiabatic. The various equilibrium quantities needed to solve the eigenmode equation are determined by assuming that all the magnetic surfaces are in the form of the alphabet 'D'. Using the shooting method with Numerov scheme the eigenmode equation is then integrated to obtain the eigen-frequencies and the mode structures.
In contrast to the large-aspect-ratio tokamak, the equilibrium modulations are found to be stronger in the low-aspect-ratio spheromak. Consequently, more than one local well can appear in the effective potential, which can localize eigenmodes at as many values of θ.
