  It is shown that steepening of the radial plasma pressure profile leads to a
decrease in the critical value of beta, above which small-scale balloon-type
perturbations in a mirror trap become unstable. This means that small-scale
ballooning instability leads to a smoothing of the radial plasma profile. This
fact seems to have received little attention in the available publications. The
critical beta values for the real magnetic field of the gas-dynamic trap was
also calculated. In the best configuration the critical beta 0.72 is obtained
for a plasma with a parabolic radial pressure profile.
