def i1beta_psim(i1, beta, psim, ax=0):
    """creates a surface plot of psim vs i1, beta"""
    if ax == 0:
        _create_3d_axis()
        ax = plt.gca()
    _plot_surface(ax, i1, beta, psim,
                  (u'I1/A', u'Beta/°', u'Psi m/Vs'),
                  azim=60)