Electron-impact double ionization of helium at high energies

Electron-impact double-ionization cross sections for the helium atom are calculated by direct solution of a nine-dimensional Schr\"odinger equation using a time-dependent close-coupling method. Previous calculations are extended to higher incident electron energies using a simple factor-of-2 reduction in the mesh spacing for the three-dimensional radial lattice. The recent calculations, computationally more than an order of magnitude more difficult, are found to be in good agreement with experiment from threshold to beyond the peak of the cross section at 2750.3em0exeV.