[en] Various mechanisms of ion acceleration in electron flux at ionization front, mechanisms of autoresonance acceleration and acceleration by focusing instability are analyzed. Upper limits are given for the acceleration mechanisms at the ionization front, due to the balance of energy introduced into the system and used to create the magnetic field and to evaluate secondary electrons, and also those due to terminality of acceleration time because of the small duration of electron flux impulse. It is shown that the ion energy increase in the ionization front accelerator is possible only at the current decrease and at the increase of impulse duration, that makes such an accelerator rather ineffective. General consideration of autoresonance and focusing acceleration is presented, which in the limit of strong and weak fields leads to the known results for autoresonance and focusing acceleration respectively. It is shown that rather strong magnetic fields and high energy of ion injections (higher than 10 MeV) are necessary to realize autoresonance acceleration. Regimes of focusing instability with moderate magnetic field are found, the regimes do not require considerable energies of ion injection. It is shown that the development of highly nonlinear self-accelerated waves of electron flux density is possible in these regimes. The problem of tolerances in cases of autoresonance and focusing accelerations is analyzed. General prospects of collective ion acceleration in the straight electron flux are discussed