In a magnetic field of mirror configuration supplemented in its central part by a microwave field (λ = 12.6 cm, P = 20 W) a steady-state plasma (n = 1 × 1010 cm-3, T ec = 40 eV) was produced. ECR condition was fulfilled in a circular region spaced at 1 cm from the plasma axis. In this "hot" zone the electron temperature was T eh = 1.5 keV. The temperature gradient creates an electrostatic well for ions in the perpendicular plane. The anisotropy of electron temperature in a mirror field caused the formation of an axial electrostatic well for ions. Thus, three-dimensional electrostatic pit was produced and the ion's life-time was as long as their charge was high. With H.F. power absorbed by the plasma 8-10W we obtained comparable quantities of Ar1+, Ar2+, Ar3+, Ar4+, Ar5+, Ar6+ and also ions of impurities C+, C2+, C3+, H+, H2 +. The total current density of ions extracted from plasma is of 20 mA cm-2. © 1978 IOP Publishing Ltd.