By the discharge of condensers, a current is driven axially through a plasma column located in a mirror field. The maximum value of the current is typically 5000 A and the frequency typically1Mc/sec. It is found that under a variety of circumstances, 3‐4% of the energy initially stored in condensers is transferred to perpendicular energy of the plasma. A substantial part of the energy is transferred to ions. The ion energy spectrum has been measured in one case and within experimental error found Maxwellian with a temperature close to 500 eV. Measurements of x rays emitted when a tantalum target is placed in the plasma show that very few high‐energy electrons (> 5keV) are present except while the axial current flows. It is found that the energy transferred to the plasma is proportional to the square of the maximum current; this suggests that efficiencies higher than 4% may be obtained.