A voltage source adapted to excite a gas-ionization electrode so as to generate copious amounts of ionized gas without, however, producing measurable amounts of undesirable reactive or toxic chemical by-products. Yielded by the source is a unipolar voltage wave having a steady state DC component which, though below the ionization potential, serves to condition the gas to promote ionization. Imposed on the steady-state component is a gas-ionization component in the form of low-frequency surges, each composed of a short series of high-frequency pulses having a brief duration and an extremely high peak amplitude. The duration of the surge pulses is insufficient to break down the gas chemically, but the amplitude thereof is such as to effect intense gas ionization. The steady-state component prevents the electric field from collapsing completely in the intervals between pulses, thereby keeping the gas at a level approaching its ionization potential.