Large quantities of gas are desorbed from the anode electrode during initial high-voltage conditioning of broad-area electrodes in a vacuum, equivalent to many monolayers and consist mostly of neutral molecules with an ionic component of a few percent. The ions are accelerated to the cathode, producing secondary electrons from the cathode and x-rays. There is still no reasonable explanation of these phenomena. Experiments have been performed to try to understand the source of the gas and radiation by using a residual gas analyzer to examine the desorption products from copper electrodes during initial high-voltage conditioning. The desorption products produced during initial high-voltage conditioning were then compared with those from thermal desorption of the same electrodes and surface preparation as they were heated in vacuum to about 600 °C, both with and without a high electric field present. Thermal desorption with an applied field showed a significant difference in the desorption spectrum compared with no applied field and produced a modest source of radiation that did not appear to be produced by field emission. At electrode temperatures beyond 450 °C, radiation production increased exponentially with temperature, likely produced by surface ionization of minor contaminants with a low ionization potential. These observations have been used as input to propose that the radiation and gas desorption observed during initial high-voltage conditioning is initiated by surface ionization from the many projections with high field enhancement factors on the anode surface.