The disclosure relates to a method of operating a gas field ion beam system in which the gas field ion beam system comprises an external housing, an internal housing, arranged within the external housing, an electrically conductive tip arranged within the internal housing, a gas supply for supplying one or more gases to the internal housing, the gas supply having a tube terminating within the internal housing, and an extractor electrode having a hole to permit ions generated in the neighborhood of the tip to pass through the hole into the external housing. The method comprises the step of regularly heating the external housing, the internal housing, the electrically conductive tip, the tube and the extractor electrode to a temperature of above 100° C.