A focused ion beam device is described comprising a gas field ion source with an emitter emitting an ion beam including ions of gas, an ion beam column and a beam current control loop comprising a beam current measurement device. Furthermore, the focused ion beam device may have a sample charge control comprising measuring the sample charge. A method of operating a focused ion beam device is provided comprising applying a voltage between an emitter an electrode, applying gas to the emitter, emitting ions of a gas from the emitter and controlling a beam current by measuring the beam current with a beam current measurement device.