1. An apparatus for controlling intensity of charged particles extracted from a circulating charged particle beam path in a synchrotron, said apparatus comprising: a radio-frequency field generator, wherein during use said radio-frequency generator applies a radio-frequency field to the circulating charged particles yielding betatron oscillating charged particles; an extraction material, wherein during use at least a portion of the betatron oscillating charged particles pass through said extraction material resulting in a secondary emission electron flow using electrons originating from the extraction material and without loss of electrons from the betatron oscillating charged particles; an intensity sensor, said intensity sensor configured to determine a measure of the electron flow; and a feedback control loop comprising an intensity controller, said intensity controller configured to provide the measure of electron flow as a feedback to said radio-frequency generator, said feedback control loop configured to control intensity of charged particles extracted from said synchrotron via control of said radio-frequency generator, wherein intensity comprises a number of the charged particles extracted as a function of time.