Momentum Distribution Measurement Of Electrons From Metal Surfaces By Highly Charged Ions Bombardment

The momentum distribution measurement of the emitted electrons during interactions of highly charged ions with solid surfaces is one of the most important ways to study this process.So far,there is nearly no report about the momentum distribution measurement of electrons in the full momentum space.We constructed a concentric-ring electron momentum computed tomography spectrometer to measure the momentum distribution of the emitted electrons from metal surfaces bombarded by highly charged ions.And the initial experiments were carried out on the 320 kV platform for multi-discipline research with highly charged ions at Institute of Modern Physics,Chinese Academy of Sciences.The spectrometer mainly consists of a concentric-rings one-dimensional position sensitive detector,a pair of Helmholtz coils and a multi-channel picoammeter.The Helmholtz coils were carefully calibrated utilizing a Gauss meter,and the relationship between the intensity of magnetic field and the current was obtained.The incident ion beam enters the spectrometer along the normal direction of the anode and hits the target which is mounted in the center of the anode.The electrons emitted from the target surface can be deflected back to the anode by electric and magnetic fields.We can get a group of position distributions by changing intensities of electric and magnetic fields independently.The momentum distribution can be acquired via complex mathematical transformation on the position distributions.Our experiments were performed on the 320 k V multi-discipline research platform at the Institute of Modern Physics,Chinese Academy of Sciences.The 428 keV(1.15v_Bhor)O²⁺,1.5 MeV(1.15v_Bhor)and 650 keV(0.75v_Bhor)Fe¹³⁺ions are employed to interact with a thin beryllium?Be?target in the experiments.For each ion beam,we get a group of position distributions by changing intensities of electric and magnetic fields independently.It indicates that the spectrometer works well.The results show that the electrons yields induced by 1.5 MeV Fe¹³⁺ions are larger than 650 keV Fe¹³⁺ions.The yields of electrons emitted from Be surface under 1.5 MeV Fe¹³⁺bombardment are larger than yields induced by O²⁺ions in the same velocity.