beam source
Gap current beam source (Efficient beam source) is used to heat molecules (such as sodium ）Evaporate, shoot out from the slit, block the divergent molecules through a collimation hole, and get a narrow and straight molecular beam to shoot Reaction chamber 。 The size of the small hole at the exit of the beam source should be smaller than the average free path of the molecular thermal movement in the beam source. The molecular velocity in the beam source is Boltzmann distribution The molecular velocity distribution is relatively wide and the divergence angle is large, so the beam intensity is small. Gap current beam source Thermal beam source 、 Diffusion beam source 、 Furnace beam source Etc. Ultrasonic molecular beam source (super molecular beam) Gas molecules are emitted from the nozzle, and pass through the outlet hole collimator get into Vacuum chamber 。 Its characteristics are that the beam source intensity is large, and the divergence of the beam is restrained by the flow along the axis direction; Due to vacuum Adiabatic expansion , the temperature can be reduced to less than 20K; The velocity distribution is narrow. because mach number M (=beam velocity/sound velocity) can reach dozens (supersonic speed), so it is also called Supersonic molecular velocity 。 The strength of molecular beam is Beam intensity (beam intensity) is the number of particles passing through the unit area perpendicular to the moving direction of the incoming beam per unit time.
Beam current (beam flux) is the unit time injection to detector Number of particles on, also known as flux 。 
