| The ultrafast electron diffraction(UED)technology gets a rapid development those years.New UED instruments have appeared or will appear in some related research group.The energy of the dc electron gun changes from dozens of kV to hundreds of kV.The new type microwave electron gun appeared recent years could produce a MeV electron pulse.The duration of the electron pulse also develops from picoseconds to femtoseconds and even attoseconds.Time resolved scanning electron microscope and transmission electron microscopy have also appeared.The UED detection extend from lattice to surface science,superconductivity material,magnetic material,plasma detect,biology,chemistry and so on.We decide to develop a multi-function time-resolved electron diffraction system operating at the voltage of 100 kV with a table size and compact structure under such background.Then necessary simulations for this system have been done first.The system which design based on the simulation contains a dc 100 kV voltage electron gun with light cathode,ultra-high vacuum chambers,device for electron pulse control,device for sample enter and control,detection and imaging system,data collection system and some other equipment.We find a big decrease in electronic pulse expansion velocity would happen when it come across the electric field boundary in our simulation of the UED system.And the ultra-fast electron pulse dynamics behavior is decided by this decrease.We develop the mean-field models of ultra-fast electron pulse and give a correctly description of the electron pulse which provide a better result than other model.The electron gun we build is based on a computer simulation which would avoid the emergence of a large electric field and guarantee the gun work well in 100 kV.A reflection mode has been designed and added to insure the production of electron to millions for one pulse irreversible process detection.A special coaxial structure has been designed to further guarante a uniform electric field.The gun has a good magnetic field shield to prove the better electron pulse.There is a big resistance shielded by an insulation protection between electron gun and its power supply.This design achieve a more stable and safe environment for the gun.The magnetic lens now use is special designed for the need of compact structure of the system which can achieve a 130 mm distance from the cathode to the sample.Without magnetic lens the distance could smaller than 100 mm.The working vacuum of the chamber is designed to 10-10 Torr which includes electron gun chamber,sample chamber,mirror chamber,faraday cup chamber,exhaust chamber and so on.The sample chamber contains numerous windows which include two special designed 34 mm diameter flange windows on the apical side.The pump laser could incidence at the opposite direction of the electron pulse.The sample chamber could also connect with other chamber or instrument for UED development in future?The device for sample enter and control could adjustment in 5-dimensional.The sample holder is also specially designed for the different needs of the experiment and could easily be replaced by other or for device development.The detection part for the UED instrument contains a faraday cup and an electronic pulse imaging system.The data collection system with a computer program in Labview language is under design.We find the diffraction spots splitting in two in our time-resolved electron reflection diffraction experiment.The distance of the splitting has a Gauss like symmetrical distribution over delay time.The distances of the split are shorter for the higher order diffraction.We believe the split is caused by the coulomb repulsion of the sample emission electrons and estimate the electrical strength to be about 107V/m.This method may do some help in the simultaneous detection of lattice and surface field. |
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