Theoretical And Experimental Study Of Several Physical Phenomena In NEA-GaAs High-voltage DC Photo-injector

High average power high-brightness electron source plays a significant role in thepath to the realization of the future high repetition short wavelength free electron lasersand energy recovery linacs, which are driven by high repetition, low emittance and shortbunch length electron beams. High-voltage(HV) DC photocathode injector is one of themost popular sources to drive these advanced facilities. This dissertation is based on theChinese first HV DC photocathode injector on CAEP FEL-THz facility, and devoted tosolving several physical problems theoretically and experimentally, including the ways toobtain and the tools to measure the high average power high-brightness electron beams.We first established a preliminary physical model on the working life-time of neg-ative electron afnity (NEA) GaAs photocathode. With this model, several problems ofthe DC injector, including the vacuum and temperature rising around the surface of cath-ode, have been found. Great eforts in the injector optimization have been made, such asthe extension of macro pulses duration, the degradation of ghost pulses for the diagnos-tics of macro pulses, the optimization of electron transport tubes’ dimensions to improvethe vacuum conditions and cathode’s indium welding to reduce the temperature risingof cathode surface. With these work, the beam life-time has been risen from about50seconds to80minutes, and stable high average power electron emission phenomena of1mA/3.3h,3mA/1.4h and5mA/0.5h are achieved, respectively.We also made some eforts in the high-brightness of the electron beams. The s-pace charge efect in the HV DC gun was studied and the emittance compensation with asolenoid was researched. The thermal emittance of NEA-GaAs photocathode was mea-sured with solenoid scan method under the condition of ultra-low charge for which the s-pace charge force induced emittance growth is negligible. The electron emission responsetime of NEA-GaAs was considered to be larger than metal photocathodes. The longitu-dinal distortion of electron beam was calculated with the difusion model which is wellagreed with experimental results around the world. Finally, with these eforts,we haveproved that the FEL-THz photocathode injector has the ability to provide high-brightnesselectron beams with emittance less than2mm·mrad and initial longitudinal FWHM lessthan16ps. Last but not the least, a non-interceptive and cost-efcient technique to measure thehigh average power high-brightness electron was studied. The technique named LaserWire (LW) is based on Thomson scattering. On the basis of the previous research aroundthe world, we paid attention to the non-gaussian distribution diagnostics and the impacton the electron beams. With theory analysis, we proved the LW applicability in thegeneral distribution measurement. The impact was also proved to be negligible exceptthat the electron has TeV degree energy. Based on the theoretical research, we built ahigh repetition LW system on FEL-THz injector. This improved LW utilizes the excesspower of the photocathode drive laser, thus making itself much cheaper and simpler. Tothe best of our knowledge, this is the first time to measurement keV high average powerelectron beams by LW method. With some eforts in reducing the noise, we have achieveda6mm FWHM longitudinal distribution signal of beam bunch.