Experimental Study On Frequency Tunable Terahertz Gyrotron

Nuclear magnetic resonance(NMR)is the spectral technique used to observe the behavior of nuclear in magnetic field,which plays an irreplaceable role in many scientific research and application fields.However,its low sensitivity limits its further applications.Dynamic nuclear polarization can effectively improve the sensitivity of NMR by transferring the spin polarization from the stable paramagnetic centers to the nuclear.The DNP-NMR needs to be driven by a microwave or terahertz source.In THz frequency band,The gyrotron is the only microwave source that can meet the requirement of dynamic nuclear polarization.The frequency-tunable gyrotron for DNP-NMR is experimentally investigated in this thesis,the main work is as follows:1.Based on the basic working principle of a gyrotron,the experimental system of a gyrotron is built and tested.Based on Labview software,the gyrotron measurement and control system is designed,Remote control,data acquisition and storage of each equipment is realized in this system.This system is helpful to improve the automation degree and accuracy of the gyrotron experiment.2.The power and frequency acquisition method of a gyrotron is investigated,and the power detector is calibrated and the noise in the power data is filtered.With the help of the designed measurement and control system,a large number of experiments are carried out,including the relationship between the power,the frequency and the voltage,the magnetic field,the beam current,etc.,and the frequency-tuning bandwidth and power range is also investigated.3.Based on the basic theory of a circular waveguide,the transmission characteristics of the over-mode corrugated waveguide are analyzed by using the boundary function analysis method.The over-mode corrugated waveguide transmission line for 263 GHz and two kinds of miter bend are designed.Based on the basic theory of the Gaussian beam,an ellipsoidal reflector is designed,and the waist radius of the Gaussian beam from the corrugated waveguide is changed from 7.68 mm to 2.4mm,which realizes the coupling of the beam from 12 mm corrugated waveguide to 3.75 mm corrugated waveguide of the NMR.The designed transmission line system is simulated and verified by FEKO,and the experimental platform is built and the experimental verification is carried out.