| Nuclear magnetic resonance(NMR)spectroscopy technology has been applied in many fields of natural science,such as material science,biology,geology.The molecules in the liquid or the solid can be investigated by NMR spectroscopy rapidly and accurately without any damage.Therefore,NMR spectroscopy has an extensive application in the fields of biology and medicine.However,the developments of NMR spectroscopy are limited by its low sensitivity and spectral resolution because the magnetic moments of the nuclear spins are too small to couple to the surrounding lattice.Dynamic nuclear polarization enhanced nuclear magnetic resonance(DNP-NMR)spectrosopy driven by terahertz(THz)wave enhances the sensitivity of NMR spectroscopy at least two orders of magnitude through transferring high polarization from the electron spins to the nuclear spins.The required power of the THz source for 300-1000 MHz DNP-NMR spectroscopy is 20-100 W and the required frequency is 200-650 GHz.Terahertz gyrotron is competent to provide continuously frequency-tunable bandwith with tens of watts,which is capable of meeting the requirments of DNP-NMR spectroscopy.In this dissertation,a 0.5 THz continuously frequency-tunable gyrotron used for DNP-NMR spectroscopy is designed and investigated theoretically and experimentally.1.The transmission line euqations are obtained based on Maxell's equations.The electromagnetic characteristics of the 0.5 THz continuously frequency-tunable gyrotron is analyzed.The cold cavity field distribution,the resonant frequency and the quality factor are investigated in detail.2.The starting currents and the beam-wave coupling coefficient of the 0.5 THz continuously frequency-tunable gyrotron are studied based on the linear theory of gyrotron,and the operating magnetic field,the operating current,the guiding center radius are investigated.At the same time,the resonant frequency,the frequency-tunable range and the quality factor are discussed in an improved muti-section gyrotron cavity.3.With the self-consistent nonlinear theory based on the guiding center coordinate system and the cylindrical coordinate system,the beam-wave interaction of the 0.5 THz continuously frequency-tunable gyrotron is investigated and the results are compared.The effects of the misaligned electron beam and the tapered magnetic field on the operating frequency,the frequency-tunable range and the beam-wave interaction efficiency for the 0.5 THz continuously frequency-tunable gyrotron are investigated.When the operating magnetic field or the operating voltage is changed,the effects of the variation of electron beam quality on the operating frequency,the frequency-tunable range and the beam-wave interaction are also studied.4.Based on the basic theory of the electronic optic system.Magnetron injection gun(MIG)of the 0.5 THz continuously frequency-tunable gyrotron is optimized and the electron beam quality is investigated in details when the operating magtic field or the operating voltage is changed.5.The 0.5 THz continuously frequency-tunable gyrotron is manufactured.The experiment platform is set up and the 0.5 THz continuously frequency-tunable gyrotron is tested.Because the superconducting magnet is getting old,the maximum mangetic field is 8.96 T which is not large enough to satisfy the 0.5 THz continuously frequency-tunable gyrotron.When the operating magnetic field is increased from 8.90 T to 8.96 T,the operating frequency is varied from 479.81 GHz to 481 GHz and the frequency-tunable range is 1.19 GHz.Additonally,the minimum output power is 20 W and the maximum output power is 380 W. |
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