Torrezan Antonio C, Han Seong-Tae, Mastovsky Ivan, Shapiro Michael A, Sirigiri Jagadishwar R, Temkin Richard J, Barnes Alexander B, Griffin Robert G
Department of Electrical Engineering and Computer Science and the Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
IEEE Trans Plasma Sci IEEE Nucl Plasma Sci Soc. 2010 Jun 1;38(6):1150-1160. doi: 10.1109/TPS.2010.2046617.
The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization. The gyrotron operates in the whispering-gallery mode TE(11,2) and has generated 16 W of output power with a 13-kV 100-mA electron beam. The start oscillation current measured over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE(11,2,q). The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%.
报道了一种连续波（CW）可调谐二次谐波460GHz回旋管的设计、运行和特性。该回旋管旨在用作700MHz核磁共振实验的亚毫米波源，通过动态核极化提高灵敏度。该回旋管工作在回音壁模式TE(11,2)，利用13kV、100mA的电子束产生了16W的输出功率。在一系列磁场值范围内测量的起振电流与从线性理论获得的连续高阶轴向模式TE(11,2,q)的理论起振电流吻合良好。最小起振电流为27mA。还进行了功率和频率调谐测量，作为电子回旋频率的函数。通过磁场调谐或束电压调谐，在工作二次谐波模式下获得了1GHz的平滑频率调谐范围。在48小时的不间断期间对长期连续波运行进行了评估，在此期间，通过计算机控制系统，回旋管的输出功率和频率分别保持在±0.7%和±6ppm的稳定范围内。还验证了为将工作回音壁模式转换为类高斯光束而实施的内部准光学模式转换器的正常运行。根据用热释电相机拍摄的回旋管输出光束图像，计算出输出光束的类高斯模式含量为92%，椭圆率为12%。
