Development of a Feasible High-Power mm Microwave Pulse Source Utilizing Superconducting Cavity

本项目的目的是开发一种可行的毫米微波脉冲源，利用超导腔的能量存储和快速提取，其时间常数可以小于10^(-2)>秒。在第一年，我们设计并建造了铌腔，毫米微波AFC电路和玻璃钢低温恒温器等。此外，设计了20 ~ 50托室温氦气的小型半圆形放电管作为输出放电天线。铌腔设计为<TE_(0,1,17)>圆柱模式，谐振频率为24.5 GHz，内径44 mm，长111 mm。在接下来的一年，也就是项目的最后一年，我们首次在室温下精确测量了铌腔的频率特性。得到了腔体的各种参数。谐振频率为23.77 GHz，负载Q值为2x <10^3>。为了提高铌腔的负载Q值，我们对铌腔的内表面进行了电抛光，估计其表面粗糙度小于0.1 <微> m，在电抛光溶液中，在铌阳极和铌腔的部分（即两个圆盘和圆柱体）之间分别施加60 mA/ <cm^2>的直流电流。电抛光耗时4小时。然后，零件在洁净室中快速制造。在抽气和烘烤后，腔内的真空度达到3x <10^(-8)> Torr。在氦温度4.2 K时，电抛光腔的负载Q值为<10^8>。此时，我们正在进行最后的实验，给放电天线施加电压20 kV，电流2000 A，时间宽度1 <微>秒。我们期望达到本项目的最终目的，即脉冲功率增益<10^4>。

It is the purpose of the present project to develop a feasible mm microwave pulse sourse, utilizing the storage and quick extraction of energy from a superconducting cavity, in which the time constants can be of the order of <10^(-2)> sec. In the first year, we designed and constructed a niobium cavity, a mm microwave AFC circuit and a FRP cryostat etc. Moreover, small semi-circular discharge tubes with 20-50 Torr helium gas at room temperature were designed to use for the output discharge antenna. Niobium cavity was designed to be <TE_(0,1,17)> cylindrical mode with resonant frequency 24.5 GHz, and the inner diameter 44 mm, the length 111 mm. In the next year, i.e., the final year of the project, we first measured precisely the frequency characteristic of the niobium cavity at room temperature. Various parameters of the cavity were obtained. The resonant frequency and the loaded Q value were, respectively, 23.77 GHz and 2x <10^3> . To increase the loaded Q value of niobium cavity, we electro-polished The inner surface of the niobium cavity, in which the roughness of the surface was estimated to be less than 0.1 <micro> m. In the electro-polishing solution, the DC current with 60 mA/ <cm^2> was given between a niobium anode and the part of the niobium cavity, i.e., the two disks and the cylinder, respectively. Electro-polishing took 4 hours. Then, the parts were fabricated quickly in a clean room. After evacuating and baking, vacuum inside the cavity was attained to be 3x <10^(-8)> Torr. The electro-polished cavity was considered to have loaded Q value of the <10^8> at helium temperature 4.2 K. At this moment, we are carrying out the final experiment to give the voltage 20 kV, current 2000 A, time width 1 <micro> sec to the discharge antenna. We are expecting to have the final purpose of the present project, i.e., pulse power gain of <10^4> .