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

本项目的目的是研制一种可行的毫米波脉冲源，它利用超导腔中能量的储存和快速提取，其中的时间常数可以达到&lt；10^(-2)&gt；秒的数量级。在第一年，我们设计和建造了一个铌腔，一个毫米微波AFC电路和一个玻璃钢低温恒温器等，并设计了室温下使用20-50托氦气体的小型半圆形放电管作为输出放电天线。Nb腔设计为-lt；TE_(0，1，17)&gt；圆柱模，谐振频率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，我们首先精确地测量了室温下Nb腔的频率特性。得到了腔体的各种参数。谐振频率和加载Q值分别为23.77 GHz和2x&lt；10^3&gt；为了提高Nb腔的负载Q值，我们对Nb腔内表面进行了电抛光，表面粗糙度估计小于0.1微米。在电抛光溶液中，在Nb阳极与Nb腔的一部分，即两个圆盘和圆柱体之间分别提供60 mA/cm2的直流电流。电抛光花了4个小时。然后，这些部件在一个干净的房间里快速组装起来。真空烘烤后，腔内真空度达到3x；10^(-8)；当氦气温度为4.2K时，认为电抛光腔加载了~lt；108&gt；的Q值。此时，我们正在进行最后的实验，给放电天线施加电压20千伏，电流2000A，时间宽度1微秒。我们期待着本项目的最终目的，即脉冲功率增益&lt；10^4&gt；。

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> .