用于铯原子喷泉频率基准的TE_(011)微波谐振腔

TE_(011) Microwave Cavity Used for Cesium Fountain Primary Frequency Standard

本文全面描述了用于中国计量科学研究院正在研制的铯原子喷泉的微波腔的结构特性和性能测量。该微波腔工作于TE0 1 1 模式。它是一种圆柱型腔 ,内径 4 3mm ,高 4 2 .9mm ;两端有截止波导管 ,内径 12mm ,长 30mm。微波馈送采用同轴 -波导转换 ,为了简化 ,腔外部未设调谐装置。腔的材料采用具有高导电率的无氧铜 ,所有的馈送部件均无磁并具有超高真空性能。对已装入喷泉管的微波腔在真空状态下的测量表明 ,其失谐量和有载Q值分别为 0 .7MHz和 8× 10 3。估算了与微波腔有关的钟频率不确定度 ,其中由腔相位差产生的频率不确定度降至 1.6× 10 - 1 6 ,它是喷泉钟准确度提高到 10 - 1 5量级的主要因素。

The structure features and performance of the microwave cavity used for the developing cesium fountain in NIM are comprehensively described .The cavity operates in mode TE 011 . It is a cylindric cavity with 43 mm in inner diameter and 42.9 mm high, and has a cut off waveguide tube with 30 mm long and 12 mm in inner diameter at its two ends. A co axial waveguide transform is used for microwave feeding, and there is no tuning arrangement outside for simplifying. The cavity is made of oxygen free copper, which has high conductivity, and all the feeding connector parts are of ultra high vacuum performance and no magnetism.Performance measurements for the cavity mounted in the foutain tube under vacuum showed that the detuning and loaded Q are about 0.7 MHz and 8×10 3 respcctively. The clock frequency uncertainties relative to the cavity have been estimated, and the frequency uncertainty due to the cavity phase difference drops down to 1.6×10 -16 , which is the main factor if the accuracy of a fountain clock is desired to the order of 10 -15 .