WU Chang-jiang1,2, GUAN Yong1, CHEN Jiang1,2,

ZHANG Hui3, RUAN Jun1,2,4, ZHANG Shou-gang1,4

(1. National Time Service Center, Chinese Academy of Sciences, Xi′an 710600, China;

2. Graduate University of Chinese Academy of Sciences, Beijing 100039, China;

3. Institute of Photonics & Photo-Technology, Northwest University, Xi′an 710069, China;

4. Key Laboratory of Time and Frequency Primary Standards, National Time Service Center,

Chinese Academy of Sciences, Xi′an 710600, China)

Abstract: The performance of the caesium atomic fountain clock is affected by the uniformity of the C field. In order to compensate the uneven magnetic field caused by the leakage in magnetic shielding region, compensation coils are introduced and the number, position and current of the coils are calculated by the least square method. The experimental results agree with the theoretical prediction and an uniform magnetic-field of 48cm with a fluctuation of less than 2 nT is obtained.

Key words: caesium fountain clock; magnetic shielding; least squares