Sigmund E E, Calder E S, Thomas G W, Mitrović V F, Bachman H N, Halperin W P, Kuhns P L, Reyes A P
Department of Physics, Northwestern University, Evanston, Illinois 60208, USA.
J Magn Reson. 2001 Feb;148(2):309-13. doi: 10.1006/jmre.2000.2246.
We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability.
我们通过核磁共振（NMR）研究了高场电阻式比特尔磁体的时间不稳定性。这种不稳定性会导致在重复和累积的NMR实验中出现横向自旋退相干，就像信号平均过程中通常所做的那样。我们在一个23-T的电阻磁体中通过哈恩回波和卡尔 - 珀塞尔 - 梅博姆 - 吉尔（CPMG）横向弛豫实验证明了这种效应。定量分析结果与磁场频率波动谱的单独测量结果一致，也与在具有可控不稳定性的磁场中进行的独立NMR实验结果一致。最后，结果表明即使在存在磁场时间不稳定性的情况下，具有短脉冲延迟的CPMG序列也能成功恢复固有自旋 - 自旋弛豫。
