小型磁偏转质谱计磁场的分析计算

ANALYSIS AND CALCULATION ON SPATIAL DISTRIBUTION OF MAGNETIC FIELD IN THE MINIATURE MAGNETIC SECTOR MASS SPECTROMETER

磁偏转质谱计是根据离子在磁分析器中运动时,不同质荷比的离子有不同的偏转半径原理来实现质量分离的。磁场大小和分布对质谱计的性能影响较大,因而设计时需要对质谱计磁场分布进行精确计算。应用有限元法建立了计算质谱计磁分析器磁场的物理模型,并利用这一模型计算了磁分析器磁感应强度在空间的分布情况。结果表明,在半径分别为20 mm和50 mm的1/4圆弧轨道上,其磁场分布规律类似。由于边缘磁场效应,在磁铁边界区域约3 mm范围内,磁感应强度基本呈直线下降,这一结果为磁分析器的结构优化和边缘场补偿提供了理论依据。

The function of the magnetic sector mass spectrometer is to resolve the ions according to their mass-to-charge ratios. Because the function of the mass spectrometer is greatly affected by the field strength of magnetic analyzer, the accurate computation of these magnetic fields is essential for realistic performance predictions at the design stage of magnetic analyzer. This paper employs the finite method to derive the calculated model on spatial magnetic field emanated from magnetic analyzer, and analyses the spatial distribution of magnetic field. It is shown that the distribution of magnetic flux density is analogous on quarter circle with the deflection radius of 20ram and 50mm. Because of the fringing magnetic field effect, the magnetic flux density almost linearly decreases on the edge of the magnet about 3mm. The result provide basis for optimizing the structure and calibrating the fringing field.