A novel non-linear ion mirror with only three elements

A novel tubular ion mirror has been designed for reflectron time-of-flight mass spectrometry (TOF-MS). This design consists of only three cylindrical elements, With this mirror, an electric field is achieved that is non-linea r along the mirror axis and has improved off-axis homogeneity compared with conventional simple geometry ion mirrors. The practical operation of this mirror Is simpler than that of conventional diaphragm ion mirrors. Design p arameters, including the relative lengths and voltages of the three element s, can be determined empirically, Once the mirror depth dimensions have bee n implemented, the voltages of the middle and rear elements are the only ad justable parameters, The electric field achieved by the mirror deviates onl y slightly from a linear mirror with constant field strength, The second-or der deviation curve reveals two regions of curvature; all ions are turned a round in the second curvature region. A plot of arrival time vs ion kinetic energy has a flattened "S" shape. The aspects of this shape are affected b y the voltages of the middle and rear elements. SIMION 7 simulation demonst rates that this new non-linear ion mirror can perform second-order kinetic energy correction for large kinetic energy variation (33%) and substantial beam dimensions. Both the ion kinetic energy variation and the mirror eleme nt voltages affect the mass resolution obtained with the mirror. Ion trajec tory simulations with a 10 mm diameter beam from a standard, two-field sour ce predict that baseline resolution can be 16,000, 7600 and 1200 for 15%, 2 6% and 33% kinetic energy variations, respectively.