| 摘要 |
<p>An electron lens comprising a first exciting coil (1), a second exciting coil (2), a casing (3) for encompassing the first and second exciting coils, and an excitation control apparatus (6) for controlling the excitation state of at least the first exciting coil independently of the second exciting coil. The excitation control apparatus independently controls currents applied to the first and second exciting coils, respectively. At this time, exothermy of each coil can be kept constant and thermal deformation of the casing can be prevented by keeping the sum of the absolute values of the currents applied to the coils. <IMAGE></p> |
