Kobayashi Hiroshi, Hondo Toshinobu, Kanematsu Yasuo, Suyama Motohiro, Toyoda Michisato
Hamamatsu Photonics K.K., Hamamatsu, Shizuoka, Japan.
Department of Physics Graduate School of Science, Osaka University, Osaka 560-0043, Japan.
Mass Spectrom (Tokyo). 2023;12(1):A0134. doi: 10.5702/massspectrometry.A0134. Epub 2023 Nov 7.
The gain of the microchannel plate temporally drops after an ion initiates an electron avalanche. Electron multiplication was expected to deplete the charge from the microchannel wall and produce the depleted charge (wall charge). Moreover, it was reported that the gain drop occurred not only in the activated channels, where the electrons are multiplied, but also in the surrounding channels. One mechanism of the gain-drop spatial extension has been considered as that the wall charges in the activated channels change the electric field in the surrounding channels. Anacker . assumed that the wall charge is a uniform line charge; the gain-drop spatial extent should be proportional to the amount of the wall charges. We considered that the wall charges exponentially increased in the channel toward the exit. In this study, the electric field produced by the wall charges was calculated, considering the distribution of the wall charges. The transverse electric field generated by the wall charges was expected to disturb the electron trajectory near the channel exit and decrease the number of secondary electrons emitted per collision (gain per collision), resulting in a gain drop. The gain per collision was calculated to decrease by 22% for the position where the gain decreased significantly in the presence of the transverse electric field of 3×10 V/m. In our model, the gain-drop spatial extent extended proportionally to the square root of the wall charges when the distance from the activated channel exceeded 50 μm.
在离子引发电子雪崩后，微通道板的增益会随时间下降。电子倍增预计会耗尽微通道壁上的电荷并产生耗尽电荷（壁电荷）。此外，据报道，增益下降不仅发生在电子倍增的激活通道中，也发生在周围的通道中。增益下降空间扩展的一种机制被认为是激活通道中的壁电荷改变了周围通道中的电场。阿纳克假设壁电荷是均匀线电荷；增益下降的空间范围应与壁电荷的数量成正比。我们认为壁电荷在通道中朝着出口呈指数增加。在本研究中，考虑壁电荷的分布计算了壁电荷产生的电场。壁电荷产生的横向电场预计会干扰通道出口附近的电子轨迹，并减少每次碰撞发射的二次电子数量（每次碰撞的增益），从而导致增益下降。对于存在3×10 V/m横向电场时增益显著下降的位置，计算得出每次碰撞的增益下降了22%。在我们的模型中，当距激活通道的距离超过50μm时，增益下降的空间范围与壁电荷的平方根成正比扩展。
