1958 年 27 巻 7 号 p. 381-384
A Van de Graaff generator for a 300 KV electron microscope has already been reported. However, it was difficult to obtain a stable high voltage of any desirable value.
This inconvenience is eliminated by the use of a new spray device. The effective spray width of the device is made adjustable with a pair of insulated covers which are driven by a servomotor.
If the spray voltage is sufficiently high so that the spray current is in a saturated state, the corona discharge from the spray needle and the spray current are not affected by the fluctuation of spray voltage. The spray current is increased proportionally to the effective spray width and the output high voltage is determined by the effective width. Thus, the output voltage from 50 KV to 400 KV can be covered continuously.
A relative fluctuation of the order of 10-4 has been obtained at 390 KV during 30 seconds by using a smoothing condenser of 0.02 pF in capacity. It is found that the gradual change;in running speed of the belt-driving motor is now the main cause of the voltage fluctuation. The construction of the spray device and some experimental results are described.