| 摘要 |
PURPOSE:To prevent dielectric breakdown due to application of high acceleration voltage by cooling a gas in a cooling device and introducing the cooled gas into an ionization chamber and simultaneously restricting the amount of the gas. CONSTITUTION:A He gas introduced from an introducing part 28 is cooled by liquid He in a heat exchanger 25, and it passes through an insulating tube 20 and via an orifice 23 and flows in an ionization chamber 3. The He gas is cooled by liquid He in a Dewar container 2. Hence, the gas is densified so as to obtain high insulating withstand voltage.
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