Vacuum discharge

Japanese: 真空放電 - しんくうほうでん（英語表記）vacuum discharge

A discharge that occurs through a gas at extremely low pressure. When a voltage of several thousand volts is applied with the electrodes at a distance of about 10 cm, a ribbon-like spark discharge first occurs at a pressure of several tens of Torr. The minimum voltage required to cause a spark discharge (spark voltage) is determined as a function of the product of the gas pressure and the distance between the electrodes, if the electric field is uniform and the temperature is constant (→Paschen's Law). In a Geissler tube with a pressure of a few Torr, the discharge spreads to the full distance between the electrodes, and becomes a glow discharge. At this time, a positive column with a beautiful color specific to the gas is noticeable, and stripes also appear. This phenomenon is familiar from neon signs and mercury lamps. When the pressure falls below 0.1 Torr, the color gradually fades and the dark area at the cathode spreads (such a vacuum discharge tube is called a Crookes tube), and when it reaches 0.01 Torr, fluorescent light appears on the inner wall of the glass tube. If the degree of vacuum is increased further, the discharge disappears. Research into vacuum discharges played an important role in the birth of modern physics.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

圧力のきわめて低い気体を通じて起る放電。電極間の距離が約 10cmのとき，数千Vの電圧をかけておくと，圧力が数十 Torrで紐状の火花放電がまず起る。火花放電を起す最小の電圧 (火花電圧) は，電場が一様で温度が一定なら，気体の圧力と電極間距離との積の関数として定まる (→パッシェンの法則 ) 。圧力が数 Torr程度のガイスラー管では，放電は電極間いっぱいに広がり，グロー放電となる。このとき，気体に特有の美しい色を帯びた陽光柱が目立ち，縞模様も現れる。この現象はネオンサインや水銀灯としてなじみ深い。圧力が 0.1Torr以下になると色がだんだん薄くなって陰極暗部が広がり (このような真空放電管をクルックス管という) ，0.01Torrに達すると，ガラス管の内壁にケイ光が現れる。真空度をさらに上げると，放電は消えてしまう。真空放電の研究は，近代物理学の誕生に重要な役割を果した。

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