Leak detection Tesla coil

The distance between electrodes in a discharge tube is fixed, as opposed to the distance between the Tesla coil and ground (this distance can vary constantly from as little as several centimeters to many meters during leak detection). 

If a leak has been located with a Tesla coil, you may find a (very) small white dot where the spark went through the glass. This dot may be hard to relocate, so it is best to clearly mark the exact location of the hole with a grease pencil or any other marker that can write on glass. Other leak detection techniques do not leave any mark, and some marking is essential. 

Vacuum Leak Detection with a Tesla Coil, Journal of Chemical Education, 68, 526-528 (1991). 

Just as in ordinary vacuum technology the primary instrument for leak detection in a glass ultrahigh vacuum system is the Tesla coil. Care is necessary in sparking graded seals. In the vicinity of field emission sources, the induction coil should not be employed since the emitter may be destroyed by arcing. 

Tesla coll A device for producing a high-frequency high-voltage current. It consists of a transformer with a high turns ratio, the primary circuit of which includes a spark gap and a fixed capacitor the secondary circuit is tuned by means of a variable capacitor to resonate with the primary. It was devised by Nikola Tesla. Tesla coils are commonly used to excite luminous discharges in glass vacuum apparatus, in order to detect leaks. 

Leak detection in vacuum systems is sometime accomplished using a Tesla coil that ionizes gases that produce a characteristic glow under low pressure. Residual air produces a blue discharge. Handheld Tesla coils operate at 10-50 kV and present a significant electrocution hazard. 

Electrical hazards of one kind or another are present in all labs. Using UL-certified equipment, not overriding safety measures, and using extra vigilance around sources of water usually prevents electrical accidents. Extremely high-voltage sources must be used with extra care. (A Tesla coil used to detect leaks in vacuum lines can have a voltage of 10-40 kV )... 

If there is a pinhole in the glass which is sufficiently large, it will attract the discharge from the Telsa coil in the form of a long blue spark which ends on the glass surface at the pinhole in a sharp, blue-white point fortunately, leaks too small to be detected by the Tesla discharge are extremely rare. 

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