The Tesla Coil is an electrical circuit invented by Nikola Tesla in 1891 that is used to produce high-voltage, low-current electricity. They are best known for brilliant sparking discharges caused by ionization of the surrounding air by the strong electric field, which allows it to conduct electricity. Ionized gases are also known as plasma , the fourth fundamental state of matter.
Here, a syringe is being used to create a near-vacuum environment that allows the electrons to travel more easily and further than under standard atmospheric conditions. This allows the plasma to persist for much longer than normal.
Source: https://youtu.be/WM25pUsrODk (ElectroBOOM)