Hollow cathode effect

The hollow cathode effect allows electrical conduction at a lower voltage or with more current in a cold-cathode gas-discharge lamp when the cathode is a conductive tube open at one end than a similar lamp with a flat cathode.^[1] The hollow cathode effect was recognized by Friedrich Paschen in 1916.^[2]

In a hollow cathode, the electron emitting surface is in the inside of the tube. Several processes contribute to enhanced performance of a hollow cathode:

• The pendulum effect, where an electron oscillates back and forth in the tube, creating secondary electrons along the way
• The photoionization effect, where photons emitted in the tube cause further ionization
• Stepwise ionization^[1]
• Sputtering^[3][4]

The hollow cathode effect is utilized in the electrodes for neon signs, in hollow-cathode lamps, and more.