Electrical discharge in low-pressure krypton

Shown here is an experimental low-pressure krypton discharge tube (T4) used for plasma studies. The lamp was made using components taken from standard compact fluorescent lamp production. Here the lamp runs at around 0.17 A on an HF 13 W fluorescent tube driver and its discharge shows a relatively constricted profile due to a fill pressure of 13.3 mbar combined with a low gas thermal conductivity which result in a thermal contraction of the plasma channel. There is a diffuse striated profile visible in the middle, a phenomenon caused by a mild modulation of the electron energy in the discharge.