Space charge characterisation. The state of art and further needs

Due to the lack of physical background it is still a question to know if space charge is the cause or the consequence of breakdown and ageing phenomena. However, an elegant method based on Raman spectroscopy and infrared spectroscopy has shown (1978) the directions to follow and ingredients were there for explaining these phenomena from dielectric processes. Several space charge characterisation techniques have been developed for various applications. Optical methods and methods using electron beams and electron spectrometers have brought a significant contribution. Particularly, they have allowed one to understand that the characterisation requires more that the investigation of the space charge distribution. It requires one to determine the maximum energy that a charged dielectric can store before the occurrence of any energy relaxation process. This work will first emphasise the importance of well-defined materials for verifying theoretical results. The control of the various space charge steps: injection, propagation and relaxation, is an experimental key point