This is a doctorate level lecture on the physics of accretion discs driving
magnetically self-confined jets, usually referred to in the literature as disc
winds. I will first review the governing magnetohydrodynamic equations and then
discuss their physical content. At that level, necessary conditions to drive
jets from keplerian accretion discs can already be derived. These conditions
are validated with self-similar calculations of accretion-ejection structures.
In a second part, I will critically discuss the biases introduced when using
self-similarity as well as some other questions such as: Are these systems
really unstable? Can a standard accretion disc provide the conditions to launch
jets in its innermost parts? What is the difference between X-winds and
disc-winds? Finally, the magnetic interaction between a protostar and its
circumstellar disc will be discussed with a focus on stellar spin down.Comment: 25 pages, 11 figures to be published in Lecture Notes in Physics,
"Jets from Young Stars: Models and Constraints", J. Ferreira, C. Dougados and
E. Whelan (eds), Springer Verla
