Problems related to the definition of a target plasma for fast neutral injection into a mirror machine are discussed. Plasma parameters and magnetic configuration are first examined in the light of instability theory; the study is concerned with: the required neutral beam current; the beam energy modulation connected to the evolution of the ion distribution function; the evolution of the plasma geometry associated with the vacuum requirements; and the deduction of suitable plasma parameters. This ensemble leads to the conclusions that an experiment to study the stability of mirror machines in a quasi-steady state relevant to reactor regimes is possible starting from a reasonable extension of present laboratory plasmas.
Assessment of the plasma start-up in Wendelstein 7-X with neutral beam injection