  When combining the numerical concept of variational discretization and
semi-smooth Newton methods for the numerical solution of pde constrained
optimization with control constraints, special emphasis has to be taken on the
implementation, convergence and globalization of the numerical algorithm. In
the present work we address all these issues. In particular we prove fast local
convergence of the algorithm and propose two different globalization strategies
which are applicable in many practically relevant mathematical settings. We
illustrate our analytical and algorithmical findings by numerical experiments.
