  We consider a space-time variational formulation of the second-order wave
equation, where integration by parts is also applied with respect to the time
variable. Conforming tensor-product finite element discretisations with
piecewise polynomials of this space-time variational formulation require a CFL
condition to ensure stability. To overcome this restriction in the case of
piecewise multilinear, continuous ansatz and test functions, a stabilisation is
well-known, which leads to an unconditionally stable space-time finite element
method. In this work, we generalise this stabilisation idea from the
lowest-order case to the higher-order case, i.e. to an arbitrary polynomial
degree. We give numerical examples for a one-dimensional spatial domain, where
the unconditional stability and optimal convergence rates in space-time norms
are illustrated.
