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For the quadratic helicity χ(2) we present a generalization of the Arnol’d inequality which relates the magnetic energy to the quadratic helicity, which poses a lower bound. We then introduce the quadratic helicity density using the classical magnetic helicity density and its derivatives along magnetic ﬁeld lines. For practical purposes we also compute the ﬂow of the quadratic helicity and show that for an α2-dynamo setting it coincides with the ﬂow of the square of the classical helicity. We then show how the quadratic helicity can be extended to obtain an invariant even under compressible deformations. Finally, we conclude with the numerical computation of χ(2) which show cases the practical usage of this higher order topological invariant.