Top: calculation of symmetric Si 111 and Si 333 Bragg reflections at 10 keV and 30 keV, respectively. At these energies the Bragg angle α is 11.403°. Bottom: DuMond diagram of a Si 111–Si 311 pair reflecting at 10 keV. Besides the fundamentals the higher harmonics Si 333 and Si 933 at 30 keV are drawn. The outlined circles mark the intersection areas of the fundamentals and the higher harmonics whereas the gray area marks the PETRA beam divergence in the vertical.