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![[Figure 5]](ye5057fig5mag.jpg)
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Figure 5
Strategies based on (de)tuning the insertion device, i.e. undulator gap, to mitigate radiation-induced effects. (a) Predicted undulator gap in the soft X-ray regime (800 lines mm−1 grating and third undulator harmonic) required to obtain maximum photon flux (100%, optimized undulator gap configuration), 52% flux and 10% flux of the optimized beam. In order to double-check the energy extrapolation beyond 540 and 860 eV, the undulator gap is detuned to obtain 52% of the maximum flux at 650 and 750 eV. The required gap values (black empty circles), 25.06 mm for 650 eV and 26.91 mm for 750 eV, are shifted 0.20 mm and 0.22 mm, respectively, from the optimized undulator gap configuration (orange line, 100% flux) and only deviate ∼5% from the values predicted using this approach (red circles, 25.05 mm and 26.90 mm, respectively). More details about the undulator gap value as a function of energy and photon flux can be found in Section S5 of the supporting information. (b) In the planar Pt | H3PO3 electrolyte system, P K-edge XAS measurements using the U17 DCM show a clear radiation-induced oxidation of the H3P3+O3 electrolyte at high photon fluxes. The highest conversion rate of P3+ to P5+ species is observed with the maximum flux configuration (optimized beam), where the spectral feature at 2152.5 eV attributed to H3P5+O4 dominates over the H3P3+O3 signal at 2150.8 eV (Wibowo, Garcia-Diez, van der Merwe et al., 2023  ). The reduction in the photon flux by detuning the undulator gap minimizes the radiation-induced oxidation until the desired situation at 16% of maximum flux, where the obtained spectrum resembles the one obtained on the 1 M aq. H3P3+O3 reference. |
![[Figure 5]](ye5057fig5.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
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