Hartley, N.J.Grenzer, J.Lu, W.Huang, L.G.Inubushi, Y.Kamimura, N.Katagiri, KKodama, R.Kon, A.Lipp, V.Makita, M.Rode, Andrei2020-10-261574-1818http://hdl.handle.net/1885/213060We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) X-ray free electron laser (XFEL) facility, using an X-ray pump, X-ray probe scheme to observe ultrafast changes in the structure of heated graphite. The 9.8 keV XFEL beam was focused to give an intensity on the order of  ∼ 1019 W/cm2, and the evolution of the diffraction pattern observed up to delays of 300 fs. The interplanar diffraction peaks weaken significantly within 10s of femtoseconds, but in-plane diffraction orders i.e. those with Miller Index (hk0), persist up to 300 fs, with the observed signal increasing. We interpret this as nonthermal damage through the breaking of interplanar bonds, which at longer timescales leads to ablation by removal of intact graphite sheets. Post-experiment examination of the graphite samples shows damage which is comparable in size to the range of the excited photoelectrons. These results highlight the challenges of accurately modelling X-ray driven heating, as it becomes a routine approach to generating high energy density states.The XFEL experiments were performed at the BL3 of SACLA with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal nos. 2017B8075 and 2018A8056). We would like to thank all staff at SACLA for their technical support on the beamtimes, Drs. L. Bischoff, P. Chekhonin and G. Hlawacek for their help in obtaining the microscopy images. N.J.H. was supported in part by JSPS KAKENHI Grant no. 16K17846. N.J.H., K.R., A.K.S. and D.K. were supported by the Helmholtz Association under VH-NG-1141. Partial financial support from the Czech Ministry of Education, Youth and Sports (Grants no. LTT17015 and No. LM2015083) is acknowledged by N.M. A.V.R. acknowledges support Australian Government through the Australian Research Council’s Discovery Project DP170100131. N.O. was supported in part by JSPS Japan-Australia Open Partnership Joint Research Project and MEXT Q-LEAP Project.application/pdfen-AU© 2019 The Authors.http://creativecommons.org/licenses/BY-NC-ND/4.0/201910.1016/j.hedp.2019.05.0022020-07-06CC BY-NC-ND license