Belikov, R.

Khiscshenko, K.

Krasiuk, I.

Rienecker, T.

Rosmej, O.

Schönlein, A.

Stuchebryukovr, I.

Tomut, M.

GSI Repository

  * Work supported by EuCARD2, grant no. 312453 #  m.tomut@gsi.de Investigation of high power laser -induced spallation phenomena in target and collimator materials for next generation accelerators*   M. Tomut1,2,#,  I. Krasiuk3, T. Rienecker4, O. Rosmej1,I. Stuchebryukovr5, A. Schönlein1, K. Khi-schenko3, R. Belikov6  1GSI, Darmstadt, Germany; 2NIMP, Bucharest, Romania;3Joint Institute for High Temperatures, RAS; 4Goethe-Universität Frankfurt, Germany;5Prokhorov General physics Institute, RAS; 6Moscow Institute for Physics and Tech-nology, Moscow, RussiaThe design of new high power accelerator facilities at FAIR, HiLumi LHC and FCC needs advanced solutions for beam intercepting devices such as production targets, collimators, beam windows, absorbers and dumps. The interaction of high energy, high intensity particle beams with solids induces shock waves, phase and density changes, nano-structuring and spallation. In order to un-derstand  the failure mode and  to predict component life-times, a concerted effort on studying the behavior of tra-ditional and novel material in conditions similar to the operating environment is going on in large collaborations projects such as EuCARD2. Both radiation hardness for high flux beam exposure and dynamic mechanical re-sponse during beam impact are investigated for traditional materials like graphite, and for novel composite materials purposely developed for high energy particle beams ap-plications.   Figure 1: Sketch of the laser – induces spallation experi-ment on thick targets (D is the shock-wave front velocity and wsp and hsp are, respectively, the velocity and thick-ness of spallation plate) [1].  Within the experiment P089, investigations of spallation phenomena in different graphite grades, copper-diamond and molybdenum-graphite composites were conducted at the Z6 experimental area, using shock waves induced by the PHELIX laser at GSI. A pulsed laser beam with a wavelength of 530 nm, 1.4 ns pulse duration and energies of 120 J was focused to a spot size of 1.3 mm on the tar-get. Typical beam intensities  were about  0.6 ´ 1013 W cm–2. For inferring the spall strength s* and strain rate	εሶ we measured the depth of spallation groove h after laser beam impact on the target. The s* and 	εሶ values were cal-culated using a numerical code based on hydrodynamics equations [2]. It was assumed that the ablation pressure pulse on the front target surface has the same shape as the laser pulse. The spallation strength was considered to be the minimum pressure modulus in the spallation plane [1]. Figure 2 shows optical microscope images of ablation crater on the laser facing side of a thick isotropic graphite target and of the rear spallation crater on the same target.    Figure 2: Optical micrographs of (a): ablation spot on the front side and (b): spallation crater on the rear face of a thick graphite target exposed to laser beam.  Raman spectroscopy has been used for first investigations of microstructural transformations induced by the laser shock wave in the sample. As shown in figure 3, the ma-terial in the spallation crater shows a higher degree of graphitization than the initial structure, indicating that the material temperature reached values above 2000 ºC. Fu-ture detailed Raman spectroscopy mappings of the craters will be performed for investigating the possible formation of high pressure carbon phases like rhombohedral graph-ite and diamond. Spallation strength values between 1 and 2 GPa were found for isotropic graphite experiencing strain rates between 106 and 107 s-1.   Figure 3: Raman spectra of graphite target after laser beam impact in the ablation crater (blue) and spallation crater (green).  [1] S.A. Abrosimov et  al., Quantum Electronics 44 (6) (2014) 530 – 534.  [2] D. Batani, V.I. Vovchenko, G.I. Kanel, et al. Dokl. Ross. Akad. Nauk, 389 (3), 328 (2003). a b GSI SCIENTIFIC REPORT 2014 APPA-MML-PP-05DOI:10.15120/GR-2015-1-APPA-MML-PP-05 279

Investigation of high power laser-induced spallation phenomena in target and collimator materials for next generation accelerators

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Investigation of high power laser-induced spallation phenomena in target and collimator materials for next generation accelerators

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