Radiation Damage of Graphite Surface, Used in First-Wall and Divertor of Tokamaks, Irradiated by Hydrogen and Argon in Plasma Focus Device

Graphite samples, used in first-wall and divertor of nuclear fusion reactors like tokamaks, were irradiated using hydrogen and argon ions produced in an MTPF-2 plasma focus device in 20 shots to study radiation damages. Ion energy spectra are
$dN_{\text {H}}\left ({E_{\text {H}} }\right)/ dE_{\text {H}}\approx E_{\text {H}}^{-2.8}$
with a minimum energy of 120 keV to a maximum of 1 MeV for hydrogen ions and
${dN_{\text {Ar}}\left ({E_{\text {Ar}} }\right)} / {dE_{\text {Ar}}}\approx E_{\text {Ar}}^{-3.5}$
with a minimum energy of 200 keV and a maximum energy of 2 MeV for argon ions. Based on the results of the SRIM code, the maximum destruction of hydrogen ions is at a depth of 900 nm, and a rate of 0.025 DPA/shot and highest hydrogen density is 0.5% at 920 nm. Conversely, the highest degradation of argon ions is at a depth of 120 nm and 0.23 DPA/shot, and the highest density of argon ions at a depth of 200 nm is 0.07%. Different maximum degradation locations and the maximum density of argon ions are due to their heavy mass compared to hydrogen. SEM micrographs show holes with high population density and some sublimated areas on hydrogen-irradiated surfaces. The predominant phenomenon due to argon ion irradiation is physical sputtering, leading to cavities with a depth of several micrometers. Based on the X-ray diffraction (XRD) spectrum, the location and intensity of peaks are changed, and irradiation reduces graphitization and increases the size of the graphite crystal.