Page 4 - Outer Divertor Damage Characterization from Deuterium Plasma Bombardment in Graphene-Coated Tungsten

where
OUTER DIVERTOR DAMAGE CHARACTERIZATION FROM DEUTERIUM PLASMA BOMBARDMENT · NAVARRO et al. 545
Fig. 3. (a) Average ion current density measured by energy analyzers for shot 107534. (b) The integrated current profile shows ion average energy changes over the discharge duration of the deuterium plasma at different time intervals during shot 107534. (c) Ion temperature distributions along different times of the plasma duration. The added shoulders on the distribution functions suggest a bi-Maxwellian distribution due to a difference in parallel and perpendicular temperature profiles. The large fluctuation in the average ion temperature across the different time steps corresponds to initial startup, heating, and crashing of the plasma.
The fluence data were calculated from the average current density data. Using the following equation, one can estimate the fluence Φ of the deuterium to the sample surface:
With the information gathered from the current profile, the samples were determined to have received a deuterium fluence of 1.19 ± 0.54 × 1018 D+/cm2 and an average deuterium ion energy of 68 ± 36 eV.
III.B. Raman Spectroscopy Results for Deuterium Exposures
Raman spectroscopy is sensitive to graphene defects. These discharges involve the introduction of numerous impurities onto the sample surface as well as some damage to the graphene. The exposures introduced defects into the graphene lattice on the coated sample, as summarized in the Raman spectrum in Fig. 4.
Φ 1⁄4
Jt Ze
 ðnumber of shotsÞ ;
J = current density
t = discharge duration
Ze = effective charge of deuterium (Z = 1).
FUSION SCIENCE AND TECHNOLOGY · VOLUME 75 · AUGUST 2019