We present the Raman microscopy ability to detect and characterize the way hydrogen is bonded with elements that will be used for ITERs plasma facing components. For this purpose we first use hydrogenated amorphous carbon samples, formed subsequently
to plasma-wall interactions (hydrogen implantation, erosion, deposition...) occurring inside tokamaks, to demonstrate how this technique can be used to retrieve useful information. We pay attention in identifying which spectroscopic parameters are sensitive to the local structure (sp 3 /sp 2) and which gives information on the hydrogen content using isothermal and linear temperature ramp studies on reference samples produced by plasma enhanced chemical vapor deposition. We then focus on the possibility to use this fast, non-destructive and non-contact technique to characterize the influence of hydrogen isotope implantation in few nanometers of graphite and beryllium as C is still used in the JT-60 tokamak and Be is used in JET and will be used as plasma-facing component in the future reactor ITER. We also pay attention on implantation in tungsten oxide which may be formed accidently in the machine.
We study the kinetics of the H release from plasma-deposited hydrogenated amorphous carbon films under isothermal heating at 450, 500 and 600 {degree}C for long times up to several days using in situ Raman microscopy. Four Raman parameters are analyz
ed. They allow the identification of different processes such as the carbon network reorganization and the H release from sp3 or sp2 carbon atoms and the corresponding timescales. Carbon reorganization with aromatization and loss of sp3 hybridization occurs first in 100 minutes at 500 {degree}C. The final organization is similar at all investigated temperatures. Full H release from sp3 carbon occurs on a longer timescale of about 10 hours while H release from sp2 carbon atoms is only partial, even after several days. All these processes occur more rapidly with higher initial H content, in agreement with what is known about the stability of these types of films. A quantitative analysis of these kinetics studies gives valuable information about the microscopic processes at the origin of the H release through the determination of activation energies.
We revisit here how Raman spectroscopy can be used to estimate the H content in hard hydrogenated amorphous carbon layers. The H content was varied from 2 at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to 1300 K and was dete
rmined independently using ion beam analysis. We examine the correlation of various Raman parameters and the consistency of their thermal evolution with thermo-desorption results. We identify a weak band at 860 cm-1 attributed to H bonded to C(sp2). We show that the HD/HG parameter (Height ratio between the D and G bands) is quasi-linear in the full range of H content and can thus be used to estimate the H content. Conversely, we show that the m/HG parameter (ratio between the photoluminescence background, m, and the height of the G band), often used to estimate the H content, should be used with care, first because it is sensitive to various photoluminescence quenching processes and second because it is not sensitive to H bonded to C(sp2).
We present a fast and simple way to determine the erosion rate and absorption coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic source based on ex-situ Raman micro-spectroscopy. Results are compared to ellipsometry measu
rement. The method is applied to films eroded at different temperatures. A maximum of the erosion rate is found at ~ 450 {degree}C in agreement with previous results. This technique is suitable for future quantitative studies on the erosion of thin carbonaceous films, especially of interest for plasma wall interactions occurring in thermonuclear fusion devices.
The structure of six tiles extracted from the erosion and deposition zones (thin and thick deposition) of the Tore Supra toroidal pump limiter (TPL) have been analysed in the framework of the DITS campaign using micro-Raman spectroscopy. This post-mo
rtem analysis gives information on both carbon structure and D content. We have found that the carbon structure is most often similar to that of plasma-deposited hard amorphous carbon layers. The role of the surface temperature during the discharge in the D content is investigated: in all locations where the temperature does not reach more than 500{degree}C the D content seems to be roughly uniform with D/D+C approx 20%.
