56
4 Responses of Plasma-Facing Surface to Power Load Given by Radiation …
Wavelength/nm
Photon intensity/Arb.
unit
Wavelength/nm
Photon intensity/Arb. unit
Wavelength shi (Δ λ /λ D )/ %
a
b
Fig. 4.8 a Emission spectra observed in front of W target exposed to deuterium plasma. The Balmer
series emission (Dα, Dβ, Dγ, and Dδ), D 2 band spectrum, and the spectrum from the impurities
were observed [14]. b Changes of Dα spectra emitted from reflected atoms with incident angle
under 20 keV D + injection on Mo [15]
4.3.2 Physical Sputtering
Early PMI studies focused on sputtering of candidate PFM. Since plasma temperature or ion energy in the plasma was not so high to sputter plasma-facing materials,
sputtering studies were mainly done using high-energy ion beams concentrating to
understand the physics of sputtering. Nevertheless, plasma confinement (temperature and density) was very poor, mostly caused by the desorption of water vapor and
hydrocarbons on PFS. Energetic hydrogen could enhance the desorption and reduction of surface oxide. Therefore, in the early stage of plasma confinement studies,
significant effort was put to remove oxygen included in the plasma, which is discussed
in this chapter in detail.
Owing to extensive studies, physics of the sputtering is well understood. Except
for very low energy region, the binary collision model fits well with the experimental
observations, and accordingly simulation codes, such as SRIM [18] and A-CAT [19],
are developed and widely used to obtain the dependence of incident energy and angle
of primary ion, angular distributions, and energy distributions of sputtered ions and
neutrals.
4 Responses of Plasma-Facing Surface to Power Load Given by Radiation …
Wavelength/nm
Photon intensity/Arb.
unit
Wavelength/nm
Photon intensity/Arb. unit
Wavelength shi (Δ λ /λ D )/ %
a
b
Fig. 4.8 a Emission spectra observed in front of W target exposed to deuterium plasma. The Balmer
series emission (Dα, Dβ, Dγ, and Dδ), D 2 band spectrum, and the spectrum from the impurities
were observed [14]. b Changes of Dα spectra emitted from reflected atoms with incident angle
under 20 keV D + injection on Mo [15]
4.3.2 Physical Sputtering
Early PMI studies focused on sputtering of candidate PFM. Since plasma temperature or ion energy in the plasma was not so high to sputter plasma-facing materials,
sputtering studies were mainly done using high-energy ion beams concentrating to
understand the physics of sputtering. Nevertheless, plasma confinement (temperature and density) was very poor, mostly caused by the desorption of water vapor and
hydrocarbons on PFS. Energetic hydrogen could enhance the desorption and reduction of surface oxide. Therefore, in the early stage of plasma confinement studies,
significant effort was put to remove oxygen included in the plasma, which is discussed
in this chapter in detail.
Owing to extensive studies, physics of the sputtering is well understood. Except
for very low energy region, the binary collision model fits well with the experimental
observations, and accordingly simulation codes, such as SRIM [18] and A-CAT [19],
are developed and widely used to obtain the dependence of incident energy and angle
of primary ion, angular distributions, and energy distributions of sputtered ions and
neutrals.