The emission rates of CH, CD and C₂spectral bands and a re-evaluation of the chemical sputtering yield of the JT-60U carbon divertor plates

Abstract

The CH photon emission rate, defined as the number of photons over a dissociation and/or ionization event of CH4, has been determined from the ratio of the measured emission intensity of the CH spectral band over the CH4 injection rate into the divertor plasma of JT-60U. Similar photon emission rates of CD for CD4, and CH and C2 for C2H4 and C2H6, have also been determined. Interestingly, the C2 spectral band intensity is found to increase during the CH4 and CD4 injection, suggesting that the injected CH4 reacts with the carbon divertor plates to form heavier hydrocarbons. Previously published chemical sputtering yields (Nakano et al 2002 Nucl. Fusion 42 689) evaluated with the photon efficiencies determined in PISCES-A (Pospieszczyk et al 1989 UCLA Report UCLA-PPG-1251) have been re-evaluated using the measured emission rates. By applying the photon emission data found here and taking into account the C2 emission process originating from CH4, the re-evaluated total chemical sputtering yield becomes lower (∼7%) compared to the original in (Nakano et al 2002 Nucl. Fusion 42 689) (∼8%), and the dependence on the incident ion flux and energy becomes weaker.

Impurity sources and fluxes in W7-X: from the plasma-facing components to the edge layer

“…The accompanying emission of the Swan band of C2 representing heavier hydrocarbon radicals was also measured during CH4 injection in other fusion devices [4]. The potential explanation is: a fraction of the injected CH4 is locally deposited and immediately re-eroded in the formation of heavier hydrocarbon [4], or the CH4 reacts with carbon divertor plate to form heavier hydrocarbons, such as C2H4 [16]. Fig.…”

Total Cross Sections for Electron and Positron Scattering on Molecules: In Search of the Dispersion Relation

“…Cross sections for electron scattering are the input data in modeling and diagnostics of industrial plasma, gas discharge [1], thermonuclear plasma [2,3], biological media [4,5], and atmospheric processes, including extra-solar planets [6]. Such modeling requires the knowledge of the total and partial (elastic, ionization, dissociation, and electronic, vibrational, rotational excitation) cross sections in a broad energy range.…”

“…† The Born direct scattering amplitude f B (E = ∞, θ = 0) is taken as the square root of the differential cross sections at zero angle and at sufficiently high energies (see Figure 8). ‡ The integral over TCS in the dispersion relation, Equation (2), is taken within limits 10 −6 eV to 10 6 eV (this range assures the independence of the result from the limits of the integration); the uncertainty of the integral is some 10%. § For dipole polarizabilities we give experimental values (see NIST database [93]).…”