Calculation of the radiative cooling coefficient for molybdenum in a low density plasma

Abstract

The radiative cooling coefficient for molybdenum (Z=42) in a low density (ne ≲ 1015 cm-3) plasma is calculated. First, the molybdenum charge state distribution (CSD) is computed using the best available atomic physics data for ground state recombination and ionization, including the rates of excitation-autoionization for Mo6+ to Mo13+ and Mo23+ to Mo32+. The emissivities of Mo4+ to Mo41+ are then found using a collisional-radiative model such that the contributions from metastable levels to an ion's emissivity are taken into account. The CSD and the radiative emissivity for all molybdenum ions are combined to yield the total radiative cooling coefficient for molybdenum in a low density plasma. A radiative loss coefficient over 2 orders of magnitude smaller than that predicted by an `average ion' model for temperatures relevant to tokamak divertor and scrape-off layer plasmas (Te ≲ 50 eV) is found. The cooling coefficient of the present work varies from a factor of 2 smaller to a factor of 2 larger than that predicted by the `average ion' model for all other plasma temperatures. The coefficient calculated in the present work is benchmarked against the measured bolometric loss profile from a molybdenum dominated shot in the Frascati Tokamak Upgrade (FTU)

Operation of Alcator C-Mod with high-Z plasma facing components and implications

“…The plasma densities for molybdenum and iron were inferred using the measured line brightnesses, Thomson scattering electron density and temperature profiles, the MIST impurity transport code, 26 transport coefficients, 27 and cooling curves. [28][29][30] Visible measurements were made with a 0.25 m focal length instrument having a spectral resolution of ϳ0.25 nm. Its primary purpose in this study was for monitoring of fully striped boron and fluorine densities near the top of the H-mode pedestal ͑6 mm inside the separatrix͒ by simultaneous measurement of the B V ͑494.4 nm͒ and F IX ͑474 nm͒ lines.…”

X-ray observations of 2l-nl' transitions and configuration-interaction effects from Kr, Mo, Nb and Zr in near neon-like charge states from tokamak plasmas

“…Collisional radiative modeling of line intensities from neon-, fluorine-, sodium-and magnesiumlike ionization states has demonstrated the importance of excitation-autoionization in overall charge state balance in tokamak plasmas [22]. Rates for this process, in conjunction with the latest dielectronic recombination rates [23], have led to a reassessment of the importance of molybdenum radiation in energy balance [24] in tokamak plasmas. Most of the work that has been done in the past has been limited to 3 − 3, 2 − 3 and 2 − 4 transitions in the Ne-I iso-electronic sequence and adjacent charge states.…”

Formation and Stability of Impurity "snakes" in Tokamak Plasmas

“…The C-Mod snake formation can be described as a three step process corresponding to the numbers in 17 m −3 and a peaked impurity concentration n M o /n e 6.3 × 10 −4 ; the latter calculation uses a Mo cooling factor L M o 7 × 10 −32 W·m 3 [9]. Such an impurity density can increase the core Z ef f , as well as the collision frequency ν ei and resistivity η, by more than 50% over the molybdenum-free state.…”