Measurement and simulation of small cryogenic neon pellet Ne-I 640 nm photon efficiency during ablation in DIII-D plasma

E. M. Hollmann, N. Naitlho, S. Yuan, R. Samulyak, P. Parks, D. Shiraki, J. Herfindal, C. Marini

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3 Scopus citations

Abstract

Small (∼1 mm) neon pellet fragments are fired into DIII-D H-mode plasmas, and resulting trajectory-averaged photon efficiencies (neutral neon ionization events for every photon emitted) of S / X B ≈ 85 are estimated for Ne-I 640 nm by dividing the estimated initial pellet fragment mass by the measured number of emitted Ne-I photons. The experiments are modeled by running the Lagrangian particle (LP) fluid/magneto-hydrodynamic pellet code to estimate axial ablation plume neon density profiles and temperature profiles at each pellet position. These solutions are then fed into the PrismSPECT collisional-radiative code, which calculates resulting neon charge states and photon emission rates, giving a profile-average of S / X B ≈ 109. The burnthrough plasma minor radius predicted by LP (ρ ≈ 0.63) is reasonably close to the experimental observation ρ ≈ 0.6. The modeling indicates that local S/XB is not constant along the pellet trajectory but tends to increase with increasing ablation rate. Non-equilibrium kinetics are predicted to be very important, while line trapping is predicted to be relatively unimportant (for Ne-I 640 nm S/XB).

Original languageEnglish
Article number092508
JournalPhysics of Plasmas
Volume29
Issue number9
DOIs
StatePublished - Sep 1 2022

Funding

This work was supported in part by the U.S. Department of Energy under Nos. DE-FG02-07ER54917, DE-FC02-04ER54698, DE-AC02-09CH11466, DE-AC05-00OR22725, DE-AC52-07NA27344, DE-FG02-04ER54744, and DE-AC05-06OR23100 and the SciDAC Center for Tokamak Transient Simulations. Diagnostic support from T. O’Gorman is gratefully acknowledged. Permission to use PrismSPECT from I. Golovkin is gratefully acknowledged. The originating developer of ADAS is the JET Joint Undertaking.

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