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Title: Heating and ablation of high-Z cryogenic pellets in high temperature plasmas

Abstract

A kinetic model is developed here to determine the power deposition from energetic electrons into the neutral gas shield of an ablating high-Z pellet. For high-Z, the velocity distribution of the hot electrons is nearly isotropic, and we use this feature to develop solutions to the kinetic equation. In contrast to pre-existing models, we consider the effect of gyro-motion as well as elastic scattering of the hot electrons. Two limits are considered: when the gyro-frequency is much greater than the elastic collision frequency, the hot electrons diffuse longitudinally along the field lines as they slow down; but if the gyro-frequency is much less than the elastic collision frequency, the hot electrons diffuse radially. In both limits, it is possible to express the kinetic equation describing the hot electrons independently of the gas density profile, and therefore, the power deposition model is universal in this respect. The emphasis on elastic scattering yields an ablation rate which scales as Z-7/6 which is different than Z-2/3 shown in Sergeev et al (2006 Plasma Phys. Rep. 32 5). It is also demonstrated that the sheath potential required to maintain ambipolarity in the cloud scales as Z-1/3. Fluid simulations yield ablation rates that scale withmore » the four-thirds power of the pellet radius in agreement with [2].« less

Authors:
 [1];  [1]
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  1. Univ. of Texas, Austin, TX (United States)
Publication Date:
Research Org.:
Univ. of Texas, Austin, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1595275
Grant/Contract Number:  
SC0016283; FG02-04ER54742
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 9; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Fontanilla, Adrian K., and Breizman, Boris N. Heating and ablation of high-Z cryogenic pellets in high temperature plasmas. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab2bd6.
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Fontanilla, Adrian K., & Breizman, Boris N. Heating and ablation of high-Z cryogenic pellets in high temperature plasmas. United States. https://doi.org/10.1088/1741-4326/ab2bd6
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Fontanilla, Adrian K., and Breizman, Boris N. Wed . "Heating and ablation of high-Z cryogenic pellets in high temperature plasmas". United States. https://doi.org/10.1088/1741-4326/ab2bd6. https://www.osti.gov/servlets/purl/1595275.
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@article{osti_1595275,
title = {Heating and ablation of high-Z cryogenic pellets in high temperature plasmas},
author = {Fontanilla, Adrian K. and Breizman, Boris N.},
abstractNote = {A kinetic model is developed here to determine the power deposition from energetic electrons into the neutral gas shield of an ablating high-Z pellet. For high-Z, the velocity distribution of the hot electrons is nearly isotropic, and we use this feature to develop solutions to the kinetic equation. In contrast to pre-existing models, we consider the effect of gyro-motion as well as elastic scattering of the hot electrons. Two limits are considered: when the gyro-frequency is much greater than the elastic collision frequency, the hot electrons diffuse longitudinally along the field lines as they slow down; but if the gyro-frequency is much less than the elastic collision frequency, the hot electrons diffuse radially. In both limits, it is possible to express the kinetic equation describing the hot electrons independently of the gas density profile, and therefore, the power deposition model is universal in this respect. The emphasis on elastic scattering yields an ablation rate which scales as Z-7/6 which is different than Z-2/3 shown in Sergeev et al (2006 Plasma Phys. Rep. 32 5). It is also demonstrated that the sheath potential required to maintain ambipolarity in the cloud scales as Z-1/3. Fluid simulations yield ablation rates that scale with the four-thirds power of the pellet radius in agreement with [2].},
doi = {10.1088/1741-4326/ab2bd6},
journal = {Nuclear Fusion},
number = 9,
volume = 59,
place = {United States},
year = {Wed Jul 31 00:00:00 EDT 2019},
month = {Wed Jul 31 00:00:00 EDT 2019}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1088/1741-4326/ab2bd6
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Cited by: 2 works
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Figures / Tables:

FIG. 1 FIG. 1: Heating rate per atom as a function of normalized line-density where the strong magnetic field/slab model using Eq. (27) is shown as a dashed black line, and the spherical model using Eq. (33) is shown in solid. Since the shape of the curves are universal, the plot ismore » a comparison of ∫ f dv2 in the two models.« less
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Works referenced in this record:

Effect of transonic flow in the ablation cloud on the lifetime of a solid hydrogen pellet in a plasma
journal, January 1978

  • Parks, P. B.; Turnbull, R. J.
  • Physics of Fluids, Vol. 21, Issue 10
  • DOI: 10.1063/1.862088

Bremsformel f�r Elektronen relativistischer Geschwindigkeit
journal, May 1932

Two-dimensional simulation of pellet ablation with atomic processes
journal, August 2004

  • Ishizaki, R.; Parks, P. B.; Nakajima, N.
  • Physics of Plasmas, Vol. 11, Issue 8
  • DOI: 10.1063/1.1769376

Analysis of low Z a impurity pellet ablation for fusion diagnostic studies
journal, March 1988

Thermal quench mitigation and current quench control by injection of mixed species shattered pellets in DIII-D
journal, June 2016

  • Shiraki, D.; Commaux, N.; Baylor, L. R.
  • Physics of Plasmas, Vol. 23, Issue 6
  • DOI: 10.1063/1.4954389

Electrostatic shielding of vaporizing surfaces exposed to hot plasmas
journal, December 1996

Ionization–recombination processes and ablation cloud structure for a carbon pellet
journal, January 2004

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