skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Possible mitigation of tokamak plasma–surface interactions using thermionic divertor plates with inverse sheaths

Abstract

Recent studies demonstrate that when a plasma-facing surface emits a sufficient flux of electrons, it will form an inverse sheath. In this work, we consider a possibility of using thermionic target plates with inverse sheaths as an innovative divertor operating scenario. We derive an electron heat flux boundary condition for inverse sheaths and show that for given power exhaust into a tokamak scrape-off-layer, an inverse sheath leads to a much lower target plasma electron temperature than a conventional sheath. Low enough target plasma temperatures for radiative divertor detachment could therefore be achieved using inverse sheaths instead of the usual need to inject neutral atoms that compromise the core plasma. Other advantages of inverse sheath detachment over conventional sheath operating scenarios include (a) ion impact energies are as low as possible, minimizing sputtering and tritium implantation, (b) surface recombination heat flux is reduced due to ion flux reduction, and (c) arcs are inhibited due to the sign of the surface electric field. This paper outlines the basic properties of inverse sheath detachment and considers the feasibility of implementation. We offer recommendations for future modeling efforts needed to better understand the effects of thermionic emission in tokamaks and whether inverse sheaths presentmore » a viable divertor solution.« less

Authors:
ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
OSTI Identifier:
1623336
Alternate Identifier(s):
OSTI ID: 1632930
Report Number(s):
LLNL-JRNL-797777
Journal ID: ISSN 1070-664X; 999617; TRN: US2106862
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 27; Journal Issue: 4; Conference: 61.Annual Meeting of the APS Division of Plasma Physics, Fort Lauderdale, FL (United States), 21-25 Oct 2019; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Thermionic emission; Tritium; Deuterium; Plasma temperature; Plasma material interactions; Plasma properties and parameters; Tokamaks; Plasma sheaths; Ion sources

Citation Formats

Campanell, M. D. Possible mitigation of tokamak plasma–surface interactions using thermionic divertor plates with inverse sheaths. United States: N. p., 2020. Web. doi:10.1063/1.5139904.
Campanell, M. D. Possible mitigation of tokamak plasma–surface interactions using thermionic divertor plates with inverse sheaths. United States. https://doi.org/10.1063/1.5139904
Campanell, M. D. 2020. "Possible mitigation of tokamak plasma–surface interactions using thermionic divertor plates with inverse sheaths". United States. https://doi.org/10.1063/1.5139904. https://www.osti.gov/servlets/purl/1623336.
@article{osti_1623336,
title = {Possible mitigation of tokamak plasma–surface interactions using thermionic divertor plates with inverse sheaths},
author = {Campanell, M. D.},
abstractNote = {Recent studies demonstrate that when a plasma-facing surface emits a sufficient flux of electrons, it will form an inverse sheath. In this work, we consider a possibility of using thermionic target plates with inverse sheaths as an innovative divertor operating scenario. We derive an electron heat flux boundary condition for inverse sheaths and show that for given power exhaust into a tokamak scrape-off-layer, an inverse sheath leads to a much lower target plasma electron temperature than a conventional sheath. Low enough target plasma temperatures for radiative divertor detachment could therefore be achieved using inverse sheaths instead of the usual need to inject neutral atoms that compromise the core plasma. Other advantages of inverse sheath detachment over conventional sheath operating scenarios include (a) ion impact energies are as low as possible, minimizing sputtering and tritium implantation, (b) surface recombination heat flux is reduced due to ion flux reduction, and (c) arcs are inhibited due to the sign of the surface electric field. This paper outlines the basic properties of inverse sheath detachment and considers the feasibility of implementation. We offer recommendations for future modeling efforts needed to better understand the effects of thermionic emission in tokamaks and whether inverse sheaths present a viable divertor solution.},
doi = {10.1063/1.5139904},
url = {https://www.osti.gov/biblio/1623336}, journal = {Physics of Plasmas},
issn = {1070-664X},
number = 4,
volume = 27,
place = {United States},
year = {Thu Apr 09 00:00:00 EDT 2020},
month = {Thu Apr 09 00:00:00 EDT 2020}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 9 works
Citation information provided by
Web of Science

Save / Share:

Works referenced in this record:

Frontiers in Thermionic Cathode Research
journal, June 2018


Bifurcation phenomena in an emissive plate — simulated divertor plasma system
journal, December 1992


Impact of gyro-motion and sheath acceleration on the flux distribution on rough surfaces
journal, August 2010


The snowflake divertor
journal, November 2015


On thermionic emission from plasma-facing components in tokamak-relevant conditions
journal, July 2017


Thermionic Cooling of the Target Plasma to a Sub-eV Temperature
journal, January 2019


Helical divertor in the large helical device
journal, December 1992


Simulations with current constraints of ELM-induced tungsten melt motion in ASDEX Upgrade
journal, September 2017


On secondary electron emission and its semi-empirical description
journal, November 2014


Effects of an Oblique Magnetic Field on Sheath Formation in the Presence of Electron Emission
journal, January 1994


Are two plasma equilibrium states possible when the emission coefficient exceeds unity?
journal, May 2017


Electron emission in a source-collector sheath system: A kinetic study
journal, October 2014


Attenuation of secondary electron emission from divertor plates due to magnetic field inclination
journal, March 2001


The role of arcing in producing metal impurities in tokamaks
journal, April 1978


Real time, in-situ measurements of secondary electron emission in DITE
journal, December 1990


A review of radiative detachment studies in tokamak advanced magnetic divertor configurations
journal, April 2017


Potential Formation Due to Contact betweenFloated Emissive Electrode and Plasma
journal, July 1991


Study of hot tungsten emissive plate in high heat flux plasma on NAGDIS-I
journal, February 1997


A new experimental classification of divertor detachment in ASDEX Upgrade
journal, November 2013


PIC code for the plasma sheath in large caesiated RF sources for negative hydrogen ions
journal, October 2009


Absence of Debye Sheaths due to Secondary Electron Emission
journal, June 2012


Analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas
journal, August 2017


Transport of negative ions across a double sheath with a virtual cathode
journal, May 2011


Simulations of thermionic suppression during tungsten transient melting experiments
journal, November 2017


Validating heat balance models for tungsten dust in cold dense plasmas
journal, September 2018


Negative plasma potential relative to electron-emitting surfaces
journal, September 2013


Kinetic simulations of the Chodura and Debye sheaths for magnetic fields with grazing incidence
journal, January 2016


Alternative divertor target concepts for next step fusion devices
journal, September 2016


Emission properties of top-layer scandate cathodes prepared by LAD
journal, February 1997


Plasma potential probes for hot plasmas: A review and some news
journal, April 2019


Sheath parameters for non-Debye plasmas: Simulations and arc damage
journal, May 2012


Effects of the plasma‐wall sheath on transport
journal, July 1987

  • Mandrekas, J.; Singer, C. E.; Ruzic, D. N.
  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 5, Issue 4
  • https://doi.org/10.1116/1.574443

A review of the experimental evidence for arcing and sputtering in tokamaks
journal, October 1980


Tungsten erosion by arcs in ASDEX upgrade
journal, August 2011


Plasma-material interactions in current tokamaks and their implications for next step fusion reactors
journal, December 2001


Electron Velocity Distribution at a Sheath Edge in the Presence of Secondary Electron Emission From a Metal Surface
journal, May 2010


Estimation of suppressed erosion by vapor shielding at Be and W walls under transient loads
journal, May 2019


Strongly Emitting Surfaces Unable to Float below Plasma Potential
journal, February 2016


On temperature bifurcation of beryllium and lithium plasma facing components
journal, December 2009


Arcing and its role in PFC erosion and dust production in DIII-D
journal, July 2013


Sheath energy transmission in a collisional plasma with collisionless sheath
journal, October 2015


Plasma–wall transition in an oblique magnetic field
journal, January 1982


Plasma detachment in divertor tokamaks
journal, February 2018


Sheath structure in negative ion sources for fusion (invited)
journal, February 2012


Influence of the inverse sheath on divertor plasma performance in tokamak edge plasma simulations
journal, December 2019


Formation of stable inverse sheath in ion–ion plasma by strong negative ion emission
journal, June 2018


Suppression of Metallic Impurities by Electron Injection in a Tokamak
journal, February 1979


Modelling of dynamics and transport of carbon dust particles in tokamaks
journal, February 2007


Thermionic Energy Converter System Using Heat Flux in Divertor Region
journal, January 2012


Plasma sheath in the presences of non-Maxwellian energetic electrons and secondary emission electrons
journal, May 2016


Secondary electron yield measurements from limiter materials in the joint European torus
journal, October 1985


An experiment on the velocity distribution of thermionic electrons
journal, December 2010


Surface heat loads on the ITER divertor vertical targets
journal, March 2017


Suppression of secondary electron emission from the material surfaces with grazing incident magnetic field in the plasma
journal, December 1996


Influence of thin dielectric layers on electron emission and plasma-surface contact stability
journal, February 2010


Heat flow through a Langmuir sheath in the presence of electron emission
journal, January 1967


SOLPS simulations with electron kinetic effects
journal, January 2019


Secondary electron emission from lithium and lithium compounds
journal, July 2016


Evidence for strong secondary electron emission in the tokamak scrape-off layer
journal, June 2012


Plasma detachment in linear devices
journal, February 2017


The influence of electron emission at the divertor target of a tokamak fusion reactor
journal, September 1978


Kinetic simulations of electron heat flux in the scrape-off layer
journal, August 2017


Ignition and Behavior of Arc Spots on Helium Irradiated Tungsten Under Fusion Relevant Condition
journal, August 2019


Current-voltage characteristic of the contact of a plasma with an electrode with a thin dielectric film on the surface
journal, February 2015


Thermionic Emission
journal, April 1949


Bohm velocity in the presence of a hot cathode
journal, August 2013


Secondary electron emission and the bifurcation of the heat flux to the targets in fusion plasmas
journal, December 2013


Suppression of secondary emission of electrons from end plate in expander of open trap
journal, January 2019


Issues in the understanding of negative ion extraction for fusion
journal, June 2016


UEDGE modelling of detached divertor operation for long-leg divertor geometries in ARC
journal, March 2018


Cooling effect of secondary electrons in high temperature divertor operation
journal, October 1997


100 years of the physics of diodes
journal, March 2017


Electron-induced secondary electron emission coefficient of lithium, tungsten and stainless steel surfaces exposed to low-pressure plasmas
journal, September 2014


Effects of cold electron emission on the plasma sheath
journal, February 1993


Active Plasma Boundary Sheath with Electron Emission
journal, January 1998


H-mode behavior induced by cross-field currents in a tokamak
journal, November 1989


Unipolar arc model
journal, December 1984


Cathode spot formation possibly explained by cathode electron emission from impact of excited state atoms
journal, August 2019


Gyrokinetic treatment of a grazing angle magnetic presheath
journal, January 2017


Space-Charge Limited Current from Plasma-Facing Material Surface
journal, April 2004


Secondary electron emission at anode, cathode, and floating plasma‐facing surfaces
journal, March 1996


Extracted current saturation in negative ion sources
journal, June 2012