Impedance of an intense plasma-cathode electron source for tokamak startup
Abstract
In this study, an impedance model is formulated and tested for the ~1kV, ~1kA/cm2, arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma (narc ≈ 1021 m-3) within the electron source, and the less dense external tokamak edge plasma (nedge ≈ 1018 m-3) into which current is injected at the applied injector voltage, Vinj. Experiments on the Pegasus spherical tokamak show the injected current, Iinj, increases with Vinj according to the standard double layer scaling Iinj ~ Vinj3/2 at low current and transitions to Iinj ~ Vinj1/2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density nb ~ Iinj/Vinj1/2. For low tokamak edge density nedge and high Iinj, the inferred beam density nb is consistent with the requirement nb ≤ nedge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, nb ~ narc is observed, consistent with a limit to nb imposed by expansion of the double layer sheath. These results suggest that narc is a viable control actuator for the source impedance.
- Publication Date:
- Research Org.:
- Univ. of Wisconsin, Madison, WI (United States)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1255444
- Alternate Identifier(s):
- OSTI ID: 1255165
- Grant/Contract Number:
- FG02-96ER54375
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Physics of Plasmas
- Additional Journal Information:
- Journal Volume: 23; Journal Issue: 5; 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; tokamaks; double layer; helicity injection; plasma cathode; electron source; plasma source; plasma sheaths; cathodes; charge injection
Citation Formats
Hinson, Edward Thomas, Barr, Jayson L., Bongard, Michael W., Burke, Marcus Galen, Fonck, Raymond J., and Perry, Justin M. Impedance of an intense plasma-cathode electron source for tokamak startup. United States: N. p., 2016.
Web. doi:10.1063/1.4952628.
Hinson, Edward Thomas, Barr, Jayson L., Bongard, Michael W., Burke, Marcus Galen, Fonck, Raymond J., & Perry, Justin M. Impedance of an intense plasma-cathode electron source for tokamak startup. United States. https://doi.org/10.1063/1.4952628
Hinson, Edward Thomas, Barr, Jayson L., Bongard, Michael W., Burke, Marcus Galen, Fonck, Raymond J., and Perry, Justin M. Tue .
"Impedance of an intense plasma-cathode electron source for tokamak startup". United States. https://doi.org/10.1063/1.4952628. https://www.osti.gov/servlets/purl/1255444.
@article{osti_1255444,
title = {Impedance of an intense plasma-cathode electron source for tokamak startup},
author = {Hinson, Edward Thomas and Barr, Jayson L. and Bongard, Michael W. and Burke, Marcus Galen and Fonck, Raymond J. and Perry, Justin M.},
abstractNote = {In this study, an impedance model is formulated and tested for the ~1kV, ~1kA/cm2, arc-plasma cathode electron source used for local helicity injection tokamak startup. A double layer sheath is established between the high-density arc plasma (narc ≈ 1021 m-3) within the electron source, and the less dense external tokamak edge plasma (nedge ≈ 1018 m-3) into which current is injected at the applied injector voltage, Vinj. Experiments on the Pegasus spherical tokamak show the injected current, Iinj, increases with Vinj according to the standard double layer scaling Iinj ~ Vinj3/2 at low current and transitions to Iinj ~ Vinj1/2 at high currents. In this high current regime, sheath expansion and/or space charge neutralization impose limits on the beam density nb ~ Iinj/Vinj1/2. For low tokamak edge density nedge and high Iinj, the inferred beam density nb is consistent with the requirement nb ≤ nedge imposed by space-charge neutralization of the beam in the tokamak edge plasma. At sufficient edge density, nb ~ narc is observed, consistent with a limit to nb imposed by expansion of the double layer sheath. These results suggest that narc is a viable control actuator for the source impedance.},
doi = {10.1063/1.4952628},
journal = {Physics of Plasmas},
number = 5,
volume = 23,
place = {United States},
year = {Tue May 31 00:00:00 EDT 2016},
month = {Tue May 31 00:00:00 EDT 2016}
}
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Public Data Set: Non-inductively Driven Tokamak Plasmas at Near-Unity βt in the Pegasus Toroidal Experiment
dataset, March 2018
- Reusch, Joshua; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5017966, 1 file (5.1 MB)
Public Data Set: Initiation and Sustainment of Tokamak Plasmas with Local Helicity Injection as the Majority Current Drive
dataset, July 2018
- Perry, Justin; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB)
Public Data Set: Radially Scanning Magnetic Probes to Study Local Helicity Injection Dynamics
dataset, July 2018
- Richner, Nathan; Bongard, Michael; Fonck, Raymond
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5036527, 1 file (9.4 MB)
Public Data Set: Advancing Local Helicity Injection for Non-Solenoidal Tokamak Startup
dataset, January 2019
- Bongard, Michael; Bodner, Grant; Burke, Marcus
- University of Wisconsin-Madison
Public Data Set: Continuous, Edge Localized Ion Heating During Non-Solenoidal Plasma Startup and Sustainment in a Low Aspect Ratio Tokamak
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dataset, January 2016
- Thome, Kathreen; Bongard, Michael; Barr, Jayson
Public Data Set: On Virial Analysis at Low Aspect Ratio
dataset, July 2016
- Bongard, Michael; Barr, Jayson; Fonck, Raymond
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.4959808, 1 file (440 KB)
Public Data Set: A Novel, Cost-Effective, Multi-Point Thomson Scattering System on the Pegasus Toroidal Experiment
dataset, September 2016
- Schlossberg, D. J.; Bodner, G. M.; Reusch, J. A.
- AIP - Review of Scientific Instruments, Vol. 87, Issue 11, 49.6 MB
Public Data Set: Control and Automation of the Pegasus Multi-point Thomson Scattering System
dataset, January 2016
- Bodner, Grant; Bongard, Michael; Fonck, Raymond
- Pegasus, 13 files
Public Data Set: Erratum: "Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment" [Rev. Sci. Instrum. 83, 10D516 (2012)]
dataset, January 2016
- Burke, Marcus; Fonck, Raymond; Bongard, Michael
Public Data Set: A Power-Balance Model for Local Helicity Injection Startup in a Spherical Tokamak
dataset, May 2018
- Barr, J. L.; Bongard, M. W.; Burke, M. G.
- Pegasus Public Data Sets
Public Data Set: Non-inductively Driven Tokamak Plasmas at Near-Unity βt in the Pegasus Toroidal Experiment
dataset, March 2018
- Reusch, Joshua; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5017966, 1 file (5.1 MB)
Public Data Set: Initiation and Sustainment of Tokamak Plasmas with Local Helicity Injection as the Majority Current Drive
dataset, July 2018
- Perry, Justin; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB)
Public Data Set: Radially Scanning Magnetic Probes to Study Local Helicity Injection Dynamics
dataset, July 2018
- Richner, Nathan; Bongard, Michael; Fonck, Raymond
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5036527, 1 file (9.4 MB)
Public Data Set: Advancing Local Helicity Injection for Non-Solenoidal Tokamak Startup
dataset, January 2019
- Bongard, Michael; Bodner, Grant; Burke, Marcus
- University of Wisconsin-Madison
Works referencing / citing this record:
Non-inductively driven tokamak plasmas at near-unity βt in the P egasus toroidal experiment
journal, May 2018
- Reusch, J. A.; Bodner, G. M.; Bongard, M. W.
- Physics of Plasmas, Vol. 25, Issue 5
Public Data Set: Impedance of an Intense Plasma-Cathode Electron Source for Tokamak Plasma Startup
dataset, October 0168
- Hinson, Edward; Barr, Jayson; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.4952628, 1 file (11.2 MB)
Public Data Set: H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment
dataset, January 2016
- Thome, Kathreen; Bongard, Michael; Barr, Jayson
Public Data Set: On Virial Analysis at Low Aspect Ratio
dataset, July 2016
- Bongard, Michael; Barr, Jayson; Fonck, Raymond
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.4959808, 1 file (440 KB)
Public Data Set: A Novel, Cost-Effective, Multi-Point Thomson Scattering System on the Pegasus Toroidal Experiment
dataset, September 2016
- Schlossberg, D. J.; Bodner, G. M.; Reusch, J. A.
- AIP - Review of Scientific Instruments, Vol. 87, Issue 11, 49.6 MB
Public Data Set: Control and Automation of the Pegasus Multi-point Thomson Scattering System
dataset, January 2016
- Bodner, Grant; Bongard, Michael; Fonck, Raymond
- Pegasus, 13 files
Public Data Set: Erratum: "Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment" [Rev. Sci. Instrum. 83, 10D516 (2012)]
dataset, January 2016
- Burke, Marcus; Fonck, Raymond; Bongard, Michael
Public Data Set: Continuous, Edge Localized Ion Heating During Non-Solenoidal Plasma Startup and Sustainment in a Low Aspect Ratio Tokamak
dataset, January 2017
- Burke, Marcus; Barr, Jayson; Bongard, Michael
Public Data Set: A Power-Balance Model for Local Helicity Injection Startup in a Spherical Tokamak
dataset, May 2018
- Barr, J. L.; Bongard, M. W.; Burke, M. G.
- Pegasus Public Data Sets
Public Data Set: Non-inductively Driven Tokamak Plasmas at Near-Unity βt in the Pegasus Toroidal Experiment
dataset, March 2018
- Reusch, Joshua; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5017966, 1 file (5.1 MB)
Public Data Set: Initiation and Sustainment of Tokamak Plasmas with Local Helicity Injection as the Majority Current Drive
dataset, July 2018
- Perry, Justin; Bodner, Grant; Bongard, Michael
- Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB)
Public Data Set: Radially Scanning Magnetic Probes to Study Local Helicity Injection Dynamics
dataset, July 2018
- Richner, Nathan; Bongard, Michael; Fonck, Raymond
- Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5036527, 1 file (9.4 MB)
Public Data Set: Spatial Heterodyne Spectroscopy for High Speed Measurements of Stark Split Neutral Beam Emission in a High Temperature Plasma
dataset, January 2018
- Burke, Marcus; Fonck, Raymond; McKee, George
- University of Wisconsin-Madison
Public Data Set: Advancing Local Helicity Injection for Non-Solenoidal Tokamak Startup
dataset, January 2019
- Bongard, Michael; Bodner, Grant; Burke, Marcus
- University of Wisconsin-Madison