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Title: Effect of polarity on beam and plasma target formation in a dense plasma focus

Abstract

Dense plasma focus (DPF) devices are conventionally operated with a polarity such that the inner electrode (IE) is the anode. It has been found that interchanging the polarity of the electrodes (i.e., IE as the cathode) can cause an order of magnitude decrease in the neutron yield. This polarity riddle has previously been studied empirically through several experiments and is yet not well understood. Herein, we have performed kinetic simulations using the particle-in-cell modeling to investigate the problem. This is the first time that both polarities have been studied with simulations in great detail. In our simulations, we have modeled the entire beam and plasma target formation processes, but we did not consider differences in break-down conditions caused by the two polarities. We have found that when using reverse polarity ions are still accelerated and, in fact, attain similar energy spectra as in the standard polarity case. The difference is that the fields are flipped and thus ions are accelerated in the opposite direction. So, in the reverse polarity case, the majority of the “plasma target” (formed by the imploding plasma) is in the opposite direction of the beam, and thus, the beam hits the IE and produces few neutrons.more » With a better inner electrode configuration, reverse polarity is able to create a high-quality ion beam as well as a high-density target. Both can be comparable to that generated by standard polarity. Furthermore, we will show that it is easier to add an additional solid catcher target to a DPF device with reverse polarity, potentially enabling it to generate more neutrons than standard polarity.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC); USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1545334
Alternate Identifier(s):
OSTI ID: 1506164; OSTI ID: 1557068; OSTI ID: 1637586
Report Number(s):
LLNL-JRNL-788428; LLNL-JRNL-746401
Journal ID: ISSN 1070-664X
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 26; Journal Issue: 4; Conference: 60.Annual Meeting of the APS Division of Plasma Physics, Portland, OR (United States), 5-9 Nov 2018; 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; Plasma focus device Neutron sources Physics of gases Particle-in-cell method Plasma sheaths Neutron spectroscopy Leptons Plasma confinement Plasma devices; Physics - Plasma physics; Plasma focus device; Neutron sources; Physics of gases; Particle-in-cell method; Plasma sheaths; Neutron spectroscopy; Leptons; Plasma confinement; Plasma devices

Citation Formats

Jiang, S., Higginson, D. P., Link, A., Holod, I., and Schmidt, A. Effect of polarity on beam and plasma target formation in a dense plasma focus. United States: N. p., 2019. Web. https://doi.org/10.1063/1.5048423.
Jiang, S., Higginson, D. P., Link, A., Holod, I., & Schmidt, A. Effect of polarity on beam and plasma target formation in a dense plasma focus. United States. https://doi.org/10.1063/1.5048423
Jiang, S., Higginson, D. P., Link, A., Holod, I., and Schmidt, A. Wed . "Effect of polarity on beam and plasma target formation in a dense plasma focus". United States. https://doi.org/10.1063/1.5048423. https://www.osti.gov/servlets/purl/1545334.
@article{osti_1545334,
title = {Effect of polarity on beam and plasma target formation in a dense plasma focus},
author = {Jiang, S. and Higginson, D. P. and Link, A. and Holod, I. and Schmidt, A.},
abstractNote = {Dense plasma focus (DPF) devices are conventionally operated with a polarity such that the inner electrode (IE) is the anode. It has been found that interchanging the polarity of the electrodes (i.e., IE as the cathode) can cause an order of magnitude decrease in the neutron yield. This polarity riddle has previously been studied empirically through several experiments and is yet not well understood. Herein, we have performed kinetic simulations using the particle-in-cell modeling to investigate the problem. This is the first time that both polarities have been studied with simulations in great detail. In our simulations, we have modeled the entire beam and plasma target formation processes, but we did not consider differences in break-down conditions caused by the two polarities. We have found that when using reverse polarity ions are still accelerated and, in fact, attain similar energy spectra as in the standard polarity case. The difference is that the fields are flipped and thus ions are accelerated in the opposite direction. So, in the reverse polarity case, the majority of the “plasma target” (formed by the imploding plasma) is in the opposite direction of the beam, and thus, the beam hits the IE and produces few neutrons. With a better inner electrode configuration, reverse polarity is able to create a high-quality ion beam as well as a high-density target. Both can be comparable to that generated by standard polarity. Furthermore, we will show that it is easier to add an additional solid catcher target to a DPF device with reverse polarity, potentially enabling it to generate more neutrons than standard polarity.},
doi = {10.1063/1.5048423},
journal = {Physics of Plasmas},
number = 4,
volume = 26,
place = {United States},
year = {2019},
month = {4}
}

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