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Title: Contribution of the backstreaming ions to the Self-Magnetic pinch (SMP) diode current

Abstract

Summary form only given. The results presented here were obtained with an SMP diode mounted at the front high voltage end of the RITS accelerator. RITS is a Self-Magnetically Insulated Transmission Line (MITL) voltage adder that adds the voltage pulses of six 1.3 MV inductively insulated cavities. Our experiments had two objectives: first to measure the contribution of the back-streaming ion currents emitted from the anode target to the diode beam current, and second to try to evaluate the energy of those ions and hence the actual Anode-Cathode (A-K) gap actual voltage. In any very high voltage inductive voltage adder (IVA) utilizing MITLs to transmit the power to the diode load, the precise knowledge of the accelerating voltage applied on the anode-cathode (A-K) gap is problematic. The accelerating voltage quoted in the literature is from estimates based on measurements of the anode and cathode currents of the MITL far upstream from the diode and utilizing the para-potential flow theories and inductive corrections. Thus it would be interesting to have another independent measurement to evaluate the A-K voltage. The diode's anode is made of a number of high Z metals in order to produce copious and energetic flash x-rays. The backstreamingmore » currents are a strong fraction of the anode materials and their stage of cleanness and gas adsorption. We have measured the back-streaming ion currents emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatments, such as heating to very high temperatures with DC and pulsed current, with RF plasma cleaning and with both plasma cleaning and heating. Finally, we have also evaluated the A-K gap voltage by ion filtering techniques.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1429832
Report Number(s):
SAND-2017-9070J
656496
DOE Contract Number:
AC04-94AL85000
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas
Country of Publication:
United States
Language:
English
Subject:
Voltage measurement; Ions; Transmission line measurements; Anodes; Current measurement; Cleaning; Switched-mode power supply

Citation Formats

Mazarakis, Michael G., Cuneo, Michael E., Fournier, Sean D., Johnston, Mark D., Kiefer, Mark L., Leckbee, Joshua J., Nielsen, Dan S., Oliver, Bryan V., Simpson, Sean, Renk, Timothy J., Webb, Timothy J., Ziska, Derek, Bennett, Nichelle, Droemer, Darryl W., Cignac, Raymond E., Obregon, Robert J., Smith, Chase C., Wilkins, Frank L., and Welch, Dale R. Contribution of the backstreaming ions to the Self-Magnetic pinch (SMP) diode current. United States: N. p., 2016. Web. doi:10.1109/PLASMA.2016.7534260.
Mazarakis, Michael G., Cuneo, Michael E., Fournier, Sean D., Johnston, Mark D., Kiefer, Mark L., Leckbee, Joshua J., Nielsen, Dan S., Oliver, Bryan V., Simpson, Sean, Renk, Timothy J., Webb, Timothy J., Ziska, Derek, Bennett, Nichelle, Droemer, Darryl W., Cignac, Raymond E., Obregon, Robert J., Smith, Chase C., Wilkins, Frank L., & Welch, Dale R. Contribution of the backstreaming ions to the Self-Magnetic pinch (SMP) diode current. United States. doi:10.1109/PLASMA.2016.7534260.
Mazarakis, Michael G., Cuneo, Michael E., Fournier, Sean D., Johnston, Mark D., Kiefer, Mark L., Leckbee, Joshua J., Nielsen, Dan S., Oliver, Bryan V., Simpson, Sean, Renk, Timothy J., Webb, Timothy J., Ziska, Derek, Bennett, Nichelle, Droemer, Darryl W., Cignac, Raymond E., Obregon, Robert J., Smith, Chase C., Wilkins, Frank L., and Welch, Dale R. Mon . "Contribution of the backstreaming ions to the Self-Magnetic pinch (SMP) diode current". United States. doi:10.1109/PLASMA.2016.7534260. https://www.osti.gov/servlets/purl/1429832.
@article{osti_1429832,
title = {Contribution of the backstreaming ions to the Self-Magnetic pinch (SMP) diode current},
author = {Mazarakis, Michael G. and Cuneo, Michael E. and Fournier, Sean D. and Johnston, Mark D. and Kiefer, Mark L. and Leckbee, Joshua J. and Nielsen, Dan S. and Oliver, Bryan V. and Simpson, Sean and Renk, Timothy J. and Webb, Timothy J. and Ziska, Derek and Bennett, Nichelle and Droemer, Darryl W. and Cignac, Raymond E. and Obregon, Robert J. and Smith, Chase C. and Wilkins, Frank L. and Welch, Dale R.},
abstractNote = {Summary form only given. The results presented here were obtained with an SMP diode mounted at the front high voltage end of the RITS accelerator. RITS is a Self-Magnetically Insulated Transmission Line (MITL) voltage adder that adds the voltage pulses of six 1.3 MV inductively insulated cavities. Our experiments had two objectives: first to measure the contribution of the back-streaming ion currents emitted from the anode target to the diode beam current, and second to try to evaluate the energy of those ions and hence the actual Anode-Cathode (A-K) gap actual voltage. In any very high voltage inductive voltage adder (IVA) utilizing MITLs to transmit the power to the diode load, the precise knowledge of the accelerating voltage applied on the anode-cathode (A-K) gap is problematic. The accelerating voltage quoted in the literature is from estimates based on measurements of the anode and cathode currents of the MITL far upstream from the diode and utilizing the para-potential flow theories and inductive corrections. Thus it would be interesting to have another independent measurement to evaluate the A-K voltage. The diode's anode is made of a number of high Z metals in order to produce copious and energetic flash x-rays. The backstreaming currents are a strong fraction of the anode materials and their stage of cleanness and gas adsorption. We have measured the back-streaming ion currents emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatments, such as heating to very high temperatures with DC and pulsed current, with RF plasma cleaning and with both plasma cleaning and heating. Finally, we have also evaluated the A-K gap voltage by ion filtering techniques.},
doi = {10.1109/PLASMA.2016.7534260},
journal = {Physics of Plasmas},
number = ,
volume = ,
place = {United States},
year = {Mon Aug 08 00:00:00 EDT 2016},
month = {Mon Aug 08 00:00:00 EDT 2016}
}
  • Abstract not provided.
  • Abstract not provided.
  • This paper describes our effort to measure the back-streaming ions emitted from the target x-ray convertor and thus estimate the ion contribution to the A-K gap bipolar current flow. Knowing the ion contribution is quite important in order to calculate the expected x-ray dose and compare it with the actual measurements. Our plans were first to measure the total ion current using B-dot monitors, Rogowski coils, and Faraday cups and then to utilize filtered Faraday cups and time of flight techniques to identify and measure the various ionic species. The kinetic energy (velocities) of the ions should help evaluate themore » actual voltage applied at the anode-cathode (A-K) gap. LSP simulations found that the most prominent ions are protons and carbon single plus (C+). For an 8-MV A-K voltage, the estimated proton current back-streaming through an 1 cm in diameter hollow cathode tip was on the average 3 kA and the carbon current 0.7 kA. Since only a small fraction of the ions will make it through the cylindrical aperture, the corresponding total currents were calculated to be respectively 25kA for proton and 7 kA for carbon ions, a quite substantial contribution to the total bipolar beam current. Hence, approximately only 10% of the total back-streaming ionic currents could make it through the hollow cathode tip aperture. Unfortunately the diagnostic cables connecting the Faraday cup and the B-dot monitors to the screen room scopes experienced a large amount of charge pick-up that obliterated our effort to directly measure those relatively small currents. However, we succeeded in measuring those currents indirectly with activation techniques [Contribution of the back-streaming ions to the self-magnetic pinch (SMP) diode Current., M. G. Mazarakis, M. G. Mazarakis, M. E. Cuneo, S. D. Fournier, M. D. Johnston, M. L. Kiefer, J. J. Leckbee, D. S. Nielsen, B.V.Oliver, M. E. Sceiford, S. C. Simpson, T. J. Renk, C. L. Ruiz, T. J. Webb, and D. Ziska. Subitted for publication.]. In the following sections we present some typical cable pick-up results and also our efforts to verify that the observed “current” scope traces were indeed not ion currents but instead cable charge pic-up. Interestingly enough we also discovered that the appearance of those “currents” are in synchronism with the A-K gap impedance variation (decrease) and the MITL sheath current re-trapping. Hence those B-dots or Faraday cups could be utilized as diode behavior diagnostics.« less
  • Abstract not provided.
  • Abstract not provided.